Dynamical dark energy: Scalar fields and running vacuum

NASA Astrophysics Data System (ADS)

Solà, Joan; Gómez-Valent, Adrià; de Cruz Pérez, Javier

2017-03-01

Recent analyses in the literature suggest that the concordance ΛCDM model with rigid cosmological term, Λ = const. may not be the best description of the cosmic acceleration. The class of “running vacuum models”, in which Λ = Λ(H) evolves with the Hubble rate, has been shown to fit the string of SNIa + BAO + H(z) + LSS + CMB data significantly better than the ΛCDM. Here, we provide further evidence on the time-evolving nature of the dark energy (DE) by fitting the same cosmological data in terms of scalar fields. As a representative model, we use the original Peebles and Ratra potential, V ∝ ϕ-α. We find clear signs of dynamical DE at ˜ 4σ c.l., thus reconfirming through a nontrivial scalar field approach the strong hints formerly found with other models and parametrizations.

Cosmology with gamma-ray bursts. II. Cosmography challenges and cosmological scenarios for the accelerated Universe

NASA Astrophysics Data System (ADS)

Demianski, Marek; Piedipalumbo, Ester; Sawant, Disha; Amati, Lorenzo

2017-02-01

Context. Explaining the accelerated expansion of the Universe is one of the fundamental challenges in physics today. Cosmography provides information about the evolution of the universe derived from measured distances, assuming only that the space time geometry is described by the Friedman-Lemaitre-Robertson-Walker metric, and adopting an approach that effectively uses only Taylor expansions of basic observables. Aims: We perform a high-redshift analysis to constrain the cosmographic expansion up to the fifth order. It is based on the Union2 type Ia supernovae data set, the gamma-ray burst Hubble diagram, a data set of 28 independent measurements of the Hubble parameter, baryon acoustic oscillations measurements from galaxy clustering and the Lyman-α forest in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), and some Gaussian priors on h and ΩM. Methods: We performed a statistical analysis and explored the probability distributions of the cosmographic parameters. By building up their regions of confidence, we maximized our likelihood function using the Markov chain Monte Carlo method. Results: Our high-redshift analysis confirms that the expansion of the Universe currently accelerates; the estimation of the jerk parameter indicates a possible deviation from the standard ΛCDM cosmological model. Moreover, we investigate implications of our results for the reconstruction of the dark energy equation of state (EOS) by comparing the standard technique of cosmography with an alternative approach based on generalized Padé approximations of the same observables. Because these expansions converge better, is possible to improve the constraints on the cosmographic parameters and also on the dark matter EOS. Conclusions: The estimation of the jerk and the DE parameters indicates at 1σ a possible deviation from the ΛCDM cosmological model.

Cosmic acceleration in a dust only universe via energy-momentum powered gravity

NASA Astrophysics Data System (ADS)

Akarsu, Özgür; Katırcı, Nihan; Kumar, Suresh

2018-01-01

We propose a modified theory of gravitation constructed by the addition of the term f (Tμ νTμ ν) to the Einstein-Hilbert action, and elaborate a particular case f (Tμ νTμ ν)=α (Tμ νTμ ν)η, where α and η are real constants, dubbed energy-momentum powered gravity (EMPG). We search for viable cosmologies arising from EMPG, especially in the context of the late-time accelerated expansion of the Universe. We investigate the ranges of the EMPG parameters (α ,η ) on theoretical as well as observational grounds leading to the late-time acceleration of the Universe with pressureless matter only, while keeping the successes of standard general relativity at early times. We find that η =0 corresponds to the Λ CDM model, whereas η ≠0 leads to a w CDM -type model. However, the underlying physics of the EMPG model is entirely different in the sense that the energy in the EMPG Universe is sourced by pressureless matter only. Moreover, the energy of the pressureless matter is not conserved, namely, in general it does not dilute as ρ ∝a-3 with the expansion of the Universe. Finally, we constrain the parameters of an EMPG-based cosmology with a recent compilation of 28 Hubble parameter measurements, and find that this model describes an evolution of the Universe similar to that in the Λ CDM model. We briefly discuss that EMPG can be unified with Starobinsky gravity to describe the complete history of the Universe including the inflationary era.

Gravitational redshift of galaxies in clusters as predicted by general relativity.

PubMed

Wojtak, Radosław; Hansen, Steen H; Hjorth, Jens

2011-09-28

The theoretical framework of cosmology is mainly defined by gravity, of which general relativity is the current model. Recent tests of general relativity within the Lambda Cold Dark Matter (ΛCDM) model have found a concordance between predictions and the observations of the growth rate and clustering of the cosmic web. General relativity has not hitherto been tested on cosmological scales independently of the assumptions of the ΛCDM model. Here we report an observation of the gravitational redshift of light coming from galaxies in clusters at the 99 per cent confidence level, based on archival data. Our measurement agrees with the predictions of general relativity and its modification created to explain cosmic acceleration without the need for dark energy (the f(R) theory), but is inconsistent with alternative models designed to avoid the presence of dark matter. © 2011 Macmillan Publishers Limited. All rights reserved

Gauging the cosmic acceleration with recent type Ia supernovae data sets

NASA Astrophysics Data System (ADS)

Velten, Hermano; Gomes, Syrios; Busti, Vinicius C.

2018-04-01

We revisit a model-independent estimator for cosmic acceleration based on type Ia supernovae distance measurements. This approach does not rely on any specific theory for gravity, energy content, nor parametrization for the scale factor or deceleration parameter and is based on falsifying the null hypothesis that the Universe never expanded in an accelerated way. By generating mock catalogs of known cosmologies, we test the robustness of this estimator, establishing its limits of applicability. We detail the pros and cons of such an approach. For example, we find that there are specific counterexamples in which the estimator wrongly provides evidence against acceleration in accelerating cosmologies. The dependence of the estimator on the H0 value is also discussed. Finally, we update the evidence for acceleration using the recent UNION2.1 and Joint Light-Curve Analysis samples. Contrary to recent claims, available data strongly favor an accelerated expansion of the Universe in complete agreement with the standard Λ CDM model.

Unifying inflation with ΛCDM epoch in modified f(R) gravity consistent with Solar System tests

NASA Astrophysics Data System (ADS)

Nojiri, Shin'ichi; Odintsov, Sergei D.

2007-12-01

We suggest two realistic f(R) and one F(G) modified gravities which are consistent with local tests and cosmological bounds. The typical property of such theories is the presence of the effective cosmological constant epochs in such a way that early-time inflation and late-time cosmic acceleration are naturally unified within single model. It is shown that classical instability does not appear here and Newton law is respected. Some discussion of possible anti-gravity regime appearance and related modification of the theory is done.

Λ(t) CDM and the present accelerating expansion of the universe from 5D scalar vacuum

NASA Astrophysics Data System (ADS)

Madriz Aguilar, José Edgar; Zamarripa, J.; Peraza, A.; Licea, J. A.

2017-12-01

In this letter we investigate some consequences of considering our 4D observable universe as locally and isometrically embedded in a 5D spacetime, where gravity is described by a Brans-Dicke theory in vacuum. Once we impose the embedding conditions we obtain that gravity on the 4D spacetime is governed by the Einstein field equations modified by an extra term that can play the role of a dynamical cosmological constant. Two examples were studied. In the first we derive a cosmological model of a universe filled only with a cosmological constant. In the second we obtain a cosmological solution describing a universe filled with matter, radiation and a dynamical cosmological constant. We constrain the model by using the current observational data combination Planck + WP + BAO + SN. The present acceleration in the expansion of the universe is explained by the geometrically induced dynamical cosmological constant avoiding the introduction of a dark energy component and without addressing the underlying cosmological constant problem. Moreover, all 4D matter sources are geometrically induced in the same manner as it is usually done in the Wesson's induced matter theory.

Testing theories of gravity and supergravity with inflation and observations of the cosmic microwave background

NASA Astrophysics Data System (ADS)

Chakravarty, G. K.; Mohanty, S.; Lambiase, G.

Cosmological and astrophysical observations lead to the emerging picture of a universe that is spatially flat and presently undertaking an accelerated expansion. The observations supporting this picture come from a range of measurements encompassing estimates of galaxy cluster masses, the Hubble diagram derived from type-Ia supernovae observations, the measurements of Cosmic Microwave Background radiation anisotropies, etc. The present accelerated expansion of the universe can be explained by admitting the existence of a cosmic fluid, with negative pressure. In the simplest scenario, this unknown component of the universe, the Dark Energy, is represented by the cosmological constant (Λ), and accounts for about 70% of the global energy budget of the universe. The remaining 30% consist of a small fraction of baryons (4%) with the rest being Cold Dark Matter (CDM). The Lambda Cold Dark Matter (ΛCDM) model, i.e. General Relativity with cosmological constant, is in good agreement with observations. It can be assumed as the first step towards a new standard cosmological model. However, despite the satisfying agreement with observations, the ΛCDM model presents lack of congruence and shortcomings and therefore theories beyond Einstein’s General Relativity are called for. Many extensions of Einstein’s theory of gravity have been studied and proposed with various motivations like the quest for a quantum theory of gravity to extensions of anomalies in observations at the solar system, galactic and cosmological scales. These extensions include adding higher powers of Ricci curvature R, coupling the Ricci curvature with scalar fields and generalized functions of R. In addition, when viewed from the perspective of Supergravity (SUGRA), many of these theories may originate from the same SUGRA theory, but interpreted in different frames. SUGRA therefore serves as a good framework for organizing and generalizing theories of gravity beyond General Relativity. All these theories when applied to inflation (a rapid expansion of early universe in which primordial gravitational waves might be generated and might still be detectable by the imprint they left or by the ripples that persist today) can have distinct signatures in the Cosmic Microwave Background radiation temperature and polarization anisotropies. We give a review of ΛCDM cosmology and survey the theories of gravity beyond Einstein’s General Relativity, specially which arise from SUGRA, and study the consequences of these theories in the context of inflation and put bounds on the theories and the parameters therein from the observational experiments like PLANCK, Keck/BICEP, etc. The possibility of testing these theories in the near future in CMB observations and new data coming from colliders like the LHC, provides an unique opportunity for constructing verifiable models of particle physics and General Relativity.

Inflation and late-time acceleration from a double-well potential with cosmological constant

NASA Astrophysics Data System (ADS)

de Haro, Jaume; Elizalde, Emilio

2016-06-01

A model of a universe without big bang singularity is presented, which displays an early inflationary period ending just before a phase transition to a kination epoch. The model produces enough heavy particles so as to reheat the universe at temperatures in the MeV regime. After the reheating, it smoothly matches the standard Λ CDM scenario.

ΛCDM Cosmology Through the Lens of Einstein's Static Universe, the Mother of Λ

NASA Astrophysics Data System (ADS)

Mitra, Abhas; Bhattacharyya, S.; Bhatt, Nilay

2013-03-01

We show here that, in the context of Einstein's static universe (ESU), the static cosmological constant Λs = 0. We do so by extending (and not contradicting) the ESU relationship from Λs = 4πρ to Λs = 4πρ = 0, where ρ is the ESU matter density (G = c = 1). This extension follows from the fact that the elements of the spacetime geometry depend on pressure and energy density (ρ). Note in the ΛCDM model, Λ is associated with "Dark Energy (DE)." And, if Λ would be considered as a fundamental constant, it should be zero even for a dynamic universe. In such a case, the observed accelerated expansion could be an artifact of inhomogeneity [D. L. Wiltshire, Phys. Rev. D80 (2009) 123512; E. W. Kolb, Class. Quantum. Grav.28 (2011) 164009] or large peculiar acceleration of the Milky way [C. Tasgas, Phys. Rev. D84 (2011) 063503] or extinction of light of distant supernovae [R. E. Schild and M. Dekker, Astron. Nachr.327 (2006) 729, arXiv:astro-ph/0512236]. The same conclusion has also been obtained in an independent manner [A. Mitra, JCAP03 (2013) 007, doi: 10.1088/1475-7516/2013/03/007].

Where the world stands still: turnaround as a strong test of ΛCDM cosmology

NASA Astrophysics Data System (ADS)

Pavlidou, V.; Tomaras, T. N.

2014-09-01

Our intuitive understanding of cosmic structure formation works best in scales small enough so that isolated, bound, relaxed gravitating systems are no longer adjusting their radius; and large enough so that space and matter follow the average expansion of the Universe. Yet one of the most robust predictions of ΛCDM cosmology concerns the scale that separates these limits: the turnaround radius, which is the non-expanding shell furthest away from the center of a bound structure. We show that the maximum possible value of the turnaround radius within the framework of the ΛCDM model is, for a given mass M, equal to (3GM/Λ c2)1/3, with G Newton's constant and c the speed of light, independently of cosmic epoch, exact nature of dark matter, or baryonic effects. We discuss the possible use of this prediction as an observational test for ΛCDM cosmology. Current data appear to favor ΛCDM over alternatives with local inhomogeneities and no Λ. However there exist several local-universe structures that have, within errors, reached their limiting size. With improved determinations of their turnaround radii and the enclosed mass, these objects may challenge the limit and ΛCDM cosmology.

Gravitationally influenced particle creation models and late-time cosmic acceleration

NASA Astrophysics Data System (ADS)

Pan, Supriya; Kumar Pal, Barun; Pramanik, Souvik

In this work, we focus on the gravitationally influenced adiabatic particle creation process, a mechanism that does not need any dark energy or modified gravity models to explain the current accelerating phase of the universe. Introducing some particle creation models that generalize some previous models in the literature, we constrain the cosmological scenarios using the latest compilation of the Type Ia Supernovae data only, the first indicator of the accelerating universe. Aside from the observational constraints on the models, we examine the models using two model independent diagnoses, namely the cosmography and Om. Further, we establish the general conditions to test the thermodynamic viabilities of any particle creation model. Our analysis shows that at late-time, the models have close resemblance to that of the ΛCDM cosmology, and the models always satisfy the generalized second law of thermodynamics under certain conditions.

Where the world stands still: turnaround as a strong test of ΛCDM cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavlidou, V.; Tomaras, T.N., E-mail: pavlidou@physics.uoc.gr, E-mail: tomaras@physics.uoc.gr

Our intuitive understanding of cosmic structure formation works best in scales small enough so that isolated, bound, relaxed gravitating systems are no longer adjusting their radius; and large enough so that space and matter follow the average expansion of the Universe. Yet one of the most robust predictions of ΛCDM cosmology concerns the scale that separates these limits: the turnaround radius, which is the non-expanding shell furthest away from the center of a bound structure. We show that the maximum possible value of the turnaround radius within the framework of the ΛCDM model is, for a given mass M, equalmore » to (3GM/Λ c{sup 2}){sup 1/3}, with G Newton's constant and c the speed of light, independently of cosmic epoch, exact nature of dark matter, or baryonic effects. We discuss the possible use of this prediction as an observational test for ΛCDM cosmology. Current data appear to favor ΛCDM over alternatives with local inhomogeneities and no Λ. However there exist several local-universe structures that have, within errors, reached their limiting size. With improved determinations of their turnaround radii and the enclosed mass, these objects may challenge the limit and ΛCDM cosmology.« less

Learn-as-you-go acceleration of cosmological parameter estimates

NASA Astrophysics Data System (ADS)

Aslanyan, Grigor; Easther, Richard; Price, Layne C.

2015-09-01

Cosmological analyses can be accelerated by approximating slow calculations using a training set, which is either precomputed or generated dynamically. However, this approach is only safe if the approximations are well understood and controlled. This paper surveys issues associated with the use of machine-learning based emulation strategies for accelerating cosmological parameter estimation. We describe a learn-as-you-go algorithm that is implemented in the Cosmo++ code and (1) trains the emulator while simultaneously estimating posterior probabilities; (2) identifies unreliable estimates, computing the exact numerical likelihoods if necessary; and (3) progressively learns and updates the error model as the calculation progresses. We explicitly describe and model the emulation error and show how this can be propagated into the posterior probabilities. We apply these techniques to the Planck likelihood and the calculation of ΛCDM posterior probabilities. The computation is significantly accelerated without a pre-defined training set and uncertainties in the posterior probabilities are subdominant to statistical fluctuations. We have obtained a speedup factor of 6.5 for Metropolis-Hastings and 3.5 for nested sampling. Finally, we discuss the general requirements for a credible error model and show how to update them on-the-fly.

Learn-as-you-go acceleration of cosmological parameter estimates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aslanyan, Grigor; Easther, Richard; Price, Layne C., E-mail: g.aslanyan@auckland.ac.nz, E-mail: r.easther@auckland.ac.nz, E-mail: lpri691@aucklanduni.ac.nz

2015-09-01

Cosmological analyses can be accelerated by approximating slow calculations using a training set, which is either precomputed or generated dynamically. However, this approach is only safe if the approximations are well understood and controlled. This paper surveys issues associated with the use of machine-learning based emulation strategies for accelerating cosmological parameter estimation. We describe a learn-as-you-go algorithm that is implemented in the Cosmo++ code and (1) trains the emulator while simultaneously estimating posterior probabilities; (2) identifies unreliable estimates, computing the exact numerical likelihoods if necessary; and (3) progressively learns and updates the error model as the calculation progresses. We explicitlymore » describe and model the emulation error and show how this can be propagated into the posterior probabilities. We apply these techniques to the Planck likelihood and the calculation of ΛCDM posterior probabilities. The computation is significantly accelerated without a pre-defined training set and uncertainties in the posterior probabilities are subdominant to statistical fluctuations. We have obtained a speedup factor of 6.5 for Metropolis-Hastings and 3.5 for nested sampling. Finally, we discuss the general requirements for a credible error model and show how to update them on-the-fly.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dirian, Yves; Foffa, Stefano; Kunz, Martin

We study the cosmological predictions of two recently proposed non-local modifications of General Relativity. Both models have the same number of parameters as ΛCDM, with a mass parameter m replacing the cosmological constant. We implement the cosmological perturbations of the non-local models into a modification of the CLASS Boltzmann code, and we make a full comparison to CMB, BAO and supernova data. We find that the non-local models fit these datasets very well, at the same level as ΛCDM. Among the vast literature on modified gravity models, this is, to our knowledge, the only example which fits data as wellmore » as ΛCDM without requiring any additional parameter. For both non-local models parameter estimation using Planck +JLA+BAO data gives a value of H{sub 0} slightly higher than in ΛCDM.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lazkoz, Ruth; Escamilla-Rivera, Celia; Salzano, Vincenzo

Cosmography provides a model-independent way to map the expansion history of the Universe. In this paper we simulate a Euclid-like survey and explore cosmographic constraints from future Baryonic Acoustic Oscillations (BAO) observations. We derive general expressions for the BAO transverse and radial modes and discuss the optimal order of the cosmographic expansion that provides reliable cosmological constraints. Through constraints on the deceleration and jerk parameters, we show that future BAO data have the potential to provide a model-independent check of the cosmic acceleration as well as a discrimination between the standard ΛCDM model and alternative mechanisms of cosmic acceleration.

A bridge between unified cosmic history by f( R)-gravity and BIonic system

NASA Astrophysics Data System (ADS)

Sepehri, Alireza; Capozziello, Salvatore; Setare, Mohammad Reza

2016-04-01

Recently, the cosmological deceleration-acceleration transition redshift in f( R) gravity has been considered in order to address consistently the problem of cosmic evolution. It is possible to show that the deceleration parameter changes sign at a given redshift according to observational data. Furthermore, a f( R) gravity cosmological model can be constructed in brane-antibrane system starting from the very early universe and accounting for the cosmological redshift at all phases of cosmic history, from inflation to late time acceleration. Here we propose a f( R) model where transition redshifts correspond to inflation-deceleration and deceleration-late time acceleration transitions starting froma BIon system. At the point where the universe was born, due to the transition of k black fundamental strings to the BIon configuration, the redshift is approximately infinity and decreases with reducing temperature (z˜ T2). The BIon is a configuration in flat space of a universe-brane and a parallel anti-universe-brane connected by a wormhole. This wormhole is a channel for flowing energy from extra dimensions into our universe, occurring at inflation and decreasing with redshift as z˜ T^{4+1/7}. Dynamics consists with the fact that the wormhole misses its energy and vanishes as soon as inflation ends and deceleration begins. Approaching two universe branes together, a tachyon is originated, it grows up and causes the formation of a wormhole. We show that, in the framework of f( R) gravity, the cosmological redshift depends on the tachyonic potential and has a significant decrease at deceleration-late time acceleration transition point (z˜ T^{2/3}). As soon as today acceleration approaches, the redshift tends to zero and the cosmological model reduces to the standard Λ CDM cosmology.

Cosmology based on f(R) gravity with O(1) eV sterile neutrino

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chudaykin, Anton S.; Gorbunov, Dmitry S.; Starobinsky, Alexei A.

2015-05-01

We address the cosmological role of an additional O(1) eV sterile neutrino in modified gravity models. We confront the present cosmological data with predictions of the FLRW cosmological model based on a variant of f(R) modified gravity proposed by one of the authors previously. This viable cosmological model which deviation from general relativity with a cosmological constant Λ decreases as R{sup −2n} for large, but not too large values of the Ricci scalar R (while no Λ is introduced by hand at small R) provides an alternative explanation of present dark energy and the accelerated expansion of the Universe (themore » case n=2 is considered in the paper). Various up-to-date cosmological data sets exploited include measurements of the cosmic microwave background (CMB) anisotropy, the CMB lensing potential, the baryon acoustic oscillations (BAO), the cluster mass function and the Hubble constant. We find that the CMB+BAO constraints strongly restrict the sum of neutrino masses from above. This excludes values of the model parameter λ∼ 1 for which distinctive cosmological features of the model are mostly pronounced as compared to the ΛCDM model, since then free streaming damping of perturbations due to neutrino rest masses is not sufficient to compensate their extra growth occurring in f(R) modified gravity. Thus, in the gravity sector we obtain λ>8.2 (2σ) with the account of systematic uncertainties in galaxy cluster mass function measurements and λ>9.4 (2σ) without them. At the same time in the latter case we find for the sterile neutrino mass 0.47 eV < m{sub ν, sterile} < 1 eV (2σ) assuming that the sterile neutrinos are thermalized and the active neutrinos are massless, not significantly larger than in the standard ΛCDM with the same data set: 0.45 eV < m{sub ν, sterile} < 0.92 eV (2σ). However, a possible discovery of a sterile neutrino with the mass m{sub ν, sterile} ≈ 1.5 eV motivated by various anomalies in neutrino oscillation experiments would favor cosmology based on f(R) gravity rather than the ΛCDM model.« less

Constraints on deviations from ΛCDM within Horndeski gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bellini, Emilio; Cuesta, Antonio J.; Jimenez, Raul

2016-02-01

Recent anomalies found in cosmological datasets such as the low multipoles of the Cosmic Microwave Background or the low redshift amplitude and growth of clustering measured by e.g., abundance of galaxy clusters and redshift space distortions in galaxy surveys, have motivated explorations of models beyond standard ΛCDM. Of particular interest are models where general relativity (GR) is modified on large cosmological scales. Here we consider deviations from ΛCDM+GR within the context of Horndeski gravity, which is the most general theory of gravity with second derivatives in the equations of motion. We adopt a parametrization in which the four additional Horndeskimore » functions of time α{sub i}(t) are proportional to the cosmological density of dark energy Ω{sub DE}(t). Constraints on this extended parameter space using a suite of state-of-the art cosmological observations are presented for the first time. Although the theory is able to accommodate the low multipoles of the Cosmic Microwave Background and the low amplitude of fluctuations from redshift space distortions, we find no significant tension with ΛCDM+GR when performing a global fit to recent cosmological data and thus there is no evidence against ΛCDM+GR from an analysis of the value of the Bayesian evidence ratio of the modified gravity models with respect to ΛCDM, despite introducing extra parameters. The posterior distribution of these extra parameters that we derive return strong constraints on any possible deviations from ΛCDM+GR in the context of Horndeski gravity. We illustrate how our results can be applied to a more general frameworks of modified gravity models.« less

Cosmological implications of different baryon acoustic oscillation data

NASA Astrophysics Data System (ADS)

Wang, Shuang; Hu, YaZhou; Li, Miao

2017-04-01

In this work, we explore the cosmological implications of different baryon acoustic oscillation (BAO) data, including the BAO data extracted by using the spherically averaged one-dimensional galaxy clustering (GC) statistics (hereafter BAO1) and the BAO data obtained by using the anisotropic two-dimensional GC statistics (hereafter BAO2). To make a comparison, we also take into account the case without BAO data (hereafter NO BAO). Firstly, making use of these BAO data, as well as the SNLS3 type Ia supernovae sample and the Planck distance priors data, we give the cosmological constraints of the ΛCDM, the wCDM, and the Chevallier-Polarski-Linder (CPL) model. Then, we discuss the impacts of different BAO data on cosmological consquences, including its effects on parameter space, equation of state (EoS), figure of merit (FoM), deceleration-acceleration transition redshift, Hubble parameter H( z), deceleration parameter q( z), statefinder hierarchy S 3 (1)( z), S 4 (1)( z) and cosmic age t( z). We find that: (1) NO BAO data always give a smallest fractional matter density Ω m0, a largest fractional curvature density Ωk0 and a largest Hubble constant h; in contrast, BAO1 data always give a largest Ω m0, a smallest Ω k0 and a smallest h. (2) For the wCDM and the CPL model, NO BAO data always give a largest EoS w; in contrast, BAO2 data always give a smallest w. (3) Compared with the case of BAO1, BAO2 data always give a slightly larger FoM, and thus can give a cosmological constraint with a slightly better accuracy. (4) The impacts of different BAO data on the cosmic evolution and the comic age are very small, and cannot be distinguished by using various dark energy diagnoses and the cosmic age data.

A tilted cold dark matter cosmological scenario

NASA Technical Reports Server (NTRS)

Cen, Renyue; Gnedin, Nickolay Y.; Kofman, Lev A.; Ostriker, Jeremiah P.

1992-01-01

A new cosmological scenario based on CDM but with a power spectrum index of about 0.7-0.8 is suggested. This model is predicted by various inflationary models with no fine tuning. This tilted CDM model, if normalized to COBE, alleviates many problems of the standard CDM model related to both small-scale and large-scale power. A physical bias of galaxies over dark matter of about two is required to fit spatial observations.

Propulsion Physics Using the Chameleon Density Model

NASA Technical Reports Server (NTRS)

Robertson, Glen A.

2011-01-01

To grow as a space faring race, future spaceflight systems will require a new theory of propulsion. Specifically one that does not require mass ejection without limiting the high thrust necessary to accelerate within or beyond our solar system and return within a normal work period or lifetime. The Chameleon Density Model (CDM) is one such model that could provide new paths in propulsion toward this end. The CDM is based on Chameleon Cosmology a dark matter theory; introduced by Khrouy and Weltman in 2004. Chameleon as it is hidden within known physics, where the Chameleon field represents a scalar field within and about an object; even in the vacuum. The CDM relates to density changes in the Chameleon field, where the density changes are related to matter accelerations within and about an object. These density changes in turn change how an object couples to its environment. Whereby, thrust is achieved by causing a differential in the environmental coupling about an object. As a demonstration to show that the CDM fits within known propulsion physics, this paper uses the model to estimate the thrust from a solid rocket motor. Under the CDM, a solid rocket constitutes a two body system, i.e., the changing density of the rocket and the changing density in the nozzle arising from the accelerated mass. Whereby, the interactions between these systems cause a differential coupling to the local gravity environment of the earth. It is shown that the resulting differential in coupling produces a calculated value for the thrust near equivalent to the conventional thrust model used in Sutton and Ross, Rocket Propulsion Elements. Even though imbedded in the equations are the Universe energy scale factor, the reduced Planck mass and the Planck length, which relates the large Universe scale to the subatomic scale.

Efficient simulations of large-scale structure in modified gravity cosmologies with comoving Lagrangian acceleration

NASA Astrophysics Data System (ADS)

Valogiannis, Georgios; Bean, Rachel

2017-05-01

We implement an adaptation of the cola approach, a hybrid scheme that combines Lagrangian perturbation theory with an N-body approach, to model nonlinear collapse in chameleon and symmetron modified gravity models. Gravitational screening is modeled effectively through the attachment of a suppression factor to the linearized Klein-Gordon equations. The adapted cola approach is benchmarked, with respect to an N-body code both for the Λ cold dark matter (Λ CDM ) scenario and for the modified gravity theories. It is found to perform well in the estimation of the dark matter power spectra, with consistency of 1% to k ˜2.5 h /Mpc . Redshift space distortions are shown to be effectively modeled through a Lorentzian parametrization with a velocity dispersion fit to the data. We find that cola performs less well in predicting the halo mass functions but has consistency, within 1 σ uncertainties of our simulations, in the relative changes to the mass function induced by the modified gravity models relative to Λ CDM . The results demonstrate that cola, proposed to enable accurate and efficient, nonlinear predictions for Λ CDM , can be effectively applied to a wider set of cosmological scenarios, with intriguing properties, for which clustering behavior needs to be understood for upcoming surveys such as LSST, DESI, Euclid, and WFIRST.

Cosmic acceleration and the helicity-0 graviton

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rham, Claudia de; Heisenberg, Lavinia; Gabadadze, Gregory

2011-05-15

We explore cosmology in the decoupling limit of a nonlinear covariant extension of Fierz-Pauli massive gravity obtained recently in arXiv:1007.0443. In this limit the theory is a scalar-tensor model of a unique form defined by symmetries. We find that it admits a self-accelerated solution, with the Hubble parameter set by the graviton mass. The negative pressure causing the acceleration is due to a condensate of the helicity-0 component of the massive graviton, and the background evolution, in the approximation used, is indistinguishable from the {Lambda}CDM model. Fluctuations about the self-accelerated background are stable for a certain range of parameters involved.more » Most surprisingly, the fluctuation of the helicity-0 field above its background decouples from an arbitrary source in the linearized theory. We also show how massive gravity can remarkably screen an arbitrarily large cosmological constant in the decoupling limit, while evading issues with ghosts. The obtained static solution is stable against small perturbations, suggesting that the degravitation of the vacuum energy is possible in the full theory. Interestingly, however, this mechanism postpones the Vainshtein effect to shorter distance scales. Hence, fifth force measurements severely constrain the value of the cosmological constant that can be neutralized, making this scheme phenomenologically not viable for solving the old cosmological constant problem. We briefly speculate on a possible way out of this issue.« less

Dark energy constraints in light of Pantheon SNe Ia, BAO, cosmic chronometers and CMB polarization and lensing data

NASA Astrophysics Data System (ADS)

Wang, Deng

2018-06-01

To explore whether there is new physics going beyond the standard cosmological model or not, we constrain seven cosmological models by combining the latest and largest Pantheon Type Ia supernovae sample with the data combination of baryonic acoustic oscillations, cosmic microwave background radiation, Planck lensing and cosmic chronometers. We find that a spatially flat universe is preferred in the framework of Λ CDM cosmology, that the constrained equation of state of dark energy is very consistent with the cosmological constant hypothesis in the ω CDM model, that there is no evidence of dynamical dark energy in the dark energy density-parametrization model, that there is no hint of interaction between dark matter and dark energy in the dark sector of the universe in the decaying vacuum model, and that there does not exist the sterile neutrino in the neutrino sector of the universe in the Λ CDM model. We also give the 95% upper limit of the total mass of three active neutrinos Σ mν<0.178 eV under the assumption of Λ CDM scenario. It is clear that there is no any departure from the standard cosmological model based on current observational datasets.

Nonlocal gravity. Conceptual aspects and cosmological predictions

NASA Astrophysics Data System (ADS)

Belgacem, Enis; Dirian, Yves; Foffa, Stefano; Maggiore, Michele

2018-03-01

Even if the fundamental action of gravity is local, the corresponding quantum effective action, that includes the effect of quantum fluctuations, is a nonlocal object. These nonlocalities are well understood in the ultraviolet regime but much less in the infrared, where they could in principle give rise to important cosmological effects. Here we systematize and extend previous work of our group, in which it is assumed that a mass scale Λ is dynamically generated in the infrared, giving rise to nonlocal terms in the quantum effective action of gravity. We give a detailed discussion of conceptual aspects related to nonlocal gravity (including causality, degrees of freedom, ambiguities related to the boundary conditions of the nonlocal operator, scenarios for the emergence of a dynamical scale in the infrared) and of the cosmological consequences of these models. The requirement of providing a viable cosmological evolution severely restricts the form of the nonlocal terms, and selects a model (the so-called RR model) that corresponds to a dynamical mass generation for the conformal mode. For such a model: (1) there is a FRW background evolution, where the nonlocal term acts as an effective dark energy with a phantom equation of state, providing accelerated expansion without a cosmological constant. (2) Cosmological perturbations are well behaved. (3) Implementing the model in a Boltzmann code and comparing with observations we find that the RR model fits the CMB, BAO, SNe, structure formation data and local H0 measurements at a level statistically equivalent to ΛCDM. (4) Bayesian parameter estimation shows that the value of H0 obtained in the RR model is higher than in ΛCDM, reducing to 2.0σ the tension with the value from local measurements. (5) The RR model provides a prediction for the sum of neutrino masses that falls within the limits set by oscillation and terrestrial experiments (in contrast to ΛCDM, where letting the sum of neutrino masses vary as a free parameter within these limits, one hits the lower bound). (6) Gravitational waves propagate at the speed of light, complying with the limit from GW170817/GRB 170817A.

Universe without dark energy: Cosmic acceleration from dark matter-baryon interactions

NASA Astrophysics Data System (ADS)

Berezhiani, Lasha; Khoury, Justin; Wang, Junpu

2017-06-01

Cosmic acceleration is widely believed to require either a source of negative pressure (i.e., dark energy), or a modification of gravity, which necessarily implies new degrees of freedom beyond those of Einstein gravity. In this paper we present a third possibility, using only dark matter (DM) and ordinary matter. The mechanism relies on the coupling between dark matter and ordinary matter through an effective metric. Dark matter couples to an Einstein-frame metric, and experiences a matter-dominated, decelerating cosmology up to the present time. Ordinary matter couples to an effective metric that depends also on the DM density, in such a way that it experiences late-time acceleration. Linear density perturbations are stable and propagate with arbitrarily small sound speed, at least in the case of "pressure" coupling. Assuming a simple parametrization of the effective metric, we show that our model can successfully match a set of basic cosmological observables, including luminosity distance, baryon acoustic oscillation measurements, angular-diameter distance to last scattering, etc. For the growth history of density perturbations, we find an intriguing connection between the growth factor and the Hubble constant. To get a growth history similar to the Λ CDM prediction, our model predicts a higher H0, closer to the value preferred by direct estimates. On the flip side, we tend to overpredict the growth of structures whenever H0 is comparable to the Planck preferred value. The model also tends to predict larger redshift-space distortions at low redshift than Λ CDM .

Consistency of the Planck CMB data and ΛCDM cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shafieloo, Arman; Hazra, Dhiraj Kumar, E-mail: shafieloo@kasi.re.kr, E-mail: dhiraj.kumar.hazra@apc.univ-paris7.fr

We test the consistency between Planck temperature and polarization power spectra and the concordance model of Λ Cold Dark Matter cosmology (ΛCDM) within the framework of Crossing statistics. We find that Planck TT best fit ΛCDM power spectrum is completely consistent with EE power spectrum data while EE best fit ΛCDM power spectrum is not consistent with TT data. However, this does not point to any systematic or model-data discrepancy since in the Planck EE data, uncertainties are much larger compared to the TT data. We also investigate the possibility of any deviation from ΛCDM model analyzing the Planck 2015more » data. Results from TT, TE and EE data analysis indicate that no deviation is required beyond the flexibility of the concordance ΛCDM model. Our analysis thus rules out any strong evidence for beyond the concordance model in the Planck spectra data. We also report a mild amplitude difference comparing temperature and polarization data, where temperature data seems to have slightly lower amplitude than expected (consistently at all multiples), as we assume both temperature and polarization data are realizations of the same underlying cosmology.« less

Weighing galaxy clusters with gas. II. On the origin of hydrostatic mass bias in ΛCDM galaxy clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, Kaylea; Nagai, Daisuke; Yu, Liang

2014-02-20

The use of galaxy clusters as cosmological probes hinges on our ability to measure their masses accurately and with high precision. Hydrostatic mass is one of the most common methods for estimating the masses of individual galaxy clusters, which suffer from biases due to departures from hydrostatic equilibrium. Using a large, mass-limited sample of massive galaxy clusters from a high-resolution hydrodynamical cosmological simulation, in this work we show that in addition to turbulent and bulk gas velocities, acceleration of gas introduces biases in the hydrostatic mass estimate of galaxy clusters. In unrelaxed clusters, the acceleration bias is comparable to themore » bias due to non-thermal pressure associated with merger-induced turbulent and bulk gas motions. In relaxed clusters, the mean mass bias due to acceleration is small (≲ 3%), but the scatter in the mass bias can be reduced by accounting for gas acceleration. Additionally, this acceleration bias is greater in the outskirts of higher redshift clusters where mergers are more frequent and clusters are accreting more rapidly. Since gas acceleration cannot be observed directly, it introduces an irreducible bias for hydrostatic mass estimates. This acceleration bias places limits on how well we can recover cluster masses from future X-ray and microwave observations. We discuss implications for cluster mass estimates based on X-ray, Sunyaev-Zel'dovich effect, and gravitational lensing observations and their impact on cluster cosmology.« less

Weighing Galaxy Clusters with Gas. II. On the Origin of Hydrostatic Mass Bias in ΛCDM Galaxy Clusters

NASA Astrophysics Data System (ADS)

Nelson, Kaylea; Lau, Erwin T.; Nagai, Daisuke; Rudd, Douglas H.; Yu, Liang

2014-02-01

The use of galaxy clusters as cosmological probes hinges on our ability to measure their masses accurately and with high precision. Hydrostatic mass is one of the most common methods for estimating the masses of individual galaxy clusters, which suffer from biases due to departures from hydrostatic equilibrium. Using a large, mass-limited sample of massive galaxy clusters from a high-resolution hydrodynamical cosmological simulation, in this work we show that in addition to turbulent and bulk gas velocities, acceleration of gas introduces biases in the hydrostatic mass estimate of galaxy clusters. In unrelaxed clusters, the acceleration bias is comparable to the bias due to non-thermal pressure associated with merger-induced turbulent and bulk gas motions. In relaxed clusters, the mean mass bias due to acceleration is small (lsim 3%), but the scatter in the mass bias can be reduced by accounting for gas acceleration. Additionally, this acceleration bias is greater in the outskirts of higher redshift clusters where mergers are more frequent and clusters are accreting more rapidly. Since gas acceleration cannot be observed directly, it introduces an irreducible bias for hydrostatic mass estimates. This acceleration bias places limits on how well we can recover cluster masses from future X-ray and microwave observations. We discuss implications for cluster mass estimates based on X-ray, Sunyaev-Zel'dovich effect, and gravitational lensing observations and their impact on cluster cosmology.

Bayesian evidences for dark energy models in light of current observational data

NASA Astrophysics Data System (ADS)

Lonappan, Anto. I.; Kumar, Sumit; Ruchika; Dinda, Bikash R.; Sen, Anjan A.

2018-02-01

We do a comprehensive study of the Bayesian evidences for a large number of dark energy models using a combination of latest cosmological data from SNIa, CMB, BAO, strong lensing time delay, growth measurements, measurements of Hubble parameter at different redshifts and measurements of angular diameter distance by Megamaser Cosmology Project. We consider a variety of scalar field models with different potentials as well as different parametrizations for the dark energy equation of state. Among 21 models that we consider in our study, we do not find strong evidences in favor of any evolving dark energy model compared to Λ CDM . For the evolving dark energy models, we show that purely nonphantom models have much better evidences compared to those models that allow both phantom and nonphantom behaviors. Canonical scalar field with exponential and tachyon field with square potential have highest evidences among all the models considered in this work. We also show that a combination of low redshift measurements decisively favors an accelerating Λ CDM model compared to a nonaccelerating power law model.

Generalized Brans-Dicke theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Felice, Antonio; Tsujikawa, Shinji, E-mail: defelice@rs.kagu.tus.ac.jp, E-mail: shinji@rs.kagu.tus.ac.jp

2010-07-01

In Brans-Dicke theory a non-linear self interaction of a scalar field φ allows a possibility of realizing the late-time cosmic acceleration, while recovering the General Relativistic behavior at early cosmological epochs. We extend this to more general modified gravitational theories in which a de Sitter solution for dark energy exists without using a field potential. We derive a condition for the stability of the de Sitter point and study the background cosmological dynamics of such theories. We also restrict the allowed region of model parameters from the demand for the avoidance of ghosts and instabilities. A peculiar evolution of themore » field propagation speed allows us to distinguish those theories from the ΛCDM model.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fasiello, Matteo; Vlah, Zvonimir

A specific value for the cosmological constant Λ can account for late-time cosmic acceleration. However, motivated by the so-called cosmological constant problem(s), several alternative mechanisms have been explored. To date, a host of well-studied dynamical dark energy and modified gravity models exists. Going beyond ΛCDM often comes with additional degrees of freedom (dofs). For these to pass existing observational tests, an efficient screening mechanism must be in place. Furthermore, the linear and quasi-linear regimes of structure formation are ideal probes of such dofs and can capture the onset of screening. We propose here a semi-phenomenological “filter” to account for screeningmore » dynamics on LSS observables, with special emphasis on Vainshtein-type screening.« less

Λ(t)CDM model as a unified origin of holographic and agegraphic dark energy models

NASA Astrophysics Data System (ADS)

Chen, Yun; Zhu, Zong-Hong; Xu, Lixin; Alcaniz, J. S.

2011-04-01

Motivated by the fact that any nonzero Λ can introduce a length scale or a time scale into Einstein's theory, r=ct=3/|Λ|. Conversely, any cosmological length scale or time scale can introduce a Λ(t), Λ(t)=3/rΛ2(t)=3/(c2tΛ2(t)). In this Letter, we investigate the time varying Λ(t) corresponding to the length scales, including the Hubble horizon, the particle horizon and the future event horizon, and the time scales, including the age of the universe and the conformal time. It is found out that, in this scenario, the Λ(t)CDM model can be taken as the unified origin of the holographic and agegraphic dark energy models with interaction between the matter and the dark energy, where the interacting term is determined by Q=-ρ. We place observational constraints on the Λ(t)CDM models originating from different cosmological length scales and time scales with the recently compiled “Union2 compilation” which consists of 557 Type Ia supernovae (SNIa) covering a redshift range 0.015⩽z⩽1.4. In conclusion, an accelerating expansion universe can be derived in the cases taking the Hubble horizon, the future event horizon, the age of the universe and the conformal time as the length scale or the time scale.

Universal subhalo accretion in cold and warm dark matter cosmologies

NASA Astrophysics Data System (ADS)

Kubik, Bogna; Libeskind, Noam I.; Knebe, Alexander; Courtois, Hélène; Yepes, Gustavo; Gottlöber, Stefan; Hoffman, Yehuda

2017-12-01

The influence of the large-scale structure on host haloes may be studied by examining the angular infall pattern of subhaloes. In particular, since warm dark matter (WDM) and cold dark matter (CDM) cosmologies predict different abundances and internal properties for haloes at the low-mass end of the mass function, it is interesting to examine if there are differences in how these low-mass haloes are accreted. The accretion events are defined as the moment a halo becomes a substructure, namely when it crosses its host's virial radius. We quantify the cosmic web at each point by the shear tensor and examine where, with respect to its eigenvectors, such accretion events occur in ΛCDM and ΛWDM (1 keV sterile neutrino) cosmological models. We find that the CDM and WDM subhaloes are preferentially accreted along the principal axis of the shear tensor corresponding to the direction of weakest collapse. The beaming strength is modulated by the host and subhalo masses and by the redshift at which the accretion event occurs. Although strongest for the most massive hosts and subhaloes at high redshift, the preferential infall is found to be always aligned with the axis of weakest collapse, thus we say that it has universal nature. We compare the strength of beaming in the ΛWDM cosmology with the one found in the ΛCDM scenario. While the main findings remain the same, the accretion in the ΛWDM model for the most massive host haloes appears more beamed than in ΛCDM cosmology across all the redshifts.

Entropy corrected holographic dark energy models in modified gravity

NASA Astrophysics Data System (ADS)

Jawad, Abdul; Azhar, Nadeem; Rani, Shamaila

We consider the power law and the entropy corrected holographic dark energy (HDE) models with Hubble horizon in the dynamical Chern-Simons modified gravity. We explore various cosmological parameters and planes in this framework. The Hubble parameter lies within the consistent range at the present and later epoch for both entropy corrected models. The deceleration parameter explains the accelerated expansion of the universe. The equation of state (EoS) parameter corresponds to quintessence and cold dark matter (ΛCDM) limit. The ωΛ-ωΛ‧ approaches to ΛCDM limit and freezing region in both entropy corrected models. The statefinder parameters are consistent with ΛCDM limit and dark energy (DE) models. The generalized second law of thermodynamics remain valid in all cases of interacting parameter. It is interesting to mention here that our results of Hubble, EoS parameter and ωΛ-ωΛ‧ plane show consistency with the present observations like Planck, WP, BAO, H0, SNLS and nine-year WMAP.

Method for Direct Measurement of Cosmic Acceleration by 21-cm Absorption Systems

NASA Astrophysics Data System (ADS)

Yu, Hao-Ran; Zhang, Tong-Jie; Pen, Ue-Li

2014-07-01

So far there is only indirect evidence that the Universe is undergoing an accelerated expansion. The evidence for cosmic acceleration is based on the observation of different objects at different distances and requires invoking the Copernican cosmological principle and Einstein's equations of motion. We examine the direct observability using recession velocity drifts (Sandage-Loeb effect) of 21-cm hydrogen absorption systems in upcoming radio surveys. This measures the change in velocity of the same objects separated by a time interval and is a model-independent measure of acceleration. We forecast that for a CHIME-like survey with a decade time span, we can detect the acceleration of a ΛCDM universe with 5σ confidence. This acceleration test requires modest data analysis and storage changes from the normal processing and cannot be recovered retroactively.

Viscous cosmology in new holographic dark energy model and the cosmic acceleration

NASA Astrophysics Data System (ADS)

Singh, C. P.; Srivastava, Milan

2018-03-01

In this work, we study a flat Friedmann-Robertson-Walker universe filled with dark matter and viscous new holographic dark energy. We present four possible solutions of the model depending on the choice of the viscous term. We obtain the evolution of the cosmological quantities such as scale factor, deceleration parameter and transition redshift to observe the effect of viscosity in the evolution. We also emphasis upon the two independent geometrical diagnostics for our model, namely the statefinder and the Om diagnostics. In the first case we study new holographic dark energy model without viscous and obtain power-law expansion of the universe which gives constant deceleration parameter and statefinder parameters. In the limit of the parameter, the model approaches to Λ CDM model. In new holographic dark energy model with viscous, the bulk viscous coefficient is assumed as ζ =ζ 0+ζ 1H, where ζ 0 and ζ 1 are constants, and H is the Hubble parameter. In this model, we obtain all possible solutions with viscous term and analyze the expansion history of the universe. We draw the evolution graphs of the scale factor and deceleration parameter. It is observed that the universe transits from deceleration to acceleration for small values of ζ in late time. However, it accelerates very fast from the beginning for large values of ζ . By illustrating the evolutionary trajectories in r-s and r-q planes, we find that our model behaves as an quintessence like for small values of viscous coefficient and a Chaplygin gas like for large values of bulk viscous coefficient at early stage. However, model has close resemblance to that of the Λ CDM cosmology in late time. The Om has positive and negative curvatures for phantom and quintessence models, respectively depending on ζ . Our study shows that the bulk viscosity plays very important role in the expansion history of the universe.

A 6% measurement of the Hubble parameter at z ∼0.45: direct evidence of the epoch of cosmic re-acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moresco, Michele; Cimatti, Andrea; Citro, Annalisa

2016-05-01

Deriving the expansion history of the Universe is a major goal of modern cosmology. To date, the most accurate measurements have been obtained with Type Ia Supernovae (SNe) and Baryon Acoustic Oscillations (BAO), providing evidence for the existence of a transition epoch at which the expansion rate changes from decelerated to accelerated. However, these results have been obtained within the framework of specific cosmological models that must be implicitly or explicitly assumed in the measurement. It is therefore crucial to obtain measurements of the accelerated expansion of the Universe independently of assumptions on cosmological models. Here we exploit the unprecedentedmore » statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS, [1-3]) Data Release 9 to provide new constraints on the Hubble parameter H ( z ) using the cosmic chronometers approach. We extract a sample of more than 130000 of the most massive and passively evolving galaxies, obtaining five new cosmology-independent H ( z ) measurements in the redshift range 0.3 < z < 0.5, with an accuracy of ∼11–16% incorporating both statistical and systematic errors. Once combined, these measurements yield a 6% accuracy constraint of H ( z = 0.4293) = 91.8 ± 5.3 km/s/Mpc. The new data are crucial to provide the first cosmology-independent determination of the transition redshift at high statistical significance, measuring z {sub t} = 0.4 ± 0.1, and to significantly disfavor the null hypothesis of no transition between decelerated and accelerated expansion at 99.9% confidence level. This analysis highlights the wide potential of the cosmic chronometers approach: it permits to derive constraints on the expansion history of the Universe with results competitive with standard probes, and most importantly, being the estimates independent of the cosmological model, it can constrain cosmologies beyond—and including—the ΛCDM model.« less

Do current cosmological observations rule out all covariant Galileons?

NASA Astrophysics Data System (ADS)

Peirone, Simone; Frusciante, Noemi; Hu, Bin; Raveri, Marco; Silvestri, Alessandra

2018-03-01

We revisit the cosmology of covariant Galileon gravity in view of the most recent cosmological data sets, including weak lensing. As a higher derivative theory, covariant Galileon models do not have a Λ CDM limit and predict a very different structure formation pattern compared with the standard Λ CDM scenario. Previous cosmological analyses suggest that this model is marginally disfavored, yet cannot be completely ruled out. In this work we use a more recent and extended combination of data, and we allow for more freedom in the cosmology, by including a massive neutrino sector with three different mass hierarchies. We use the Planck measurements of cosmic microwave background temperature and polarization; baryonic acoustic oscillations measurements by BOSS DR12; local measurements of H0; the joint light-curve analysis supernovae sample; and, for the first time, weak gravitational lensing from the KiDS Collaboration. We find, that in order to provide a reasonable fit, a nonzero neutrino mass is indeed necessary, but we do not report any sizable difference among the three neutrino hierarchies. Finally, the comparison of the Bayesian evidence to the Λ CDM one shows that in all the cases considered, covariant Galileon models are statistically ruled out by cosmological data.

Hubble Parameter and Baryon Acoustic Oscillation Measurement Constraints on the Hubble Constant, the Deviation from the Spatially Flat ΛCDM Model, the Deceleration–Acceleration Transition Redshift, and Spatial Curvature

NASA Astrophysics Data System (ADS)

Yu, Hai; Ratra, Bharat; Wang, Fa-Yin

2018-03-01

We compile a complete collection of reliable Hubble parameter H(z) data to redshift z ≤ 2.36 and use them with the Gaussian Process method to determine continuous H(z) functions for various data subsets. From these continuous H(z)'s, summarizing across the data subsets considered, we find H 0 ∼ 67 ± 4 km s‑1 Mpc‑1, more consistent with the recent lower values determined using a variety of techniques. In most data subsets, we see a cosmological deceleration–acceleration transition at 2σ significance, with the data subsets transition redshifts varying over 0.33< {z}da}< 1.0 at 1σ significance. We find that the flat-ΛCDM model is consistent with the H(z) data to a z of 1.5 to 2.0, depending on data subset considered, with 2σ deviations from flat-ΛCDM above this redshift range. Using the continuous H(z) with baryon acoustic oscillation distance-redshift observations, we constrain the current spatial curvature density parameter to be {{{Ω }}}K0=-0.03+/- 0.21, consistent with a flat universe, but the large error bar does not rule out small values of spatial curvature that are now under debate.

Large-scale structure in superfluid Chaplygin gas cosmology

NASA Astrophysics Data System (ADS)

Yang, Rongjia

2014-03-01

We investigate the growth of the large-scale structure in the superfluid Chaplygin gas (SCG) model. Both linear and nonlinear growth, such as σ8 and the skewness S3, are discussed. We find the growth factor of SCG reduces to the Einstein-de Sitter case at early times while it differs from the cosmological constant model (ΛCDM) case in the large a limit. We also find there will be more stricture growth on large scales in the SCG scenario than in ΛCDM and the variations of σ8 and S3 between SCG and ΛCDM cannot be discriminated.

Dark Energy Survey Year 1 Results: Cosmological Constraints from Galaxy Clustering and Weak Lensing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbott, T.M.C.; et al.

We present cosmological results from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 degmore » $^2$ of $griz$ imaging data from the first year of the Dark Energy Survey (DES Y1). We combine three two-point functions: (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. To demonstrate the robustness of these results, we use independent pairs of galaxy shape, photometric redshift estimation and validation, and likelihood analysis pipelines. To prevent confirmation bias, the bulk of the analysis was carried out while blind to the true results; we describe an extensive suite of systematics checks performed and passed during this blinded phase. The data are modeled in flat $$\\Lambda$$CDM and $w$CDM cosmologies, marginalizing over 20 nuisance parameters, varying 6 (for $$\\Lambda$$CDM) or 7 (for $w$CDM) cosmological parameters including the neutrino mass density and including the 457 $$\\times$$ 457 element analytic covariance matrix. We find consistent cosmological results from these three two-point functions, and from their combination obtain $$S_8 \\equiv \\sigma_8 (\\Omega_m/0.3)^{0.5} = 0.783^{+0.021}_{-0.025}$$ and $$\\Omega_m = 0.264^{+0.032}_{-0.019}$$ for $$\\Lambda$$CDM for $w$CDM, we find $$S_8 = 0.794^{+0.029}_{-0.027}$$, $$\\Omega_m = 0.279^{+0.043}_{-0.022}$$, and $$w=-0.80^{+0.20}_{-0.22}$$ at 68% CL. The precision of these DES Y1 results rivals that from the Planck cosmic microwave background measurements, allowing a comparison of structure in the very early and late Universe on equal terms. Although the DES Y1 best-fit values for $$S_8$$ and $$\\Omega_m$$ are lower than the central values from Planck ...« less

Galileon gravity in light of ISW, CMB, BAO and H0 data

NASA Astrophysics Data System (ADS)

Renk, Janina; Zumalacárregui, Miguel; Montanari, Francesco; Barreira, Alexandre

2017-10-01

Cosmological models with Galileon gravity are an alternative to the standard ΛCDM paradigm with testable predictions at the level of its self-accelerating solutions for the expansion history, as well as large-scale structure formation. Here, we place constraints on the full parameter space of these models using data from the cosmic microwave background (CMB) (including lensing), baryonic acoustic oscillations (BAO) and the Integrated Sachs-Wolfe (ISW) effect. We pay special attention to the ISW effect for which we use the cross-spectra, ClTg, of CMB temperature maps and foreground galaxies from the WISE survey. The sign of ClTg is set by the time evolution of the lensing potential in the redshift range of the galaxy sample: it is positive if the potential decays (like in ΛCDM), negative if it deepens. We constrain three subsets of Galileon gravity separately known as the Cubic, Quartic and Quintic Galileons. The cubic Galileon model predicts a negative ClTg and exhibits a 7.8σ tension with the data, which effectively rules it out. For the quartic and quintic models the ISW data also rule out a significant portion of the parameter space but permit regions where the goodness-of-fit is comparable to ΛCDM. The data prefers a non zero sum of the neutrino masses (∑mν ≈ 0.5eV) with ~ 5σ significance in these models. The best-fitting models have values of H0 consistent with local determinations, thereby avoiding the tension that exists in ΛCDM. We also identify and discuss a ~ 2σ tension that Galileon gravity exhibits with recent BAO measurements. Our analysis shows overall that Galileon cosmologies cannot be ruled out by current data but future lensing, BAO and ISW data hold strong potential to do so.

Dynamics of cosmological perturbations in modified Brans-Dicke cosmology with matter-scalar field interaction

NASA Astrophysics Data System (ADS)

Kofinas, Georgios; Lima, Nelson A.

2017-10-01

In this work we focus on a novel completion of the well-known Brans-Dicke theory that introduces an interaction between the dark energy and dark matter sectors, known as complete Brans-Dicke (CBD) theory. We obtain viable cosmological accelerating solutions that fit supernovae observations with great precision without any scalar potential V (ϕ ). We use these solutions to explore the impact of the CBD theory on the large scale structure by studying the dynamics of its linear perturbations. We observe a growing behavior of the lensing potential Φ+ at late-times, while the growth rate is actually suppressed relatively to Λ CDM , which allows the CBD theory to provide a competitive fit to current RSD measurements of f σ8. However, we also observe that the theory exhibits a pathological change of sign in the effective gravitational constant concerning the perturbations on subhorizon scales that could pose a challenge to its validity.

Screening in perturbative approaches to LSS

DOE PAGES

Fasiello, Matteo; Vlah, Zvonimir

2017-08-24

A specific value for the cosmological constant Λ can account for late-time cosmic acceleration. However, motivated by the so-called cosmological constant problem(s), several alternative mechanisms have been explored. To date, a host of well-studied dynamical dark energy and modified gravity models exists. Going beyond ΛCDM often comes with additional degrees of freedom (dofs). For these to pass existing observational tests, an efficient screening mechanism must be in place. Furthermore, the linear and quasi-linear regimes of structure formation are ideal probes of such dofs and can capture the onset of screening. We propose here a semi-phenomenological “filter” to account for screeningmore » dynamics on LSS observables, with special emphasis on Vainshtein-type screening.« less

Accelerated cosmological expansion without tension in the Hubble parameter. Fast evolution of the Hubble parameter H(z)

NASA Astrophysics Data System (ADS)

van Putten, Maurice H. P. M.

2018-01-01

The H0-tension problem poses a confrontation of dark energy driving latetime cosmological expansion measured by the Hubble parameter H(z) over an extended range of redshifts z. Distinct values H0 ≃ 73 km s-1 Mpcs-1 and H0 ≃ 68 km s-1 Mpcs-1 obtain from surveys of the Local Universe and, respectively, ΛCBM analysis of the CMB. These are representative of accelerated expansion with H'(0) ≃ 0 by and, respectively, H'(0) > 0 in ΛCDM, where is a fundamental frequency of the cosmological horizon in a Friedmann-Robertson-Walker universe with deceleration parameter q(z) = -1 + (1+z)H-1 H'(z). Explicit solution H(z) = H0 and, respectively, H(z) = H0 are here compared with recent data on H(z) over 0 ≲ z ≲ 2.The first is found to be free of tension with H0 from local surveys, while the latter is disfavored at 2:7σ A further confrontation obtains in galaxy dynamics by a finite sensitivity of inertia to background cosmology in weak gravity, putting an upper bound of m ≲ 10-30 eV on the mass of dark matter. A C0 onset to weak gravity at the de Sitter scale of acceleration adS = cH(z), where c denotes the velocity of light, can be seen in galaxy rotation curves covering 0 ≲ z ≲ 2 Weak gravity in galaxy dynamics hereby provides a proxy for cosmological evolution.

Cosmological tests of modified gravity.

PubMed

Koyama, Kazuya

2016-04-01

We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years.

Higgs-dilaton cosmology: An inflation-dark-energy connection and forecasts for future galaxy surveys

NASA Astrophysics Data System (ADS)

Casas, Santiago; Pauly, Martin; Rubio, Javier

2018-02-01

The Higgs-dilaton model is a scale-invariant extension of the Standard Model nonminimally coupled to gravity and containing just one additional degree of freedom on top of the Standard Model particle content. This minimalistic scenario predicts a set of measurable consistency relations between the inflationary observables and the dark-energy equation-of-state parameter. We present an alternative derivation of these consistency relations that highlights the connections and differences with the α -attractor scenario. We study how far these constraints allow one to distinguish the Higgs-dilaton model from Λ CDM and w CDM cosmologies. To this end we first analyze existing data sets using a Markov chain Monte Carlo approach. Second, we perform forecasts for future galaxy surveys using a Fisher matrix approach, both for galaxy clustering and weak lensing probes. Assuming that the best fit values in the different models remain comparable to the present ones, we show that both Euclid- and SKA2-like missions will be able to discriminate a Higgs-dilaton cosmology from Λ CDM and w CDM .

Constraints on Cosmological Parameters from the Angular Power Spectrum of a Combined 2500 deg$^2$ SPT-SZ and Planck Gravitational Lensing Map

DOE PAGES

Simard, G.; et al.

2018-06-20

We report constraints on cosmological parameters from the angular power spectrum of a cosmic microwave background (CMB) gravitational lensing potential map created using temperature data from 2500 degmore » $^2$ of South Pole Telescope (SPT) data supplemented with data from Planck in the same sky region, with the statistical power in the combined map primarily from the SPT data. We fit the corresponding lensing angular power spectrum to a model including cold dark matter and a cosmological constant ($$\\Lambda$$CDM), and to models with single-parameter extensions to $$\\Lambda$$CDM. We find constraints that are comparable to and consistent with constraints found using the full-sky Planck CMB lensing data. Specifically, we find $$\\sigma_8 \\Omega_{\\rm m}^{0.25}=0.598 \\pm 0.024$$ from the lensing data alone with relatively weak priors placed on the other $$\\Lambda$$CDM parameters. In combination with primary CMB data from Planck, we explore single-parameter extensions to the $$\\Lambda$$CDM model. We find $$\\Omega_k = -0.012^{+0.021}_{-0.023}$$ or $$M_{\

Constraints on Cosmological Parameters from the Angular Power Spectrum of a Combined 2500 deg$^2$ SPT-SZ and Planck Gravitational Lensing Map

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simard, G.; et al.

We report constraints on cosmological parameters from the angular power spectrum of a cosmic microwave background (CMB) gravitational lensing potential map created using temperature data from 2500 degmore » $^2$ of South Pole Telescope (SPT) data supplemented with data from Planck in the same sky region, with the statistical power in the combined map primarily from the SPT data. We fit the corresponding lensing angular power spectrum to a model including cold dark matter and a cosmological constant ($$\\Lambda$$CDM), and to models with single-parameter extensions to $$\\Lambda$$CDM. We find constraints that are comparable to and consistent with constraints found using the full-sky Planck CMB lensing data. Specifically, we find $$\\sigma_8 \\Omega_{\\rm m}^{0.25}=0.598 \\pm 0.024$$ from the lensing data alone with relatively weak priors placed on the other $$\\Lambda$$CDM parameters. In combination with primary CMB data from Planck, we explore single-parameter extensions to the $$\\Lambda$$CDM model. We find $$\\Omega_k = -0.012^{+0.021}_{-0.023}$$ or $$M_{\

Addressing Beyond Standard Model physics using cosmology

NASA Astrophysics Data System (ADS)

Ghalsasi, Akshay

We have consensus models for both particle physics (i.e. standard model) and cosmology (i.e. LambdaCDM). Given certain assumptions about the initial conditions of the universe, the marriage of the standard model (SM) of particle physics and LambdaCDM cosmology has been phenomenally successful in describing the universe we live in. However it is quite clear that all is not well. The three biggest problems that the SM faces today are baryogenesis, dark matter and dark energy. These problems, along with the problem of neutrino masses, indicate the existence of physics beyond SM. Evidence of baryogenesis, dark matter and dark energy all comes from astrophysical and cosmological observations. Cosmology also provides the best (model dependent) constraints on neutrino masses. In this thesis I will try address the following problems 1) Addressing the origin of dark energy (DE) using non-standard neutrino cosmology and exploring the effects of the non-standard neutrino cosmology on terrestrial and cosmological experiments. 2) Addressing the matter anti-matter asymmetry of the universe.

Searching for sterile neutrinos in dynamical dark energy cosmologies

NASA Astrophysics Data System (ADS)

Feng, Lu; Zhang, Jing-Fei; Zhang, Xin

2018-05-01

We investigate how the dark energy properties change the cosmological limits on sterile neutrino parameters by using recent cosmological observations. We consider the simplest dynamical dark energy models, the wCDM model and the holographic dark energy (HDE) model, to make an analysis. The cosmological observations used in this work include the Planck 2015 CMB temperature and polarization data, the baryon acoustic oscillation data, the type Ia supernova data, the Hubble constant direct measurement data, and the Planck CMB lensing data. We find that, m v,terile ff < 0.2675 eV and Ne f f < 3.5718 for ACDM cosmology, m v,terile ff < 0.5313 eV and Ne f f < 3.5008 for wCDM cosmology, and raffterile < 0.1989 eV and Ne f f < 3.6701 for HDE cosmology, from the constraints of the combination of these data. Thus, without the addition of measurements of growth of structure, only upper limits on both m v,terile ff and Ne f f can be derived, indicating that no evidence of the existence of a sterile neutrino species with eV-scale mass is found in this analysis. Moreover, compared to the ACDM model, in the wCDM model the limit on m v,terile ff becomes much looser, but in the HDE model the limit becomes much tighter. Therefore, the dark energy properties could significantly influence the constraint limits of sterile neutrino parameters.

Beyond Λ CDM: Problems, solutions, and the road ahead

NASA Astrophysics Data System (ADS)

Bull, Philip; Akrami, Yashar; Adamek, Julian; Baker, Tessa; Bellini, Emilio; Beltrán Jiménez, Jose; Bentivegna, Eloisa; Camera, Stefano; Clesse, Sébastien; Davis, Jonathan H.; Di Dio, Enea; Enander, Jonas; Heavens, Alan; Heisenberg, Lavinia; Hu, Bin; Llinares, Claudio; Maartens, Roy; Mörtsell, Edvard; Nadathur, Seshadri; Noller, Johannes; Pasechnik, Roman; Pawlowski, Marcel S.; Pereira, Thiago S.; Quartin, Miguel; Ricciardone, Angelo; Riemer-Sørensen, Signe; Rinaldi, Massimiliano; Sakstein, Jeremy; Saltas, Ippocratis D.; Salzano, Vincenzo; Sawicki, Ignacy; Solomon, Adam R.; Spolyar, Douglas; Starkman, Glenn D.; Steer, Danièle; Tereno, Ismael; Verde, Licia; Villaescusa-Navarro, Francisco; von Strauss, Mikael; Winther, Hans A.

2016-06-01

Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, Λ CDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of Λ CDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.

Generalized framework for testing gravity with gravitational-wave propagation. II. Constraints on Horndeski theory

NASA Astrophysics Data System (ADS)

Arai, Shun; Nishizawa, Atsushi

2018-05-01

Gravitational waves (GW) are generally affected by modification of a gravity theory during propagation at cosmological distances. We numerically perform a quantitative analysis on Horndeski theory at the cosmological scale to constrain the Horndeski theory by GW observations in a model-independent way. We formulate a parametrization for a numerical simulation based on the Monte Carlo method and obtain the classification of the models that agrees with cosmic accelerating expansion within observational errors of the Hubble parameter. As a result, we find that a large group of the models in the Horndeski theory that mimic cosmic expansion of the Λ CDM model can be excluded from the simultaneous detection of a GW and its electromagnetic transient counterpart. Based on our result and the latest detection of GW170817 and GRB170817A, we conclude that the subclass of Horndeski theory including arbitrary functions G4 and G5 can hardly explain cosmic accelerating expansion without fine-tuning.

On the anisotropic satellite distribution around Milky-way-like galaxies in cosmological simulations.

NASA Astrophysics Data System (ADS)

Kihm, Seoneui; Seo, Seongu; Yoon, Suk-jin

2018-01-01

The presence of "anisotropic satellite distribution (ASD)" around massive galaxies is often taken as evidence against the ΛCDM cosmology. To address whether such anisotropy can be reconciled with the standard cosmology, we examine the spatial distributions of satellites around central galaxies in the hydrodynamic cosmological simulation, Illustris. In an attempt to understand the ASD of our Galaxy, we limit our analysis to the systems consisting of a MW-sized host and at least 11 satellites. We find that ASDs are rather a common feature in the simulation and that ASD systems tend to possess a larger fraction of recently accreted satellites than isotropy systems. We discuss a possible link of ASD formation to the surrounding environment in the ΛCDM setting.

Effective field theory of cosmic acceleration: Constraining dark energy with CMB data

NASA Astrophysics Data System (ADS)

Raveri, Marco; Hu, Bin; Frusciante, Noemi; Silvestri, Alessandra

2014-08-01

We introduce EFTCAMB/EFTCosmoMC as publicly available patches to the commonly used camb/CosmoMC codes. We briefly describe the structure of the codes, their applicability and main features. To illustrate the use of these patches, we obtain constraints on parametrized pure effective field theory and designer f(R) models, both on ΛCDM and wCDM background expansion histories, using data from Planck temperature and lensing potential spectra, WMAP low-ℓ polarization spectra (WP), and baryon acoustic oscillations (BAO). Upon inspecting the theoretical stability of the models on the given background, we find nontrivial parameter spaces that we translate into viability priors. We use different combinations of data sets to show their individual effects on cosmological and model parameters. Our data analysis results show that, depending on the adopted data sets, in the wCDM background case these viability priors could dominate the marginalized posterior distributions. Interestingly, with Planck +WP+BAO+lensing data, in f(R) gravity models, we get very strong constraints on the constant dark energy equation of state, w0∈(-1,-0.9997) (95% C.L.).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wojtak, Radosław; Prada, Francisco

The standard relation between the cosmological redshift and cosmic scale factor underlies cosmological inference from virtually all kinds of cosmological observations, leading to the emergence of the LambdaCDM cosmological model. This relation is not a fundamental theory and thus observational determination of this function (redshift remapping) should be regarded as an insightful alternative to holding its standard form in analyses of cosmological data. We present non-parametric reconstructions of redshift remapping in dark-matter-dominated models and constraints on cosmological parameters from a joint analysis of all primary cosmological probes including the local measurement of the Hubble constant, Type Ia supernovae, baryonic acousticmore » oscillations (BAO), Planck observations of the cosmic microwave background (CMB) radiation (temperature power spectrum) and cosmic chronometers. The reconstructed redshift remapping points to an additional boost of redshift operating in late epoch of cosmic evolution, but affecting both low-redshift observations and the CMB. The model then predicts a significant difference between the actual Hubble constant, h=0.48±0.02, and its local determination, h obs=0.73±0.02. The ratio of these two values coincides closely with the maximum expansion rate inside voids formed in the corresponding open cosmological model with Ω m=0.87±0.03, whereas the actual value of the Hubble constant implies the age of the Universe that is compatible with the Planck LambdaCDM cosmology. The new dark-matter-dominated model with redshift remapping provides excellent fits to all data and eliminates recently reported tensions between the Planck LambdaCDM cosmology, the local determination of the Hubble constant and the BAO measurements from the Ly α forest of high-redshift quasars.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dhawan, Suhail; Goobar, Ariel; Mörtsell, Edvard

Recent re-calibration of the Type Ia supernova (SNe Ia) magnitude-redshift relation combined with cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) data have provided excellent constraints on the standard cosmological model. Here, we examine particular classes of alternative cosmologies, motivated by various physical mechanisms, e.g. scalar fields, modified gravity and phase transitions to test their consistency with observations of SNe Ia and the ratio of the angular diameter distances from the CMB and BAO. Using a model selection criterion for a relative comparison of the models (the Bayes Factor), we find moderate to strong evidence that the data prefermore » flat ΛCDM over models invoking a thawing behaviour of the quintessence scalar field. However, some exotic models like the growing neutrino mass cosmology and vacuum metamorphosis still present acceptable evidence values. The bimetric gravity model with only the linear interaction term as well as a simplified Galileon model can be ruled out by the combination of SNe Ia and CMB/BAO datasets whereas the model with linear and quadratic interaction terms has a comparable evidence value to standard ΛCDM. Thawing models are found to have significantly poorer evidence compared to flat ΛCDM cosmology under the assumption that the CMB compressed likelihood provides an adequate description for these non-standard cosmologies. We also present estimates for constraints from future data and find that geometric probes from oncoming surveys can put severe limits on non-standard cosmological models.« less

A cosmology-independent calibration of type Ia supernovae data

NASA Astrophysics Data System (ADS)

Hauret, C.; Magain, P.; Biernaux, J.

2018-06-01

Recently, the common methodology used to transform type Ia supernovae (SNe Ia) into genuine standard candles has been suffering criticism. Indeed, it assumes a particular cosmological model (namely the flat ΛCDM) to calibrate the standardisation corrections parameters, i.e. the dependency of the supernova peak absolute magnitude on its colour, post-maximum decline rate and host galaxy mass. As a result, this assumption could make the data compliant to the assumed cosmology and thus nullify all works previously conducted on model comparison. In this work, we verify the viability of these hypotheses by developing a cosmology-independent approach to standardise SNe Ia data from the recent JLA compilation. Our resulting corrections turn out to be very close to the ΛCDM-based corrections. Therefore, even if a ΛCDM-based calibration is questionable from a theoretical point of view, the potential compliance of SNe Ia data does not happen in practice for the JLA compilation. Previous works of model comparison based on these data do not have to be called into question. However, as this cosmology-independent standardisation method has the same degree of complexity than the model-dependent one, it is worth using it in future works, especially if smaller samples are considered, such as the superluminous type Ic supernovae.

Integrated cosmological probes: concordance quantified

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nicola, Andrina; Amara, Adam; Refregier, Alexandre, E-mail: andrina.nicola@phys.ethz.ch, E-mail: adam.amara@phys.ethz.ch, E-mail: alexandre.refregier@phys.ethz.ch

2017-10-01

Assessing the consistency of parameter constraints derived from different cosmological probes is an important way to test the validity of the underlying cosmological model. In an earlier work [1], we computed constraints on cosmological parameters for ΛCDM from an integrated analysis of CMB temperature anisotropies and CMB lensing from Planck, galaxy clustering and weak lensing from SDSS, weak lensing from DES SV as well as Type Ia supernovae and Hubble parameter measurements. In this work, we extend this analysis and quantify the concordance between the derived constraints and those derived by the Planck Collaboration as well as WMAP9, SPT andmore » ACT. As a measure for consistency, we use the Surprise statistic [2], which is based on the relative entropy. In the framework of a flat ΛCDM cosmological model, we find all data sets to be consistent with one another at a level of less than 1σ. We highlight that the relative entropy is sensitive to inconsistencies in the models that are used in different parts of the analysis. In particular, inconsistent assumptions for the neutrino mass break its invariance on the parameter choice. When consistent model assumptions are used, the data sets considered in this work all agree with each other and ΛCDM, without evidence for tensions.« less

Cosmic acceleration in non-flat f( T) cosmology

NASA Astrophysics Data System (ADS)

Capozziello, Salvatore; Luongo, Orlando; Pincak, Richard; Ravanpak, Arvin

2018-05-01

We study f( T) cosmological models inserting a non-vanishing spatial curvature and discuss its consequences on cosmological dynamics. To figure this out, a polynomial f( T) model and a double torsion model are considered. We first analyze those models with cosmic data, employing the recent surveys of Union 2.1, baryonic acoustic oscillation and cosmic microwave background measurements. We then emphasize that the two popular f( T) models enable the crossing of the phantom divide line due to dark torsion. Afterwards, we compute numerical bounds up to 3-σ confidence level, emphasizing the fact that Ω _{k0} turns out to be non-compatible with zero at least at 1σ . Moreover, we underline that, even increasing the accuracy, one cannot remove the degeneracy between our models and the Λ CDM paradigm. So that, we show that our treatments contain the concordance paradigm and we analyze the equation of state behaviors at different redshift domains. We also take into account gamma ray bursts and we describe the evolution of both the f( T) models with high redshift data. We calibrate the gamma ray burst measurements through small redshift surveys of data and we thus compare the main differences between non-flat and flat f( T) cosmology at different redshift ranges. We finally match the corresponding outcomes with small redshift bounds provided by cosmography. To do so, we analyze the deceleration parameters and their variations, proportional to the jerk term. Even though the two models well fit late-time data, we notice that the polynomial f( T) approach provides an effective de-Sitter phase, whereas the second f( T) framework shows analogous results compared with the Λ CDM predictions.

Hidden from view: coupled dark sector physics and small scales

NASA Astrophysics Data System (ADS)

Elahi, Pascal J.; Lewis, Geraint F.; Power, Chris; Carlesi, Edoardo; Knebe, Alexander

2015-09-01

We study cluster mass dark matter (DM) haloes, their progenitors and surroundings in a coupled dark matter-dark energy (DE) model and compare it to quintessence and Λ cold dark matter (ΛCDM) models with adiabatic zoom simulations. When comparing cosmologies with different expansions histories, growth functions and power spectra, care must be taken to identify unambiguous signatures of alternative cosmologies. Shared cosmological parameters, such as σ8, need not be the same for optimal fits to observational data. We choose to set our parameters to ΛCDM z = 0 values. We find that in coupled models, where DM decays into DE, haloes appear remarkably similar to ΛCDM haloes despite DM experiencing an additional frictional force. Density profiles are not systematically different and the subhalo populations have similar mass, spin, and spatial distributions, although (sub)haloes are less concentrated on average in coupled cosmologies. However, given the scatter in related observables (V_max,R_{V_max}), this difference is unlikely to distinguish between coupled and uncoupled DM. Observations of satellites of Milky Way and M31 indicate a significant subpopulation reside in a plane. Coupled models do produce planar arrangements of satellites of higher statistical significance than ΛCDM models; however, in all models these planes are dynamically unstable. In general, the non-linear dynamics within and near large haloes masks the effects of a coupled dark sector. The sole environmental signature we find is that small haloes residing in the outskirts are more deficient in baryons than their ΛCDM counterparts. The lack of a pronounced signal for a coupled dark sector strongly suggests that such a phenomena would be effectively hidden from view.

Cosmological test with the QSO Hubble diagram

NASA Astrophysics Data System (ADS)

López-Corredoira, M.; Melia, F.; Lusso, E.; Risaliti, G.

2016-03-01

A Hubble diagram (HD) has recently been constructed in the redshift range 0 ≲ z ≲ 6.5 using a nonlinear relation between the ultraviolet (UV) and X-ray luminosities of quasi stellar objects (QSOs). The Type Ia Supernovae (SN) HD has already provided a high-precision test of cosmological models, but the fact that the QSO distribution extends well beyond the supernova range (z ≲ 1.8), in principle provides us with an important complementary diagnostic whose significantly greater leverage in z can impose tighter constraints on the distance versus redshift relationship. In this paper, we therefore perform an independent test of nine different cosmological models, among which six are expanding, while three are static. Many of these are disfavored by other kinds of observations (including the aforementioned Type Ia SNe). We wish to examine whether the QSO HD confirms or rejects these earlier conclusions. We find that four of these models (Einstein-de Sitter, the Milne universe, the static universe with simple tired light and the static universe with plasma tired light) are excluded at the > 99% C.L. The quasi-steady state model is excluded at > 95% C.L. The remaining four models (ΛCDM/wCDM, the Rh = ct universe, the Friedmann open universe and a static universe with a linear Hubble law) all pass the test. However, only ΛCDM/wCDM and Rh = ct also pass the Alcock-Paczyński (AP) test. The optimized parameters in ΛCDM/wCDM are Ωm = 0.20-0.20+0.24 and wde = -1.2-∞+1.6 (the dark energy equation-of-state). Combined with the AP test, these values become Ωm = 0.38-0.19+0.20 and wde = -0.28-0.40+0.52. But whereas this optimization of parameters in ΛCDM/wCDM creates some tension with their concordance values, the Rh = ct universe has the advantage of fitting the QSO and AP data without any free parameters.

Kaluza-Klein cosmological model in f(R, T) gravity with Λ(T)

NASA Astrophysics Data System (ADS)

Sahoo, P. K.; Mishra, B.; Tripathy, S. K.

2016-04-01

A class of Kaluza-Klein cosmological models in $f(R,T)$ theory of gravity have been investigated. In the work, we have considered the functional $f(R,T)$ to be in the form $f(R,T)=f(R)+f(T)$ with $f(R)=\\lambda R$ and $f(T)=\\lambda T$. Such a choice of the functional $f(R,T)$ leads to an evolving effective cosmological constant $\\Lambda$ which depends on the stress energy tensor. The source of the matter field is taken to be a perfect cosmic fluid. The exact solutions of the field equations are obtained by considering a constant deceleration parameter which leads two different aspects of the volumetric expansion namely a power law and an exponential volumetric expansion. Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models have been discussed. From statefinder diagnostic pair we found that the model with exponential volumetric expansion behaves more like a $\\Lambda$CDM model.

Updated reduced CMB data and constraints on cosmological parameters

NASA Astrophysics Data System (ADS)

Cai, Rong-Gen; Guo, Zong-Kuan; Tang, Bo

2015-07-01

We obtain the reduced CMB data {lA, R, z∗} from WMAP9, WMAP9+BKP, Planck+WP and Planck+WP+BKP for the ΛCDM and wCDM models with or without spatial curvature. We then use these reduced CMB data in combination with low-redshift observations to put constraints on cosmological parameters. We find that including BKP results in a higher value of the Hubble constant especially when the equation of state (EOS) of dark energy and curvature are allowed to vary. For the ΛCDM model with curvature, the estimate of the Hubble constant with Planck+WP+Lensing is inconsistent with the one derived from Planck+WP+BKP at about 1.2σ confidence level (CL).

Dynamical dark energy vs. Λ = const in light of observations

NASA Astrophysics Data System (ADS)

Solà Peracaula, Joan; de Cruz Pérez, Javier; Gómez-Valent, Adrià

2018-02-01

After about two decades of the first observational papers confirming the accelerated expansion of the universe, we are still facing the question whether the cause of it is a rigid cosmological constant Λ-term or a mildly evolving dynamical dark energy (DDE). While studies focusing mainly on CMB measurements do not perceive signs of physics beyond the ΛCDM, in this work we show that if we take a large string SNIa+BAO+H(z)+LSS+CMB of modern cosmological observations, in which not only the CMB but also a rich sample of large-scale structure formation data are included, one can extract ∼3.3σ signs of DDE using a simple XCDM parameterization. These signs can be enhanced up to near 3.8σ in the context of the running vacuum model (RVM), in which the vacuum energy density is in interaction with dark matter. Recently, the RVM has been shown to provide an efficient and economical solution to the σ8 -tension, which is one of the intriguing phenomenological problems that has not been possible to solve within the ΛCDM so far. This fact contributes to strengthen the possibility that dynamical vacuum energy, or in general DDE, could be presently favored by the observations.

Dynamics of supersymmetric chameleons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brax, Philippe; Davis, Anne-Christine; Sakstein, Jeremy, E-mail: Philippe.Brax@cea.fr, E-mail: A.C.Davis@damtp.cam.ac.uk, E-mail: J.A.Sakstein@damtp.cam.ac.uk

2013-10-01

We investigate the cosmological dynamics of a class of supersymmetric chameleon models coupled to cold dark matter fermions. The model includes a cosmological constant in the form of a Fayet-Illiopoulos term, which emerges at late times due to the coupling of the chameleon to two charged scalars. Supergravity corrections ensure that the supersymmetric chameleons are efficiently screened in all astrophysical objects of interest, however this does not preclude the enhancement of gravity on linear cosmological scales. We solve the modified equations for the growth of cold dark matter density perturbations in closed form in the matter era. Using this, wemore » go on to derive the modified linear power spectrum which is characterised by two scales, the horizon size at matter-radiation equality and at the redshift when the chameleon reaches the minimum of its effective potential. We analyse the deviations from the ΛCDM predictions in the linear regime. We find that there is generically a region in the model's parameter space where the model's background cosmology coincides with that of the ΛCDM model. Furthermore, we find that characteristic deviations from ΛCDM are present on the matter power spectrum providing a clear signature of supersymmetric chameleons.« less

From Planck Data to Planck Era: Observational Tests of Holographic Cosmology

NASA Astrophysics Data System (ADS)

Afshordi, Niayesh; Corianò, Claudio; Delle Rose, Luigi; Gould, Elizabeth; Skenderis, Kostas

2017-01-01

We test a class of holographic models for the very early Universe against cosmological observations and find that they are competitive to the standard cold dark matter model with a cosmological constant (Λ CDM ) of cosmology. These models are based on three-dimensional perturbative superrenormalizable quantum field theory (QFT), and, while they predict a different power spectrum from the standard power law used in Λ CDM , they still provide an excellent fit to the data (within their regime of validity). By comparing the Bayesian evidence for the models, we find that Λ CDM does a better job globally, while the holographic models provide a (marginally) better fit to the data without very low multipoles (i.e., l ≲30 ), where the QFT becomes nonperturbative. Observations can be used to exclude some QFT models, while we also find models satisfying all phenomenological constraints: The data rule out the dual theory being a Yang-Mills theory coupled to fermions only but allow for a Yang-Mills theory coupled to nonminimal scalars with quartic interactions. Lattice simulations of 3D QFTs can provide nonperturbative predictions for large-angle statistics of the cosmic microwave background and potentially explain its apparent anomalies.

From Planck Data to Planck Era: Observational Tests of Holographic Cosmology.

PubMed

Afshordi, Niayesh; Corianò, Claudio; Delle Rose, Luigi; Gould, Elizabeth; Skenderis, Kostas

2017-01-27

We test a class of holographic models for the very early Universe against cosmological observations and find that they are competitive to the standard cold dark matter model with a cosmological constant (ΛCDM) of cosmology. These models are based on three-dimensional perturbative superrenormalizable quantum field theory (QFT), and, while they predict a different power spectrum from the standard power law used in ΛCDM, they still provide an excellent fit to the data (within their regime of validity). By comparing the Bayesian evidence for the models, we find that ΛCDM does a better job globally, while the holographic models provide a (marginally) better fit to the data without very low multipoles (i.e., l≲30), where the QFT becomes nonperturbative. Observations can be used to exclude some QFT models, while we also find models satisfying all phenomenological constraints: The data rule out the dual theory being a Yang-Mills theory coupled to fermions only but allow for a Yang-Mills theory coupled to nonminimal scalars with quartic interactions. Lattice simulations of 3D QFTs can provide nonperturbative predictions for large-angle statistics of the cosmic microwave background and potentially explain its apparent anomalies.

Hydrodynamical simulations of coupled and uncoupled quintessence models - II. Galaxy clusters

NASA Astrophysics Data System (ADS)

Carlesi, Edoardo; Knebe, Alexander; Lewis, Geraint F.; Yepes, Gustavo

2014-04-01

We study the z = 0 properties of clusters (and large groups) of galaxies within the context of interacting and non-interacting quintessence cosmological models, using a series of adiabatic SPH simulations. Initially, we examine the average properties of groups and clusters, quantifying their differences in ΛCold Dark Matter (ΛCDM), uncoupled Dark Energy (uDE) and coupled Dark Energy (cDE) cosmologies. In particular, we focus upon radial profiles of the gas density, temperature and pressure, and we also investigate how the standard hydrodynamic equilibrium hypothesis holds in quintessence cosmologies. While we are able to confirm previous results about the distribution of baryons, we also find that the main discrepancy (with differences up to 20 per cent) can be seen in cluster pressure profiles. We then switch attention to individual structures, mapping each halo in quintessence cosmology to its ΛCDM counterpart. We are able to identify a series of small correlations between the coupling in the dark sector and halo spin, triaxiality and virialization ratio. When looking at spin and virialization of dark matter haloes, we find a weak (5 per cent) but systematic deviation in fifth force scenarios from ΛCDM.

THE CHALLENGE OF THE LARGEST STRUCTURES IN THE UNIVERSE TO COSMOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Changbom; Choi, Yun-Young; Kim, Sungsoo S.

2012-11-01

Large galaxy redshift surveys have long been used to constrain cosmological models and structure formation scenarios. In particular, the largest structures discovered observationally are thought to carry critical information on the amplitude of large-scale density fluctuations or homogeneity of the universe, and have often challenged the standard cosmological framework. The Sloan Great Wall (SGW) recently found in the Sloan Digital Sky Survey (SDSS) region casts doubt on the concordance cosmological model with a cosmological constant (i.e., the flat {Lambda}CDM model). Here we show that the existence of the SGW is perfectly consistent with the {Lambda}CDM model, a result that onlymore » our very large cosmological N-body simulation (the Horizon Run 2, HR2) could supply. In addition, we report on the discovery of a void complex in the SDSS much larger than the SGW, and show that such size of the largest void is also predicted in the {Lambda}CDM paradigm. Our results demonstrate that an initially homogeneous isotropic universe with primordial Gaussian random phase density fluctuations growing in accordance with the general relativity can explain the richness and size of the observed large-scale structures in the SDSS. Using the HR2 simulation we predict that a future galaxy redshift survey about four times deeper or with 3 mag fainter limit than the SDSS should reveal a largest structure of bright galaxies about twice as big as the SGW.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Renk, Janina; Zumalacárregui, Miguel; Montanari, Francesco

Cosmological models with Galileon gravity are an alternative to the standard ΛCDM paradigm with testable predictions at the level of its self-accelerating solutions for the expansion history, as well as large-scale structure formation. Here, we place constraints on the full parameter space of these models using data from the cosmic microwave background (CMB) (including lensing), baryonic acoustic oscillations (BAO) and the Integrated Sachs-Wolfe (ISW) effect. We pay special attention to the ISW effect for which we use the cross-spectra, C {sub ℓ}{sup Tg}, of CMB temperature maps and foreground galaxies from the WISE survey. The sign of C {sub ℓ}{supmore » Tg} is set by the time evolution of the lensing potential in the redshift range of the galaxy sample: it is positive if the potential decays (like in ΛCDM), negative if it deepens. We constrain three subsets of Galileon gravity separately known as the Cubic, Quartic and Quintic Galileons. The cubic Galileon model predicts a negative C {sub ℓ}{sup Tg} and exhibits a 7.8σ tension with the data, which effectively rules it out. For the quartic and quintic models the ISW data also rule out a significant portion of the parameter space but permit regions where the goodness-of-fit is comparable to ΛCDM. The data prefers a non zero sum of the neutrino masses (∑ m {sub ν} ≈ 0.5eV) with ∼ 5σ significance in these models. The best-fitting models have values of H {sub 0} consistent with local determinations, thereby avoiding the tension that exists in ΛCDM. We also identify and discuss a ∼ 2σ tension that Galileon gravity exhibits with recent BAO measurements. Our analysis shows overall that Galileon cosmologies cannot be ruled out by current data but future lensing, BAO and ISW data hold strong potential to do so.« less

What Expands in an Expanding Universe?

PubMed

Pacheco, José A De Freitas

2015-01-01

In the present investigation, the possible effects of the expansion of the Universe on systems bonded either by gravitational or electromagnetic forces, are reconsidered. It will be shown that the acceleration (positive or negative) of the expanding background, is the determinant factor affecting planetary orbits and atomic sizes. In the presently accepted cosmology (ΛCDM) all bonded systems are expanding at a decreasing rate that tends to be zero as the universe enters in a de Sitter phase. It is worth mentioning that the estimated expansion rates are rather small and they can be neglected for all practical purposes.

An analytic formula for the supercluster mass function

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Seunghwan; Lee, Jounghun, E-mail: slim@astro.umass.edu, E-mail: jounghun@astro.snu.ac.kr

2014-03-01

We present an analytic formula for the supercluster mass function, which is constructed by modifying the extended Zel'dovich model for the halo mass function. The formula has two characteristic parameters whose best-fit values are determined by fitting to the numerical results from N-body simulations for the standard ΛCDM cosmology. The parameters are found to be independent of redshifts and robust against variation of the key cosmological parameters. Under the assumption that the same formula for the supercluster mass function is valid for non-standard cosmological models, we show that the relative abundance of the rich superclusters should be a powerful indicatormore » of any deviation of the real universe from the prediction of the standard ΛCDM model.« less

Non-local gravity and comparison with observational datasets. II. Updated results and Bayesian model comparison with ΛCDM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dirian, Yves; Foffa, Stefano; Kunz, Martin

We present a comprehensive and updated comparison with cosmological observations of two non-local modifications of gravity previously introduced by our group, the so called RR and RT models. We implement the background evolution and the cosmological perturbations of the models in a modified Boltzmann code, using CLASS. We then test the non-local models against the Planck 2015 TT, TE, EE and Cosmic Microwave Background (CMB) lensing data, isotropic and anisotropic Baryonic Acoustic Oscillations (BAO) data, JLA supernovae, H {sub 0} measurements and growth rate data, and we perform Bayesian parameter estimation. We then compare the RR, RT and ΛCDM models,more » using the Savage-Dickey method. We find that the RT model and ΛCDM perform equally well, while the performance of the RR model with respect to ΛCDM depends on whether or not we include a prior on H {sub 0} based on local measurements.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simard, G.; et al.

We report constraints on cosmological parameters from the angular power spectrum of a cosmic microwave background (CMB) gravitational lensing potential map created using temperature data from 2500 degmore » $^2$ of South Pole Telescope (SPT) data supplemented with data from Planck in the same sky region, with the statistical power in the combined map primarily from the SPT data. We fit the corresponding lensing angular power spectrum to a model including cold dark matter and a cosmological constant ($$\\Lambda$$CDM), and to models with single-parameter extensions to $$\\Lambda$$CDM. We find constraints that are comparable to and consistent with constraints found using the full-sky Planck CMB lensing data. Specifically, we find $$\\sigma_8 \\Omega_{\\rm m}^{0.25}=0.598 \\pm 0.024$$ from the lensing data alone with relatively weak priors placed on the other $$\\Lambda$$CDM parameters. In combination with primary CMB data from Planck, we explore single-parameter extensions to the $$\\Lambda$$CDM model. We find $$\\Omega_k = -0.012^{+0.021}_{-0.023}$$ or $$M_{\

Pairwise velocities in the "Running FLRW" cosmological model

NASA Astrophysics Data System (ADS)

Bibiano, Antonio; Croton, Darren J.

2017-05-01

We present an analysis of the pairwise velocity statistics from a suite of cosmological N-body simulations describing the 'Running Friedmann-Lemaître-Robertson-Walker' (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends Λ cold dark matter (CDM) with a time-evolving vacuum energy density, ρ _Λ. To enforce local conservation of matter, a time-evolving gravitational coupling is also included. Our results constitute the first study of velocities in the R-FLRW cosmology, and we also compare with other dark energy simulations suites, repeating the same analysis. We find a strong degeneracy between the pairwise velocity and σ8 at z = 0 for almost all scenarios considered, which remains even when we look back to epochs as early as z = 2. We also investigate various coupled dark energy models, some of which show minimal degeneracy, and reveal interesting deviations from ΛCDM that could be readily exploited by future cosmological observations to test and further constrain our understanding of dark energy.

Is there a concordance value for H0?

NASA Astrophysics Data System (ADS)

Luković, Vladimir V.; D'Agostino, Rocco; Vittorio, Nicola

2016-11-01

Context. We test the theoretical predictions of several cosmological models against different observables to compare the indirect estimates of the current expansion rate of the Universe determined from model fitting with the direct measurements based on Cepheids data published recently. Aims: We perform a statistical analysis of type Ia supernova (SN Ia), Hubble parameter, and baryon acoustic oscillation data. A joint analysis of these datasets allows us to better constrain cosmological parameters, but also to break the degeneracy that appears in the distance modulus definition between H0 and the absolute B-band magnitude of SN Ia, M0. Methods: From the theoretical side, we considered spatially flat and curvature-free ΛCDM, wCDM, and inhomogeneous Lemaître-Tolman-Bondi (LTB) models. To analyse SN Ia we took into account the distributions of SN Ia intrinsic parameters. Results: For the ΛCDM model we find that Ωm = 0.35 ± 0.02, H0 = (67.8 ± 1.0) km s-1 Mpc-1, while the corrected SN absolute magnitude has a normal distribution N(19.13,0.11). The wCDM model provides the same value for Ωm, while H0 = (66.5 ± 1.8) km s-1 Mpc-1 and w = -0.93 ± 0.07. When an inhomogeneous LTB model is considered, the combined fit provides H0 = (64.2 ± 1.9) km s-1 Mpc-1. Conclusions: Both the Akaike information criterion and the Bayes factor analysis cannot clearly distinguish between ΛCDM and wCDM cosmologies, while they clearly disfavour the LTB model. For the ΛCDM, our joint analysis of the SN Ia, the Hubble parameter, and the baryon acoustic oscillation datasets provides H0 values that are consistent with cosmic microwave background (CMB)-only Planck measurements, but they differ by 2.5σ from the value based on Cepheids data.

The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Double-probe measurements from BOSS galaxy clustering and Planck data – towards an analysis without informative priors

DOE PAGES

Pellejero-Ibanez, Marco; Chuang, Chia -Hsun; Rubino-Martin, J. A.; ...

2016-03-28

Here, we develop a new methodology called double-probe analysis with the aim of minimizing informative priors in the estimation of cosmological parameters. We extract the dark-energy-model-independent cosmological constraints from the joint data sets of Baryon Oscillation Spectroscopic Survey (BOSS) galaxy sample and Planck cosmic microwave background (CMB) measurement. We measure the mean values and covariance matrix of {R, l a, Ω bh 2, n s, log(A s), Ω k, H(z), D A(z), f(z)σ 8(z)}, which give an efficient summary of Planck data and 2-point statistics from BOSS galaxy sample, where R = √Ω mH 2 0, and l a =more » πr(z *)/r s(z *), z * is the redshift at the last scattering surface, and r(z *) and r s(z *) denote our comoving distance to z * and sound horizon at z * respectively. The advantage of this method is that we do not need to put informative priors on the cosmological parameters that galaxy clustering is not able to constrain well, i.e. Ω bh 2 and n s. Using our double-probe results, we obtain Ω m = 0.304 ± 0.009, H 0 = 68.2 ± 0.7, and σ 8 = 0.806 ± 0.014 assuming ΛCDM; and Ω k = 0.002 ± 0.003 and w = –1.00 ± 0.07 assuming owCDM. The results show no tension with the flat ΛCDM cosmological paradigm. By comparing with the full-likelihood analyses with fixed dark energy models, we demonstrate that the double-probe method provides robust cosmological parameter constraints which can be conveniently used to study dark energy models. We extend our study to measure the sum of neutrino mass and obtain Σm ν < 0.10/0.22 (68%/95%) assuming ΛCDM and Σm ν < 0.26/0.52 (68%/95%) assuming wCDM. This paper is part of a set that analyses the final galaxy clustering dataset from BOSS.« less

Cosmological models with running cosmological term and decaying dark matter

NASA Astrophysics Data System (ADS)

Szydłowski, Marek; Stachowski, Aleksander

2017-03-01

We investigate the dynamics of the generalized ΛCDM model, which the Λ term is running with the cosmological time. On the example of the model Λ(t) =Λbare + α2/t2 we show the existence of a mechanism of the modification of the scaling law for energy density of dark matter: ρdm ∝a - 3 + λ(t). We use an approach developed by Urbanowski in which properties of unstable vacuum states are analyzed from the point of view of the quantum theory of unstable states. We discuss the evolution of Λ(t) term and pointed out that during the cosmic evolution there is a long phase in which this term is approximately constant. We also present the statistical analysis of both the Λ(t) CDM model with dark energy and decaying dark matter and the ΛCDM standard cosmological model. We use data such as Planck, SNIa, BAO, H(z) and AP test. While for the former we find the best fit value of the parameter Ωα2,0 is negative (energy transfer is from the dark matter to dark energy sector) and the parameter Ωα2,0 belongs to the interval (- 0 . 000040 , - 0 . 000383) at 2- σ level. The decaying dark matter causes to lowering a mass of dark matter particles which are lighter than CDM particles and remain relativistic. The rate of the process of decaying matter is estimated. Our model is consistent with the decaying mechanism producing unstable particles (e.g. sterile neutrinos) for which α2 is negative.

Simulating cosmologies beyond ΛCDM with PINOCCHIO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rizzo, Luca A.; Villaescusa-Navarro, Francisco; Monaco, Pierluigi

2017-01-01

We present a method that extends the capabilities of the PINpointing Orbit-Crossing Collapsed HIerarchical Objects (PINOCCHIO) code, allowing it to generate accurate dark matter halo mock catalogues in cosmological models where the linear growth factor and the growth rate depend on scale. Such cosmologies comprise, among others, models with massive neutrinos and some classes of modified gravity theories. We validate the code by comparing the halo properties from PINOCCHIO against N-body simulations, focusing on cosmologies with massive neutrinos: νΛCDM. We analyse the halo mass function, halo two-point correlation function and halo power spectrum, showing that PINOCCHIO reproduces the results frommore » simulations with the same level of precision as the original code (∼ 5–10%). We demonstrate that the abundance of halos in cosmologies with massless and massive neutrinos from PINOCCHIO matches very well the outcome of simulations, and point out that PINOCCHIO can reproduce the Ω{sub ν}–σ{sub 8} degeneracy that affects the halo mass function. We finally show that the clustering properties of the halos from PINOCCHIO matches accurately those from simulations both in real and redshift-space, in the latter case up to k = 0.3 h Mpc{sup −1}. We emphasize that the computational time required by PINOCCHIO to generate mock halo catalogues is orders of magnitude lower than the one needed for N-body simulations. This makes this tool ideal for applications like covariance matrix studies within the standard ΛCDM model but also in cosmologies with massive neutrinos or some modified gravity theories.« less

Characterizing Dark Energy Through Supernovae

NASA Astrophysics Data System (ADS)

Davis, Tamara M.; Parkinson, David

Type Ia supernovae are a powerful cosmological probe that gave the first strong evidence that the expansion of the universe is accelerating. Here we provide an overview of how supernovae can go further to reveal information about what is causing the acceleration, be it dark energy or some modification to our laws of gravity. We first review the methods of statistical inference that are commonly used, making a point of separating parameter estimation from model selection. We then summarize the many different approaches used to explain or test the acceleration, including parametric models (like the standard model, ΛCDM), nonparametric models, dark fluid models such as quintessence, and extensions to standard gravity. Finally, we also show how supernova data can be used beyond the Hubble diagram, to give information on gravitational lensing and peculiar velocities that can be used to distinguish between models that predict the same expansion history.

Planck 2015 results. XIII. Cosmological parameters

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Battye, R.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chiang, H. C.; Chluba, J.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Di Valentino, E.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Farhang, M.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Gauthier, C.; Gerbino, M.; Ghosh, T.; Giard, M.; Giraud-Héraud, Y.; Giusarma, E.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hamann, J.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huang, Z.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marchini, A.; Maris, M.; Martin, P. G.; Martinelli, M.; Martínez-González, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Melin, J.-B.; Mendes, L.; Mennella, A.; Migliaccio, M.; Millea, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rouillé d'Orfeuil, B.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Said, N.; Salvatelli, V.; Salvati, L.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Serra, P.; Shellard, E. P. S.; Spencer, L. D.; Spinelli, M.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Trombetti, T.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, F.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, M.; White, S. D. M.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.

2016-09-01

This paper presents cosmological results based on full-mission Planck observations of temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation. Our results are in very good agreement with the 2013 analysis of the Planck nominal-mission temperature data, but with increased precision. The temperature and polarization power spectra are consistent with the standard spatially-flat 6-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations (denoted "base ΛCDM" in this paper). From the Planck temperature data combined with Planck lensing, for this cosmology we find a Hubble constant, H0 = (67.8 ± 0.9) km s-1Mpc-1, a matter density parameter Ωm = 0.308 ± 0.012, and a tilted scalar spectral index with ns = 0.968 ± 0.006, consistent with the 2013 analysis. Note that in this abstract we quote 68% confidence limits on measured parameters and 95% upper limits on other parameters. We present the first results of polarization measurements with the Low Frequency Instrument at large angular scales. Combined with the Planck temperature and lensing data, these measurements give a reionization optical depth of τ = 0.066 ± 0.016, corresponding to a reionization redshift of z_re=8.8+1.7-1.4. These results are consistent with those from WMAP polarization measurements cleaned for dust emission using 353-GHz polarization maps from the High Frequency Instrument. We find no evidence for any departure from base ΛCDM in the neutrino sector of the theory; for example, combining Planck observations with other astrophysical data we find Neff = 3.15 ± 0.23 for the effective number of relativistic degrees of freedom, consistent with the value Neff = 3.046 of the Standard Model of particle physics. The sum of neutrino masses is constrained to ∑ mν < 0.23 eV. The spatial curvature of our Universe is found to be very close to zero, with | ΩK | < 0.005. Adding a tensor component as a single-parameter extension to base ΛCDM we find an upper limit on the tensor-to-scalar ratio of r0.002< 0.11, consistent with the Planck 2013 results and consistent with the B-mode polarization constraints from a joint analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP B-mode data to our analysis leads to a tighter constraint of r0.002 < 0.09 and disfavours inflationarymodels with a V(φ) ∝ φ2 potential. The addition of Planck polarization data leads to strong constraints on deviations from a purely adiabatic spectrum of fluctuations. We find no evidence for any contribution from isocurvature perturbations or from cosmic defects. Combining Planck data with other astrophysical data, including Type Ia supernovae, the equation of state of dark energy is constrained to w = -1.006 ± 0.045, consistent with the expected value for a cosmological constant. The standard big bang nucleosynthesis predictions for the helium and deuterium abundances for the best-fit Planck base ΛCDM cosmology are in excellent agreement with observations. We also constraints on annihilating dark matter and on possible deviations from the standard recombination history. In neither case do we find no evidence for new physics. The Planck results for base ΛCDM are in good agreement with baryon acoustic oscillation data and with the JLA sample of Type Ia supernovae. However, as in the 2013 analysis, the amplitude of the fluctuation spectrum is found to be higher than inferred from some analyses of rich cluster counts and weak gravitational lensing. We show that these tensions cannot easily be resolved with simple modifications of the base ΛCDM cosmology. Apart from these tensions, the base ΛCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.

Chameleon f(R) gravity on the Virgo cluster scale

NASA Astrophysics Data System (ADS)

Moran, C. Corbett; Teyssier, R.; Li, B.

2015-03-01

Models of modified gravity offer promising alternatives to the concordance Λ cold dark matter (ΛCDM) cosmology to explain the late-time acceleration of the universe. A popular such model is f(R) gravity, in which the Ricci scalar in the Einstein-Hilbert action is replaced by a general function of it. We study the f(R) model of Hu & Sawicki, which recovers standard general relativity in high-density regimes, while reproducing the desired late time acceleration at cosmological scales. We run a suite of high-resolution zoom simulations using the ECOSMOG code to examine the effect of f(R) gravity on the properties of a halo that is analogous to the Virgo cluster. We show that the velocity dispersion profiles can potentially discriminate between f(R) models and ΛCDM, and provide complementary analysis of lensing signal profiles to explore the possibility to further distinguish the different f(R) models. Our results confirm the techniques explored by Cabré et al. to quantify the effect of environment in the behaviour of f(R) gravity, and we extend them to study halo satellites at various redshifts. We find that the modified gravity effects in our models are most observable at low redshifts, and that effects are generally stronger for satellites far from the centre of the main halo. We show that the screening properties of halo satellites trace very well that of dark matter particles, which means that low-resolution simulations in which subhaloes are not very well resolved can in principle be used to study satellite properties. We discuss observables, particularly for halo satellites, that can potentially be used to constrain the observational viability of f(R) gravity.

Constraining Cosmological Models with Different Observations

NASA Astrophysics Data System (ADS)

Wei, J. J.

2016-07-01

With the observations of Type Ia supernovae (SNe Ia), scientists discovered that the Universe is experiencing an accelerated expansion, and then revealed the existence of dark energy in 1998. Since the amazing discovery, cosmology has became a hot topic in the physical research field. Cosmology is a subject that strongly depends on the astronomical observations. Therefore, constraining different cosmological models with all kinds of observations is one of the most important research works in the modern cosmology. The goal of this thesis is to investigate cosmology using the latest observations. The observations include SNe Ia, Type Ic Super Luminous supernovae (SLSN Ic), Gamma-ray bursts (GRBs), angular diameter distance of galaxy cluster, strong gravitational lensing, and age measurements of old passive galaxies, etc. In Chapter 1, we briefly review the research background of cosmology, and introduce some cosmological models. Then we summarize the progress on cosmology from all kinds of observations in more details. In Chapter 2, we present the results of our studies on the supernova cosmology. The main difficulty with the use of SNe Ia as standard candles is that one must optimize three or four nuisance parameters characterizing SN luminosities simultaneously with the parameters of an expansion model of the Universe. We have confirmed that one should optimize all of the parameters by carrying out the method of maximum likelihood estimation in any situation where the parameters include an unknown intrinsic dispersion. The commonly used method, which estimates the dispersion by requiring the reduced χ^{2} to equal unity, does not take into account all possible variances among the parameters. We carry out such a comparison of the standard ΛCDM cosmology and the R_{h}=ct Universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. Moreover, it is quite evident that SLSNe Ic may be useful cosmological probes, perhaps even out to redshifts much greater (z≫2) than those accessible using SNe Ia. However, the currently available sample of SNe Ia is still quite small. Our simulations have shown that if SLSNe Ic can be commonly detected in the future, they have the potential of greatly refining the measurement of cosmological parameters, particularly the parameter w_{de} of the dark energy equation of state. In Chapter 3, we focus on GRB cosmology. We firstly use GRBs as standard candles in constructing the Hubble diagram at redshifts beyond the current reach of SNe Ia observations. Then we measure high-z star formation rate (SFR) using GRBs. We confirm that the latest Swift sample of GRBs reveals an increasing evolution in the GRB rate relative to SFR at high redshifts. The observed discrepancy between the GRB rate and the SFR may be eliminated by assuming a cosmic evolution in metallicity. Assuming that the SFR and GRB rate are related via an evolving metallicity, we find that the GRB data constrain the slope of the high-z SFR to be -2.41_{-2.09}^{+1.87}. In addition, first stars can only form in structures that are suitably dense, which can be parameterized by the minimum dark matter halo mass M_{min}. M_{min} must play an important role in star formation. We can constrain M_{min}<10^{12.5} M_{⊙} at 68% confidence level from the GRB data. In Chapter 4, we assemble a catalog of 69 strong gravitational lensing systems, and carefully introduce how to constrain cosmological parameters using these important data. We find that both ΛCDM and the R_{h}=ct Universe account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. In Chapters 5 and 6, we use measurements of the galaxy-cluster angular diameter distances and 32 age measurements of passively evolving galaxies to test and compare the standard model (ΛCDM) and the R_{h}=ct Universe, respectively. We show that both models appear to account for these two data very well. However, because of the different number of free parameters in these models, we have to judge the goodness-of-fit of cosmological models with selection tools, such as the Akaike, Kullback, and Bayes Information Criteria, favoring R_{h}=ct over ΛCDM with a likelihood of about 70%, 75%, and 80%, respectively. Finally, some open questions and an outlook in the cosmology field are summarized in Chapter 7.

Early cosmology constrained

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verde, Licia; Jimenez, Raul; Bellini, Emilio

We investigate our knowledge of early universe cosmology by exploring how much additional energy density can be placed in different components beyond those in the ΛCDM model. To do this we use a method to separate early- and late-universe information enclosed in observational data, thus markedly reducing the model-dependency of the conclusions. We find that the 95% credibility regions for extra energy components of the early universe at recombination are: non-accelerating additional fluid density parameter Ω{sub MR} < 0.006 and extra radiation parameterised as extra effective neutrino species 2.3 < N {sub eff} < 3.2 when imposing flatness. Our constraintsmore » thus show that even when analyzing the data in this largely model-independent way, the possibility of hiding extra energy components beyond ΛCDM in the early universe is seriously constrained by current observations. We also find that the standard ruler, the sound horizon at radiation drag, can be well determined in a way that does not depend on late-time Universe assumptions, but depends strongly on early-time physics and in particular on additional components that behave like radiation. We find that the standard ruler length determined in this way is r {sub s} = 147.4 ± 0.7 Mpc if the radiation and neutrino components are standard, but the uncertainty increases by an order of magnitude when non-standard dark radiation components are allowed, to r {sub s} = 150 ± 5 Mpc.« less

Early cosmology constrained

NASA Astrophysics Data System (ADS)

Verde, Licia; Bellini, Emilio; Pigozzo, Cassio; Heavens, Alan F.; Jimenez, Raul

2017-04-01

We investigate our knowledge of early universe cosmology by exploring how much additional energy density can be placed in different components beyond those in the ΛCDM model. To do this we use a method to separate early- and late-universe information enclosed in observational data, thus markedly reducing the model-dependency of the conclusions. We find that the 95% credibility regions for extra energy components of the early universe at recombination are: non-accelerating additional fluid density parameter ΩMR < 0.006 and extra radiation parameterised as extra effective neutrino species 2.3 < Neff < 3.2 when imposing flatness. Our constraints thus show that even when analyzing the data in this largely model-independent way, the possibility of hiding extra energy components beyond ΛCDM in the early universe is seriously constrained by current observations. We also find that the standard ruler, the sound horizon at radiation drag, can be well determined in a way that does not depend on late-time Universe assumptions, but depends strongly on early-time physics and in particular on additional components that behave like radiation. We find that the standard ruler length determined in this way is rs = 147.4 ± 0.7 Mpc if the radiation and neutrino components are standard, but the uncertainty increases by an order of magnitude when non-standard dark radiation components are allowed, to rs = 150 ± 5 Mpc.

MATTER IN THE BEAM: WEAK LENSING, SUBSTRUCTURES, AND THE TEMPERATURE OF DARK MATTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahdi, Hareth S.; Elahi, Pascal J.; Lewis, Geraint F.

2016-08-01

Warm dark matter (WDM) models offer an attractive alternative to the current cold dark matter (CDM) cosmological model. We present a novel method to differentiate between WDM and CDM cosmologies, namely, using weak lensing; this provides a unique probe as it is sensitive to all of the “matter in the beam,” not just dark matter haloes and the galaxies that reside in them, but also the diffuse material between haloes. We compare the weak lensing maps of CDM clusters to those in a WDM model corresponding to a thermally produced 0.5 keV dark matter particle. Our analysis clearly shows thatmore » the weak lensing magnification, convergence, and shear distributions can be used to distinguish between CDM and WDM models. WDM models increase the probability of weak magnifications, with the differences being significant to ≳5 σ , while leaving no significant imprint on the shear distribution. WDM clusters analyzed in this work are more homogeneous than CDM ones, and the fractional decrease in the amount of material in haloes is proportional to the average increase in the magnification. This difference arises from matter that would be bound in compact haloes in CDM being smoothly distributed over much larger volumes at lower densities in WDM. Moreover, the signature does not solely lie in the probability distribution function but in the full spatial distribution of the convergence field.« less

Reconciling Dwarf Galaxies with ΛCDM Cosmology: Simulating a Realistic Population of Satellites around a Milky Way-mass Galaxy

NASA Astrophysics Data System (ADS)

Wetzel, Andrew R.; Hopkins, Philip F.; Kim, Ji-hoon; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot

2016-08-01

Low-mass “dwarf” galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group (LG) of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present first results from the Latte Project: the Milky Way on Feedback in Realistic Environments (FIRE). This simulation models the formation of an MW-mass galaxy to z=0 within ΛCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon particle mass of 7070 {M}⊙ with gas kernel/softening that adapts down to 1 {pc} (with a median of 25{--}60 {pc} at z=0). Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE-2 model for star formation and explicit feedback within a multi-phase interstellar medium. For the first time, Latte self-consistently resolves the spatial scales corresponding to half-light radii of dwarf galaxies that form around an MW-mass host down to {M}{star}≳ {10}5 {M}⊙ . Latte’s population of dwarf galaxies agrees with the LG across a broad range of properties: (1) distributions of stellar masses and stellar velocity dispersions (dynamical masses), including their joint relation; (2) the mass-metallicity relation; and (3) diverse range of star formation histories, including their mass dependence. Thus, Latte produces a realistic population of dwarf galaxies at {M}{star}≳ {10}5 {M}⊙ that does not suffer from the “missing satellites” or “too big to fail” problems of small-scale structure formation. We conclude that baryonic physics can reconcile observed dwarf galaxies with standard ΛCDM cosmology.

A comparison of cosmological models using time delay lenses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio, E-mail: jjwei@pmo.ac.cn, E-mail: xfwu@pmo.ac.cn, E-mail: fmelia@email.arizona.edu

2014-06-20

The use of time-delay gravitational lenses to examine the cosmological expansion introduces a new standard ruler with which to test theoretical models. The sample suitable for this kind of work now includes 12 lens systems, which have thus far been used solely for optimizing the parameters of ΛCDM. In this paper, we broaden the base of support for this new, important cosmic probe by using these observations to carry out a one-on-one comparison between competing models. The currently available sample indicates a likelihood of ∼70%-80% that the R {sub h} = ct universe is the correct cosmology versus ∼20%-30% formore » the standard model. This possibly interesting result reinforces the need to greatly expand the sample of time-delay lenses, e.g., with the successful implementation of the Dark Energy Survey, the VST ATLAS survey, and the Large Synoptic Survey Telescope. In anticipation of a greatly expanded catalog of time-delay lenses identified with these surveys, we have produced synthetic samples to estimate how large they would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the real cosmology is ΛCDM, a sample of ∼150 time-delay lenses would be sufficient to rule out R {sub h} = ct at this level of accuracy, while ∼1000 time-delay lenses would be required to rule out ΛCDM if the real universe is instead R {sub h} = ct. This difference in required sample size reflects the greater number of free parameters available to fit the data with ΛCDM.« less

Beyond six parameters: Extending Λ CDM

NASA Astrophysics Data System (ADS)

Di Valentino, Eleonora; Melchiorri, Alessandro; Silk, Joseph

2015-12-01

Cosmological constraints are usually derived under the assumption of a six-parameter Λ CDM theoretical framework or simple one-parameter extensions. In this paper we present, for the first time, cosmological constraints in a significantly extended scenario, varying up to 12 cosmological parameters simultaneously, including the sum of neutrino masses, the neutrino effective number, the dark energy equation of state, the gravitational wave background and the running of the spectral index of primordial perturbations. Using the latest Planck 2015 data release (with polarization), we found no significant indication for extensions to the standard Λ CDM scenario, with the notable exception of the angular power spectrum lensing amplitude, Alens , which is larger than the expected value at more than 2 standard deviations, even when combining the Planck data with BAO and supernovae type Ia external data sets. In our extended cosmological framework, we find that a combined Planck+BAO analysis constrains the value of the rms density fluctuation parameter to σ8=0.781-0.063+0.065 at 95 % C.L., helping to relieve the possible tensions with the CFHTlenS cosmic shear survey. We also find a lower value for the reionization optical depth τ =0.058-0.043+0.040 at 95 % C.L. with respect to the one derived under the assumption of Λ CDM . The scalar spectral index nS is now compatible with a Harrison-Zeldovich spectrum to within 2.5 standard deviations. Combining the Planck data set with the Hubble Space Telescope prior on the Hubble constant provides a value for the equation of state w <-1 at more than 2 standard deviations, while the neutrino effective number is fully compatible with the expectations of the standard three neutrino framework.

Colliders as a simultaneous probe of supersymmetric dark matter and Terascale cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barenboim, Gabriela; /Valencia U.; Lykken, Joseph D.

2006-08-01

Terascale supersymmetry has the potential to provide a natural explanation of the dominant dark matter component of the standard {Lambda}CDM cosmology. However once we impose the constraints on minimal supersymmetry parameters from current particle physics data, a satisfactory dark matter abundance is no longer prima facie natural. This Neutralino Tuning Problem could be a hint of nonstandard cosmology during and/or after the Terascale era. To quantify this possibility, we introduce an alternative cosmological benchmark based upon a simple model of quintessential inflation. This benchmark has no free parameters, so for a given supersymmetry model it allows an unambiguous prediction ofmore » the dark matter relic density. As a example, we scan over the parameter space of the CMSSM, comparing the neutralino relic density predictions with the bounds from WMAP. We find that the WMAP-allowed regions of the CMSSM are an order of magnitude larger if we use the alternative cosmological benchmark, as opposed to {Lambda}CDM. Initial results from the CERN Large Hadron Collider will distinguish between the two allowed regions.« less

Non-linear structure formation in the `Running FLRW' cosmological model

NASA Astrophysics Data System (ADS)

Bibiano, Antonio; Croton, Darren J.

2016-07-01

We present a suite of cosmological N-body simulations describing the `Running Friedmann-Lemaïtre-Robertson-Walker' (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends Lambda cold dark matter (ΛCDM) with a time-evolving vacuum density, Λ(z), and time-evolving gravitational Newton's coupling, G(z). In this paper, we review the model and introduce the necessary analytical treatment needed to adapt a reference N-body code. Our resulting simulations represent the first realization of the full growth history of structure in the R-FLRW cosmology into the non-linear regime, and our normalization choice makes them fully consistent with the latest cosmic microwave background data. The post-processing data products also allow, for the first time, an analysis of the properties of the halo and sub-halo populations. We explore the degeneracies of many statistical observables and discuss the steps needed to break them. Furthermore, we provide a quantitative description of the deviations of R-FLRW from ΛCDM, which could be readily exploited by future cosmological observations to test and further constrain the model.

Production of primordial gravitational waves in a simple class of running vacuum cosmologies

NASA Astrophysics Data System (ADS)

Tamayo, D. A.; Lima, J. A. S.; Bessada, D. F. A.

The problem of cosmological production of gravitational waves (GWs) is discussed in the framework of an expanding, spatially homogeneous and isotropic FRW type universe with time-evolving vacuum energy density. The GW equation is established and its modified time-dependent part is analytically resolved for different epochs in the case of a flat geometry. Unlike the standard ΛCDM cosmology (no interacting vacuum), we show that GWs are produced in the radiation era even in the context of general relativity. We also show that for all values of the free parameter, the high frequency modes are damped out even faster than in the standard cosmology both in the radiation and matter-vacuum dominated epoch. The formation of the stochastic background of gravitons and the remnant power spectrum generated at different cosmological eras are also explicitly evaluated. It is argued that measurements of the CMB polarization (B-modes) and its comparison with the rigid ΛCDM model plus the inflationary paradigm may become a crucial test for dynamical dark energy models in the near future.

Colliders as a simultaneous probe of supersymmetric dark matter and Terascale cosmology

NASA Astrophysics Data System (ADS)

Barenboim, Gabriela; Lykken, Joseph D.

2006-12-01

Terascale supersymmetry has the potential to provide a natural explanation of the dominant dark matter component of the standard ΛCDM cosmology. However once we impose the constraints on minimal supersymmetry parameters from current particle physics data, a satisfactory dark matter abundance is no longer prima facie natural. This Neutralino Tuning Problem could be a hint of nonstandard cosmology during and/or after the Terascale era. To quantify this possibility, we introduce an alternative cosmological benchmark based upon a simple model of quintessential inflation. This benchmark has no free parameters, so for a given supersymmetry model it allows an unambiguous prediction of the dark matter relic density. As a example, we scan over the parameter space of the CMSSM, comparing the neutralino relic density predictions with the bounds from WMAP. We find that the WMAP allowed regions of the CMSSM are an order of magnitude larger if we use the alternative cosmological benchmark, as opposed to ΛCDM. Initial results from the CERN Large Hadron Collider will distinguish between the two allowed regions.

First star formation in ultralight particle dark matter cosmology

NASA Astrophysics Data System (ADS)

Hirano, Shingo; Sullivan, James M.; Bromm, Volker

2018-01-01

The formation of the first stars in the high-redshift Universe is a sensitive probe of the small-scale, particle physics nature of dark matter (DM). We carry out cosmological simulations of primordial star formation in ultralight, axion-like particle DM cosmology, with masses of 10-22 and 10-21 eV, with de Broglie wavelengths approaching galactic scales (˜ kpc). The onset of star formation is delayed, and shifted to more massive host structures. For the lightest DM particle mass explored here, first stars form at z ˜ 7 in structures with ˜109 M⊙, compared to the standard minihalo environment within the Λ cold dark matter (ΛCDM) cosmology, where z ˜ 20-30 and ˜105-106 M⊙. Despite this greatly altered DM host environment, the thermodynamic behaviour of the metal-free gas as it collapses into the DM potential well asymptotically approaches a very similar evolutionary track. Thus, the fragmentation properties are predicted to remain the same as in ΛCDM cosmology, implying a similar mass scale for the first stars. These results predict intense starbursts in the axion cosmologies, which may be amenable to observations with the James Webb Space Telescope.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wright, Bill S.; Winther, Hans A.; Koyama, Kazuya, E-mail: bill.wright@port.ac.uk, E-mail: hans.winther@port.ac.uk, E-mail: kazuya.koyama@port.ac.uk

The effect of massive neutrinos on the growth of cold dark matter perturbations acts as a scale-dependent Newton's constant and leads to scale-dependent growth factors just as we often find in models of gravity beyond General Relativity. We show how to compute growth factors for ΛCDM and general modified gravity cosmologies combined with massive neutrinos in Lagrangian perturbation theory for use in COLA and extensions thereof. We implement this together with the grid-based massive neutrino method of Brandbyge and Hannestad in MG-PICOLA and compare COLA simulations to full N -body simulations of ΛCDM and f ( R ) gravity withmore » massive neutrinos. Our implementation is computationally cheap if the underlying cosmology already has scale-dependent growth factors and it is shown to be able to produce results that match N -body to percent level accuracy for both the total and CDM matter power-spectra up to k ∼< 1 h /Mpc.« less

COLA with massive neutrinos

NASA Astrophysics Data System (ADS)

Wright, Bill S.; Winther, Hans A.; Koyama, Kazuya

2017-10-01

The effect of massive neutrinos on the growth of cold dark matter perturbations acts as a scale-dependent Newton's constant and leads to scale-dependent growth factors just as we often find in models of gravity beyond General Relativity. We show how to compute growth factors for ΛCDM and general modified gravity cosmologies combined with massive neutrinos in Lagrangian perturbation theory for use in COLA and extensions thereof. We implement this together with the grid-based massive neutrino method of Brandbyge and Hannestad in MG-PICOLA and compare COLA simulations to full N-body simulations of ΛCDM and f(R) gravity with massive neutrinos. Our implementation is computationally cheap if the underlying cosmology already has scale-dependent growth factors and it is shown to be able to produce results that match N-body to percent level accuracy for both the total and CDM matter power-spectra up to klesssim 1 h/Mpc.

New observational constraints on f ( T ) gravity from cosmic chronometers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nunes, Rafael C.; Pan, Supriya; Saridakis, Emmanuel N., E-mail: nunes@ecm.ub.edu, E-mail: span@iiserkol.ac.in, E-mail: Emmanuel_Saridakis@baylor.edu

2016-08-01

We use the local value of the Hubble constant recently measured with 2.4% precision, as well as the latest compilation of cosmic chronometers data, together with standard probes such as Supernovae Type Ia and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f ( T ) gravity models, where T is the torsion scalar in teleparallel gravity. In particular, we consider three f ( T ) models with two parameters, out of which one is independent, and we quantify their deviation from ΛCDM cosmology through a sole parameter. Our analysis reveals thatmore » for one of the models a small but non-zero deviation from ΛCDM cosmology is slightly favored, while for the other models the best fit is very close to ΛCDM scenario. Clearly, f ( T ) gravity is consistent with observations, and it can serve as a candidate for modified gravity.« less

Large scale structures in the kinetic gravity braiding model that can be unbraided

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kimura, Rampei; Yamamoto, Kazuhiro, E-mail: rampei@theo.phys.sci.hiroshima-u.ac.jp, E-mail: kazuhiro@hiroshima-u.ac.jp

2011-04-01

We study cosmological consequences of a kinetic gravity braiding model, which is proposed as an alternative to the dark energy model. The kinetic braiding model we study is characterized by a parameter n, which corresponds to the original galileon cosmological model for n = 1. We find that the background expansion of the universe of the kinetic braiding model is the same as the Dvali-Turner's model, which reduces to that of the standard cold dark matter model with a cosmological constant (ΛCDM model) for n equal to infinity. We also find that the evolution of the linear cosmological perturbation inmore » the kinetic braiding model reduces to that of the ΛCDM model for n = ∞. Then, we focus our study on the growth history of the linear density perturbation as well as the spherical collapse in the nonlinear regime of the density perturbations, which might be important in order to distinguish between the kinetic braiding model and the ΛCDM model when n is finite. The theoretical prediction for the large scale structure is confronted with the multipole power spectrum of the luminous red galaxy sample of the Sloan Digital Sky survey. We also discuss future prospects of constraining the kinetic braiding model using a future redshift survey like the WFMOS/SuMIRe PFS survey as well as the cluster redshift distribution in the South Pole Telescope survey.« less

Disentangling interacting dark energy cosmologies with the three-point correlation function

NASA Astrophysics Data System (ADS)

Moresco, Michele; Marulli, Federico; Baldi, Marco; Moscardini, Lauro; Cimatti, Andrea

2014-10-01

We investigate the possibility of constraining coupled dark energy (cDE) cosmologies using the three-point correlation function (3PCF). Making use of the CODECS N-body simulations, we study the statistical properties of cold dark matter (CDM) haloes for a variety of models, including a fiducial ΛCDM scenario and five models in which dark energy (DE) and CDM mutually interact. We measure both the halo 3PCF, ζ(θ), and the reduced 3PCF, Q(θ), at different scales (2 < r [h-1 Mpc ] < 40) and redshifts (0 ≤ z ≤ 2). In all cDE models considered in this work, Q(θ) appears flat at small scales (for all redshifts) and at low redshifts (for all scales), while it builds up the characteristic V-shape anisotropy at increasing redshifts and scales. With respect to the ΛCDM predictions, cDE models show lower (higher) values of the halo 3PCF for perpendicular (elongated) configurations. The effect is also scale-dependent, with differences between ΛCDM and cDE models that increase at large scales. We made use of these measurements to estimate the halo bias, that results in fair agreement with the one computed from the two-point correlation function (2PCF). The main advantage of using both the 2PCF and 3PCF is to break the bias-σ8 degeneracy. Moreover, we find that our bias estimates are approximately independent of the assumed strength of DE coupling. This study demonstrates the power of a higher order clustering analysis in discriminating between alternative cosmological scenarios, for both present and forthcoming galaxy surveys, such as e.g. Baryon Oscillation Spectroscopic Survey and Euclid.

Cosmological implications of quantum mechanics parametrization of dark energy

NASA Astrophysics Data System (ADS)

Szydłowski, Marek; Stachowski, Aleksander; Urbanowski, Krzysztof

2017-08-01

We consider the cosmology with the running dark energy. The parametrization of dark energy is derived from the quantum process of transition from the false vacuum state to the true vacuum state. This model is the generalized interacting CDM model. We consider the energy density of dark energy parametrization, which is given by the Breit-Wigner energy distribution function. The idea of the process of the quantum mechanical decay of unstable states was formulated by Krauss and Dent. We used this idea in our considerations. In this model is an energy transfer in the dark sector. In this evolutional scenario the universe starts from the false vacuum state and goes to the true vacuum state of the present day universe. The intermediate regime during the passage from false to true vacuum states takes place. In this way the cosmological constant problem can be tried to solve. We estimate the cosmological parameters for this model. This model is in a good agreement with the astronomical data and is practically indistinguishable from CDM model.

f( R) gravity modifications: from the action to the data

NASA Astrophysics Data System (ADS)

Lazkoz, Ruth; Ortiz-Baños, María; Salzano, Vincenzo

2018-03-01

It is a very well established matter nowadays that many modified gravity models can offer a sound alternative to General Relativity for the description of the accelerated expansion of the universe. But it is also equally well known that no clear and sharp discrimination between any alternative theory and the classical one has been found so far. In this work, we attempt at formulating a different approach starting from the general class of f( R) theories as test probes: we try to reformulate f( R) Lagrangian terms as explicit functions of the redshift, i.e., as f( z). In this context, the f( R) setting to the consensus cosmological model, the Λ CDM model, can be written as a polynomial including just a constant and a third-order term. Starting from this result, we propose various different polynomial parameterizations f( z), including new terms which would allow for deviations from Λ CDM, and we thoroughly compare them with observational data. While on the one hand we have found no statistically preference for our proposals (even if some of them are as good as Λ CDM by using Bayesian Evidence comparison), we think that our novel approach could provide a different perspective for the development of new and observationally reliable alternative models of gravity.

ΛCDM model with dissipative nonextensive viscous dark matter

NASA Astrophysics Data System (ADS)

Gimenes, H. S.; Viswanathan, G. M.; Silva, R.

2018-03-01

Many models in cosmology typically assume the standard bulk viscosity. We study an alternative interpretation for the origin of the bulk viscosity. Using nonadditive statistics proposed by Tsallis, we propose a bulk viscosity component that can only exist by a nonextensive effect through the nonextensive/dissipative correspondence (NexDC). In this paper, we consider a ΛCDM model for a flat universe with a dissipative nonextensive viscous dark matter component, following the Eckart theory of bulk viscosity, without any perturbative approach. In order to analyze cosmological constraints, we use one of the most recent observations of Type Ia Supernova, baryon acoustic oscillations and cosmic microwave background data.

Planck 2015 results: XIII. Cosmological parameters

DOE PAGES

Ade, P. A. R.; Aghanim, N.; Arnaud, M.; ...

2016-09-20

Here, this paper presents cosmological results based on full-mission Planck observations of temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation. Our results are in very good agreement with the 2013 analysis of the Planck nominal-mission temperature data, but with increased precision. The temperature and polarization power spectra are consistent with the standard spatially-flat 6-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations (denoted “base ΛCDM” in this paper). From the Planck temperature data combined with Planck lensing, for this cosmology we find a Hubble constant, H 0 = (67.8 ± 0.9) km s -1Mpc -1, a matter density parameter Ω m = 0.308 ± 0.012, and a tilted scalar spectral index with n s = 0.968 ± 0.006, consistent with the 2013 analysis. Note that in this abstract we quote 68% confidence limits on measured parameters and 95% upper limits on other parameters. We present the first results of polarization measurements with the Low Frequency Instrument at large angular scales. Combined with the Planck temperature and lensing data, these measurements give a reionization optical depth of τ = 0.066 ± 0.016, corresponding to a reionization redshift of z re= 8.8more » $$+1.7\\atop{-1.4}$$. These results are consistent with those from WMAP polarization measurements cleaned for dust emission using 353-GHz polarization maps from the High Frequency Instrument. We find no evidence for any departure from base ΛCDM in the neutrino sector of the theory; for example, combining Planck observations with other astrophysical data we find N eff = 3.15 ± 0.23 for the effective number of relativistic degrees of freedom, consistent with the value N eff = 3.046 of the Standard Model of particle physics. The sum of neutrino masses is constrained to Σ m ν < 0.23 eV. The spatial curvature of our Universe is found to be very close to zero, with | Ω K | < 0.005. Adding a tensor component as a single-parameter extension to base ΛCDM we find an upper limit on the tensor-to-scalar ratio of r 0.002< 0.11, consistent with the Planck 2013 results and consistent with the B-mode polarization constraints from a joint analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP B-mode data to our analysis leads to a tighter constraint of r 0.002 < 0.09 and disfavours inflationarymodels with a V(φ) ∝ φ 2 potential. The addition of Planck polarization data leads to strong constraints on deviations from a purely adiabatic spectrum of fluctuations. We find no evidence for any contribution from isocurvature perturbations or from cosmic defects. Combining Planck data with other astrophysical data, including Type Ia supernovae, the equation of state of dark energy is constrained to w = -1.006 ± 0.045, consistent with the expected value for a cosmological constant. The standard big bang nucleosynthesis predictions for the helium and deuterium abundances for the best-fit Planck base ΛCDM cosmology are in excellent agreement with observations. We also constraints on annihilating dark matter and on possible deviations from the standard recombination history. In neither case do we find no evidence for new physics. The Planck results for base ΛCDM are in good agreement with baryon acoustic oscillation data and with the JLA sample of Type Ia supernovae. However, as in the 2013 analysis, the amplitude of the fluctuation spectrum is found to be higher than inferred from some analyses of rich cluster counts and weak gravitational lensing. We show that these tensions cannot easily be resolved with simple modifications of the base ΛCDM cosmology. Finally, apart from these tensions, the base ΛCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.« less

Planck 2015 results: XIII. Cosmological parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ade, P. A. R.; Aghanim, N.; Arnaud, M.

Here, this paper presents cosmological results based on full-mission Planck observations of temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation. Our results are in very good agreement with the 2013 analysis of the Planck nominal-mission temperature data, but with increased precision. The temperature and polarization power spectra are consistent with the standard spatially-flat 6-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations (denoted “base ΛCDM” in this paper). From the Planck temperature data combined with Planck lensing, for this cosmology we find a Hubble constant, H 0 = (67.8 ± 0.9) km s -1Mpc -1, a matter density parameter Ω m = 0.308 ± 0.012, and a tilted scalar spectral index with n s = 0.968 ± 0.006, consistent with the 2013 analysis. Note that in this abstract we quote 68% confidence limits on measured parameters and 95% upper limits on other parameters. We present the first results of polarization measurements with the Low Frequency Instrument at large angular scales. Combined with the Planck temperature and lensing data, these measurements give a reionization optical depth of τ = 0.066 ± 0.016, corresponding to a reionization redshift of z re= 8.8more » $$+1.7\\atop{-1.4}$$. These results are consistent with those from WMAP polarization measurements cleaned for dust emission using 353-GHz polarization maps from the High Frequency Instrument. We find no evidence for any departure from base ΛCDM in the neutrino sector of the theory; for example, combining Planck observations with other astrophysical data we find N eff = 3.15 ± 0.23 for the effective number of relativistic degrees of freedom, consistent with the value N eff = 3.046 of the Standard Model of particle physics. The sum of neutrino masses is constrained to Σ m ν < 0.23 eV. The spatial curvature of our Universe is found to be very close to zero, with | Ω K | < 0.005. Adding a tensor component as a single-parameter extension to base ΛCDM we find an upper limit on the tensor-to-scalar ratio of r 0.002< 0.11, consistent with the Planck 2013 results and consistent with the B-mode polarization constraints from a joint analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP B-mode data to our analysis leads to a tighter constraint of r 0.002 < 0.09 and disfavours inflationarymodels with a V(φ) ∝ φ 2 potential. The addition of Planck polarization data leads to strong constraints on deviations from a purely adiabatic spectrum of fluctuations. We find no evidence for any contribution from isocurvature perturbations or from cosmic defects. Combining Planck data with other astrophysical data, including Type Ia supernovae, the equation of state of dark energy is constrained to w = -1.006 ± 0.045, consistent with the expected value for a cosmological constant. The standard big bang nucleosynthesis predictions for the helium and deuterium abundances for the best-fit Planck base ΛCDM cosmology are in excellent agreement with observations. We also constraints on annihilating dark matter and on possible deviations from the standard recombination history. In neither case do we find no evidence for new physics. The Planck results for base ΛCDM are in good agreement with baryon acoustic oscillation data and with the JLA sample of Type Ia supernovae. However, as in the 2013 analysis, the amplitude of the fluctuation spectrum is found to be higher than inferred from some analyses of rich cluster counts and weak gravitational lensing. We show that these tensions cannot easily be resolved with simple modifications of the base ΛCDM cosmology. Finally, apart from these tensions, the base ΛCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.« less

Dark interactions and cosmological fine-tuning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quartin, Miguel; Calvao, Mauricio O; Joras, Sergio E

2008-05-15

Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied, but there have been claims that observational data seem to narrow (some of) them down to something annoyingly close to the {Lambda}CDM (CDM: cold dark matter) model, thus greatly reducing their ability to deal with the problem in the first place. The smallness problem of the initial energy density of dark energy has also been a target of cosmological models in recent years. Making use of a moderately general coupling scheme,more » this paper aims to unite these different approaches and shed some light on whether this class of models has any true perspective in suppressing the aforementioned issues that plague our current understanding of the universe, in a quantitative and unambiguous way.« less

Constraints on cosmological parameters in power-law cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rani, Sarita; Singh, J.K.; Altaibayeva, A.

In this paper, we examine observational constraints on the power law cosmology; essentially dependent on two parameters H{sub 0} (Hubble constant) and q (deceleration parameter). We investigate the constraints on these parameters using the latest 28 points of H(z) data and 580 points of Union2.1 compilation data and, compare the results with the results of ΛCDM . We also forecast constraints using a simulated data set for the future JDEM, supernovae survey. Our studies give better insight into power law cosmology than the earlier done analysis by Kumar [arXiv:1109.6924] indicating it tuning well with Union2.1 compilation data but not withmore » H(z) data. However, the constraints obtained on and i.e. H{sub 0} average and q average using the simulated data set for the future JDEM, supernovae survey are found to be inconsistent with the values obtained from the H(z) and Union2.1 compilation data. We also perform the statefinder analysis and find that the power-law cosmological models approach the standard ΛCDM model as q → −1. Finally, we observe that although the power law cosmology explains several prominent features of evolution of the Universe, it fails in details.« less

Enhanced peculiar velocities in brane-induced gravity

NASA Astrophysics Data System (ADS)

Wyman, Mark; Khoury, Justin

2010-08-01

The mounting evidence for anomalously large peculiar velocities in our Universe presents a challenge for the ΛCDM paradigm. The recent estimates of the large-scale bulk flow by Watkins et al. are inconsistent at the nearly 3σ level with ΛCDM predictions. Meanwhile, Lee and Komatsu have recently estimated that the occurrence of high-velocity merging systems such as the bullet cluster (1E0657-57) is unlikely at a 6.5-5.8σ level, with an estimated probability between 3.3×10-11 and 3.6×10-9 in ΛCDM cosmology. We show that these anomalies are alleviated in a broad class of infrared-modifed gravity theories, called brane-induced gravity, in which gravity becomes higher-dimensional at ultralarge distances. These theories include additional scalar forces that enhance gravitational attraction and therefore speed up structure formation at late times and on sufficiently large scales. The peculiar velocities are enhanced by 24-34% compared to standard gravity, with the maximal enhancement nearly consistent at the 2σ level with bulk flow observations. The occurrence of the bullet cluster in these theories is ≈104 times more probable than in ΛCDM cosmology.

Enhanced peculiar velocities in brane-induced gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wyman, Mark; Khoury, Justin

The mounting evidence for anomalously large peculiar velocities in our Universe presents a challenge for the {Lambda}CDM paradigm. The recent estimates of the large-scale bulk flow by Watkins et al. are inconsistent at the nearly 3{sigma} level with {Lambda}CDM predictions. Meanwhile, Lee and Komatsu have recently estimated that the occurrence of high-velocity merging systems such as the bullet cluster (1E0657-57) is unlikely at a 6.5-5.8{sigma} level, with an estimated probability between 3.3x10{sup -11} and 3.6x10{sup -9} in {Lambda}CDM cosmology. We show that these anomalies are alleviated in a broad class of infrared-modifed gravity theories, called brane-induced gravity, in which gravitymore » becomes higher-dimensional at ultralarge distances. These theories include additional scalar forces that enhance gravitational attraction and therefore speed up structure formation at late times and on sufficiently large scales. The peculiar velocities are enhanced by 24-34% compared to standard gravity, with the maximal enhancement nearly consistent at the 2{sigma} level with bulk flow observations. The occurrence of the bullet cluster in these theories is {approx_equal}10{sup 4} times more probable than in {Lambda}CDM cosmology.« less

Cosmological model-independent test of ΛCDM with two-point diagnostic by the observational Hubble parameter data

NASA Astrophysics Data System (ADS)

Cao, Shu-Lei; Duan, Xiao-Wei; Meng, Xiao-Lei; Zhang, Tong-Jie

2018-04-01

Aiming at exploring the nature of dark energy (DE), we use forty-three observational Hubble parameter data (OHD) in the redshift range 0 < z ≤slant 2.36 to make a cosmological model-independent test of the ΛCDM model with two-point Omh^2(z2;z1) diagnostic. In ΛCDM model, with equation of state (EoS) w=-1, two-point diagnostic relation Omh^2 ≡ Ωmh^2 is tenable, where Ωm is the present matter density parameter, and h is the Hubble parameter divided by 100 {km s^{-1 Mpc^{-1}}}. We utilize two methods: the weighted mean and median statistics to bin the OHD to increase the signal-to-noise ratio of the measurements. The binning methods turn out to be promising and considered to be robust. By applying the two-point diagnostic to the binned data, we find that although the best-fit values of Omh^2 fluctuate as the continuous redshift intervals change, on average, they are continuous with being constant within 1 σ confidence interval. Therefore, we conclude that the ΛCDM model cannot be ruled out.

Unified cosmic history in modified gravity: From F(R) theory to Lorentz non-invariant models

NASA Astrophysics Data System (ADS)

Nojiri, Shin'Ichi; Odintsov, Sergei D.

2011-08-01

The classical generalization of general relativity is considered as the gravitational alternative for a unified description of the early-time inflation with late-time cosmic acceleration. The structure and cosmological properties of a number of modified theories, including traditional F(R) and Hořava-Lifshitz F(R) gravity, scalar-tensor theory, string-inspired and Gauss-Bonnet theory, non-local gravity, non-minimally coupled models, and power-counting renormalizable covariant gravity are discussed. Different representations of and relations between such theories are investigated. It is shown that some versions of the above theories may be consistent with local tests and may provide a qualitatively reasonable unified description of inflation with the dark energy epoch. The cosmological reconstruction of different modified gravities is provided in great detail. It is demonstrated that eventually any given universe evolution may be reconstructed for the theories under consideration, and the explicit reconstruction is applied to an accelerating spatially flat Friedmann-Robertson-Walker (FRW) universe. Special attention is paid to Lagrange multiplier constrained and conventional F(R) gravities, for latter F(R) theory, the effective ΛCDM era and phantom divide crossing acceleration are obtained. The occurrences of the Big Rip and other finite-time future singularities in modified gravity are reviewed along with their solutions via the addition of higher-derivative gravitational invariants.

Relativistic weak lensing from a fully non-linear cosmological density field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, D.B.; Bruni, M.; Wands, D., E-mail: thomas.daniel@ucy.ac.cy, E-mail: marco.bruni@port.ac.uk, E-mail: david.wands@port.ac.uk

2015-09-01

In this paper we examine cosmological weak lensing on non-linear scales and show that there are Newtonian and relativistic contributions and that the latter can also be extracted from standard Newtonian simulations. We use the post-Friedmann formalism, a post-Newtonian type framework for cosmology, to derive the full weak-lensing deflection angle valid on non-linear scales for any metric theory of gravity. We show that the only contributing term that is quadratic in the first order deflection is the expected Born correction and lens-lens coupling term. We use this deflection angle to analyse the vector and tensor contributions to the E- andmore » B- mode cosmic shear power spectra. In our approach, once the gravitational theory has been specified, the metric components are related to the matter content in a well-defined manner. Specifying General Relativity, we write down a complete set of equations for a GR+ΛCDM universe for computing all of the possible lensing terms from Newtonian N-body simulations. We illustrate this with the vector potential and show that, in a GR+ΛCDM universe, its contribution to the E-mode is negligible with respect to that of the conventional Newtonian scalar potential, even on non-linear scales. Thus, under the standard assumption that Newtonian N-body simulations give a good approximation of the matter dynamics, we show that the standard ray tracing approach gives a good description for a ΛCDM cosmology.« less

Observational constraints on generalized Proca theories

NASA Astrophysics Data System (ADS)

De Felice, Antonio; Heisenberg, Lavinia; Tsujikawa, Shinji

2017-06-01

In a model of the late-time cosmic acceleration within the framework of generalized Proca theories, there exists a de Sitter attractor preceded by the dark energy equation of state wDE=-1 -s , where s is a positive constant. We run the Markov-chain-Monte Carlo code to confront the model with the observational data of the cosmic microwave background (CMB), baryon acoustic oscillations, supernovae type Ia, and local measurements of the Hubble expansion rate for the background cosmological solutions and obtain the bound s =0.254-0.097+0.118 at 95% confidence level (C.L.). Existence of the additional parameter s to those in the Λ -cold-dark-matter (Λ CDM ) model allows to reduce tensions of the Hubble constant H0 between the CMB and the low-redshift measurements. Including the cosmic growth data of redshift-space distortions in the galaxy power spectrum and taking into account no-ghost and stability conditions of cosmological perturbations, we find that the bound on s is shifted to s =0.1 6-0.08+0.08 (95% C.L.) and hence the model with s >0 is still favored over the Λ CDM model. Apart from the quantities s ,H0 and the today's matter density parameter Ωm 0, the constraints on other model parameters associated with perturbations are less stringent, reflecting the fact that there are different sets of parameters that give rise to a similar cosmic expansion and growth history.

Constraints on Non-flat Cosmologies with Massive Neutrinos after Planck 2015

NASA Astrophysics Data System (ADS)

Chen, Yun; Ratra, Bharat; Biesiada, Marek; Li, Song; Zhu, Zong-Hong

2016-10-01

We investigate two dark energy cosmological models (I.e., the ΛCDM and ϕCDM models) with massive neutrinos assuming two different neutrino mass hierarchies in both the spatially flat and non-flat scenarios, where in the ϕCDM model the scalar field possesses an inverse power-law potential, V(ϕ) ∝ ϕ -α (α > 0). Cosmic microwave background data from Planck 2015, baryon acoustic oscillation data from 6dFGS, SDSS-MGS, BOSS-LOWZ and BOSS CMASS-DR11, the joint light-curve analysis compilation of SNe Ia apparent magnitude observations, and the Hubble Space Telescope H 0 prior, are jointly employed to constrain the model parameters. We first determine constraints assuming three species of degenerate massive neutrinos. In the spatially flat (non-flat) ΛCDM model, the sum of neutrino masses is bounded as Σm ν < 0.165(0.299) eV at 95% confidence level (CL). Correspondingly, in the flat (non-flat) ϕCDM model, we find Σm ν < 0.164(0.301) eV at 95% CL. The inclusion of spatial curvature as a free parameter results in a significant broadening of confidence regions for Σm ν and other parameters. In the scenario where the total neutrino mass is dominated by the heaviest neutrino mass eigenstate, we obtain similar conclusions to those obtained in the degenerate neutrino mass scenario. In addition, the results show that the bounds on Σm ν based on two different neutrino mass hierarchies have insignificant differences in the spatially flat case for both the ΛCDM and ϕCDM models; however, the corresponding differences are larger in the non-flat case.

Constraints on Dark Energy from Baryon Acoustic Peak and Galaxy Cluster Gas Mass Measurements

NASA Astrophysics Data System (ADS)

Samushia, Lado; Ratra, Bharat

2009-10-01

We use baryon acoustic peak measurements by Eisenstein et al. and Percival et al., together with the Wilkinson Microwave Anisotropy Probe (WMAP) measurement of the apparent acoustic horizon angle, and galaxy cluster gas mass fraction measurements of Allen et al., to constrain a slowly rolling scalar field dark energy model, phiCDM, in which dark energy's energy density changes in time. We also compare our phiCDM results with those derived for two more common dark energy models: the time-independent cosmological constant model, ΛCDM, and the XCDM parameterization of dark energy's equation of state. For time-independent dark energy, the Percival et al. measurements effectively constrain spatial curvature and favor a close to the spatially flat model, mostly due to the WMAP cosmic microwave background prior used in the analysis. In a spatially flat model the Percival et al. data less effectively constrain time-varying dark energy. The joint baryon acoustic peak and galaxy cluster gas mass constraints on the phiCDM model are consistent with but tighter than those derived from other data. A time-independent cosmological constant in a spatially flat model provides a good fit to the joint data, while the α parameter in the inverse power-law potential phiCDM model is constrained to be less than about 4 at 3σ confidence level.

Observational Role of Dark Matter in f(R) Models for Structure Formation

NASA Astrophysics Data System (ADS)

Verma, Murli Manohar; Yadav, Bal Krishna

The fixed points for the dynamical system in the phase space have been calculated with dark matter in the f(R) gravity models. The stability conditions of these fixed points are obtained in the ongoing accelerated phase of the universe, and the values of the Hubble parameter and Ricci scalar are obtained for various evolutionary stages of the universe. We present a range of some modifications of general relativistic action consistent with the ΛCDM model. We elaborate upon the fact that the upcoming cosmological observations would further constrain the bounds on the possible forms of f(R) with greater precision that could in turn constrain the search for dark matter in colliders.

Reconstructing f(R) modified gravity with dark energy parametrization

NASA Astrophysics Data System (ADS)

Morita, Masaaki; Takahashi, Hirotaka

2014-03-01

We demonstrate the reconstruction of f(R) modified gravity theory with late-time accelerated cosmic expansion. A second-order differential equation for Lagrangian density is obtained from the field equation, and is solved as a function of the cosmic scale factor in two cases. First we begin with the case of a wCDM cosmological model, in which a dark-energy equation-of-state parameter w is constant, for simplicity. Next we extend the method to a case in which the parameter w is epoch-dependent and is expressed as the Chevallier-Polarski-Linder parametrization. Thus we can represent Lagrangian density of f(R) modified gravity theory in terms of dark energy parameters.

COLA with scale-dependent growth: applications to screened modified gravity models

NASA Astrophysics Data System (ADS)

Winther, Hans A.; Koyama, Kazuya; Manera, Marc; Wright, Bill S.; Zhao, Gong-Bo

2017-08-01

We present a general parallelized and easy-to-use code to perform numerical simulations of structure formation using the COLA (COmoving Lagrangian Acceleration) method for cosmological models that exhibit scale-dependent growth at the level of first and second order Lagrangian perturbation theory. For modified gravity theories we also include screening using a fast approximate method that covers all the main examples of screening mechanisms in the literature. We test the code by comparing it to full simulations of two popular modified gravity models, namely f(R) gravity and nDGP, and find good agreement in the modified gravity boost-factors relative to ΛCDM even when using a fairly small number of COLA time steps.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winther, Hans A.; Koyama, Kazuya; Wright, Bill S.

We present a general parallelized and easy-to-use code to perform numerical simulations of structure formation using the COLA (COmoving Lagrangian Acceleration) method for cosmological models that exhibit scale-dependent growth at the level of first and second order Lagrangian perturbation theory. For modified gravity theories we also include screening using a fast approximate method that covers all the main examples of screening mechanisms in the literature. We test the code by comparing it to full simulations of two popular modified gravity models, namely f ( R ) gravity and nDGP, and find good agreement in the modified gravity boost-factors relative tomore » ΛCDM even when using a fairly small number of COLA time steps.« less

Inflationary cosmology with Chaplygin gas in Palatini formalism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borowiec, Andrzej; Wojnar, Aneta; Stachowski, Aleksander

2016-01-01

We present a simple generalisation of the ΛCDM model which on the one hand reaches very good agreement with the present day experimental data and provides an internal inflationary mechanism on the other hand. It is based on Palatini modified gravity with quadratic Starobinsky term and generalized Chaplygin gas as a matter source providing, besides a current accelerated expansion, the epoch of endogenous inflation driven by type III freeze singularity. It follows from our statistical analysis that astronomical data favors negative value of the parameter coupling quadratic term into Einstein-Hilbert Lagrangian and as a consequence the bounce instead of initialmore » Big-Bang singularity is preferred.« less

Consequences of energy conservation violation: late time solutions of Λ (T) CDM subclass of f(R,T) gravity using dynamical system approach

NASA Astrophysics Data System (ADS)

Shabani, Hamid; Ziaie, Amir Hadi

2017-05-01

Very recently, Josset and Perez (Phys. Rev. Lett. 118:021102, 2017) have shown that a violation of the energy-momentum tensor ( EMT) could result in an accelerated expansion state via the appearance of an effective cosmological constant, in the context of unimodular gravity. Inspired by this outcome, in this paper we investigate cosmological consequences of a violation of the EMT conservation in a particular class of f(R,T) gravity when only the pressure-less fluid is present. In this respect, we focus on the late time solutions of models of the type f(R,T)=R+β Λ (-T). As the first task, we study the solutions when the conservation of EMT is respected, and then we proceed with those in which violation occurs. We have found, provided that the EMT conservation is violated, that there generally exist two accelerated expansion solutions of which the stability properties depend on the underlying model. More exactly, we obtain a dark energy solution for which the effective equation of state depends on the model parameters and a de Sitter solution. We present a method to parametrize the Λ (-T) function, which is useful in a dynamical system approach and has been employed in the model. Also, we discuss the cosmological solutions for models with Λ (-T)=8π G(-T)^{α } in the presence of ultra-relativistic matter.

Bayesian analysis of anisotropic cosmologies: Bianchi VIIh and WMAP

NASA Astrophysics Data System (ADS)

McEwen, J. D.; Josset, T.; Feeney, S. M.; Peiris, H. V.; Lasenby, A. N.

2013-12-01

We perform a definitive analysis of Bianchi VIIh cosmologies with Wilkinson Microwave Anisotropy Probe (WMAP) observations of the cosmic microwave background (CMB) temperature anisotropies. Bayesian analysis techniques are developed to study anisotropic cosmologies using full-sky and partial-sky masked CMB temperature data. We apply these techniques to analyse the full-sky internal linear combination (ILC) map and a partial-sky masked W-band map of WMAP 9 yr observations. In addition to the physically motivated Bianchi VIIh model, we examine phenomenological models considered in previous studies, in which the Bianchi VIIh parameters are decoupled from the standard cosmological parameters. In the two phenomenological models considered, Bayes factors of 1.7 and 1.1 units of log-evidence favouring a Bianchi component are found in full-sky ILC data. The corresponding best-fitting Bianchi maps recovered are similar for both phenomenological models and are very close to those found in previous studies using earlier WMAP data releases. However, no evidence for a phenomenological Bianchi component is found in the partial-sky W-band data. In the physical Bianchi VIIh model, we find no evidence for a Bianchi component: WMAP data thus do not favour Bianchi VIIh cosmologies over the standard Λ cold dark matter (ΛCDM) cosmology. It is not possible to discount Bianchi VIIh cosmologies in favour of ΛCDM completely, but we are able to constrain the vorticity of physical Bianchi VIIh cosmologies at (ω/H)0 < 8.6 × 10-10 with 95 per cent confidence.

Planck 2013 results. XV. CMB power spectra and likelihood

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chiang, H. C.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Gaier, T. C.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jewell, J.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kiiveri, K.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Laureijs, R. J.; Lawrence, C. R.; Le Jeune, M.; Leach, S.; Leahy, J. P.; Leonardi, R.; León-Tavares, J.; Lesgourgues, J.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; Lindholm, V.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Marinucci, D.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Menegoni, E.; Mennella, A.; Migliaccio, M.; Millea, M.; Mitra, S.; Miville-Deschênes, M.-A.; Molinari, D.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Orieux, F.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Paykari, P.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Rahlin, A.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ringeval, C.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Sanselme, L.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Varis, J.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, M.; White, S. D. M.; Yvon, D.; Zacchei, A.; Zonca, A.

2014-11-01

This paper presents the Planck 2013 likelihood, a complete statistical description of the two-point correlation function of the CMB temperature fluctuations that accounts for all known relevant uncertainties, both instrumental and astrophysical in nature. We use this likelihood to derive our best estimate of the CMB angular power spectrum from Planck over three decades in multipole moment, ℓ, covering 2 ≤ ℓ ≤ 2500. The main source of uncertainty at ℓ ≲ 1500 is cosmic variance. Uncertainties in small-scale foreground modelling and instrumental noise dominate the error budget at higher ℓs. For ℓ < 50, our likelihood exploits all Planck frequency channels from 30 to 353 GHz, separating the cosmological CMB signal from diffuse Galactic foregrounds through a physically motivated Bayesian component separation technique. At ℓ ≥ 50, we employ a correlated Gaussian likelihood approximation based on a fine-grained set of angular cross-spectra derived from multiple detector combinations between the 100, 143, and 217 GHz frequency channels, marginalising over power spectrum foreground templates. We validate our likelihood through an extensive suite of consistency tests, and assess the impact of residual foreground and instrumental uncertainties on the final cosmological parameters. We find good internal agreement among the high-ℓ cross-spectra with residuals below a few μK2 at ℓ ≲ 1000, in agreement with estimated calibration uncertainties. We compare our results with foreground-cleaned CMB maps derived from all Planck frequencies, as well as with cross-spectra derived from the 70 GHz Planck map, and find broad agreement in terms of spectrum residuals and cosmological parameters. We further show that the best-fit ΛCDM cosmology is in excellent agreement with preliminary PlanckEE and TE polarisation spectra. We find that the standard ΛCDM cosmology is well constrained by Planck from the measurements at ℓ ≲ 1500. One specific example is the spectral index of scalar perturbations, for which we report a 5.4σ deviation from scale invariance, ns = 1. Increasing the multipole range beyond ℓ ≃ 1500 does not increase our accuracy for the ΛCDM parameters, but instead allows us to study extensions beyond the standard model. We find no indication of significant departures from the ΛCDM framework. Finally, we report a tension between the Planck best-fit ΛCDM model and the low-ℓ spectrum in the form of a power deficit of 5-10% at ℓ ≲ 40, with a statistical significance of 2.5-3σ. Without a theoretically motivated model for this power deficit, we do not elaborate further on its cosmological implications, but note that this is our most puzzling finding in an otherwise remarkably consistent data set.

Curvaton as dark matter with secondary inflation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Jinn-Ouk; Kitajima, Naoya; Terada, Takahiro, E-mail: jinn-ouk.gong@apctp.org, E-mail: naoya.kitajima@apctp.org, E-mail: terada@kias.re.kr

2017-03-01

We consider a novel cosmological scenario in which a curvaton is long-lived and plays the role of cold dark matter (CDM) in the presence of a short, secondary inflation. Non-trivial evolution of the large scale cosmological perturbation in the curvaton scenario can affect the duration of the short term inflation, resulting in the inhomogeneous end of inflation. Non-linear parameters of the curvature perturbation are predicted to be f {sub NL} ≈ 5/4 and g {sub NL} ≈ 0. The curvaton abundance can be well diluted by the short-term inflation and accordingly, it does not have to decay into the Standardmore » Model particles. Then the curvaton can account for the present CDM with the isocurvature perturbation being sufficiently suppressed because both the adiabatic and CDM isocurvature perturbations have the same origin. As an explicit example, we consider the thermal inflation scenario and a string axion as a candidate for this curvaton-dark matter. We further discuss possibilities to identify the curvaton-dark matter with the QCD axion.« less

Robust model comparison disfavors power law cosmology

NASA Astrophysics Data System (ADS)

Shafer, Daniel L.

2015-05-01

Late-time power law expansion has been proposed as an alternative to the standard cosmological model and shown to be consistent with some low-redshift data. We test power law expansion against the standard flat Λ CDM cosmology using goodness-of-fit and model comparison criteria. We consider type Ia supernova (SN Ia) data from two current compilations (JLA and Union2.1) along with a current set of baryon acoustic oscillation (BAO) measurements that includes the high-redshift Lyman-α forest measurements from BOSS quasars. We find that neither power law expansion nor Λ CDM is strongly preferred over the other when the SN Ia and BAO data are analyzed separately but that power law expansion is strongly disfavored by the combination. We treat the Rh=c t cosmology (a constant rate of expansion) separately and find that it is conclusively disfavored by all combinations of data that include SN Ia observations and a poor overall fit when systematic errors in the SN Ia measurements are ignored, despite a recent claim to the contrary. We discuss this claim and some concerns regarding hidden model dependence in the SN Ia data.

Goldstone models of modified gravity

NASA Astrophysics Data System (ADS)

Brax, Philippe; Valageas, Patrick

2017-02-01

We investigate scalar-tensor theories where matter couples to the scalar field via a kinetically dependent conformal coupling. These models can be seen as the low-energy description of invariant field theories under a global Abelian symmetry. The scalar field is then identified with the Goldstone mode of the broken symmetry. It turns out that the properties of these models are very similar to the ones of ultralocal theories where the scalar-field value is directly determined by the local matter density. This leads to a complete screening of the fifth force in the Solar System and between compact objects, through the ultralocal screening mechanism. On the other hand, the fifth force can have large effects in extended structures with large-scale density gradients, such as galactic halos. Interestingly, it can either amplify or damp Newtonian gravity, depending on the model parameters. We also study the background cosmology and the linear cosmological perturbations. The background cosmology is hardly different from its Λ -CDM counterpart while cosmological perturbations crucially depend on whether the coupling function is convex or concave. For concave functions, growth is hindered by the repulsiveness of the fifth force while it is enhanced in the convex case. In both cases, the departures from the Λ -CDM cosmology increase on smaller scales and peak for galactic structures. For concave functions, the formation of structure is largely altered below some characteristic mass, as smaller structures are delayed and would form later through fragmentation, as in some warm dark matter scenarios. For convex models, small structures form more easily than in the Λ -CDM scenario. This could lead to an over-abundance of small clumps. We use a thermodynamic analysis and show that although convex models have a phase transition between homogeneous and inhomogeneous phases, on cosmological scales the system does not enter the inhomogeneous phase. On the other hand, for galactic halos, the coexistence of small and large substructures in their outer regions could lead to observational signatures of these models.

Power law cosmology model comparison with CMB scale information

NASA Astrophysics Data System (ADS)

Tutusaus, Isaac; Lamine, Brahim; Blanchard, Alain; Dupays, Arnaud; Zolnierowski, Yves; Cohen-Tanugi, Johann; Ealet, Anne; Escoffier, Stéphanie; Le Fèvre, Olivier; Ilić, Stéphane; Pisani, Alice; Plaszczynski, Stéphane; Sakr, Ziad; Salvatelli, Valentina; Schücker, Thomas; Tilquin, André; Virey, Jean-Marc

2016-11-01

Despite the ability of the cosmological concordance model (Λ CDM ) to describe the cosmological observations exceedingly well, power law expansion of the Universe scale radius, R (t )∝tn, has been proposed as an alternative framework. We examine here these models, analyzing their ability to fit cosmological data using robust model comparison criteria. Type Ia supernovae (SNIa), baryonic acoustic oscillations (BAO) and acoustic scale information from the cosmic microwave background (CMB) have been used. We find that SNIa data either alone or combined with BAO can be well reproduced by both Λ CDM and power law expansion models with n ˜1.5 , while the constant expansion rate model (n =1 ) is clearly disfavored. Allowing for some redshift evolution in the SNIa luminosity essentially removes any clear preference for a specific model. The CMB data are well known to provide the most stringent constraints on standard cosmological models, in particular, through the position of the first peak of the temperature angular power spectrum, corresponding to the sound horizon at recombination, a scale physically related to the BAO scale. Models with n ≥1 lead to a divergence of the sound horizon and do not naturally provide the relevant scales for the BAO and the CMB. We retain an empirical footing to overcome this issue: we let the data choose the preferred values for these scales, while we recompute the ionization history in power law models, to obtain the distance to the CMB. In doing so, we find that the scale coming from the BAO data is not consistent with the observed position of the first peak of the CMB temperature angular power spectrum for any power law cosmology. Therefore, we conclude that when the three standard probes (SNIa, BAO, and CMB) are combined, the Λ CDM model is very strongly favored over any of these alternative models, which are then essentially ruled out.

VizieR Online Data Catalog: [CII], [OI] and [OIII] line emission from z~6 gal. (Olsen+, 2017)

NASA Astrophysics Data System (ADS)

Olsen, K.; Greve, T. R.; Narayanan, D.; Thompson, R.; Dave, R.; Rios, L. N.; Stawinski, S.

2018-05-01

We use cosmological zoom simulations of galaxies extracted from the MUFASA cosmological simulation (Dave+ 2016MNRAS.462.3265D, 2017MNRAS.467..115D); see section 2. For the purposes of this paper, we updated SIGAME from the version presented in Olsen+ (2015ApJ...814...76O); see section 3. Throughout, we adopt a flat cold dark matter (ΛCDM) cosmology with cosmological parameters ΩΛ=0.7, ΩM=0.3, and h=0.68. (1 data file).

Effective Dark Matter Halo Catalog in f(R) Gravity.

PubMed

He, Jian-Hua; Hawken, Adam J; Li, Baojiu; Guzzo, Luigi

2015-08-14

We introduce the idea of an effective dark matter halo catalog in f(R) gravity, which is built using the effective density field. Using a suite of high resolution N-body simulations, we find that the dynamical properties of halos, such as the distribution of density, velocity dispersion, specific angular momentum and spin, in the effective catalog of f(R) gravity closely mimic those in the cold dark matter model with a cosmological constant (ΛCDM). Thus, when using effective halos, an f(R) model can be viewed as a ΛCDM model. This effective catalog therefore provides a convenient way for studying the baryonic physics, the galaxy halo occupation distribution and even semianalytical galaxy formation in f(R) cosmologies.

The lightest supersymmetric particle and the extragalactic gamma-ray background

NASA Technical Reports Server (NTRS)

Gao, Yi-Tian; Stecker, Floyd W.; Cline, David B.

1991-01-01

The possibility that cosmological photino annihilation is caused by the extragalactic gamma-ray background (EGB) is examined with particular attention given to the lightest supersymmetric particle (LSP). The LSP is considered a general type of the best-motivated candidates for cosmic dark matter (CDM). The theoretical analysis employs a corrected assumption for the annihilation cross section, and cosmological integrations are performed through the early phases of the universe. Romberg's method is used for numerical integration, and the total optical depth is developed for the gamma-ray region. The computed LSP-type annihilation fluxes are found to be negligible when compared to the total EGB observed, suggesting that the LSP candidates for CDM are not significant contributors to the EGB.

Galaxy motions cause trouble for cosmology

NASA Astrophysics Data System (ADS)

Boylan-Kolchin, Michael

2018-02-01

According to the widely accepted dark energy plus cold dark matter (ΛCDM) model, dark matter is responsible for both the growth of cosmological structures and the motions of galaxies relative to the expansion of the universe. The dynamics of small galaxies orbiting larger ones provides a crucial window into this mysterious dark matter, which leaves its gravitational mark throughout the universe but has not yet been detected directly. On page 534 of this issue, Müller et al. (1) describe observations of satellite galaxies around Centaurus A, the largest galaxy system in the vicinity of the Milky Way. The results may lead to either a better understanding of galaxy formation within the ΛCDM model or a push to overthrow its underlying assumptions.

Cosmological constraints from galaxy clustering in the presence of massive neutrinos

NASA Astrophysics Data System (ADS)

Zennaro, M.; Bel, J.; Dossett, J.; Carbone, C.; Guzzo, L.

2018-06-01

The clustering ratio is defined as the ratio between the correlation function and the variance of the smoothed overdensity field. In Λ cold dark matter (ΛCDM) cosmologies without massive neutrinos, it has already been proven to be independent of bias and redshift space distortions on a range of linear scales. It therefore can provide us with a direct comparison of predictions (for matter in real space) against measurements (from galaxies in redshift space). In this paper we first extend the applicability of such properties to cosmologies that account for massive neutrinos, by performing tests against simulated data. We then investigate the constraining power of the clustering ratio on cosmological parameters such as the total neutrino mass and the equation of state of dark energy. We analyse the joint posterior distribution of the parameters that satisfy both measurements of the galaxy clustering ratio in the SDSS-DR12, and the angular power spectra of cosmic microwave background temperature and polarization anisotropies measured by the Planck satellite. We find the clustering ratio to be very sensitive to the CDM density parameter, but less sensitive to the total neutrino mass. We also forecast the constraining power the clustering ratio will achieve, predicting the amplitude of its errors with a Euclid-like galaxy survey. First we compute parameter forecasts using the Planck covariance matrix alone, then we add information from the clustering ratio. We find a significant improvement on the constraint of all considered parameters, and in particular an improvement of 40 per cent for the CDM density and 14 per cent for the total neutrino mass.

Vacuum phase transition solves the H0 tension

NASA Astrophysics Data System (ADS)

Di Valentino, Eleonora; Linder, Eric V.; Melchiorri, Alessandro

2018-02-01

Taking the Planck cosmic microwave background data and the more direct Hubble constant measurement data as unaffected by systematic offsets, the values of the Hubble constant H0 interpreted within the Λ CDM cosmological constant and cold dark matter cosmological model are in ˜3.3 σ tension. We show that the Parker vacuum metamorphosis (VM) model, physically motivated by quantum gravitational effects and with the same number of parameters as Λ CDM , can remove the H0 tension and can give an improved fit to data (up to a mean Δ χ2=-7.5 ). It also ameliorates tensions with weak lensing data and the high redshift Lyman alpha forest data. Considering Bayesian evidence, we found in the case of the Planck data set alone positive evidence for a VM model against a cosmological constant both in the six- and nine-parameter framework. When the R16 data set is also considered, we found a strong evidence for the VM model against a cosmological constant in nine-parameter space. We separately consider a scale-dependent scaling of the gravitational lensing amplitude, such as provided by modified gravity, neutrino mass, or cold dark energy, motivated by the somewhat different cosmological parameter estimates for low and high CMB multipoles. We find that no such scale dependence is preferred.

Concordance cosmology without dark energy

NASA Astrophysics Data System (ADS)

Rácz, Gábor; Dobos, László; Beck, Róbert; Szapudi, István; Csabai, István

2017-07-01

According to the separate universe conjecture, spherically symmetric sub-regions in an isotropic universe behave like mini-universes with their own cosmological parameters. This is an excellent approximation in both Newtonian and general relativistic theories. We estimate local expansion rates for a large number of such regions, and use a scale parameter calculated from the volume-averaged increments of local scale parameters at each time step in an otherwise standard cosmological N-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical estimation of the effect of non-linear evolution of structure on the expansion rate. Using our algorithm, a simulation with an initial Ωm = 1 Einstein-de Sitter setting closely tracks the expansion and structure growth history of the Λ cold dark matter (ΛCDM) cosmology. Due to small but characteristic differences, our model can be distinguished from the ΛCDM model by future precision observations. Moreover, our model can resolve the emerging tension between local Hubble constant measurements and the Planck best-fitting cosmology. Further improvements to the simulation are necessary to investigate light propagation and confirm full consistency with cosmic microwave background observations.

Hierarchy of N-point functions in the ΛCDM and ReBEL cosmologies

NASA Astrophysics Data System (ADS)

Hellwing, Wojciech A.; Juszkiewicz, Roman; van de Weygaert, Rien

2010-11-01

In this work we investigate higher-order statistics for the ΛCDM and ReBEL scalar-interacting dark matter models by analyzing 180h-1Mpc dark matter N-body simulation ensembles. The N-point correlation functions and the related hierarchical amplitudes, such as skewness and kurtosis, are computed using the counts-in-cells method. Our studies demonstrate that the hierarchical amplitudes Sn of the scalar-interacting dark matter model significantly deviate from the values in the ΛCDM cosmology on scales comparable and smaller than the screening length rs of a given scalar-interacting model. The corresponding additional forces that enhance the total attractive force exerted on dark matter particles at galaxy scales lower the values of the hierarchical amplitudes Sn. We conclude that hypothetical additional exotic interactions in the dark matter sector should leave detectable markers in the higher-order correlation statistics of the density field. We focused in detail on the redshift evolution of the dark matter field’s skewness and kurtosis. From this investigation we find that the deviations from the canonical ΛCDM model introduced by the presence of the “fifth” force attain a maximum value at redshifts 0.5

A new f(R) model in the light of local gravity test and late-time cosmology

NASA Astrophysics Data System (ADS)

Nautiyal, Akhilesh; Panda, Sukanta; Patel, Avani

We propose a new model of f(R) gravity containing Arctan function in the Lagrangian. We show here that this model satisfies fifth force constraint unlike a similar model in 2013 by Kruglov. In addition to this, we carry out the fixed point analysis as well as comment on the existence of curvature singularity in this model. The cosmological evolution for this f(R) gravity model is also analyzed in the Friedmann-Robertson-Walker (FRW) background. To understand observational significance of the model, cosmological parameters are obtained numerically and compared with those of Lambda cold dark matter (ΛCDM) model. We also scrutinize the model with supernova data. We apply Om diagnostic given by Sahni et al. in 2008 to the model. Using this diagnostic, we detect the distinction between cosmic evolution caused by the f(R) model and ΛCDM. We find best-fit parameter values of the model using baryon acoustic oscillations data.

Is the continuous matter creation cosmology an alternative to ΛCDM?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fabris, J.C.; Pacheco, J.A. de Freitas; Piattella, O.F., E-mail: fabris@pq.cnpq.br, E-mail: pacheco@oca.eu, E-mail: oliver.piattella@pq.cnpq.br

2014-06-01

The matter creation cosmology is revisited, including the evolution of baryons and dark matter particles. The creation process affects only dark matter and not baryons. The dynamics of the ΛCDM model can be reproduced only if two conditions are satisfied: 1) the entropy density production rate and the particle density variation rate are equal and 2) the (negative) pressure associated to the creation process is constant. However, the matter creation model predicts a present dark matter-to-baryon ratio much larger than that observed in massive X-ray clusters of galaxies, representing a potential difficulty for the model. In the linear regime, amore » fully relativistic treatment indicates that baryons are not affected by the creation process but this is not the case for dark matter. Both components evolve together at early phases but lately the dark matter density contrast decreases since the background tends to a constant value. This behaviour produces a negative growth factor, in disagreement with observations, being a further problem for this cosmology.« less

Padé Approximant and Minimax Rational Approximation in Standard Cosmology

NASA Astrophysics Data System (ADS)

Zaninetti, Lorenzo

2016-02-01

The luminosity distance in the standard cosmology as given by $\\Lambda$CDM and consequently the distance modulus for supernovae can be defined by the Pad\\'e approximant. A comparison with a known analytical solution shows that the Pad\\'e approximant for the luminosity distance has an error of $4\\%$ at redshift $= 10$. A similar procedure for the Taylor expansion of the luminosity distance gives an error of $4\\%$ at redshift $=0.7 $; this means that for the luminosity distance, the Pad\\'e approximation is superior to the Taylor series. The availability of an analytical expression for the distance modulus allows applying the Levenberg--Marquardt method to derive the fundamental parameters from the available compilations for supernovae. A new luminosity function for galaxies derived from the truncated gamma probability density function models the observed luminosity function for galaxies when the observed range in absolute magnitude is modeled by the Pad\\'e approximant. A comparison of $\\Lambda$CDM with other cosmologies is done adopting a statistical point of view.

Combined cosmological tests of a bivalent tachyonic dark energy scalar field model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keresztes, Zoltán; Gergely, László Á., E-mail: zkeresztes@titan.physx.u-szeged.hu, E-mail: gergely@physx.u-szeged.hu

A recently investigated tachyonic scalar field dark energy dominated universe exhibits a bivalent future: depending on initial parameters can run either into a de Sitter exponential expansion or into a traversable future soft singularity followed by a contraction phase. We also include in the model (i) a tiny amount of radiation, (ii) baryonic matter (Ω{sub b}h{sup 2} = 0.022161, where the Hubble constant is fixed as h = 0.706) and (iii) cold dark matter (CDM). Out of a variety of six types of evolutions arising in a more subtle classification, we identify two in which in the past the scalar field effectively degenerates intomore » a dust (its pressure drops to an insignificantly low negative value). These are the evolutions of type IIb converging to de Sitter and type III hitting the future soft singularity. We confront these background evolutions with various cosmological tests, including the supernova type Ia Union 2.1 data, baryon acoustic oscillation distance ratios, Hubble parameter-redshift relation and the cosmic microwave background (CMB) acoustic scale. We determine a subset of the evolutions of both types which at 1σ confidence level are consistent with all of these cosmological tests. At perturbative level we derive the CMB temperature power spectrum to find the best agreement with the Planck data for Ω{sub CDM} = 0.22. The fit is as good as for the ΛCDM model at high multipoles, but the power remains slightly overestimated at low multipoles, for both types of evolutions. The rest of the CDM is effectively generated by the tachyonic field, which in this sense acts as a combined dark energy and dark matter model.« less

Investigating the Cosmic Web with Topological Data Analysis

NASA Astrophysics Data System (ADS)

Cisewski-Kehe, Jessi; Wu, Mike; Fasy, Brittany; Hellwing, Wojciech; Lovell, Mark; Rinaldo, Alessandro; Wasserman, Larry

2018-01-01

Data exhibiting complicated spatial structures are common in many areas of science (e.g. cosmology, biology), but can be difficult to analyze. Persistent homology is a popular approach within the area of Topological Data Analysis that offers a new way to represent, visualize, and interpret complex data by extracting topological features, which can be used to infer properties of the underlying structures. In particular, TDA may be useful for analyzing the large-scale structure (LSS) of the Universe, which is an intricate and spatially complex web of matter. In order to understand the physics of the Universe, theoretical and computational cosmologists develop large-scale simulations that allow for visualizing and analyzing the LSS under varying physical assumptions. Each point in the 3D data set represents a galaxy or a cluster of galaxies, and topological summaries ("persistent diagrams") can be obtained summarizing the different ordered holes in the data (e.g. connected components, loops, voids).The topological summaries are interesting and informative descriptors of the Universe on their own, but hypothesis tests using the topological summaries would provide a way to make more rigorous comparisons of LSS under different theoretical models. For example, the received cosmological model has cold dark matter (CDM); however, while the case is strong for CDM, there are some observational inconsistencies with this theory. Another possibility is warm dark matter (WDM). It is of interest to see if a CDM Universe and WDM Universe produce LSS that is topologically distinct.We present several possible test statistics for two-sample hypothesis tests using the topological summaries, carryout a simulation study to investigate the suitableness of the proposed test statistics using simulated data from a variation of the Voronoi foam model, and finally we apply the proposed inference framework to WDM vs. CDM cosmological simulation data.

Cosmic microwave background anisotropies in cold dark matter models with cosmological constant: The intermediate versus large angular scales

NASA Technical Reports Server (NTRS)

Stompor, Radoslaw; Gorski, Krzysztof M.

1994-01-01

We obtain predictions for cosmic microwave background anisotropies at angular scales near 1 deg in the context of cold dark matter models with a nonzero cosmological constant, normalized to the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) detection. The results are compared to those computed in the matter-dominated models. We show that the coherence length of the Cosmic Microwave Background (CMB) anisotropy is almost insensitive to cosmological parameters, and the rms amplitude of the anisotropy increases moderately with decreasing total matter density, while being most sensitive to the baryon abundance. We apply these results in the statistical analysis of the published data from the UCSB South Pole (SP) experiment (Gaier et al. 1992; Schuster et al. 1993). We reject most of the Cold Dark Matter (CDM)-Lambda models at the 95% confidence level when both SP scans are simulated together (although the combined data set renders less stringent limits than the Gaier et al. data alone). However, the Schuster et al. data considered alone as well as the results of some other recent experiments (MAX, MSAM, Saskatoon), suggest that typical temperature fluctuations on degree scales may be larger than is indicated by the Gaier et al. scan. If so, CDM-Lambda models may indeed provide, from a point of view of CMB anisotropies, an acceptable alternative to flat CDM models.

Theoretical implications of the galactic radial acceleration relation of McGaugh, Lelli, and Schombert

NASA Astrophysics Data System (ADS)

Nesbet, Robert K.

2018-05-01

Velocities in stable circular orbits about galaxies, a measure of centripetal gravitation, exceed the expected Kepler/Newton velocity as orbital radius increases. Standard Λ cold dark matter (ΛCDM) attributes this anomaly to galactic dark matter. McGaugh et al. have recently shown for 153 disc galaxies that observed radial acceleration is an apparently universal function of classical acceleration computed for observed galactic baryonic mass density. This is consistent with the empirical modified Newtonian dynamics (MOND) model, not requiring dark matter. It is shown here that suitably constrained ΛCDM and conformal gravity (CG) also produce such a universal correlation function. ΛCDM requires a very specific dark matter distribution, while the implied CG non-classical acceleration must be independent of galactic mass. All three constrained radial acceleration functions agree with the empirical baryonic v4 Tully-Fisher relation. Accurate rotation data in the nominally flat velocity range could distinguish between MOND, ΛCDM, and CG.

Comparison between the Logotropic and ΛCDM models at the cosmological scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chavanis, Pierre-Henri; Kumar, Suresh, E-mail: chavanis@irsamc.ups-tlse.fr, E-mail: suresh.kumar@pilani.bits-pilani.ac.in

We perform a detailed comparison between the Logotropic model [P.H. Chavanis, Eur. Phys. J. Plus, 130 (2015)] and the ΛCDM model. These two models behave similarly at large (cosmological) scales up to the present. Differences will appear only in the far future, in about 25 Gyrs, when the Logotropic Universe becomes phantom while the ΛCDM Universe enters in the de Sitter era. However, the Logotropic model differs from the ΛCDM model at small (galactic) scales, where the latter encounters serious problems. Having a nonvanishing pressure, the Logotropic model can solve the cusp problem and the missing satellite problem of themore » ΛCDM model. In addition, it leads to dark matter halos with a constant surface density Σ{sub 0}=ρ{sub 0} r {sub h} , and can explain its observed value Σ{sub 0}=141 M {sub ⊙}/pc{sup 2} without adjustable parameter. This makes the logotropic model rather unique among all the models attempting to unify dark matter and dark energy. In this paper, we compare the Logotropic and ΛCDM models at the cosmological scale where they are very close to each other in order to determine quantitatively how much they differ. This comparison is facilitated by the fact that these models depend on only two parameters, the Hubble constant H {sub 0} and the present fraction of dark matter Ω{sub m0}. Using the latest observational data from Planck 2015+Lensing+BAO+JLA+HST, we find that the best fit values of H {sub 0} and Ω{sub m0} are H {sub 0}=68.30 km s{sup −1} Mpc{sup −1} and Ω{sub m0}=0.3014 for the Logotropic model, and H {sub 0}=68.02 km s{sup −1} Mpc{sup −1} and Ω{sub m0}=0.3049 for the ΛCDM model. The difference between the two models is at the percent level. As a result, the Logotropic model competes with the ΛCDM model at large scales and solves its problems at small scales. It may therefore represent a viable alternative to the ΛCDM model. Our study provides an explicit example of a theoretically motivated model that is almost indistinguishable from the ΛCDM model at the present time while having a completely different (phantom) evolution in the future. We analytically derive the statefinders of the Logotropic model for all values of the logotropic constant B . We show that the parameter s {sub 0} is directly related to this constant since s {sub 0}=− B /( B +1) independently of any other parameter like H {sub 0} or Ω{sub m0}. For the predicted value of B =3.53× 10{sup −3}, we obtain ( q {sub 0}, r {sub 0}, s {sub 0})=(−0.5516,1.011,−0.003518) instead of ( q {sub 0}, r {sub 0}, s {sub 0})=(−0.5427,1,0) for the ΛCDM model corresponding to 0 B =.« less

A two-point diagnostic for the H II galaxy Hubble diagram

NASA Astrophysics Data System (ADS)

Leaf, Kyle; Melia, Fulvio

2018-03-01

A previous analysis of starburst-dominated H II galaxies and H II regions has demonstrated a statistically significant preference for the Friedmann-Robertson-Walker cosmology with zero active mass, known as the Rh = ct universe, over Λcold dark matter (ΛCDM) and its related dark-matter parametrizations. In this paper, we employ a two-point diagnostic with these data to present a complementary statistical comparison of Rh = ct with Planck ΛCDM. Our two-point diagnostic compares, in a pairwise fashion, the difference between the distance modulus measured at two redshifts with that predicted by each cosmology. Our results support the conclusion drawn by a previous comparative analysis demonstrating that Rh = ct is statistically preferred over Planck ΛCDM. But we also find that the reported errors in the H II measurements may not be purely Gaussian, perhaps due to a partial contamination by non-Gaussian systematic effects. The use of H II galaxies and H II regions as standard candles may be improved even further with a better handling of the systematics in these sources.

A comparison of cosmological models using strong gravitational lensing galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melia, Fulvio; Wei, Jun-Jie; Wu, Xue-Feng, E-mail: fmelia@email.arizona.edu, E-mail: jjwei@pmo.ac.cn, E-mail: xfwu@pmo.ac.cn, E-mail: fmelia@email.arizona.edu, E-mail: jjwei@pmo.ac.cn, E-mail: xfwu@pmo.ac.cn

2015-01-01

Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems from the Sloan Lens ACS and Lens Structure and Dynamics surveys suitable for this analysis, and carry out a one-on-one comparison between the standard model, ΛCDM, and the R{sub h}=ct universe, which has thus far been favored by the application of model selection tools to other kinds of data. We find that both models account for the lens observations quite well, thoughmore » the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution modeled as a singular isothermal ellipsoid, though with some scatter among individual sources. Future work can greatly improve the precision of these measurements by focusing on lensing systems with galaxies as close as possible to the background sources. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the real cosmology is ΛCDM, a sample of ∼200 strong gravitational lenses would be sufficient to rule out R{sub h}=ct at this level of accuracy, while ∼300 strong gravitational lenses would be required to rule out ΛCDM if the real universe were instead R{sub h}=ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with ΛCDM. We point out that, should the R{sub h}=ct universe eventually emerge as the correct cosmology, its lack of any free parameters for this kind of work will provide a remarkably powerful probe of the mass structure in lensing galaxies, and a means of better understanding the origin of the bulge-halo conspiracy.« less

Constraints on holographic cosmologies from strong lensing systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cárdenas, Víctor H.; Bonilla, Alexander; Motta, Verónica

We use strongly gravitationally lensed (SGL) systems to put additional constraints on a set of holographic dark energy models. Data available in the literature (redshift and velocity dispersion) is used to obtain the Einstein radius and compare it with model predictions. We found that the ΛCDM is the best fit to the data. Although a preliminary statistical analysis seems to indicate that two of the holographic models studied show interesting agreement with observations, a stringent test lead us to the result that neither of the holographic models are competitive with the ΛCDM. These results highlight the importance of Strong Lensingmore » measurements to provide additional observational constraints to alternative cosmological models, which are necessary to shed some light into the dark universe.« less

Cosmic microwave background snapshots: pre-WMAP and post-WMAP.

PubMed

Bond, J Richard; Contaldi, Carlo; Pogosyan, Dmitry

2003-11-15

We highlight the remarkable evolution in the cosmic microwave background (CMB) power spectrum C(l) as a function of multipole l over the past few years, and in the cosmological parameters for minimal inflation models derived from it: from anisotropy results before 2000; in 2000 and 2001 from Boomerang, Maxima and the Degree Angular Scale Interferometer (DASI), extending l to approximately 1000; and in 2002 from the Cosmic Background Imager (CBI), Very Small Array (VSA), ARCHEOPS and Arcminute Cosmology Bolometer Array Receiver (ACBAR), extending l to approximately 3000, with more from Boomerang and DASI as well. Pre-WMAP (pre-Wilkinson Microwave Anisotropy Probe) optimal band powers are in good agreement with each other and with the exquisite one-year WMAP results, unveiled in February 2003, which now dominate the l less, similar 600 bands. These CMB experiments significantly increased the case for accelerated expansion in the early Universe (the inflationary paradigm) and at the current epoch (dark energy dominance) when they were combined with "prior" probabilities on the parameters. The minimal inflation parameter set, [omega(b), omega(cdm), Omega(tot), Omega(Lambda), n(s), tau(C), sigma(8)], is applied in the same way to the evolving data. C(l) database and Monte Carlo Markov Chain (MCMC) methods are shown to give similar values, which are highly stable over time and for different prior choices, with the increasing precision best characterized by decreasing errors on uncorrelated "parameter eigenmodes". Priors applied range from weak ones to stronger constraints from the expansion rate (HST-h), from cosmic acceleration from supernovae (SN1) and from galaxy clustering, gravitational lensing and local cluster abundance (LSS). After marginalizing over the other cosmic and experimental variables for the weak + LSS prior, the pre-WMAP data of January 2003 compared with the post-WMAP data of March 2003 give Omega(tot) = 1.03(-0.04)(+0.05) compared with 1.02(-0.03)(+0.04), consistent with (non-Baroque) inflation theory. Adding the flat Omega(tot) = 1 prior, we find a nearly scale-invariant spectrum, n(s) = 0.95(-0.04)(+0.07) compared with 0.97(-0.02)(+0.02). The evidence for a logarithmic variation of the spectral tilt is less than or approximately 2sigma. The densities are for: baryons, omega(b) identical with Omega(b)h(2) = 0.0217(-0.002)(+0.002) (compared with 0.0228(-0.001)(+0.001)), near the Big Bang nucleosynthesis (BBN) estimate of 0.0214 +/- 0.002; CDM, omega(cdm) = Omega(cdm)h(2) = 0.126(-0.012)(+0.012) (compared with 0.121(-0.010)(+0.010)); the substantial dark (unclustered) energy, Omega(Lambda) approximately 0.66(-0.09)(+0.07) (compared with 0.70(-0.05)(+0.05)). The dark energy pressure-to-density ratio w(Q) is not well constrained by our weak + LSS prior, but adding SN1 gives w(Q) less than or approximately -0.7 for January 2003 and March 2003, consistent with the w(Q) = -1 cosmological constant case. We find sigma(8) = 0.89(-0.07)(+0.06) (compared with 0.86(-0.04)(+0.04)), implying a sizable Sunyaev-Zel'dovich (SZ) effect from clusters and groups; the high-l power found in the January 2003 data suggest sigma(8) approximately 0.94(-0.16)(+0.08) is needed to be SZ-compatible.

An analytic cosmology solution of Poincaré gauge gravity

NASA Astrophysics Data System (ADS)

Lu, Jianbo; Chee, Guoying

2016-06-01

A cosmology of Poincaré gauge theory is developed. An analytic solution is obtained. The calculation results agree with observation data and can be compared with the ΛCDM model. The cosmological constant puzzle is the coincidence and fine tuning problem are solved naturally at the same time. The cosmological constant turns out to be the intrinsic torsion and curvature of the vacuum universe, and is derived from the theory naturally rather than added artificially. The dark energy originates from geometry, includes the cosmological constant but differs from it. The analytic expression of the state equations of the dark energy and the density parameters of the matter and the geometric dark energy are derived. The full equations of linear cosmological perturbations and the solutions are obtained.

H0LiCOW - V. New COSMOGRAIL time delays of HE 0435-1223: H0 to 3.8 per cent precision from strong lensing in a flat ΛCDM model

NASA Astrophysics Data System (ADS)

Bonvin, V.; Courbin, F.; Suyu, S. H.; Marshall, P. J.; Rusu, C. E.; Sluse, D.; Tewes, M.; Wong, K. C.; Collett, T.; Fassnacht, C. D.; Treu, T.; Auger, M. W.; Hilbert, S.; Koopmans, L. V. E.; Meylan, G.; Rumbaugh, N.; Sonnenfeld, A.; Spiniello, C.

2017-03-01

We present a new measurement of the Hubble Constant H0 and other cosmological parameters based on the joint analysis of three multiply imaged quasar systems with measured gravitational time delays. First, we measure the time delay of HE 0435-1223 from 13-yr light curves obtained as part of the COSMOGRAIL project. Companion papers detail the modelling of the main deflectors and line-of-sight effects, and how these data are combined to determine the time-delay distance of HE 0435-1223. Crucially, the measurements are carried out blindly with respect to cosmological parameters in order to avoid confirmation bias. We then combine the time-delay distance of HE 0435-1223 with previous measurements from systems B1608+656 and RXJ1131-1231 to create a Time Delay Strong Lensing probe (TDSL). In flat Λ cold dark matter (ΛCDM) with free matter and energy density, we find H0 =71.9^{+2.4}_{-3.0} {km s^{-1} Mpc^{-1}} and Ω _{Λ }=0.62^{+0.24}_{-0.35}. This measurement is completely independent of, and in agreement with, the local distance ladder measurements of H0. We explore more general cosmological models combining TDSL with other probes, illustrating its power to break degeneracies inherent to other methods. The joint constraints from TDSL and Planck are H0 = 69.2_{-2.2}^{+1.4} {km s^{-1} Mpc^{-1}}, Ω _{Λ }=0.70_{-0.01}^{+0.01} and Ω _k=0.003_{-0.006}^{+0.004} in open ΛCDM and H0 =79.0_{-4.2}^{+4.4} {km s^{-1} Mpc^{-1}}, Ω _de=0.77_{-0.03}^{+0.02} and w=-1.38_{-0.16}^{+0.14} in flat wCDM. In combination with Planck and baryon acoustic oscillation data, when relaxing the constraints on the numbers of relativistic species we find Neff = 3.34_{-0.21}^{+0.21} in NeffΛCDM and when relaxing the total mass of neutrinos we find Σmν ≤ 0.182 eV in mνΛCDM. Finally, in an open wCDM in combination with Planck and cosmic microwave background lensing, we find H0 =77.9_{-4.2}^{+5.0} {km s^{-1} Mpc^{-1}}, Ω _de=0.77_{-0.03}^{+0.03}, Ω _k=-0.003_{-0.004}^{+0.004} and w=-1.37_{-0.23}^{+0.18}.

Angular distribution of cosmological parameters as a probe of inhomogeneities: a kinematic parametrisation

NASA Astrophysics Data System (ADS)

Carvalho, C. Sofia; Basilakos, Spyros

2016-08-01

We use a kinematic parametrisation of the luminosity distance to measure the angular distribution on the sky of time derivatives of the scale factor, in particular the Hubble parameter H0, the deceleration parameter q0, and the jerk parameter j0. We apply a recently published method to complement probing the inhomogeneity of the large-scale structure by means of the inhomogeneity in the cosmic expansion. This parametrisation is independent of the cosmological equation of state, which renders it adequate to test interpretations of the cosmic acceleration alternative to the cosmological constant. For the same analytical toy model of an inhomogeneous ensemble of homogenous pixels, we derive the backreaction term in j0 due to the fluctuations of { H0,q0 } and measure it to be of order 10-2 times the corresponding average over the pixels in the absence of backreaction. In agreement with that computed using a ΛCDM parametrisation of the luminosity distance, the backreaction effect on q0 remains below the detection threshold. Although the backreaction effect on j0 is about ten times that on q0, it is also below the detection threshold. Hence backreaction remains unobservable both in q0 and in j0.

Nonparametric test of consistency between cosmological models and multiband CMB measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aghamousa, Amir; Shafieloo, Arman, E-mail: amir@apctp.org, E-mail: shafieloo@kasi.re.kr

2015-06-01

We present a novel approach to test the consistency of the cosmological models with multiband CMB data using a nonparametric approach. In our analysis we calibrate the REACT (Risk Estimation and Adaptation after Coordinate Transformation) confidence levels associated with distances in function space (confidence distances) based on the Monte Carlo simulations in order to test the consistency of an assumed cosmological model with observation. To show the applicability of our algorithm, we confront Planck 2013 temperature data with concordance model of cosmology considering two different Planck spectra combination. In order to have an accurate quantitative statistical measure to compare betweenmore » the data and the theoretical expectations, we calibrate REACT confidence distances and perform a bias control using many realizations of the data. Our results in this work using Planck 2013 temperature data put the best fit ΛCDM model at 95% (∼ 2σ) confidence distance from the center of the nonparametric confidence set while repeating the analysis excluding the Planck 217 × 217 GHz spectrum data, the best fit ΛCDM model shifts to 70% (∼ 1σ) confidence distance. The most prominent features in the data deviating from the best fit ΛCDM model seems to be at low multipoles  18 < ℓ < 26 at greater than 2σ, ℓ ∼ 750 at ∼1 to 2σ and ℓ ∼ 1800 at greater than 2σ level. Excluding the 217×217 GHz spectrum the feature at ℓ ∼ 1800 becomes substantially less significance at ∼1 to 2σ confidence level. Results of our analysis based on the new approach we propose in this work are in agreement with other analysis done using alternative methods.« less

Bright high z SnIa: A challenge for ΛCDM

NASA Astrophysics Data System (ADS)

Perivolaropoulos, L.; Shafieloo, A.

2009-06-01

It has recently been pointed out by Kowalski et. al. [Astrophys. J. 686, 749 (2008).ASJOAB0004-637X10.1086/589937] that there is “an unexpected brightness of the SnIa data at z>1.” We quantify this statement by constructing a new statistic which is applicable directly on the type Ia supernova (SnIa) distance moduli. This statistic is designed to pick up systematic brightness trends of SnIa data points with respect to a best fit cosmological model at high redshifts. It is based on binning the normalized differences between the SnIa distance moduli and the corresponding best fit values in the context of a specific cosmological model (e.g. ΛCDM). These differences are normalized by the standard errors of the observed distance moduli. We then focus on the highest redshift bin and extend its size toward lower redshifts until the binned normalized difference (BND) changes sign (crosses 0) at a redshift zc (bin size Nc). The bin size Nc of this crossing (the statistical variable) is then compared with the corresponding crossing bin size Nmc for Monte Carlo data realizations based on the best fit model. We find that the crossing bin size Nc obtained from the Union08 and Gold06 data with respect to the best fit ΛCDM model is anomalously large compared to Nmc of the corresponding Monte Carlo data sets obtained from the best fit ΛCDM in each case. In particular, only 2.2% of the Monte Carlo ΛCDM data sets are consistent with the Gold06 value of Nc while the corresponding probability for the Union08 value of Nc is 5.3%. Thus, according to this statistic, the probability that the high redshift brightness bias of the Union08 and Gold06 data sets is realized in the context of a (w0,w1)=(-1,0) model (ΛCDM cosmology) is less than 6%. The corresponding realization probability in the context of a (w0,w1)=(-1.4,2) model is more than 30% for both the Union08 and the Gold06 data sets indicating a much better consistency for this model with respect to the BND statistic.

Testing ΛCDM cosmology at turnaround: where to look for violations of the bound?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanoglidis, D.; Pavlidou, V.; Tomaras, T.N., E-mail: dtanogl@physics.uoc.gr, E-mail: pavlidou@physics.uoc.gr, E-mail: tomaras@physics.uoc.gr

In ΛCDM cosmology, structure formation is halted shortly after dark energy dominates the mass/energy budget of the Universe. A manifestation of this effect is that in such a cosmology the turnaround radius—the non-expanding mass shell furthest away from the center of a structure— has an upper bound. Recently, a new, local, test for the existence of dark energy in the form of a cosmological constant was proposed based on this turnaround bound. Before designing an experiment that, through high-precision determination of masses and —independently— turnaround radii, will challenge ΛCDM cosmology, we have to answer two important questions: first, when turnaround-scalemore » structures are predicted to be close enough to their maximum size, so that a possible violation of the bound may be observable. Second, which is the best mass scale to target for possible violations of the bound. These are the questions we address in the present work. Using the Press-Schechter formalism, we find that turnaround structures have in practice already stopped forming, and consequently, the turnaround radius of structures must be very close to the maximum value today. We also find that the mass scale of ∼ 10{sup 13} M{sub ⊙} characterizes the turnaround structures that start to form in a statistically important number density today —and even at an infinite time in the future, since structure formation has almost stopped. This mass scale also separates turnaround structures with qualitatively different cosmological evolution: smaller structures are no longer readjusting their mass distribution inside the turnaround scale, they asymptotically approach their ultimate abundance from higher values, and they are common enough to have, at some epoch, experienced major mergers with structures of comparable mass; larger structures exhibit the opposite behavior. We call this mass scale the transitional mass scale and we argue that it is the optimal for the purpose outlined above. As a corollary, we explain the different accretion behavior of small and larger structures observed in already conducted numerical simulations.« less

Cosmography of f(R)-brane cosmology

NASA Astrophysics Data System (ADS)

Bouhmadi-López, Mariam; Capozziello, Salvatore; Cardone, Vincenzo F.

2010-11-01

Cosmography is a useful tool to constrain cosmological models, in particular, dark energy models. In the case of modified theories of gravity, where the equations of motion are generally quite complicated, cosmography can contribute to select realistic models without imposing arbitrary choices a priori. Indeed, its reliability is based on the assumptions that the universe is homogeneous and isotropic on large scale and luminosity distance can be “tracked” by the derivative series of the scale factor a(t). We apply this approach to induced gravity brane-world models where an f(R) term is present in the brane effective action. The virtue of the model is to self-accelerate the normal and healthy Dvali-Gabadadze-Porrati branch once the f(R) term deviates from the Hilbert-Einstein action. We show that the model, coming from a fundamental theory, is consistent with the ΛCDM scenario at low redshift. We finally estimate the cosmographic parameters fitting the Union2 Type Ia Supernovae data set and the distance priors from baryon acoustic oscillations and then provide constraints on the present day values of f(R) and its second and third derivatives.

Model Selection with Strong-lensing Systems

NASA Astrophysics Data System (ADS)

Leaf, Kyle; Melia, Fulvio

2018-05-01

In this paper, we use an unprecedentedly large sample (158) of confirmed strong lens systems for model selection, comparing five well studied Friedmann-Robertson-Walker cosmologies: ΛCDM, wCDM (the standard model with a variable dark-energy equation of state), the Rh = ct universe, the (empty) Milne cosmology, and the classical Einstein-de Sitter (matter dominated) universe. We first use these sources to optimize the parameters in the standard model and show that they are consistent with Planck, though the quality of the best fit is not satisfactory. We demonstrate that this is likely due to under-reported errors, or to errors yet to be included in this kind of analysis. We suggest that the missing dispersion may be due to scatter about a pure single isothermal sphere (SIS) model that is often assumed for the mass distribution in these lenses. We then use the Bayes information criterion, with the inclusion of a suggested SIS dispersion, to calculate the relative likelihoods and ranking of these models, showing that Milne and Einstein-de Sitter are completely ruled out, while Rh = ct is preferred over ΛCDM/wCDM with a relative probability of ˜73% versus ˜24%. The recently reported sample of new strong lens candidates by the Dark Energy Survey, if confirmed, may be able to demonstrate which of these two models is favoured over the other at a level exceeding 3σ.

Clustering of galaxies in a hierarchical universe - I. Methods and results at z=0

NASA Astrophysics Data System (ADS)

Kauffmann, Guinevere; Colberg, Jorg M.; Diaferio, Antonaldo; White, Simon D. M.

1999-02-01

We introduce a new technique for following the formation and evolution of galaxies in cosmological N-body simulations. Dissipationless simulations are used to track the formation and merging of dark matter haloes as a function of redshift. Simple prescriptions, taken directly from semi-analytic models of galaxy formation, are adopted for gas cooling, star formation, supernova feedback and the merging of galaxies within the haloes. This scheme enables us to explore the clustering properties of galaxies, and to investigate how selection by luminosity, colour or type influences the results. In this paper we study the properties of the galaxy distribution at z=0. These include B- and K-band luminosity functions, two-point correlation functions, pairwise peculiar velocities, cluster mass-to-light ratios, B-V colours, and star formation rates. We focus on two variants of a cold dark matter (CDM) cosmology: a high-density (Omega =1) model with shape-parameter Gamma =0.21 (tau CDM), and a low-density model with Omega =0.3 and Lambda =0.7 (Lambda CDM). Both models are normalized to reproduce the I-band Tully-Fisher relation of Giovanelli et al. near a circular velocity of 220 km s^-1. Our results depend strongly both on this normalization and on the adopted prescriptions for star formation and feedback. Very different assumptions are required to obtain an acceptable model in the two cases. For tau CDM, efficient feedback is required to suppress the growth of galaxies, particularly in low-mass field haloes. Without it, there are too many galaxies and the correlation function exhibits a strong turnover on scales below 1 Mpc. For Lambda CDM, feedback must be weaker, otherwise too few L_* galaxies are produced and the correlation function is too steep. Although neither model is perfect, both come close to reproducing most of the data. Given the uncertainties in modelling some of the critical physical processes, we conclude that it is not yet possible to draw firm conclusions about the values of cosmological parameters from studies of this kind. Further observational work on global star formation and feedback effects is required to narrow the range of possibilities.

LRS Bianchi type-I cosmological model with constant deceleration parameter in f(R,T) gravity

NASA Astrophysics Data System (ADS)

Bishi, Binaya K.; Pacif, S. K. J.; Sahoo, P. K.; Singh, G. P.

A spatially homogeneous anisotropic LRS Bianchi type-I cosmological model is studied in f(R,T) gravity with a special form of Hubble's parameter, which leads to constant deceleration parameter. The parameters involved in the considered form of Hubble parameter can be tuned to match, our models with the ΛCDM model. With the present observed value of the deceleration parameter, we have discussed physical and kinematical properties of a specific model. Moreover, we have discussed the cosmological distances for our model.

New observational constraints on f ( R ) gravity from cosmic chronometers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nunes, Rafael C.; Pan, Supriya; Saridakis, Emmanuel N.

We use the recently released cosmic chronometer data and the latest measured value of the local Hubble parameter, combined with the latest joint light curves of Supernovae Type Ia, and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f ( R ) gravity models. We consider four f ( R ) models, namely the Hu-Sawicki, the Starobinsky, the Tsujikawa, and the exponential one, and we parametrize them introducing a distortion parameter b that quantifies the deviation from ΛCDM cosmology. Our analysis reveals that a small but non-zero deviation from ΛCDM cosmology ismore » slightly favored, with the corresponding fittings exhibiting very efficient AIC and BIC Information Criteria values. Clearly, f ( R ) gravity is consistent with observations, and it can serve as a candidate for modified gravity.« less

Observing the clustering properties of galaxy clusters in dynamical dark-energy cosmologies

NASA Astrophysics Data System (ADS)

Fedeli, C.; Moscardini, L.; Bartelmann, M.

2009-06-01

We study the clustering properties of galaxy clusters expected to be observed by various forthcoming surveys both in the X-ray and sub-mm regimes by the thermal Sunyaev-Zel'dovich effect. Several different background cosmological models are assumed, including the concordance ΛCDM and various cosmologies with dynamical evolution of the dark energy. Particular attention is paid to models with a significant contribution of dark energy at early times which affects the process of structure formation. Past light cone and selection effects in cluster catalogs are carefully modeled by realistic scaling relations between cluster mass and observables and by properly taking into account the selection functions of the different instruments. The results show that early dark-energy models are expected to produce significantly lower values of effective bias and both spatial and angular correlation amplitudes with respect to the standard ΛCDM model. Among the cluster catalogs studied in this work, it turns out that those based on eRosita, Planck, and South Pole Telescope observations are the most promising for distinguishing between various dark-energy models.

Local gravity and large-scale structure

NASA Technical Reports Server (NTRS)

Juszkiewicz, Roman; Vittorio, Nicola; Wyse, Rosemary F. G.

1990-01-01

The magnitude and direction of the observed dipole anisotropy of the galaxy distribution can in principle constrain the amount of large-scale power present in the spectrum of primordial density fluctuations. This paper confronts the data, provided by a recent redshift survey of galaxies detected by the IRAS satellite, with the predictions of two cosmological models with very different levels of large-scale power: the biased Cold Dark Matter dominated model (CDM) and a baryon-dominated model (BDM) with isocurvature initial conditions. Model predictions are investigated for the Local Group peculiar velocity, v(R), induced by mass inhomogeneities distributed out to a given radius, R, for R less than about 10,000 km/s. Several convergence measures for v(R) are developed, which can become powerful cosmological tests when deep enough samples become available. For the present data sets, the CDM and BDM predictions are indistinguishable at the 2 sigma level and both are consistent with observations. A promising discriminant between cosmological models is the misalignment angle between v(R) and the apex of the dipole anisotropy of the microwave background.

Statefinder diagnostic and constraints on the Palatini f(R) gravity theories

NASA Astrophysics Data System (ADS)

Cao, Shu-Lei; Li, Song; Yu, Hao-Ran; Zhang, Tong-Jie

2018-03-01

We focus on a series of f(R) gravity theories in Palatini formalism to investigate the probabilities of producing late-time acceleration for the flat Friedmann-Robertson-Walker (FRW) universe. We apply a statefinder diagnostic to these cosmological models for chosen series of parameters to see if they can be distinguished from one another. The diagnostic involves the statefinder pair {r, s}, where r is derived from the scale factor a and its higher derivatives with respect to the cosmic time t, and s is expressed by r and the deceleration parameter q. In conclusion, we find that although two types of f(R) theories: (i) f(R) = R + αRm – βR ‑n and (ii) f(R) = R + α ln R – β can lead to late-time acceleration, their evolutionary trajectories in the r – s and r – q planes reveal different evolutionary properties, which certainly justify the merits of the statefinder diagnostic. Additionally, we utilize the observational Hubble parameter data (OHD) to constrain these models of f(R) gravity. As a result, except for m = n = 1/2 in case (i), α = 0 in case (i) and case (ii) allow the ΛCDM model to exist in the 1σ confidence region. After applying the statefinder diagnostic to the best-fit models, we find that all the best-fit models are capable of going through the deceleration/acceleration transition stage with a late-time acceleration epoch, and all these models turn to the de Sitter point ({r, s} = {1, 0}) in the future. Also, the evolutionary differences between these models are distinct, especially in the r – s plane, which makes the statefinder diagnostic more reliable in discriminating cosmological models.

The cosmological Janus model: comparison with observational data

NASA Astrophysics Data System (ADS)

Petit, Jean-Pierre; Dagostini, Gilles

2017-01-01

In 2014 we presented a model based on a system of two coupled field equations to describe two populations of particles, one positive and the other mass of negative mass. The analysis of this system by Newtonian approximation show that the masses of the same signs attract according to Newton's law while the masses of opposite signs repel according to an anti-Newton law. This eliminates the runaway phenomenon. It uses the time-dependent exact solution of this system to build the bolometric magnitude distribution of the red-shift. Comparing the prediction of our model -which requires adjustment with a single parameter- with the data from 740 supernovae highlighting the acceleration of the universe gives an excellent agreement. The comparison is then made with the multi-parametric Λ CDM model.

The abundance of galaxy clusters in modified Newtonian dynamics: cosmological simulations with massive neutrinos

NASA Astrophysics Data System (ADS)

Angus, G. W.; Diaferio, Antonaldo

2011-10-01

We present a new particle mesh cosmological N-body code for accurately solving the modified Poisson equation of the quasi-linear formulation of modified Newtonian dynamics (MOND). We generate initial conditions for the Angus cosmological model, which is identical to Λ cold dark matter (ΛCDM) except that the CDM is switched for a single species of thermal sterile neutrinos. We set the initial conditions at z= 250 for a (512 Mpc h-1)3 box with 2563 particles, and we evolve them down to z= 0. We clearly demonstrate the ability of MOND to develop the large-scale structure in a hot dark matter cosmology and contradict the naive expectation that MOND cannot form galaxy clusters. We find that the correct order of magnitude of X-ray clusters (with TX > 4.5 keV) can be formed, but that we overpredict the number of very rich clusters and seriously underpredict the number of lower mass clusters. We present evidence that suggests the density profiles of our simulated clusters are compatible with those of the observed X-ray clusters in MOND. As a last test, we computed the relative velocity between pairs of haloes within 10 Mpc and find that pairs with velocities larger than 3000 km s-1, like the bullet cluster, can form without difficulty.

Cosmological perturbations in the ΛCDM-like limit of a polytropic dark matter model

NASA Astrophysics Data System (ADS)

Kleidis, K.; Spyrou, N. K.

2017-10-01

It has recently been proposed that both dark matter (DM) and dark energy (DE) can be treated as a single component when they are considered in the context of a polytropic DM fluid with thermodynamical content. Depending on only one free parameter, that is, the polytropic exponent, - 0.103 < Γ ≤ 0, this unified DM model reproduces the distance measurements performed with the aid of the supernovae Type Ia (SNe Ia) standard candles to high accuracy. It avoids the age problem and the coincidence problem, meaning that it allows interpreting not only when, but also why the Universe so recently transited from deceleration to acceleration. However, a critical problem still remains that the polytropic DM model is also required to solve, that is, it needs to demonstrate its compatibility with current observational data on structure formation. We begin to untie this knot here by discussing the evolution of cosmological perturbations in the ΛCDM-like (I.e., Γ = 0) limit of the polytropic DM model. The corresponding results are quite encouraging because this model reproduces every major effect known from conventional (I.e., pressureless cold dark matter - CDM) structure formation theory, such as the constancy of metric perturbations in the vicinity of recombination and the (late-time) Meszaros effect on their rest-mass density counterparts. The non-zero (polytropic) pressure, on the other hand, drives the evolution of small-scale velocity perturbations along the lines of the root-mean-square velocity law of conventional statistical physics. As a consequence, peculiar velocities in this model slightly increase instead of being redshifted away by cosmic expansion. This result might comprise a convenient probe of the polytropic DM model with Γ = 0. Even more importantly, however, upon consideration of scale-invariant metric perturbations, the spectrum of their rest-mass density counterparts exhibits an effective power-law dependence on the (physical) wavenumber, kph, of the form kph3+nseff, with the associated scalar spectral index, nseff, being equal to nseff = 0.970. This theoretical value reproduces the corresponding observational Planck result, that is, nsobs = 0.968 ± 0.006.

Testing averaged cosmology with type Ia supernovae and BAO data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santos, B.; Alcaniz, J.S.; Coley, A.A.

An important problem in precision cosmology is the determination of the effects of averaging and backreaction on observational predictions, particularly in view of the wealth of new observational data and improved statistical techniques. In this paper, we discuss the observational viability of a class of averaged cosmologies which consist of a simple parametrized phenomenological two-scale backreaction model with decoupled spatial curvature parameters. We perform a Bayesian model selection analysis and find that this class of averaged phenomenological cosmological models is favored with respect to the standard ΛCDM cosmological scenario when a joint analysis of current SNe Ia and BAO datamore » is performed. In particular, the analysis provides observational evidence for non-trivial spatial curvature.« less

Relaxing the σ 8-tension through running vacuum in the Universe

NASA Astrophysics Data System (ADS)

Gómez-Valent, Adrià; Solà, Joan

2017-11-01

It has recently been shown that the class of running vacuum models (RVMs) has the capacity to fit the overall cosmological observations better than the concordance ΛCDM model, therefore supporting the possibility of dynamical dark energy (DE). Apart from the cosmic microwave background (CMB) anisotropies, the most crucial datasets involved are: i) baryonic acoustic oscillations (BAO), and ii) direct large scale structure (LSS) formation data. Analyses mainly focusing on CMB and with insufficient BAO + LSS input generally fail to capture the dynamical DE signature, whereas the few existing studies accounting for the wealth of known CMB+BAO+LSS data (see in particular Solà, Gómez-Valent and de Cruz Pérez (2015), (2017); and Zhao et al. (2017)) do converge to the remarkable conclusion that dynamical DE might well be encoded in the current cosmological observations at 3-4σ c.l. A decisive factor is the persistent σ 8-tension between the ΛCDM and the data. Because the issue is obviously pressing, we devote this work to explain how and why running vacuum in the expanding universe successfully relaxes the existing σ 8-tension and describes the LSS formation data significantly better than the ΛCDM.

First Evidence of Running Cosmic Vacuum: Challenging the Concordance Model

NASA Astrophysics Data System (ADS)

Solà, Joan; Gómez-Valent, Adrià; de Cruz Pérez, Javier

2017-02-01

Despite the fact that a rigid {{Λ }}-term is a fundamental building block of the concordance ΛCDM model, we show that a large class of cosmological scenarios with dynamical vacuum energy density {ρ }{{Λ }} together with a dynamical gravitational coupling G or a possible non-conservation of matter, are capable of seriously challenging the traditional phenomenological success of the ΛCDM. In this paper, we discuss these “running vacuum models” (RVMs), in which {ρ }{{Λ }}={ρ }{{Λ }}(H) consists of a nonvanishing constant term and a series of powers of the Hubble rate. Such generic structure is potentially linked to the quantum field theoretical description of the expanding universe. By performing an overall fit to the cosmological observables SN Ia+BAO+H(z)+LSS+BBN+CMB (in which the WMAP9, Planck 2013, and Planck 2015 data are taken into account), we find that the class of RVMs appears significantly more favored than the ΛCDM, namely, at an unprecedented level of ≳ 4.2σ . Furthermore, the Akaike and Bayesian information criteria confirm that the dynamical RVMs are strongly preferred compared to the conventional rigid {{Λ }}-picture of the cosmic evolution.

A Solution to the Cosmological Problem of Relativity Theory

NASA Astrophysics Data System (ADS)

Janzen, Daryl

After nearly a century of scientific investigation, the standard cosmological theory continues to have many unexplained problems, which invariably amount to one troubling statement: we know of no good reason for the Universe to appear just as it does, which is described extremely well by the flat ΛCDM cosmological model. Therefore, the problem is not that the physical model is at all incompatible with observation, but that, as our empirical results have been increasingly constrained, it has also become increasingly obvious that the Universe does not meet our prior expectations; e.g., the evidence suggests that the Universe began from a singularity of the theory that is used to describe it, and with space expanding thereafter in cosmic time, even though relativity theory is thought to imply that no such objective foliation of the spacetime continuum should reasonably exist. Furthermore, the expanding Universe is well-described as being flat, isotropic, and homogeneous, even though its shape and expansion rate are everywhere supposed to be the products of local energy-content---and the necessary prior uniform distribution, of just the right amount of matter for all three of these conditions to be met, could not have been causally determined to begin with. And finally, the empirically constrained density parameters now indicate that all of the matter that we directly observe should make up only four percent of the total, so that the dominant forms of energy in the Universe should be dark energy in the form of a cosmological constant, Λ, and cold dark matter (CDM). The most common ways of attacking these problems have been: to apply modifications to the basic physical model, e.g. as in the inflation and quintessence theories which strive to resolve the horizon, flatness, and cosmological constant problems; to use particle physics techniques in order to formulate the description of dark matter candidates that might fit with observations; and, in the case of the Big Bang singularity, to appeal to the need for a quantum theory of gravity. This thesis takes a very different approach to the problem, in hypothesising that, because our physical model really does appear to do a very good job of describing the observed cosmic expansion rate, and all the data indicate that our Universe might well expand precisely according to the flat ΛCDM scale-factor, it may not be the model, but our basic expectations that need to be modified in order to derive a physical theory that stands in reasonable agreement with the empirical results; i.e., that it may actually be that we need to re-examine, and rationally modify our expectations of what should theoretically be, so that we might derive a theory to explain the empirical results of cosmology, which would be based solely on reasonably acceptable first principles. Therefore, a self-consistent theory is constructed here, upon re-consideration of the cosmological foundations of relativity theory, which eventually does afford an explanation of the cosmological problem, as it provides good reason to actually expect observations in the fundamental rest-frame to be described precisely by the flat ΛCDM scale-factor which has been empirically constrained.

Planck 2013 results. XVI. Cosmological parameters

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cappellini, B.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chen, X.; Chiang, H. C.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Gaier, T. C.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Haissinski, J.; Hamann, J.; Hansen, F. K.; Hanson, D.; Harrison, D.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hou, Z.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jewell, J.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leahy, J. P.; Leonardi, R.; León-Tavares, J.; Lesgourgues, J.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Melin, J.-B.; Mendes, L.; Menegoni, E.; Mennella, A.; Migliaccio, M.; Millea, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, D.; Pearson, T. J.; Peiris, H. V.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Platania, P.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, M.; White, S. D. M.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.

2014-11-01

This paper presents the first cosmological results based on Planck measurements of the cosmic microwave background (CMB) temperature and lensing-potential power spectra. We find that the Planck spectra at high multipoles (ℓ ≳ 40) are extremely well described by the standard spatially-flat six-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations. Within the context of this cosmology, the Planck data determine the cosmological parameters to high precision: the angular size of the sound horizon at recombination, the physical densities of baryons and cold dark matter, and the scalar spectral index are estimated to be θ∗ = (1.04147 ± 0.00062) × 10-2, Ωbh2 = 0.02205 ± 0.00028, Ωch2 = 0.1199 ± 0.0027, and ns = 0.9603 ± 0.0073, respectively(note that in this abstract we quote 68% errors on measured parameters and 95% upper limits on other parameters). For this cosmology, we find a low value of the Hubble constant, H0 = (67.3 ± 1.2) km s-1 Mpc-1, and a high value of the matter density parameter, Ωm = 0.315 ± 0.017. These values are in tension with recent direct measurements of H0 and the magnitude-redshift relation for Type Ia supernovae, but are in excellent agreement with geometrical constraints from baryon acoustic oscillation (BAO) surveys. Including curvature, we find that the Universe is consistent with spatial flatness to percent level precision using Planck CMB data alone. We use high-resolution CMB data together with Planck to provide greater control on extragalactic foreground components in an investigation of extensions to the six-parameter ΛCDM model. We present selected results from a large grid of cosmological models, using a range of additional astrophysical data sets in addition to Planck and high-resolution CMB data. None of these models are favoured over the standard six-parameter ΛCDM cosmology. The deviation of the scalar spectral index from unity isinsensitive to the addition of tensor modes and to changes in the matter content of the Universe. We find an upper limit of r0.002< 0.11 on the tensor-to-scalar ratio. There is no evidence for additional neutrino-like relativistic particles beyond the three families of neutrinos in the standard model. Using BAO and CMB data, we find Neff = 3.30 ± 0.27 for the effective number of relativistic degrees of freedom, and an upper limit of 0.23 eV for the sum of neutrino masses. Our results are in excellent agreement with big bang nucleosynthesis and the standard value of Neff = 3.046. We find no evidence for dynamical dark energy; using BAO and CMB data, the dark energy equation of state parameter is constrained to be w = -1.13-0.10+0.13. We also use the Planck data to set limits on a possible variation of the fine-structure constant, dark matter annihilation and primordial magnetic fields. Despite the success of the six-parameter ΛCDM model in describing the Planck data at high multipoles, we note that this cosmology does not provide a good fit to the temperature power spectrum at low multipoles. The unusual shape of the spectrum in the multipole range 20 ≲ ℓ ≲ 40 was seen previously in the WMAP data and is a real feature of the primordial CMB anisotropies. The poor fit to the spectrum at low multipoles is not of decisive significance, but is an "anomaly" in an otherwise self-consistent analysis of the Planck temperature data.

CMB constraints on β-exponential inflationary models

NASA Astrophysics Data System (ADS)

Santos, M. A.; Benetti, M.; Alcaniz, J. S.; Brito, F. A.; Silva, R.

2018-03-01

We analyze a class of generalized inflationary models proposed in ref. [1], known as β-exponential inflation. We show that this kind of potential can arise in the context of brane cosmology, where the field describing the size of the extra-dimension is interpreted as the inflaton. We discuss the observational viability of this class of model in light of the latest Cosmic Microwave Background (CMB) data from the Planck Collaboration through a Bayesian analysis, and impose tight constraints on the model parameters. We find that the CMB data alone prefer weakly the minimal standard model (ΛCDM) over the β-exponential inflation. However, when current local measurements of the Hubble parameter, H0, are considered, the β-inflation model is moderately preferred over the ΛCDM cosmology, making the study of this class of inflationary models interesting in the context of the current H0 tension.

Cosmology with the cosmic microwave background temperature-polarization correlation

NASA Astrophysics Data System (ADS)

Couchot, F.; Henrot-Versillé, S.; Perdereau, O.; Plaszczynski, S.; Rouillé d'Orfeuil, B.; Spinelli, M.; Tristram, M.

2017-06-01

We demonstrate that the cosmic microwave background (CMB) temperature-polarization cross-correlation provides accurate and robust constraints on cosmological parameters. We compare them with the results from temperature or polarization and investigate the impact of foregrounds, cosmic variance, and instrumental noise. This analysis makes use of the Planck high-ℓ HiLLiPOP likelihood based on angular power spectra, which takes into account systematics from the instrument and foreground residuals directly modelled using Planck measurements. The temperature-polarization correlation (TE) spectrum is less contaminated by astrophysical emissions than the temperature power spectrum (TT), allowing constraints that are less sensitive to foreground uncertainties to be derived. For ΛCDM parameters, TE gives very competitive results compared to TT. For basic ΛCDM model extensions (such as AL, ∑mν, or Neff), it is still limited by the instrumental noise level in the polarization maps.

Second-order Cosmological Perturbations Engendered by Point-like Masses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brilenkov, Ruslan; Eingorn, Maxim, E-mail: ruslan.brilenkov@gmail.com, E-mail: maxim.eingorn@gmail.com

2017-08-20

In the ΛCDM framework, presenting nonrelativistic matter inhomogeneities as discrete massive particles, we develop the second‐order cosmological perturbation theory. Our approach relies on the weak gravitational field limit. The derived equations for the second‐order scalar, vector, and tensor metric corrections are suitable at arbitrary distances, including regions with nonlinear contrasts of the matter density. We thoroughly verify fulfillment of all Einstein equations, as well as self‐consistency of order assignments. In addition, we achieve logical positive results in the Minkowski background limit. Feasible investigations of the cosmological back-reaction manifestations by means of relativistic simulations are also outlined.

A model for the distribution of dark matter, galaxies, and the intergalactic medium in a cold dark matter-dominated universe

NASA Technical Reports Server (NTRS)

Ryu, Dongsu; Vishniac, Ethan T.; Chiang, Wei-Hwan

1989-01-01

The spatial distribution of the cold-dark-matter (CDM) and baryonic components of CDM-dominated cosmological models are characterized, summarizing the results of recent theoretical investigations. The evolution and distribution of matter in an Einstein-de Sitter universe on length scales small enough so that the Newtonian approximation is valid is followed chronologically, assuming (1) that the galaxies, CDM, and the intergalactic medium (IGM) are coupled by gravity, (2) that galaxies form by taking mass and momentum from the IGM, and (3) that the IGM responds to the energy input from the galaxies. The results of the numerical computations are presented in extensive graphs and discussed in detail.

A non-parametric consistency test of the ΛCDM model with Planck CMB data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aghamousa, Amir; Shafieloo, Arman; Hamann, Jan, E-mail: amir@aghamousa.com, E-mail: jan.hamann@unsw.edu.au, E-mail: shafieloo@kasi.re.kr

Non-parametric reconstruction methods, such as Gaussian process (GP) regression, provide a model-independent way of estimating an underlying function and its uncertainty from noisy data. We demonstrate how GP-reconstruction can be used as a consistency test between a given data set and a specific model by looking for structures in the residuals of the data with respect to the model's best-fit. Applying this formalism to the Planck temperature and polarisation power spectrum measurements, we test their global consistency with the predictions of the base ΛCDM model. Our results do not show any serious inconsistencies, lending further support to the interpretation ofmore » the base ΛCDM model as cosmology's gold standard.« less

No Evidence for Extensions to the Standard Cosmological Model.

PubMed

Heavens, Alan; Fantaye, Yabebal; Sellentin, Elena; Eggers, Hans; Hosenie, Zafiirah; Kroon, Steve; Mootoovaloo, Arrykrishna

2017-09-08

We compute the Bayesian evidence for models considered in the main analysis of Planck cosmic microwave background data. By utilizing carefully defined nearest-neighbor distances in parameter space, we reuse the Monte Carlo Markov chains already produced for parameter inference to compute Bayes factors B for many different model-data set combinations. The standard 6-parameter flat cold dark matter model with a cosmological constant (ΛCDM) is favored over all other models considered, with curvature being mildly favored only when cosmic microwave background lensing is not included. Many alternative models are strongly disfavored by the data, including primordial correlated isocurvature models (lnB=-7.8), nonzero scalar-to-tensor ratio (lnB=-4.3), running of the spectral index (lnB=-4.7), curvature (lnB=-3.6), nonstandard numbers of neutrinos (lnB=-3.1), nonstandard neutrino masses (lnB=-3.2), nonstandard lensing potential (lnB=-4.6), evolving dark energy (lnB=-3.2), sterile neutrinos (lnB=-6.9), and extra sterile neutrinos with a nonzero scalar-to-tensor ratio (lnB=-10.8). Other models are less strongly disfavored with respect to flat ΛCDM. As with all analyses based on Bayesian evidence, the final numbers depend on the widths of the parameter priors. We adopt the priors used in the Planck analysis, while performing a prior sensitivity analysis. Our quantitative conclusion is that extensions beyond the standard cosmological model are disfavored by Planck data. Only when newer Hubble constant measurements are included does ΛCDM become disfavored, and only mildly, compared with a dynamical dark energy model (lnB∼+2).

No Evidence for Extensions to the Standard Cosmological Model

NASA Astrophysics Data System (ADS)

Heavens, Alan; Fantaye, Yabebal; Sellentin, Elena; Eggers, Hans; Hosenie, Zafiirah; Kroon, Steve; Mootoovaloo, Arrykrishna

2017-09-01

We compute the Bayesian evidence for models considered in the main analysis of Planck cosmic microwave background data. By utilizing carefully defined nearest-neighbor distances in parameter space, we reuse the Monte Carlo Markov chains already produced for parameter inference to compute Bayes factors B for many different model-data set combinations. The standard 6-parameter flat cold dark matter model with a cosmological constant (Λ CDM ) is favored over all other models considered, with curvature being mildly favored only when cosmic microwave background lensing is not included. Many alternative models are strongly disfavored by the data, including primordial correlated isocurvature models (ln B =-7.8 ), nonzero scalar-to-tensor ratio (ln B =-4.3 ), running of the spectral index (ln B =-4.7 ), curvature (ln B =-3.6 ), nonstandard numbers of neutrinos (ln B =-3.1 ), nonstandard neutrino masses (ln B =-3.2 ), nonstandard lensing potential (ln B =-4.6 ), evolving dark energy (ln B =-3.2 ), sterile neutrinos (ln B =-6.9 ), and extra sterile neutrinos with a nonzero scalar-to-tensor ratio (ln B =-10.8 ). Other models are less strongly disfavored with respect to flat Λ CDM . As with all analyses based on Bayesian evidence, the final numbers depend on the widths of the parameter priors. We adopt the priors used in the Planck analysis, while performing a prior sensitivity analysis. Our quantitative conclusion is that extensions beyond the standard cosmological model are disfavored by Planck data. Only when newer Hubble constant measurements are included does Λ CDM become disfavored, and only mildly, compared with a dynamical dark energy model (ln B ˜+2 ).

Cosmology in beyond-generalized Proca theories

NASA Astrophysics Data System (ADS)

Nakamura, Shintaro; Kase, Ryotaro; Tsujikawa, Shinji

2017-05-01

The beyond-generalized Proca theories are the extension of second-order massive vector-tensor theories (dubbed generalized Proca theories) with two transverse vector modes and one longitudinal scalar besides two tensor polarizations. Even with this extension, the propagating degrees of freedom remain unchanged on the isotropic cosmological background without an Ostrogradski instability. We study the cosmology in beyond-generalized Proca theories by paying particular attention to the dynamics of late-time cosmic acceleration and resulting observational consequences. We derive conditions for avoiding ghosts and instabilities of tensor, vector, and scalar perturbations and discuss viable parameter spaces in concrete models allowing the dark energy equation of state smaller than -1 . The propagation speeds of those perturbations are subject to modifications beyond the domain of generalized Proca theories. There is a mixing between scalar and matter sound speeds, but such a mixing is suppressed during most of the cosmic expansion history without causing a new instability. On the other hand, we find that derivative interactions arising in beyond-generalized Proca theories give rise to important modifications to the cosmic growth history. The growth rate of matter perturbations can be compatible with the redshift-space distortion data due to the realization of gravitational interaction weaker than that in generalized Proca theories. Thus, it is possible to distinguish the dark energy model in beyond-generalized Proca theories from the counterpart in generalized Proca theories as well as from the Λ CDM model.

ETHOS - an effective theory of structure formation: predictions for the high-redshift Universe - abundance of galaxies and reionization

NASA Astrophysics Data System (ADS)

Lovell, Mark R.; Zavala, Jesús; Vogelsberger, Mark; Shen, Xuejian; Cyr-Racine, Francis-Yan; Pfrommer, Christoph; Sigurdson, Kris; Boylan-Kolchin, Michael; Pillepich, Annalisa

2018-07-01

We contrast predictions for the high-redshift galaxy population and reionization history between cold dark matter (CDM) and an alternative self-interacting dark matter model based on the recently developed ETHOS framework that alleviates the small-scale CDM challenges within the Local Group. We perform the highest resolution hydrodynamical cosmological simulations (a 36 Mpc3 volume with gas cell mass of ˜ 105 M_{⊙} and minimum gas softening of ˜180 pc) within ETHOS to date - plus a CDM counterpart - to quantify the abundance of galaxies at high redshift and their impact on reionization. We find that ETHOS predicts galaxies with higher ultraviolet (UV) luminosities than their CDM counterparts and a faster build-up of the faint end of the UV luminosity function. These effects, however, make the optical depth to reionization less sensitive to the power spectrum cut-off: the ETHOS model differs from the CDM τ value by only 10 per cent and is consistent with Planck limits if the effective escape fraction of UV photons is 0.1-0.5. We conclude that current observations of high-redshift luminosity functions cannot differentiate between ETHOS and CDM models, but deep James Webb Space Telescope surveys of strongly lensed, inherently faint galaxies have the potential to test non-CDM models that offer attractive solutions to CDM's Local Group problems.

The expansion rate of the intermediate universe in light of Planck

NASA Astrophysics Data System (ADS)

Verde, Licia; Protopapas, Pavlos; Jimenez, Raul

2014-12-01

We use cosmology-independent measurements of the expansion history in the redshift range 0.1 ≲ z < 1.2 and compare them with the Cosmic Microwave Background-derived expansion history predictions. The motivation is to investigate if the tension between the local (cosmology independent) Hubble constant H0 value and the Planck-derived H0 is also present at other redshifts. We conclude that there is no tension between Planck and cosmology independent-measurements of the Hubble parameter H(z) at 0.1 ≲ z < 1.2 for the ΛCDM model (odds of tension are only 1:15, statistically not significant). Considering extensions of the ΛCDM model does not improve these odds (actually makes them worse), thus favouring the simpler model over its extensions. On the other hand the H(z) data are also not in tension with the local H0 measurements but the combination of all three data-sets shows a highly significant tension (odds ∼1:400). Thus the new data deepen the mystery of the mismatch between Planck and local H0 measurements, and cannot univocally determine whether it is an effect localised at a particular redshift. Having said this, we find that assuming the NGC4258 maser distance as the correct anchor for H0, brings the odds to comfortable values. Further, using only the expansion history measurements we constrain, within the ΛCDM model, H0 = 68.5 ± 3.5 and Ωm = 0.32 ± 0.05 (at 68% confidence) without relying on any CMB prior. We also address the question of how smooth the expansion history of the Universe is given the cosmology independent data and conclude that there is no evidence for deviations from smoothness on the expansion history, neither variations with time in the value of the equation of state of dark energy.

Cosmological bound from the neutron star merger GW170817 in scalar-tensor and F(R) gravity theories

NASA Astrophysics Data System (ADS)

Nojiri, Shin'ichi; Odintsov, Sergei D.

2018-04-01

We consider the evolution of cosmological gravitational waves in scalar-tensor theory and F (R) gravity theory as typical models of the modified gravity. Although the propagation speed is not changed from the speed of light, the propagation phase changes when we compare the propagation in these modified gravity theories with the propagation in the ΛCDM model. The phase change might be detected in future observations.

TESTING NONSTANDARD COSMOLOGICAL MODELS WITH SNLS3 SUPERNOVA DATA AND OTHER COSMOLOGICAL PROBES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Zhengxiang; Yu Hongwei; Wu Puxun, E-mail: hwyu@hunnu.edu.cn

2012-01-10

We investigate the implications for some nonstandard cosmological models using data from the first three years of the Supernova Legacy Survey (SNLS3), assuming a spatially flat universe. A comparison between the constraints from the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2, SDSS-II, and Constitution samples, is given and the effects of different light-curve fitters are considered. We find that analyzing SNe Ia with SALT2 or SALT or SiFTO can give consistent results and the tensions between different data sets and different light-curve fitters are obvious for fewer-free-parameters models. At the same time, we alsomore » study the constraints from SNLS3 along with data from the cosmic microwave background and the baryonic acoustic oscillations (CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model selection criteria such as {chi}{sup 2}/dof, goodness of fit, Akaike information criterion, and Bayesian information criterion, we find that, among all the cosmological models considered here ({Lambda}CDM, constant w, varying w, Dvali-Gabadadze-Porrati (DGP), modified polytropic Cardassian, and the generalized Chaplygin gas), the flat DGP is favored by SNLS3 alone. However, when additional CMB/BAO or H(z) constraints are included, this is no longer the case, and the flat {Lambda}CDM becomes preferred.« less

The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Cosmological implications of the Fourier space wedges of the final sample

NASA Astrophysics Data System (ADS)

Grieb, Jan Niklas; Sánchez, Ariel G.; Salazar-Albornoz, Salvador; Scoccimarro, Román; Crocce, Martín; Dalla Vecchia, Claudio; Montesano, Francesco; Gil-Marín, Héctor; Ross, Ashley J.; Beutler, Florian; Rodríguez-Torres, Sergio; Chuang, Chia-Hsun; Prada, Francisco; Kitaura, Francisco-Shu; Cuesta, Antonio J.; Eisenstein, Daniel J.; Percival, Will J.; Vargas-Magaña, Mariana; Tinker, Jeremy L.; Tojeiro, Rita; Brownstein, Joel R.; Maraston, Claudia; Nichol, Robert C.; Olmstead, Matthew D.; Samushia, Lado; Seo, Hee-Jong; Streblyanska, Alina; Zhao, Gong-bo

2017-05-01

We extract cosmological information from the anisotropic power-spectrum measurements from the recently completed Baryon Oscillation Spectroscopic Survey (BOSS), extending the concept of clustering wedges to Fourier space. Making use of new fast-Fourier-transform-based estimators, we measure the power-spectrum clustering wedges of the BOSS sample by filtering out the information of Legendre multipoles ℓ > 4. Our modelling of these measurements is based on novel approaches to describe non-linear evolution, bias and redshift-space distortions, which we test using synthetic catalogues based on large-volume N-body simulations. We are able to include smaller scales than in previous analyses, resulting in tighter cosmological constraints. Using three overlapping redshift bins, we measure the angular-diameter distance, the Hubble parameter and the cosmic growth rate, and explore the cosmological implications of our full-shape clustering measurements in combination with cosmic microwave background and Type Ia supernova data. Assuming a Λ cold dark matter (ΛCDM) cosmology, we constrain the matter density to Ω M= 0.311_{-0.010}^{+0.009} and the Hubble parameter to H_0 = 67.6_{-0.6}^{+0.7} km s^{-1 Mpc^{-1}}, at a confidence level of 68 per cent. We also allow for non-standard dark energy models and modifications of the growth rate, finding good agreement with the ΛCDM paradigm. For example, we constrain the equation-of-state parameter to w = -1.019_{-0.039}^{+0.048}. This paper is part of a set that analyses the final galaxy-clustering data set from BOSS. The measurements and likelihoods presented here are combined with others in Alam et al. to produce the final cosmological constraints from BOSS.

Beyond δ: Tailoring marked statistics to reveal modified gravity

NASA Astrophysics Data System (ADS)

Valogiannis, Georgios; Bean, Rachel

2018-01-01

Models which attempt to explain the accelerated expansion of the universe through large-scale modifications to General Relativity (GR), must satisfy the stringent experimental constraints of GR in the solar system. Viable candidates invoke a “screening” mechanism, that dynamically suppresses deviations in high density environments, making their overall detection challenging even for ambitious future large-scale structure surveys. We present methods to efficiently simulate the non-linear properties of such theories, and consider how a series of statistics that reweight the density field to accentuate deviations from GR can be applied to enhance the overall signal-to-noise ratio in differentiating the models from GR. Our results demonstrate that the cosmic density field can yield additional, invaluable cosmological information, beyond the simple density power spectrum, that will enable surveys to more confidently discriminate between modified gravity models and ΛCDM.

Holographic equipartition and the maximization of entropy

NASA Astrophysics Data System (ADS)

Krishna, P. B.; Mathew, Titus K.

2017-09-01

The accelerated expansion of the Universe can be interpreted as a tendency to satisfy holographic equipartition. It can be expressed by a simple law, Δ V =Δ t (Nsurf-ɛ Nbulk) , where V is the Hubble volume in Planck units, t is the cosmic time in Planck units, and Nsurf /bulk is the number of degrees of freedom on the horizon/bulk of the Universe. We show that this holographic equipartition law effectively implies the maximization of entropy. In the cosmological context, a system that obeys the holographic equipartition law behaves as an ordinary macroscopic system that proceeds to an equilibrium state of maximum entropy. We consider the standard Λ CDM model of the Universe and show that it is consistent with the holographic equipartition law. Analyzing the entropy evolution, we find that it also proceeds to an equilibrium state of maximum entropy.

Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results

NASA Technical Reports Server (NTRS)

Bennett, C. L.; Larson, D.; Weiland, J. L.; Jaorsik, N.; Hinshaw, G.; Odegard, N.; Smith, K. M.; Hill, R. S.; Gold, B.; Halpern, M;

Cosmological Parameters From Pre-Planck CMB Measurements: A 2017 Update

NASA Technical Reports Server (NTRS)

Calabrese, Erminia; Hlolzek, Renee A.; Bond, J. Richard; Devlin, Mark J.; Dunkley, Joanna; Halpern, Mark; Hincks, Adam D.; Irwin, Kent D.; Kosowsky, Arthur; Moodley, Kavilan;

The Abacus Cosmos: A Suite of Cosmological N-body Simulations

NASA Astrophysics Data System (ADS)

Garrison, Lehman H.; Eisenstein, Daniel J.; Ferrer, Douglas; Tinker, Jeremy L.; Pinto, Philip A.; Weinberg, David H.

2018-06-01

We present a public data release of halo catalogs from a suite of 125 cosmological N-body simulations from the ABACUS project. The simulations span 40 wCDM cosmologies centered on the Planck 2015 cosmology at two mass resolutions, 4 × 1010 h ‑1 M ⊙ and 1 × 1010 h ‑1 M ⊙, in 1.1 h ‑1 Gpc and 720 h ‑1 Mpc boxes, respectively. The boxes are phase-matched to suppress sample variance and isolate cosmology dependence. Additional volume is available via 16 boxes of fixed cosmology and varied phase; a few boxes of single-parameter excursions from Planck 2015 are also provided. Catalogs spanning z = 1.5 to 0.1 are available for friends-of-friends and ROCKSTAR halo finders and include particle subsamples. All data products are available at https://lgarrison.github.io/AbacusCosmos.

Properties of Local Group galaxies in hydrodynamical simulations of sterile neutrino dark matter cosmologies

NASA Astrophysics Data System (ADS)

Lovell, Mark R.; Bose, Sownak; Boyarsky, Alexey; Crain, Robert A.; Frenk, Carlos S.; Hellwing, Wojciech A.; Ludlow, Aaron D.; Navarro, Julio F.; Ruchayskiy, Oleg; Sawala, Till; Schaller, Matthieu; Schaye, Joop; Theuns, Tom

2017-07-01

We study galaxy formation in sterile neutrino dark matter models that differ significantly from both cold and from 'warm thermal relic' models. We use the eagle code to carry out hydrodynamic simulations of the evolution of pairs of galaxies chosen to resemble the Local Group, as part of the APOSTLE simulations project. We compare cold dark matter (CDM) with two sterile neutrino models with 7 keV mass: one, the warmest among all models of this mass (LA120) and the other, a relatively cold case (LA10). We show that the lower concentration of sterile neutrino subhaloes compared to their CDM counterparts makes the inferred inner dark matter content of galaxies like Fornax (or Magellanic Clouds) less of an outlier in the sterile neutrino cosmologies. In terms of the galaxy number counts, the LA10 simulations are indistinguishable from CDM when one takes into account halo-to-halo (or 'simulation-to-simulation') scatter. In order for the LA120 model to match the number of Local Group dwarf galaxies, a higher fraction of low-mass haloes is required to form galaxies than is predicted by the eagle simulations. As the census of the Local Group galaxies nears completion, this population may provide a strong discriminant between cold and warm dark matter models.

Cosmological Parameters from the QUAD CMB Polarization Experiment

NASA Astrophysics Data System (ADS)

Castro, P. G.; Ade, P.; Bock, J.; Bowden, M.; Brown, M. L.; Cahill, G.; Church, S.; Culverhouse, T.; Friedman, R. B.; Ganga, K.; Gear, W. K.; Gupta, S.; Hinderks, J.; Kovac, J.; Lange, A. E.; Leitch, E.; Melhuish, S. J.; Memari, Y.; Murphy, J. A.; Orlando, A.; Pryke, C.; Schwarz, R.; O'Sullivan, C.; Piccirillo, L.; Rajguru, N.; Rusholme, B.; Taylor, A. N.; Thompson, K. L.; Turner, A. H.; Wu, E. Y. S.; Zemcov, M.; QUa D Collaboration

2009-08-01

In this paper, we present a parameter estimation analysis of the polarization and temperature power spectra from the second and third season of observations with the QUaD experiment. QUaD has for the first time detected multiple acoustic peaks in the E-mode polarization spectrum with high significance. Although QUaD-only parameter constraints are not competitive with previous results for the standard six-parameter ΛCDM cosmology, they do allow meaningful polarization-only parameter analyses for the first time. In a standard six-parameter ΛCDM analysis, we find the QUaD TT power spectrum to be in good agreement with previous results. However, the QUaD polarization data show some tension with ΛCDM. The origin of this 1σ-2σ tension remains unclear, and may point to new physics, residual systematics, or simple random chance. We also combine QUaD with the five-year WMAP data set and the SDSS luminous red galaxies 4th data release power spectrum, and extend our analysis to constrain individual isocurvature mode fractions, constraining cold dark matter density, αcdmi < 0.11 (95% confidence limit (CL)), neutrino density, αndi < 0.26 (95% CL), and neutrino velocity, αnvi < 0.23 (95% CL), modes. Our analysis sets a benchmark for future polarization experiments.

Observational tests for Λ(t)CDM cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pigozzo, C.; Carneiro, S.; Dantas, M.A.

2011-08-01

We investigate the observational viability of a class of cosmological models in which the vacuum energy density decays linearly with the Hubble parameter, resulting in a production of cold dark matter particles at late times. Similarly to the flat ΛCDM case, there is only one free parameter to be adjusted by the data in this class of Λ(t)CDM scenarios, namely, the matter density parameter. To perform our analysis we use three of the most recent SNe Ia compilation sets (Union2, SDSS and Constitution) along with the current measurements of distance to the BAO peaks at z = 0.2 and zmore » = 0.35 and the position of the first acoustic peak of the CMB power spectrum. We show that in terms of χ{sup 2} statistics both models provide good fits to the data and similar results. A quantitative analysis discussing the differences in parameter estimation due to SNe light-curve fitting methods (SALT2 and MLCS2k2) is studied using the current SDSS and Constitution SNe Ia compilations. A matter power spectrum analysis using the 2dFGRS is also performed, providing a very good concordance with the constraints from the SDSS and Constitution MLCS2k2 data.« less

Mass Function of Galaxy Clusters in Relativistic Inhomogeneous Cosmology

NASA Astrophysics Data System (ADS)

Ostrowski, Jan J.; Buchert, Thomas; Roukema, Boudewijn F.

The current cosmological model (ΛCDM) with the underlying FLRW metric relies on the assumption of local isotropy, hence homogeneity of the Universe. Difficulties arise when one attempts to justify this model as an average description of the Universe from first principles of general relativity, since in general, the Einstein tensor built from the averaged metric is not equal to the averaged stress-energy tensor. In this context, the discrepancy between these quantities is called "cosmological backreaction" and has been the subject of scientific debate among cosmologists and relativists for more than 20 years. Here we present one of the methods to tackle this problem, i.e. averaging the scalar parts of the Einstein equations, together with its application, the cosmological mass function of galaxy clusters.

Null tests of the standard model using the linear model formalism

NASA Astrophysics Data System (ADS)

Marra, Valerio; Sapone, Domenico

2018-04-01

We test both the Friedmann-Lemaître-Robertson-Walker geometry and Λ CDM cosmology in a model-independent way by reconstructing the Hubble function H (z ), the comoving distance D (z ), and the growth of structure f σ8(z ) using the most recent data available. We use the linear model formalism in order to optimally reconstruct the above cosmological functions, together with their derivatives and integrals. We then evaluate four of the null tests available in the literature that probe both background and perturbation assumptions. For all the four tests, we find agreement, within the errors, with the standard cosmological model.

Ultra-compact structure in intermediate-luminosity radio quasars: building a sample of standard cosmological rulers and improving the dark energy constraints up to z 3

NASA Astrophysics Data System (ADS)

Cao, Shuo; Zheng, Xiaogang; Biesiada, Marek; Qi, Jingzhao; Chen, Yun; Zhu, Zong-Hong

2017-09-01

Context. Ultra-compact structure in radio sources (especially in quasars that can be observed up to very high redshifts), with milliarcsecond angular sizes measured by very-long-baseline interferometry (VLBI), is becoming an important astrophysical tool for probing both cosmology and the physical properties of AGN. Aims: We present a newly compiled data set of 120 milliarcsec. compact radio sources representing intermediate-luminosity quasars covering the redshift range 0.46 < z < 2.76 and check the possibility of using these sources as independent cosmological probes. These quasars observed at 2.29 GHz show negligible dependence on redshifts and intrinsic luminosity, and thus represent a fixed comoving-length of standard ruler. Methods: For a cosmological ruler with intrinsic length lm, the angular size-redshift relation can be written as θ(z) = lm/DA(z, where θ(z) is the angular size at redshift z, and DA(z) is the corresponding angular diameter distance. We use a compilation of angular size and redshift data for ultra-compact radio sources from a well-known VLBI survey, and implement a new cosmology-independent technique to calibrate the linear size of this standard ruler, which is also used to test different cosmological models with and without the flat universe assumption. Results: We determine the linear size of this standard ruler as lm = 11.03 ± 0.25 pc, which is the typical radius at which AGN jets become opaque at the observed frequency ν 2 GHz. Our measurement of this linear size is also consistent with the previous and recent radio observations at other different frequencies. In the framework of flat ΛCDM model, we find a high value of the matter density parameter, Ωm = 0.322+0.244-0.141, and a low value of the Hubble constant, H0 = 67.6+7.8-7.4 km s-1 Mpc-1, which is in excellent agreement with the cosmic microwave background (CMB) anisotropy measurements by Planck. We obtain Ωm = 0.309+0.215-0.151, w = -0.970+0.500-1.730 at 68.3% CL for the constant w of a dynamical dark-energy model, which demonstrates no significant deviation from the concordance ΛCDM model. Consistent fitting results are also obtained for other cosmological models explaining the cosmic acceleration, like Ricci dark energy (RDE) or the Dvali-Gabadadze-Porrati (DGP) brane-world scenario. While no significant change in w with redshift is detected, there is still considerable room for evolution in w and the transition redshift at which w departing from -1 is located at z 2.0. Our results demonstrate that the method extensively investigated in our work on observational radio quasar data can be used to effectively derive cosmological information. Finally, we find the combination of high-redshift quasars and low-redshift clusters may provide an important source of angular diameter distances, considering the redshift coverage of these two astrophysical probes.

Apocalypse soon

NASA Astrophysics Data System (ADS)

Jackson, J. C.

1998-05-01

Based upon a simple vacuum Lagrangian, comprising cosmological and quadratic scalar field terms, a cosmological model is presented the history of which is indistinguishable from that of an innocuous low-density cold dark matter (CDM) universe, but the future of which is very much shorter. For sensible values of the deceleration parameter (0

Cosmic shear results from the deep lens survey. II. Full cosmological parameter constraints from tomography

DOE PAGES

Jee, M. James; Tyson, J. Anthony; Hilbert, Stefan; ...

2016-06-15

Here, we present a tomographic cosmic shear study from the Deep Lens Survey (DLS), which, providing a limiting magnitudemore » $${r}_{\\mathrm{lim}}\\sim 27$$ ($$5\\sigma $$), is designed as a precursor Large Synoptic Survey Telescope (LSST) survey with an emphasis on depth. Using five tomographic redshift bins, we study their auto- and cross-correlations to constrain cosmological parameters. We use a luminosity-dependent nonlinear model to account for the astrophysical systematics originating from intrinsic alignments of galaxy shapes. We find that the cosmological leverage of the DLS is among the highest among existing $$\\gt 10$$ deg2 cosmic shear surveys. Combining the DLS tomography with the 9 yr results of the Wilkinson Microwave Anisotropy Probe (WMAP9) gives $${{\\rm{\\Omega }}}_{m}={0.293}_{-0.014}^{+0.012}$$, $${\\sigma }_{8}={0.833}_{-0.018}^{+0.011}$$, $${H}_{0}={68.6}_{-1.2}^{+1.4}\\;{\\text{km s}}^{-1}\\;{{\\rm{Mpc}}}^{-1}$$, and $${{\\rm{\\Omega }}}_{b}=0.0475\\pm 0.0012$$ for ΛCDM, reducing the uncertainties of the WMAP9-only constraints by ~50%. When we do not assume flatness for ΛCDM, we obtain the curvature constraint $${{\\rm{\\Omega }}}_{k}=-{0.010}_{-0.015}^{+0.013}$$ from the DLS+WMAP9 combination, which, however, is not well constrained when WMAP9 is used alone. The dark energy equation-of-state parameter w is tightly constrained when baryonic acoustic oscillation (BAO) data are added, yielding $$w=-{1.02}_{-0.09}^{+0.10}$$ with the DLS+WMAP9+BAO joint probe. The addition of supernova constraints further tightens the parameter to $$w=-1.03\\pm 0.03$$. Our joint constraints are fully consistent with the final Planck results and also with the predictions of a ΛCDM universe.« less

Exploring the evolution of color-luminosity parameter β and its effects on parameter estimation

NASA Astrophysics Data System (ADS)

Wang, Shuang; Li, Yun-He; Zhang, Xin

2014-03-01

It has been found in previous studies that, for the Supernova Legacy Survey three-year (SNLS3) data, there is strong evidence for the redshift evolution of color-luminosity parameter β. In this paper, using the three simplest dark energy models, i.e., the Λ-cold-dark-matter (ΛCDM) model, the wCDM model, and the Chevallier-Polarski-Linder model, we further explore the evolution of β and its effects on parameter estimation. In addition to the SNLS3 data, we also take into account the Planck distance priors data of the cosmic microwave background (CMB), as well as the latest galaxy clustering (GC) data extracted from SDSS DR7 and BOSS. We find that, for all the models, adding a parameter of β can reduce χmin2 by ˜36, indicating that β1=0 is ruled out at 6σ confidence levels. In other words, β deviates from a constant at 6σ confidence levels. This conclusion is insensitive to the dark energy models considered, showing the importance of considering the evolution of β in the cosmology fits. Furthermore, it is found that varying β can significantly change the fitting results of various cosmological parameters: using the SNLS3 data alone, varying β yields a larger Ωm for the ΛCDM model; using the SNLS3+CMB +GC data, varying β yields a larger Ωm and a smaller h for all the models. Moreover, we find that these results are much closer to those given by the CMB +GC data compared to the cases of treating β as a constant. This indicates that considering the evolution of β is very helpful for reducing the tension between supernova and other cosmological observations.

Testing feedback-modified dark matter haloes with galaxy rotation curves: estimation of halo parameters and consistency with ΛCDM scaling relations

NASA Astrophysics Data System (ADS)

Katz, Harley; Lelli, Federico; McGaugh, Stacy S.; Di Cintio, Arianna; Brook, Chris B.; Schombert, James M.

2017-04-01

Cosmological N-body simulations predict dark matter (DM) haloes with steep central cusps (e.g. NFW). This contradicts observations of gas kinematics in low-mass galaxies that imply the existence of shallow DM cores. Baryonic processes such as adiabatic contraction and gas outflows can, in principle, alter the initial DM density profile, yet their relative contributions to the halo transformation remain uncertain. Recent high-resolution, cosmological hydrodynamic simulations by Di Cintio et al. (DC14) predict that inner density profiles depend systematically on the ratio of stellar-to-DM mass (M*/Mhalo). Using a Markov Chain Monte Carlo approach, we test the NFW and the M*/Mhalo-dependent DC14 halo models against a sample of 147 galaxy rotation curves from the new Spitzer Photometry and Accurate Rotation Curves data set. These galaxies all have extended H I rotation curves from radio interferometry as well as accurate stellar-mass-density profiles from near-infrared photometry. The DC14 halo profile provides markedly better fits to the data compared to the NFW profile. Unlike NFW, the DC14 halo parameters found in our rotation-curve fits naturally fall within two standard deviations of the mass-concentration relation predicted by Λ cold dark matter (ΛCDM) and the stellar mass-halo mass relation inferred from abundance matching with few outliers. Halo profiles modified by baryonic processes are therefore more consistent with expectations from ΛCDM cosmology and provide better fits to galaxy rotation curves across a wide range of galaxy properties than do halo models that neglect baryonic physics. Our results offer a solution to the decade long cusp-core discrepancy.

Constraints on Cosmological Parameters from the Angular Power Spectrum of a Combined 2500 deg2 SPT-SZ and Planck Gravitational Lensing Map

NASA Astrophysics Data System (ADS)

Simard, G.; Omori, Y.; Aylor, K.; Baxter, E. J.; Benson, B. A.; Bleem, L. E.; Carlstrom, J. E.; Chang, C. L.; Cho, H.-M.; Chown, R.; Crawford, T. M.; Crites, A. T.; de Haan, T.; Dobbs, M. A.; Everett, W. B.; George, E. M.; Halverson, N. W.; Harrington, N. L.; Henning, J. W.; Holder, G. P.; Hou, Z.; Holzapfel, W. L.; Hrubes, J. D.; Knox, L.; Lee, A. T.; Leitch, E. M.; Luong-Van, D.; Manzotti, A.; McMahon, J. J.; Meyer, S. S.; Mocanu, L. M.; Mohr, J. J.; Natoli, T.; Padin, S.; Pryke, C.; Reichardt, C. L.; Ruhl, J. E.; Sayre, J. T.; Schaffer, K. K.; Shirokoff, E.; Staniszewski, Z.; Stark, A. A.; Story, K. T.; Vanderlinde, K.; Vieira, J. D.; Williamson, R.; Wu, W. L. K.

2018-06-01

We report constraints on cosmological parameters from the angular power spectrum of a cosmic microwave background (CMB) gravitational lensing potential map created using temperature data from 2500 deg2 of South Pole Telescope (SPT) data supplemented with data from Planck in the same sky region, with the statistical power in the combined map primarily from the SPT data. We fit the lensing power spectrum to a model including cold dark matter and a cosmological constant ({{Λ }}{CDM}), and to models with single-parameter extensions to {{Λ }}{CDM}. We find constraints that are comparable to and consistent with those found using the full-sky Planck CMB lensing data, e.g., {σ }8{{{Ω }}}{{m}}0.25 = 0.598 ± 0.024 from the lensing data alone with weak priors placed on other parameters. Combining with primary CMB data, we explore single-parameter extensions to {{Λ }}{CDM}. We find {{{Ω }}}k =-{0.012}-0.023+0.021 or {M}ν < 0.70 eV at 95% confidence, in good agreement with results including the lensing potential as measured by Planck. We include two parameters that scale the effect of lensing on the CMB: {A}L, which scales the lensing power spectrum in both the lens reconstruction power and in the smearing of the acoustic peaks, and {A}φ φ , which scales only the amplitude of the lensing reconstruction power spectrum. We find {A}φ φ × {A}L = 1.01 ± 0.08 for the lensing map made from combined SPT and Planck data, indicating that the amount of lensing is in excellent agreement with expectations from the observed CMB angular power spectrum when not including the information from smearing of the acoustic peaks.

A hydrodynamic approach to cosmology - Texture-seeded cold dark matter and hot dark matter cosmogonies

NASA Technical Reports Server (NTRS)

Cen, R. Y.; Ostriker, J. P.; Spergel, D. N.; Turok, N.

1991-01-01

Hydrodynamical simulations of galaxy formation in a texture-seeded cosmology are presented, with attention given to Omega = 1 galaxies dominated by both hot dark matter (HDM) and cold dark matter (CDM). The simulations include both gravitational and hydrodynamical physics with a detailed treatment of collisional and radiative thermal processes, and use a cooling criterion to estimate galaxy formation. Background radiation fields and Zel'dovich-Sunyaev fluctuations are explicitly computed. The derived galaxy mass function is well fitted by the observed Schechter luminosity function for a baryonic M/L of 3 and total M/L of 60 in galaxies. In both HDM and CDM texture scenarios, the 'galaxies' and 'clusters' are significantly more strongly correlated than the dark matter due to physical bias processes. The slope of the correlation function in both cases is consistent with observations. In contrast to Gaussian models, peaks in the dark matter density distributrion are less correlated than average.

Off-shell dark matter: A cosmological relic of quantum gravity

NASA Astrophysics Data System (ADS)

Saravani, Mehdi; Afshordi, Niayesh

2017-02-01

We study a novel proposal for the origin of cosmological cold dark matter (CDM) which is rooted in the quantum nature of spacetime. In this model, off-shell modes of quantum fields can exist in asymptotic states as a result of spacetime nonlocality (expected in generic theories of quantum gravity) and play the role of CDM, which we dub off-shell dark matter (O f DM ). However, their rate of production is suppressed by the scale of nonlocality (e.g. Planck length). As a result, we show that O f DM is only produced in the first moments of big bang, and then effectively decouples (except through its gravitational interactions). We examine the observational predictions of this model: In the context of cosmic inflation, we show that this proposal relates the reheating temperature to the inflaton mass, which narrows down the uncertainty in the number of e -foldings of specific inflationary scenarios. We also demonstrate that O f DM is indeed cold, and discuss potentially observable signatures on small scale matter power spectrum.

Structure formation in f(T) gravity and a solution for H0 tension

NASA Astrophysics Data System (ADS)

Nunes, Rafael C.

2018-05-01

We investigate the evolution of scalar perturbations in f(T) teleparallel gravity and its effects on the cosmic microwave background (CMB) anisotropy. The f(T) gravity generalizes the teleparallel gravity which is formulated on the Weitzenböck spacetime, characterized by the vanishing curvature tensor (absolute parallelism) and the non-vanishing torsion tensor. For the first time, we derive the observational constraints on the modified teleparallel gravity using the CMB temperature power spectrum from Planck's estimation, in addition to data from baryonic acoustic oscillations (BAO) and local Hubble constant measurements. We find that a small deviation of the f(T) gravity model from the ΛCDM cosmology is slightly favored. Besides that, the f(T) gravity model does not show tension on the Hubble constant that prevails in the ΛCDM cosmology. It is clear that f(T) gravity is also consistent with the CMB observations, and undoubtedly it can serve as a viable candidate amongst other modified gravity theories.

Confronting Alternative Cosmological Models with the Highest-Redshift Type Ia Supernovae

NASA Astrophysics Data System (ADS)

Shafer, Daniel; Scolnic, Daniel; Riess, Adam

2018-01-01

High-redshift Type Ia supernovae (SNe Ia) from the HST CANDELS and CLASH programs significantly extend the Hubble diagram with 7 SNe at z > 1.5 suitable for cosmology, including one at z = 2.3. This unique leverage helps us distinguish "alternative" cosmological models from the standard Lambda-CDM model. Analyzing the Pantheon SN compilation, which includes these high-z SNe, we employ model comparison statistics to quantify the extent to which several proposed alternative expansion histories (e.g., empty universe, power law expansion, timescape cosmology) are disfavored even with SN Ia data alone. Using mock data, we demonstrate that some likelihood analyses used in the literature to support these models are sensitive to unrealistic assumptions and are therefore unsuitable for analysis of realistic SN Ia data.

Cosmological Constraints from Fourier Phase Statistics

NASA Astrophysics Data System (ADS)

Ali, Kamran; Obreschkow, Danail; Howlett, Cullan; Bonvin, Camille; Llinares, Claudio; Oliveira Franco, Felipe; Power, Chris

2018-06-01

Most statistical inference from cosmic large-scale structure relies on two-point statistics, i.e. on the galaxy-galaxy correlation function (2PCF) or the power spectrum. These statistics capture the full information encoded in the Fourier amplitudes of the galaxy density field but do not describe the Fourier phases of the field. Here, we quantify the information contained in the line correlation function (LCF), a three-point Fourier phase correlation function. Using cosmological simulations, we estimate the Fisher information (at redshift z = 0) of the 2PCF, LCF and their combination, regarding the cosmological parameters of the standard ΛCDM model, as well as a Warm Dark Matter (WDM) model and the f(R) and Symmetron modified gravity models. The galaxy bias is accounted for at the level of a linear bias. The relative information of the 2PCF and the LCF depends on the survey volume, sampling density (shot noise) and the bias uncertainty. For a volume of 1h^{-3}Gpc^3, sampled with points of mean density \\bar{n} = 2× 10^{-3} h3 Mpc^{-3} and a bias uncertainty of 13%, the LCF improves the parameter constraints by about 20% in the ΛCDM cosmology and potentially even more in alternative models. Finally, since a linear bias only affects the Fourier amplitudes (2PCF), but not the phases (LCF), the combination of the 2PCF and the LCF can be used to break the degeneracy between the linear bias and σ8, present in 2-point statistics.

Testing and selection of cosmological models with (1+z){sup 6} corrections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szydlowski, Marek; Marc Kac Complex Systems Research Centre, Jagiellonian University, ul. Reymonta 4, 30-059 Cracow; Godlowski, Wlodzimierz

2008-02-15

In the paper we check whether the contribution of (-)(1+z){sup 6} type in the Friedmann equation can be tested. We consider some astronomical tests to constrain the density parameters in such models. We describe different interpretations of such an additional term: geometric effects of loop quantum cosmology, effects of braneworld cosmological models, nonstandard cosmological models in metric-affine gravity, and models with spinning fluid. Kinematical (or geometrical) tests based on null geodesics are insufficient to separate individual matter components when they behave like perfect fluid and scale in the same way. Still, it is possible to measure their overall effect. Wemore » use recent measurements of the coordinate distances from the Fanaroff-Riley type IIb radio galaxy data, supernovae type Ia data, baryon oscillation peak and cosmic microwave background radiation observations to obtain stronger bounds for the contribution of the type considered. We demonstrate that, while {rho}{sup 2} corrections are very small, they can be tested by astronomical observations--at least in principle. Bayesian criteria of model selection (the Bayesian factor, AIC, and BIC) are used to check if additional parameters are detectable in the present epoch. As it turns out, the {lambda}CDM model is favored over the bouncing model driven by loop quantum effects. Or, in other words, the bounds obtained from cosmography are very weak, and from the point of view of the present data this model is indistinguishable from the {lambda}CDM one.« less

Relativistic numerical cosmology with silent universes

NASA Astrophysics Data System (ADS)

Bolejko, Krzysztof

2018-01-01

Relativistic numerical cosmology is most often based either on the exact solutions of the Einstein equations, or perturbation theory, or weak-field limit, or the BSSN formalism. The silent universe provides an alternative approach to investigate relativistic evolution of cosmological systems. The silent universe is based on the solution of the Einstein equations in 1  +  3 comoving coordinates with additional constraints imposed. These constraints include: the gravitational field is sourced by dust and cosmological constant only, both rotation and magnetic part of the Weyl tensor vanish, and the shear is diagnosable. This paper describes the code simsilun (free software distributed under the terms of the reposi General Public License), which implements the equations of the silent universe. The paper also discusses applications of the silent universe and it uses the Millennium simulation to set up the initial conditions for the code simsilun. The simulation obtained this way consists of 16 777 216 worldlines, which are evolved from z  =  80 to z  =  0. Initially, the mean evolution (averaged over the whole domain) follows the evolution of the background ΛCDM model. However, once the evolution of cosmic structures becomes nonlinear, the spatial curvature evolves from ΩK =0 to ΩK ≈ 0.1 at the present day. The emergence of the spatial curvature is associated with ΩM and Ω_Λ being smaller by approximately 0.05 compared to the ΛCDM.

Cosmological perturbation theory using the FFTLog: formalism and connection to QFT loop integrals

NASA Astrophysics Data System (ADS)

Simonović, Marko; Baldauf, Tobias; Zaldarriaga, Matias; Carrasco, John Joseph; Kollmeier, Juna A.

2018-04-01

We present a new method for calculating loops in cosmological perturbation theory. This method is based on approximating a ΛCDM-like cosmology as a finite sum of complex power-law universes. The decomposition is naturally achieved using an FFTLog algorithm. For power-law cosmologies, all loop integrals are formally equivalent to loop integrals of massless quantum field theory. These integrals have analytic solutions in terms of generalized hypergeometric functions. We provide explicit formulae for the one-loop and the two-loop power spectrum and the one-loop bispectrum. A chief advantage of our approach is that the difficult part of the calculation is cosmology independent, need be done only once, and can be recycled for any relevant predictions. Evaluation of standard loop diagrams then boils down to a simple matrix multiplication. We demonstrate the promise of this method for applications to higher multiplicity/loop correlation functions.

Neutrino Mass Bounds from 0{nu}{beta}{beta} Decays and Large Scale Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keum, Y.-Y.; Department of Physics, National Taiwan University, Taipei, Taiwan 10672; Ichiki, K.

2008-05-21

We investigate the way how the total mass sum of neutrinos can be constrained from the neutrinoless double beta decay and cosmological probes with cosmic microwave background (WMAP 3-year results), large scale structures including 2dFGRS and SDSS data sets. First we discuss, in brief, on the current status of neutrino mass bounds from neutrino beta decays and cosmic constrain within the flat {lambda}CMD model. In addition, we explore the interacting neutrino dark-energy model, where the evolution of neutrino masses is determined by quintessence scalar filed, which is responsable for cosmic acceleration today. Assuming the flatness of the universe, the constraintmore » we can derive from the current observation is {sigma}m{sub {nu}}<0.87 eV at the 95% confidence level, which is consistent with {sigma}m{sub {nu}}<0.68 eV in the flat {lambda}CDM model.« less

Integrated Sachs-Wolfe effect in massive bigravity

NASA Astrophysics Data System (ADS)

Enander, Jonas; Akrami, Yashar; Mörtsell, Edvard; Renneby, Malin; Solomon, Adam R.

2015-04-01

We study the integrated Sachs-Wolfe (ISW) effect in ghost-free, massive bigravity. We focus on the infinite-branch bigravity (IBB) model which exhibits viable cosmic expansion histories and stable linear perturbations, while the cosmological constant is set to zero and the late-time accelerated expansion of the Universe is due solely to the gravitational interaction terms. The ISW contribution to the CMB auto-correlation power spectrum is predicted, as well as the cross-correlation between the CMB temperature anisotropies and large-scale structure. We use ISW amplitudes as inferred from the WMAP 9-year temperature data together with galaxy and AGN data provided by the WISE mission in order to compare the theoretical predictions to the observations. The ISW amplitudes in IBB are found to be larger than the corresponding ones in the standard Λ CDM model by roughly a factor of 1.5, but are still consistent with the observations.

Interpretation of the cosmic microwave background radiation anisotropy detected by the COBE Differential Microwave Radiometer

NASA Technical Reports Server (NTRS)

Wright, E. L.; Meyer, S. S.; Bennett, C. L.; Boggess, N. W.; Cheng, E. S.; Hauser, M. G.; Kogut, A.; Lineweaver, C.; Mather, J. C.; Smoot, G. F.

1992-01-01

The large-scale cosmic background anisotropy detected by the COBE Differential Microwave Radiometer (DMR) instrument is compared to the sensitive previous measurements on various angular scales, and to the predictions of a wide variety of models of structure formation driven by gravitational instability. The observed anisotropy is consistent with all previously measured upper limits and with a number of dynamical models of structure formation. For example, the data agree with an unbiased cold dark matter (CDM) model with H0 = 50 km/s Mpc and Delta-M/M = 1 in a 16 Mpc radius sphere. Other models, such as CDM plus massive neutrinos (hot dark matter (HDM)), or CDM with a nonzero cosmological constant are also consistent with the COBE detection and can provide the extra power seen on 5-10,000 km/s scales.

Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows.

PubMed

Governato, F; Brook, C; Mayer, L; Brooks, A; Rhee, G; Wadsley, J; Jonsson, P; Willman, B; Stinson, G; Quinn, T; Madau, P

2010-01-14

For almost two decades the properties of 'dwarf' galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies-bulgeless and with shallow central dark-matter profiles-arise naturally in these simulations.

Solar system and equivalence principle constraints on f(R) gravity by the chameleon approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capozziello, Salvatore; Tsujikawa, Shinji

2008-05-15

We study constraints on f(R) dark energy models from solar system experiments combined with experiments on the violation of the equivalence principle. When the mass of an equivalent scalar field degree of freedom is heavy in a region with high density, a spherically symmetric body has a thin shell so that an effective coupling of the fifth force is suppressed through a chameleon mechanism. We place experimental bounds on the cosmologically viable models recently proposed in the literature that have an asymptotic form f(R)=R-{lambda}R{sub c}[1-(R{sub c}/R){sup 2n}] in the regime R>>R{sub c}. From the solar system constraints on the post-Newtonianmore » parameter {gamma}, we derive the bound n>0.5, whereas the constraints from the violations of the weak and strong equivalence principles give the bound n>0.9. This allows a possibility to find the deviation from the {lambda}-cold dark matter ({lambda}CDM) cosmological model. For the model f(R)=R-{lambda}R{sub c}(R/R{sub c}){sup p} with 0

Gravitational Lensing Corrections in Flat ΛCDM Cosmology

NASA Astrophysics Data System (ADS)

Kantowski, Ronald; Chen, Bin; Dai, Xinyu

2010-08-01

We compute the deflection angle to order (m/r 0)2 and m/r 0 × Λr 2 0 for a light ray traveling in a flat ΛCDM cosmology that encounters a completely condensed mass region. We use a Swiss cheese model for the inhomogeneities and find that the most significant correction to the Einstein angle occurs not because of the nonlinear terms but instead occurs because the condensed mass is embedded in a background cosmology. The Swiss cheese model predicts a decrease in the deflection angle of ~2% for weakly lensed galaxies behind the rich cluster A1689 and that the reduction can be as large as ~5% for similar rich clusters at z ≈ 1. Weak-lensing deflection angles caused by galaxies can likewise be reduced by as much as ~4%. We show that the lowest order correction in which Λ appears is proportional to m/r_0× √{Λ r_0^2}}} and could cause as much as a ~0.02% increase in the deflection angle for light that passes through a rich cluster. The lowest order nonlinear correction in the mass is proportional to m/r_0× √{m/r_0} and can increase the deflection angle by ~0.005% for weak lensing by galaxies.

The Diversity of Assembly Histories Leading to Disc Galaxy Formation in a ΛCDM Model

NASA Astrophysics Data System (ADS)

Font, Andreea S.; McCarthy, Ian G.; Le Brun, Amandine M. C.; Crain, Robert A.; Kelvin, Lee S.

2017-11-01

Disc galaxies forming in a LambdaCDM cosmology often experience violent mergers. The fact that disc galaxies are ubiquitous suggests that quiescent histories are not necessary. Modern cosmological simulations can now obtain realistic populations of disc galaxies, but it is still unclear how discs manage to survive massive mergers. Here we use a suite of hydrodynamical cosmological simulations to elucidate the fate of discs encountering massive mergers. We follow the changes in the post-merger disc-to-total ratios (D/T) of simulated galaxies and examine the relations between their present-day morphology, assembly history and gas fractions. We find that approximately half of present-day disc galaxies underwent at least one merger with a satellite more massive the host's stellar component and a third had mergers with satellites three times as massive. These mergers lead to a sharp, but often temporary, decrease in the D/T of the hosts, implying that discs are usually disrupted but then quickly re-grow. To do so, high cold gas fractions are required post-merger, as well as a relatively quiescent recent history (over a few Gyrs before z = 0). Our results show that discs can form via diverse merger pathways and that quiescent histories are not the dominant mode of disc formation.

KiDS-450: testing extensions to the standard cosmological model

NASA Astrophysics Data System (ADS)

Joudaki, Shahab; Mead, Alexander; Blake, Chris; Choi, Ami; de Jong, Jelte; Erben, Thomas; Fenech Conti, Ian; Herbonnet, Ricardo; Heymans, Catherine; Hildebrandt, Hendrik; Hoekstra, Henk; Joachimi, Benjamin; Klaes, Dominik; Köhlinger, Fabian; Kuijken, Konrad; McFarland, John; Miller, Lance; Schneider, Peter; Viola, Massimo

2017-10-01

We test extensions to the standard cosmological model with weak gravitational lensing tomography using 450 deg2 of imaging data from the Kilo Degree Survey (KiDS). In these extended cosmologies, which include massive neutrinos, non-zero curvature, evolving dark energy, modified gravity and running of the scalar spectral index, we also examine the discordance between KiDS and cosmic microwave background (CMB) measurements from Planck. The discordance between the two data sets is largely unaffected by a more conservative treatment of the lensing systematics and the removal of angular scales most sensitive to non-linear physics. The only extended cosmology that simultaneously alleviates the discordance with Planck and is at least moderately favoured by the data includes evolving dark energy with a time-dependent equation of state (in the form of the w0 - wa parametrization). In this model, the respective S_8=σ _8√{Ω m/0.3} constraints agree at the 1σ level, and there is 'substantial concordance' between the KiDS and Planck data sets when accounting for the full parameter space. Moreover, the Planck constraint on the Hubble constant is wider than in Λ cold dark matter (ΛCDM) and in agreement with the Riess et al. (2016) direct measurement of H0. The dark energy model is moderately favoured as compared to ΛCDM when combining the KiDS and Planck measurements, and marginalized constraints in the w0-wa plane are discrepant with a cosmological constant at the 3σ level. KiDS further constrains the sum of neutrino masses to 4.0 eV (95% CL), finds no preference for time or scale-dependent modifications to the metric potentials, and is consistent with flatness and no running of the spectral index.

Testing Modified Gravity Theories via Wide Binaries and GAIA

NASA Astrophysics Data System (ADS)

Pittordis, Charalambos; Sutherland, Will

2018-06-01

The standard ΛCDM model based on General Relativity (GR) including cold dark matter (CDM) is very successful at fitting cosmological observations, but recent non-detections of candidate dark matter (DM) particles mean that various modified-gravity theories remain of significant interest. The latter generally involve modifications to GR below a critical acceleration scale ˜10-10 m s-2. Wide-binary (WB) star systems with separations ≳ 5 kAU provide an interesting test for modified gravity, due to being in or near the low-acceleration regime and presumably containing negligible DM. Here, we explore the prospects for new observations pending from the GAIA spacecraft to provide tests of GR against MOND or TeVes-like theories in a regime only partially explored to date. In particular, we find that a histogram of (3D) binary relative velocities, relative to equilibrium circular velocity predicted from the (2D) projected separation predicts a rather sharp feature in this distribution for standard gravity, with an 80th (90th) percentile value close to 1.025 (1.14) with rather weak dependence on the eccentricity distribution. However, MOND/TeVeS theories produce a shifted distribution, with a significant increase in these upper percentiles. In MOND-like theories without an external field effect, there are large shifts of order unity. With the external field effect included, the shifts are considerably reduced to ˜0.04 - 0.08, but are still potentially detectable statistically given reasonably large samples and good control of contaminants. In principle, followup of GAIA-selected wide binaries with ground-based radial velocities accurate to ≲ 0.03 { km s^{-1}} should be able to produce an interesting new constraint on modified-gravity theories.

Tidal stripping and the structure of dwarf galaxies in the Local Group

NASA Astrophysics Data System (ADS)

Fattahi, Azadeh; Navarro, Julio F.; Frenk, Carlos S.; Oman, Kyle A.; Sawala, Till; Schaller, Matthieu

2018-05-01

The shallow faint-end slope of the galaxy mass function is usually reproduced in Λ cold dark matter (ΛCDM) galaxy formation models by assuming that the fraction of baryons that turn into stars drops steeply with decreasing halo mass and essentially vanishes in haloes with maximum circular velocities Vmax < 20-30 km s-1. Dark-matter-dominated dwarfs should therefore have characteristic velocities of about that value, unless they are small enough to probe only the rising part of the halo circular velocity curve (i.e. half-mass radii, r1/2 ≪ 1 kpc). Many dwarfs have properties in disagreement with this prediction: they are large enough to probe their halo Vmax but their characteristic velocities are well below 20 km s-1. These `cold faint giants' (an extreme example is the recently discovered Crater 2 Milky Way satellite) can only be reconciled with our ΛCDM models if they are the remnants of once massive objects heavily affected by tidal stripping. We examine this possibility using the APOSTLE cosmological hydrodynamical simulations of the Local Group. Assuming that low-velocity-dispersion satellites have been affected by stripping, we infer their progenitor masses, radii, and velocity dispersions, and find them in remarkable agreement with those of isolated dwarfs. Tidal stripping also explains the large scatter in the mass discrepancy-acceleration relation in the dwarf galaxy regime: tides remove preferentially dark matter from satellite galaxies, lowering their accelerations below the amin ˜ 10-11 m s-2 minimum expected for isolated dwarfs. In many cases, the resulting velocity dispersions are inconsistent with the predictions from Modified Newtonian Dynamics, a result that poses a possibly insurmountable challenge to that scenario.

CMB-galaxy correlation in Unified Dark Matter scalar field cosmologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bertacca, Daniele; Bartolo, Nicola; Matarrese, Sabino

We present an analysis of the cross-correlation between the CMB and the large-scale structure (LSS) of the Universe in Unified Dark Matter (UDM) scalar field cosmologies. We work out the predicted cross-correlation function in UDM models, which depends on the speed of sound of the unified component, and compare it with observations from six galaxy catalogues (NVSS, HEAO, 2MASS, and SDSS main galaxies, luminous red galaxies, and quasars). We sample the value of the speed of sound and perform a likelihood analysis, finding that the UDM model is as likely as the ΛCDM, and is compatible with observations for amore » range of values of c{sub ∞} (the value of the sound speed at late times) on which structure formation depends. In particular, we obtain an upper bound of c{sub ∞}{sup 2} ≤ 0.009 at 95% confidence level, meaning that the ΛCDM model, for which c{sub ∞}{sup 2} = 0, is a good fit to the data, while the posterior probability distribution peaks at the value c{sub ∞}{sup 2} = 10{sup −4} . Finally, we study the time dependence of the deviation from ΛCDM via a tomographic analysis using a mock redshift distribution and we find that the largest deviation is for low-redshift sources, suggesting that future low-z surveys will be best suited to constrain UDM models.« less

Constraints to Dark Energy Using PADE Parameterizations

NASA Astrophysics Data System (ADS)

Rezaei, M.; Malekjani, M.; Basilakos, S.; Mehrabi, A.; Mota, D. F.

2017-07-01

We put constraints on dark energy (DE) properties using PADE parameterization, and compare it to the same constraints using Chevalier-Polarski-Linder (CPL) and ΛCDM, at both the background and the perturbation levels. The DE equation of the state parameter of the models is derived following the mathematical treatment of PADE expansion. Unlike CPL parameterization, PADE approximation provides different forms of the equation of state parameter that avoid the divergence in the far future. Initially we perform a likelihood analysis in order to put constraints on the model parameters using solely background expansion data, and we find that all parameterizations are consistent with each other. Then, combining the expansion and the growth rate data, we test the viability of PADE parameterizations and compare them with CPL and ΛCDM models, respectively. Specifically, we find that the growth rate of the current PADE parameterizations is lower than ΛCDM model at low redshifts, while the differences among the models are negligible at high redshifts. In this context, we provide for the first time a growth index of linear matter perturbations in PADE cosmologies. Considering that DE is homogeneous, we recover the well-known asymptotic value of the growth index (namely {γ }∞ =\\tfrac{3({w}∞ -1)}{6{w}∞ -5}), while in the case of clustered DE, we obtain {γ }∞ ≃ \\tfrac{3{w}∞ (3{w}∞ -5)}{(6{w}∞ -5)(3{w}∞ -1)}. Finally, we generalize the growth index analysis in the case where γ is allowed to vary with redshift, and we find that the form of γ (z) in PADE parameterization extends that of the CPL and ΛCDM cosmologies, respectively.

THE INNER STRUCTURE OF DWARF-SIZED HALOS IN WARM AND COLD DARK MATTER COSMOLOGIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

González-Samaniego, A.; Avila-Reese, V.; Colín, P.

2016-03-10

By means of N-body + hydrodynamic zoom-in simulations we study the evolution of the inner dark matter and stellar mass distributions of central dwarf galaxies formed in halos of virial masses M{sub v} = (2–3) × 10{sup 10} h{sup −1} M{sub ⊙} at z = 0, both in a warm dark matter (WDM) and cold dark matter (CDM) cosmology. The half-mode mass in the WDM power spectrum of our simulations is M{sub f} = 2 × 10{sup 10} h{sup −1} M{sub ⊙}. In the dark matter (DM) only simulations halo density profiles are well described by the Navarro–Frenk–White parametric fit in both cosmologies, though the WDM halos have concentrations lower bymore » factors of 1.5–2.0 than their CDM counterparts. In the hydrodynamic simulations, the effects of baryons significantly flatten the inner density, velocity dispersion, and pseudo phase space density profiles of the WDM halos but not of the CDM ones. The density slope, measured at ≈0.02R{sub v}, α{sub 0.02}, becomes shallow in periods of 2–5 Gyr in the WDM runs. We explore whether this flattening process correlates with the global star formation (SF), M{sub s}/M{sub v} ratio, gas outflow, and internal specific angular momentum histories. We do not find any clear trends, but when α{sub 0.02} is shallower than −0.5, M{sub s}/M{sub v} is always between 0.25% and 1%. We conclude that the main reason for the formation of the shallow core is the presence of strong gas mass fluctuations inside the inner halo, which are a consequence of the feedback driven by a very bursty and sustained SF history in shallow gravitational potentials. Our WDM halos, which assemble late and are less concentrated than the CDM ones, obey these conditions. There are also (rare) CDM systems with extended mass assembly histories that obey these conditions and form shallow cores. The dynamical heating and expansion processes behind the DM core flattening apply also to the stars in such a way that the stellar age and metallicity gradients of the dwarfs are softened, their stellar half-mass radii strongly grow with time, and their central surface densities decrease.« less

Geometrothermodynamic model for the evolution of the Universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gruber, Christine; Quevedo, Hernando, E-mail: christine.gruber@correo.nucleares.unam.mx, E-mail: quevedo@nucleares.unam.mx

Using the formalism of geometrothermodynamics to derive a fundamental thermodynamic equation, we construct a cosmological model in the framework of relativistic cosmology. In a first step, we describe a system without thermodynamic interaction, and show it to be equivalent to the standard ΛCDM paradigm. The second step includes thermodynamic interaction and produces a model consistent with the main features of inflation. With the proposed fundamental equation we are thus able to describe all the known epochs in the evolution of our Universe, starting from the inflationary phase.

The cosmic microwave background

NASA Technical Reports Server (NTRS)

Silk, Joseph

1991-01-01

Recent limits on spectral distortions and angular anisotropies in the cosmic microwave background are reviewed. The various backgrounds are described, and the theoretical implications are assessed. Constraints on inflationary cosmology dominated by cold dark matter (CDM) and on open cosmological models dominated by baryonic dark matter (BDM), with, respectively, primordial random phase scale-invariant curvature fluctuations or non-gaussian isocurvature fluctuations are described. More exotic theories are addressed, and I conclude with the 'bottom line': what theorists expect experimentalists to be measuring within the next two to three years without having to abandon their most cherished theories.

Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results

NASA Technical Reports Server (NTRS)

Hinshaw, G.; Larson, D.; Komatsu, E.; Spergel, D. N.; Bennett, C. L.; Dunkley, J.; Nolta, M. R.; Halpern, M.; Hill, R. S.; Odegard, N.;

Cosmological reconstructed solutions in extended teleparallel gravity theories with a teleparallel Gauss-Bonnet term

NASA Astrophysics Data System (ADS)

de la Cruz-Dombriz, Álvaro; Farrugia, Gabriel; Levi Said, Jackson; Sáez-Chillón Gómez, Diego

2017-12-01

In the context of extended teleparallel gravity theories with a 3  +  1 dimensions Gauss-Bonnet analog term, we address the possibility of these theories reproducing several well-known cosmological solutions. In particular when applied to a Friedmann-Lemaître-Robertson-Walker geometry in four-dimensional spacetime with standard fluids exclusively. We study different types of gravitational Lagrangians and reconstruct solutions provided by analytical expressions for either the cosmological scale factor or the Hubble parameter. We also show that it is possible to find Lagrangians of this type without a cosmological constant such that the behaviour of the ΛCDM model is precisely mimicked. The new Lagrangians may also lead to other phenomenological consequences opening up the possibility for new theories to compete directly with other extensions of General Relativity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakstein, Jeremy; Wilcox, Harry; Bacon, David

The Beyond Horndeski class of alternative gravity theories allow for Self-accelerating de-Sitter cosmologies with no need for a cosmological constant. This makes them viable alternatives to ΛCDM and so testing their small-scale predictions against General Relativity is of paramount importance. These theories generically predict deviations in both the Newtonian force law and the gravitational lensing of light inside extended objects. Therefore, by simultaneously fitting the X-ray and lensing profiles of galaxy clusters new constraints can be obtained. In this work, we apply this methodology to the stacked profiles of 58 high-redshift (0.1 < z < 1.2) clusters using X-ray surfacemore » brightness profiles from the XMM Cluster Survey and weak lensing profiles from CFHTLenS. By performing a multi-parameter Markov chain Monte Carlo analysis, we are able to place new constraints on the parameters governing deviations from Newton's law Υ{sub 1} = −0.11{sup +0.93}{sub −0.67} and light bending Υ{sub 2} = −0.22{sup +1.22}{sub −1.19}. Both constraints are consistent with General Relativity, for which Υ{sub 1} = Υ{sub 2} = 0. We present here the first observational constraints on Υ{sub 2}, as well as the first extragalactic measurement of both parameters.« less

Cluster-void degeneracy breaking: Modified gravity in the balance

NASA Astrophysics Data System (ADS)

Sahlén, Martin; Silk, Joseph

2018-05-01

Combining galaxy cluster and void abundances is a novel, powerful way to constrain deviations from general relativity and the Λ CDM model. For a flat w CDM model with growth of large-scale structure parametrized by the redshift-dependent growth index γ (z )=γ0+γ1z /(1 +z ) of linear matter perturbations, combining void and cluster abundances in future surveys with Euclid and the four-meter multiobject spectroscopic telescope could improve the figure of merit for (w ,γ0,γ1) by a factor of 20 compared to individual abundances. In an ideal case, improvement on current cosmological data is a figure of merit factor 600 or more.

The Formation of Shell Galaxies Similar to NGC 7600 in the Cold Dark Matter Cosmogony

NASA Astrophysics Data System (ADS)

Cooper, Andrew P.; Martínez-Delgado, David; Helly, John; Frenk, Carlos; Cole, Shaun; Crawford, Ken; Zibetti, Stefano; Carballo-Bello, Julio A.; GaBany, R. Jay

2011-12-01

We present new deep observations of "shell" structures in the halo of the nearby elliptical galaxy NGC 7600, alongside a movie of galaxy formation in a cold dark matter (CDM) universe. The movie, based on an ab initio cosmological simulation, shows how continuous accretion of clumps of dark matter and stars creates a swath of diffuse circumgalactic structures. The disruption of a massive clump on a near-radial orbit creates a complex system of transient concentric shells which bare a striking resemblance to those of NGC 7600. With the aid of the simulation we interpret NGC 7600 in the context of the CDM model.

A ROBUST MEASURE OF DARK MATTER HALO ELLIPTICITIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Evslin, Jarah

2016-08-01

In simulations of the standard cosmological model (ΛCDM), dark matter halos are aspherical. However, so far the asphericity of an individual galaxy’s halo has never been robustly established. We use the Jeans equations to define a quantity that robustly characterizes a deviation from rotational symmetry. This quantity is essentially the gravitational torque and it roughly provides the ellipticity projected along the line of sight. We show that the Thirty Meter Telescope (TMT), with a single epoch of observations combined with those of the Gaia Space Telescope , can distinguish the ΛCDM value of the torque from zero for each Sculptor-likemore » dwarf galaxy with a confidence between 0 and 5 σ , depending on the orientation of each halo. With two epochs of observations, TMT will achieve a 5 σ discovery of torque and thus asphericity for most such galaxies, thus providing a new and powerful test of the ΛCDM model.« less

Cosmological structure formation in Decaying Dark Matter models

NASA Astrophysics Data System (ADS)

Cheng, Dalong; Chu, M.-C.; Tang, Jiayu

2015-07-01

The standard cold dark matter (CDM) model predicts too many and too dense small structures. We consider an alternative model that the dark matter undergoes two-body decays with cosmological lifetime τ into only one type of massive daughters with non-relativistic recoil velocity Vk. This decaying dark matter model (DDM) can suppress the structure formation below its free-streaming scale at time scale comparable to τ. Comparing with warm dark matter (WDM), DDM can better reduce the small structures while being consistent with high redshfit observations. We study the cosmological structure formation in DDM by performing self-consistent N-body simulations and point out that cosmological simulations are necessary to understand the DDM structures especially on non-linear scales. We propose empirical fitting functions for the DDM suppression of the mass function and the concentration-mass relation, which depend on the decay parameters lifetime τ, recoil velocity Vk and redshift. The fitting functions lead to accurate reconstruction of the the non-linear power transfer function of DDM to CDM in the framework of halo model. Using these results, we set constraints on the DDM parameter space by demanding that DDM does not induce larger suppression than the Lyman-α constrained WDM models. We further generalize and constrain the DDM models to initial conditions with non-trivial mother fractions and show that the halo model predictions are still valid after considering a global decayed fraction. Finally, we point out that the DDM is unlikely to resolve the disagreement on cluster numbers between the Planck primary CMB prediction and the Sunyaev-Zeldovich (SZ) effect number count for τ ~ H0-1.

Testing gravity using large-scale redshift-space distortions

NASA Astrophysics Data System (ADS)

Raccanelli, Alvise; Bertacca, Daniele; Pietrobon, Davide; Schmidt, Fabian; Samushia, Lado; Bartolo, Nicola; Doré, Olivier; Matarrese, Sabino; Percival, Will J.

2013-11-01

We use luminous red galaxies from the Sloan Digital Sky Survey (SDSS) II to test the cosmological structure growth in two alternatives to the standard Λ cold dark matter (ΛCDM)+general relativity (GR) cosmological model. We compare observed three-dimensional clustering in SDSS Data Release 7 (DR7) with theoretical predictions for the standard vanilla ΛCDM+GR model, unified dark matter (UDM) cosmologies and the normal branch Dvali-Gabadadze-Porrati (nDGP). In computing the expected correlations in UDM cosmologies, we derive a parametrized formula for the growth factor in these models. For our analysis we apply the methodology tested in Raccanelli et al. and use the measurements of Samushia et al. that account for survey geometry, non-linear and wide-angle effects and the distribution of pair orientation. We show that the estimate of the growth rate is potentially degenerate with wide-angle effects, meaning that extremely accurate measurements of the growth rate on large scales will need to take such effects into account. We use measurements of the zeroth and second-order moments of the correlation function from SDSS DR7 data and the Large Suite of Dark Matter Simulations (LasDamas), and perform a likelihood analysis to constrain the parameters of the models. Using information on the clustering up to rmax = 120 h-1 Mpc, and after marginalizing over the bias, we find, for UDM models, a speed of sound c∞ ≤ 6.1e-4, and, for the nDGP model, a cross-over scale rc ≥ 340 Mpc, at 95 per cent confidence level.

Towards Accurate Modelling of Galaxy Clustering on Small Scales: Testing the Standard ΛCDM + Halo Model

NASA Astrophysics Data System (ADS)

Sinha, Manodeep; Berlind, Andreas A.; McBride, Cameron K.; Scoccimarro, Roman; Piscionere, Jennifer A.; Wibking, Benjamin D.

2018-04-01

Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and dark matter halos. Unfortunately, the modelling is typically not sufficiently accurate for ruling out models statistically. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. In this paper, we attempt to push halo modelling into the "accurate" regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. With our forward-modelling approach, we can incorporate clustering statistics beyond the traditional two-point statistics. We use this modelling methodology to test the standard ΛCDM + halo model against the clustering of SDSS DR7 galaxies. Specifically, we use the projected correlation function, group multiplicity function and galaxy number density as constraints. We find that while the model fits each statistic separately, it struggles to fit them simultaneously. Adding group statistics leads to a more stringent test of the model and significantly tighter constraints on model parameters. We explore the impact of varying the adopted halo definition and cosmological model and find that changing the cosmology makes a significant difference. The most successful model we tried (Planck cosmology with Mvir halos) matches the clustering of low luminosity galaxies, but exhibits a 2.3σ tension with the clustering of luminous galaxies, thus providing evidence that the "standard" halo model needs to be extended. This work opens the door to adding interesting freedom to the halo model and including additional clustering statistics as constraints.

Cosmological constraints from Galaxy Clusters in 2500 square-degree SPT-SZ survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haan, T. de; Benson, B. A.; Bleem, L. E.

We present cosmological parameter constraints obtained from galaxy clusters identified by their SunyaevZel'dovich effect signature in the 2500 square-degree South Pole Telescope Sunyaev Zel'dovich (SPT-SZ) survey. We consider the 377 cluster candidates identified at z > 0.25 with a detection significance greater than five, corresponding to the 95% purity threshold for the survey. We compute constraints on cosmological models using the measured cluster abundance as a function of mass and redshift. We include additional constraints from multi-wavelength observations, including Chandra X-ray data for 82 clusters and a weak lensing-based prior on the normalization of the mass-observable scaling relations. Assuming amore » spatially flat Lambda CDM cosmology, we combine the cluster data with a prior on H-0 and find sigma(8)= 0.784. +/- 0.039 and Omega(m) = 0.289. +/- 0.042, with the parameter combination sigma(8) (Omega(m)/0.27)(0.3) = 0.797 +/- 0.031. These results are in good agreement with constraints from the cosmic microwave background (CMB) from SPT, WMAP, and Planck, as well as with constraints from other cluster data sets. We also consider several extensions to Lambda CDM, including models in which the equation of state of dark energy w, the species-summed neutrino mass, and/or the effective number of relativistic species (N-eff) are free parameters. When combined with constraints from the Planck CMB, H-0, baryon acoustic oscillation, and SNe, adding the SPT cluster data improves the w constraint by 14%, to w = -1.023 +/- 0.042.« less

DICE/ColDICE: 6D collisionless phase space hydrodynamics using a lagrangian tesselation

NASA Astrophysics Data System (ADS)

Sousbie, Thierry

2018-01-01

DICE is a C++ template library designed to solve collisionless fluid dynamics in 6D phase space using massively parallel supercomputers via an hybrid OpenMP/MPI parallelization. ColDICE, based on DICE, implements a cosmological and physical VLASOV-POISSON solver for cold systems such as dark matter (CDM) dynamics.

Growth index and statefinder diagnostic of oscillating dark energy

NASA Astrophysics Data System (ADS)

Panotopoulos, Grigoris; Rincón, Ángel

2018-05-01

We study in some detail the cosmology of oscillating dark energy described by concrete equations-of-state introduced recently in the literature. In particular, we compute the statefinder parameters, the growth index, as well as the combination parameter A =f σ8, and a comparison with the concordance Λ CDM is made.

Massive Galaxies Are Larger in Dense Environments: Environmental Dependence of Mass-Size Relation of Early-type Galaxies

NASA Astrophysics Data System (ADS)

Yoon, Yongmin; Im, Myungshin; Kim, Jae-Woo

2017-01-01

Under the Λ cold dark matter (ΛCDM) cosmological models, massive galaxies are expected to be larger in denser environments through frequent hierarchical mergers with other galaxies. Yet, observational studies of low-redshift early-type galaxies have shown no such trend, standing as a puzzle to solve during the past decade. We analyzed 73,116 early-type galaxies at 0.1 ≤ z < 0.15, adopting a robust nonparametric size measurement technique and extending the analysis to many massive galaxies. We find for the first time that local early-type galaxies heavier than 1011.2 M⊙ show a clear environmental dependence in mass-size relation, in such a way that galaxies are as much as 20%-40% larger in the densest environments than in underdense environments. Splitting the sample into the brightest cluster galaxies (BCGs) and non-BCGs does not affect the result. This result agrees with the ΛCDM cosmological simulations and suggests that mergers played a significant role in the growth of massive galaxies in dense environments as expected in theory.

Accurate Modeling of Galaxy Clustering on Small Scales: Testing the Standard ΛCDM + Halo Model

NASA Astrophysics Data System (ADS)

Sinha, Manodeep; Berlind, Andreas A.; McBride, Cameron; Scoccimarro, Roman

2015-01-01

The large-scale distribution of galaxies can be explained fairly simply by assuming (i) a cosmological model, which determines the dark matter halo distribution, and (ii) a simple connection between galaxies and the halos they inhabit. This conceptually simple framework, called the halo model, has been remarkably successful at reproducing the clustering of galaxies on all scales, as observed in various galaxy redshift surveys. However, none of these previous studies have carefully modeled the systematics and thus truly tested the halo model in a statistically rigorous sense. We present a new accurate and fully numerical halo model framework and test it against clustering measurements from two luminosity samples of galaxies drawn from the SDSS DR7. We show that the simple ΛCDM cosmology + halo model is not able to simultaneously reproduce the galaxy projected correlation function and the group multiplicity function. In particular, the more luminous sample shows significant tension with theory. We discuss the implications of our findings and how this work paves the way for constraining galaxy formation by accurate simultaneous modeling of multiple galaxy clustering statistics.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Yongmin; Im, Myungshin; Kim, Jae-Woo, E-mail: yymx2@astro.snu.ac.kr, E-mail: mim@astro.snu.ac.kr

Under the Λ cold dark matter (ΛCDM) cosmological models, massive galaxies are expected to be larger in denser environments through frequent hierarchical mergers with other galaxies. Yet, observational studies of low-redshift early-type galaxies have shown no such trend, standing as a puzzle to solve during the past decade. We analyzed 73,116 early-type galaxies at 0.1 ≤  z  < 0.15, adopting a robust nonparametric size measurement technique and extending the analysis to many massive galaxies. We find for the first time that local early-type galaxies heavier than 10{sup 11.2} M {sub ⊙} show a clear environmental dependence in mass–size relation, in such amore » way that galaxies are as much as 20%–40% larger in the densest environments than in underdense environments. Splitting the sample into the brightest cluster galaxies (BCGs) and non-BCGs does not affect the result. This result agrees with the ΛCDM cosmological simulations and suggests that mergers played a significant role in the growth of massive galaxies in dense environments as expected in theory.« less

Imprints of non-standard dark energy and dark matter models on the 21cm intensity map power spectrum

NASA Astrophysics Data System (ADS)

Carucci, Isabella P.; Corasaniti, Pier-Stefano; Viel, Matteo

2017-12-01

We study the imprint of non-standard dark energy (DE) and dark matter (DM) models on the 21cm intensity map power spectra from high-redshift neutral hydrogen (HI) gas. To this purpose we use halo catalogs from N-body simulations of dynamical DE models and DM scenarios which are as successful as the standard Cold Dark Matter model with Cosmological Constant (ΛCDM) at interpreting available cosmological observations. We limit our analysis to halo catalogs at redshift z=1 and 2.3 which are common to all simulations. For each catalog we model the HI distribution by using a simple prescription to associate the HI gas mass to N-body halos. We find that the DE models leave a distinct signature on the HI spectra across a wide range of scales, which correlates with differences in the halo mass function and the onset of the non-linear regime of clustering. In the case of the non-standard DM model significant differences of the HI spectra with respect to the ΛCDM model only arise from the suppressed abundance of low mass halos. These cosmological model dependent features also appear in the 21cm spectra. In particular, we find that future SKA measurements can distinguish the imprints of DE and DM models at high statistical significance.

Definitive test of the Rh = ct universe using redshift drift

NASA Astrophysics Data System (ADS)

Melia, Fulvio

2016-11-01

The redshift drift of objects moving in the Hubble flow has been proposed as a powerful model-independent probe of the underlying cosmology. A measurement of the first- and second-order redshift derivatives appears to be well within the reach of upcoming surveys using as the Extremely Large Telescope high resolution spectrometer (ELT-HIRES) and the Square Kilometer Phase 2 Array (SKA). Here we show that an unambiguous prediction of the Rh = ct cosmology is zero drift at all redshifts, contrasting sharply with all other models in which the expansion rate is variable. For example, multiyear monitoring of sources at redshift z = 5 with the ELT-HIRES is expected to show a velocity shift Δv = -15 cm s-1 yr-1 due to the redshift drift in Planck ΛCDM, while Δv = 0 cm s-1 yr-1 in Rh = ct. With an anticipated ELT-HIRES measurement error of ±5 cm s-1 yr-1 after 5 yr, these upcoming redshift drift measurements might therefore be able to differentiate between Rh = ct and Planck ΛCDM at ˜3σ, assuming that any possible source evolution is well understood. Such a result would provide the strongest evidence yet in favour of the Rh = ct cosmology. With a 20-yr baseline, these observations could favour one of these models over the other at better than 5σ.

The Lopsidedness of Satellite Galaxy Systems in ΛCDM Simulations

NASA Astrophysics Data System (ADS)

Pawlowski, Marcel S.; Ibata, Rodrigo A.; Bullock, James S.

2017-12-01

The spatial distribution of satellite galaxies around pairs of galaxies in the Sloan Digital Sky Survey (SDSS) have been found to bulge significantly toward the respective partner. Highly anisotropic, planar distributions of satellite galaxies are in conflict with expectations derived from cosmological simulations. Does the lopsided distribution of satellite systems around host galaxy pairs constitute a similar challenge to the standard model of cosmology? We investigate whether such satellite distributions are present around stacked pairs of hosts extracted from the ΛCDM simulations Millennium-I, Millennium-II, Exploring the Local Volume in Simulations, and Illustris-1. By utilizing this set of simulations covering different volumes, resolutions, and physics, we implicitly test whether a lopsided signal exists for different ranges of satellite galaxy masses, and whether the inclusion of hydrodynamical effects produces significantly different results. All simulations display a lopsidedness similar to the observed situation. The signal is highly significant for simulations containing a sufficient number of hosts and resolved satellite galaxies (up to 5 σ for Millennium-II). We find a projected signal that is up to twice as strong as that reported for the SDSS systems for certain opening angles (∼16% more satellites in the direction between the pair than expected for uniform distributions). Considering that the SDSS signal is a lower limit owing to likely back- and foreground contamination, the ΛCDM simulations appear to be consistent with this particular empirical property of galaxy pairs.

Cold dark matter: Controversies on small scales.

PubMed

Weinberg, David H; Bullock, James S; Governato, Fabio; Kuzio de Naray, Rachel; Peter, Annika H G

2015-10-06

The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. We review the current observational and theoretical status of these "small-scale controversies." Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years.

The dynamics of the Local Group as a probe of dark energy and modified gravity

NASA Astrophysics Data System (ADS)

Carlesi, Edoardo; Mota, David F.; Winther, Hans A.

2017-04-01

In this work, we study the dynamics of the Local Group (LG) within the context of cosmological models beyond General Relativity (GR). Using observable kinematic quantities to identify candidate pairs, we build up samples of simulated LG-like objects drawing from f(R), symmetron, Dvali, Gabadadze & Porrati and quintessence N-body simulations together with their Λ cold dark matter (ΛCDM) counterparts featuring the same initial random phase realizations. The variables and intervals used to define LG-like objects are referred to as LG model; different models are used throughout this work and adapted to study their dynamical and kinematic properties. The aim is to determine how well the observed LG dynamics can be reproduced within cosmological theories beyond GR, We compute kinematic properties of samples drawn from alternative theories and ΛCDM and compare them to actual observations of the LG mass, velocity and position. As a consequence of the additional pull, pairwise tangential and radial velocities are enhanced in modified gravity and coupled dark energy with respect to ΛCDM inducing significant changes to the total angular momentum and energy of the LG. For example, in models such as f(R) and the symmetron this increase can be as large as 60 per cent, peaking well outside of the 95 per cent confidence region allowed by the data. This shows how simple considerations about the LG dynamics can lead to clear small-scale observational signatures for alternative scenarios, without the need of expensive high-resolution simulations.

Rotation curves of galaxies and the stellar mass-to-light ratio

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Khodadadi, Aziz; Ghari, Amir; Zonoozi, Akram Hasani; Kroupa, Pavel

2018-03-01

Mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c - Mvir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration and virial mass. Although accounting for a NFW dark halo profile can explain rotation curve observations, the implied c - Mvir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L -color correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L - ratios of 51 galaxies (30% of our sample) have unphysically negative values in the framework of the ΛCDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of ΛCDM cosmological structure formation, is not an appropriate profile for the dark halos of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disk galaxies.

Rotation curves of galaxies and the stellar mass-to-light ratio

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Khodadadi, Aziz; Ghari, Amir; Zonoozi, Akram Hasani; Kroupa, Pavel

2018-07-01

Mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c-Mvir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration, and virial mass. Although accounting for a NFW dark halo profile can explain RC observations, the implied c-Mvir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L-colour correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L ratios of 51 galaxies (30 per cent of our sample) have unphysically negative values in the framework of the ΛCDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of ΛCDM cosmological structure formation, is not an appropriate profile for the dark haloes of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disc galaxies.

Real- and redshift-space halo clustering in f(R) cosmologies

NASA Astrophysics Data System (ADS)

Arnalte-Mur, Pablo; Hellwing, Wojciech A.; Norberg, Peder

2017-05-01

We present two-point correlation function statistics of the mass and the haloes in the chameleon f(R) modified gravity scenario using a series of large-volume N-body simulations. Three distinct variations of f(R) are considered (F4, F5 and F6) and compared to a fiducial Λ cold dark matter (ΛCDM) model in the redshift range z ∈ [0, 1]. We find that the matter clustering is indistinguishable for all models except for F4, which shows a significantly steeper slope. The ratio of the redshift- to real-space correlation function at scales >20 h-1 Mpc agrees with the linear General Relativity (GR) Kaiser formula for the viable f(R) models considered. We consider three halo populations characterized by spatial abundances comparable to that of luminous red galaxies and galaxy clusters. The redshift-space halo correlation functions of F4 and F5 deviate significantly from ΛCDM at intermediate and high redshift, as the f(R) halo bias is smaller than or equal to that of the ΛCDM case. Finally, we introduce a new model-independent clustering statistic to distinguish f(R) from GR: the relative halo clustering ratio - R. The sampling required to adequately reduce the scatter in R will be available with the advent of the next-generation galaxy redshift surveys. This will foster a prospective avenue to obtain largely model-independent cosmological constraints on this class of modified gravity models.

Model-independent Evidence for Dark Energy Evolution from Baryon Acoustic Oscillations

NASA Astrophysics Data System (ADS)

Sahni, V.; Shafieloo, A.; Starobinsky, A. A.

2014-10-01

Baryon acoustic oscillations (BAOs) allow us to determine the expansion history of the universe, thereby shedding light on the nature of dark energy. Recent observations of BAOs in the Sloan Digital Sky Survey (SDSS) DR9 and DR11 have provided us with statistically independent measurements of H(z) at redshifts of 0.57 and 2.34, respectively. We show that these measurements can be used to test the cosmological constant hypothesis in a model-independent manner by means of an improved version of the Om diagnostic. Our results indicate that the SDSS DR11 measurement of H(z) = 222 ± 7 km s-1 Mpc-1 at z = 2.34, when taken in tandem with measurements of H(z) at lower redshifts, imply considerable tension with the standard ΛCDM model. Our estimation of the new diagnostic Omh 2 from SDSS DR9 and DR11 data, namely, Omh 2 ≈ 0.122 ± 0.01, which is equivalent to Ω0m h 2 for the spatially flat ΛCDM model, is in tension with the value Ω0m h 2 = 0.1426 ± 0.0025 determined for ΛCDM from Planck+WP. This tension is alleviated in models in which the cosmological constant was dynamically screened (compensated) in the past. Such evolving dark energy models display a pole in the effective equation of state of dark energy at high redshifts, which emerges as a smoking gun test for these theories.

Voids and constraints on nonlinear clustering of galaxies

NASA Technical Reports Server (NTRS)

Vogeley, Michael S.; Geller, Margaret J.; Park, Changbom; Huchra, John P.

1994-01-01

Void statistics of the galaxy distribution in the Center for Astrophysics Redshift Survey provide strong constraints on galaxy clustering in the nonlinear regime, i.e., on scales R equal to or less than 10/h Mpc. Computation of high-order moments of the galaxy distribution requires a sample that (1) densely traces the large-scale structure and (2) covers sufficient volume to obtain good statistics. The CfA redshift survey densely samples structure on scales equal to or less than 10/h Mpc and has sufficient depth and angular coverage to approach a fair sample on these scales. In the nonlinear regime, the void probability function (VPF) for CfA samples exhibits apparent agreement with hierarchical scaling (such scaling implies that the N-point correlation functions for N greater than 2 depend only on pairwise products of the two-point function xi(r)) However, simulations of cosmological models show that this scaling in redshift space does not necessarily imply such scaling in real space, even in the nonlinear regime; peculiar velocities cause distortions which can yield erroneous agreement with hierarchical scaling. The underdensity probability measures the frequency of 'voids' with density rho less than 0.2 -/rho. This statistic reveals a paucity of very bright galaxies (L greater than L asterisk) in the 'voids.' Underdensities are equal to or greater than 2 sigma more frequent in bright galaxy samples than in samples that include fainter galaxies. Comparison of void statistics of CfA samples with simulations of a range of cosmological models favors models with Gaussian primordial fluctuations and Cold Dark Matter (CDM)-like initial power spectra. Biased models tend to produce voids that are too empty. We also compare these data with three specific models of the Cold Dark Matter cosmogony: an unbiased, open universe CDM model (omega = 0.4, h = 0.5) provides a good match to the VPF of the CfA samples. Biasing of the galaxy distribution in the 'standard' CDM model (omega = 1, b = 1.5; see below for definitions) and nonzero cosmological constant CDM model (omega = 0.4, h = 0.6 lambda(sub 0) = 0.6, b = 1.3) produce voids that are too empty. All three simulations match the observed VPF and underdensity probability for samples of very bright (M less than M asterisk = -19.2) galaxies, but produce voids that are too empty when compared with samples that include fainter galaxies.

Massive Structures of Galaxies at High Redshifts in the Great Observatories Origins Deep Survey Fields

NASA Astrophysics Data System (ADS)

Kang, Eugene; Im, Myungshin

2015-02-01

If the Universe is dominated by cold dark matter and dark energy as in the currently popular ΛCDM cosmology, it is expected that large scale structures form gradually, with galaxy clusters of mass M & 1014M? appearing at around 6 Gy rs after the Big Bang (z ? 1). Here, we report the discovery of 59 massive structures of galaxies with masses greater than a few times 1013M? at redshifts between z = 0.6 and 4.5 in the Great Observatories Origins Deep Survey fields. The massive structures are identified by running top-hat filters on the two dimensional spatial distribution of magnitude-limited samples of galaxies using a combination of spectroscopic and photometric redshifts. We analyze the Millennium simulation data in a similar way to the analysis of the observational data in order to test the ΛCDM cosmology. We find that there are too many massive structures (M > 7?1013M?) observed at z > 2 in comparison with the simulation predictions by a factor of a few, giving a probability of < 1/2500 of the observed data being consistent with the simulation. Our result suggests that massive structures have emerged early, but the reason for the discrepancy with the simulation is unclear. It could be due to the limitation of the simulation such as the lack of key, unrecognized ingredients (strong non-Gaussianity or other baryonic physics), or simply a difficulty in the halo mass estimation from observation, or a fundamental problem of the ΛCDM cosmology. On the other hand, the over-abundance of massive structures at high redshifts does not favor heavy neutrino mass of ? 0.3 eV or larger, as heavy neutrinos make the discrepancy between the observation and the simulation more pronounced by a factor of 3 or more.

Tachyon cosmology, supernovae data, and the big brake singularity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keresztes, Z.; Gergely, L. A.; Gorini, V.

2009-04-15

We compare the existing observational data on type Ia supernovae with the evolutions of the Universe predicted by a one-parameter family of tachyon models which we have introduced recently [Phys. Rev. D 69, 123512 (2004)]. Among the set of the trajectories of the model which are compatible with the data there is a consistent subset for which the Universe ends up in a new type of soft cosmological singularity dubbed big brake. This opens up yet another scenario for the future history of the Universe besides the one predicted by the standard {lambda}CDM model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamanini, Nicola; Wright, Matthew, E-mail: nicola.tamanini@cea.fr, E-mail: matthew.wright.13@ucl.ac.uk

We investigate the cosmological dynamics of the recently proposed extended chameleon models at both background and linear perturbation levels. Dynamical systems techniques are employed to fully characterize the evolution of the universe at the largest distances, while structure formation is analysed at sub-horizon scales within the quasi-static approximation. The late time dynamical transition from dark matter to dark energy domination can be well described by almost all extended chameleon models considered, with no deviations from ΛCDM results at both background and perturbation levels. The results obtained in this work confirm the cosmological viability of extended chameleons as alternative dark energymore » models.« less

A Comparative Analysis of the Supernova Legacy Survey Sample With ΛCDM and the Rh=ct Universe

NASA Astrophysics Data System (ADS)

Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio; Maier, Robert S.

2015-03-01

The use of Type Ia supernovae (SNe Ia) has thus far produced the most reliable measurement of the expansion history of the universe, suggesting that ΛCDM offers the best explanation for the redshift-luminosity distribution observed in these events. However, analysis of other kinds of sources, such as cosmic chronometers, gamma-ray bursts, and high-z quasars, conflicts with this conclusion, indicating instead that the constant expansion rate implied by the Rh = ct universe is a better fit to the data. The central difficulty with the use of SNe Ia as standard candles is that one must optimize three or four nuisance parameters characterizing supernova (SN) luminosities simultaneously with the parameters of an expansion model. Hence, in comparing competing models, one must reduce the data independently for each. We carry out such a comparison of ΛCDM and the Rh = ct universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. However, since Rh = ct has only one free parameter (the Hubble constant), it follows from a standard model selection technique that it is to be preferred over ΛCDM, the minimalist version of which has three (the Hubble constant, the scaled matter density, and either the spatial curvature constant or the dark energy equation-of-state parameter). We estimate using the Bayes Information Criterion that in a pairwise comparison, the likelihood of Rh = ct is ˜90%, compared with only ˜10% for a minimalist form of ΛCDM, in which dark energy is simply a cosmological constant. Compared to Rh = ct, versions of the standard model with more elaborate parametrizations of dark energy are judged to be even less likely. This work is dedicated to the memory of Prof. Tan Lu, who sadly passed away 2014 December 3. Among his many achievements, he is considered to be one of the founders of high-energy astrophysics, and a pioneer in modern cosmology, in China.

The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: towards a computationally efficient analysis without informative priors

NASA Astrophysics Data System (ADS)

Pellejero-Ibanez, Marcos; Chuang, Chia-Hsun; Rubiño-Martín, J. A.; Cuesta, Antonio J.; Wang, Yuting; Zhao, Gongbo; Ross, Ashley J.; Rodríguez-Torres, Sergio; Prada, Francisco; Slosar, Anže; Vazquez, Jose A.; Alam, Shadab; Beutler, Florian; Eisenstein, Daniel J.; Gil-Marín, Héctor; Grieb, Jan Niklas; Ho, Shirley; Kitaura, Francisco-Shu; Percival, Will J.; Rossi, Graziano; Salazar-Albornoz, Salvador; Samushia, Lado; Sánchez, Ariel G.; Satpathy, Siddharth; Seo, Hee-Jong; Tinker, Jeremy L.; Tojeiro, Rita; Vargas-Magaña, Mariana; Brownstein, Joel R.; Nichol, Robert C.; Olmstead, Matthew D.

2017-07-01

We develop a new computationally efficient methodology called double-probe analysis with the aim of minimizing informative priors (those coming from extra probes) in the estimation of cosmological parameters. Using our new methodology, we extract the dark energy model-independent cosmological constraints from the joint data sets of the Baryon Oscillation Spectroscopic Survey (BOSS) galaxy sample and Planck cosmic microwave background (CMB) measurements. We measure the mean values and covariance matrix of {R, la, Ωbh2, ns, log(As), Ωk, H(z), DA(z), f(z)σ8(z)}, which give an efficient summary of the Planck data and two-point statistics from the BOSS galaxy sample. The CMB shift parameters are R=√{Ω _m H_0^2} r(z_*) and la = πr(z*)/rs(z*), where z* is the redshift at the last scattering surface, and r(z*) and rs(z*) denote our comoving distance to the z* and sound horizon at z*, respectively; Ωb is the baryon fraction at z = 0. This approximate methodology guarantees that we will not need to put informative priors on the cosmological parameters that galaxy clustering is unable to constrain, I.e. Ωbh2 and ns. The main advantage is that the computational time required for extracting these parameters is decreased by a factor of 60 with respect to exact full-likelihood analyses. The results obtained show no tension with the flat Λ cold dark matter (ΛCDM) cosmological paradigm. By comparing with the full-likelihood exact analysis with fixed dark energy models, on one hand we demonstrate that the double-probe method provides robust cosmological parameter constraints that can be conveniently used to study dark energy models, and on the other hand we provide a reliable set of measurements assuming dark energy models to be used, for example, in distance estimations. We extend our study to measure the sum of the neutrino mass using different methodologies, including double-probe analysis (introduced in this study), full-likelihood analysis and single-probe analysis. From full-likelihood analysis, we obtain Σmν < 0.12 (68 per cent), assuming ΛCDM and Σmν < 0.20 (68 per cent) assuming owCDM. We also find that there is degeneracy between observational systematics and neutrino masses, which suggests that one should take great care when estimating these parameters in the case of not having control over the systematics of a given sample.

Scalar-tensor extension of the ΛCDM model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Algoner, W.C.; Velten, H.E.S.; Zimdahl, W., E-mail: w.algoner@cosmo-ufes.org, E-mail: velten@pq.cnpq.br, E-mail: winfried.zimdahl@pq.cnpq.br

2016-11-01

We construct a cosmological scalar-tensor-theory model in which the Brans-Dicke type scalar Φ enters the effective (Jordan-frame) Hubble rate as a simple modification of the Hubble rate of the ΛCDM model. This allows us to quantify differences between the background dynamics of scalar-tensor theories and general relativity (GR) in a transparent and observationally testable manner in terms of one single parameter. Problems of the mapping of the scalar-field degrees of freedom on an effective fluid description in a GR context are discused. Data from supernovae, the differential age of old galaxies and baryon acoustic oscillations are shown to strongly limitmore » potential deviations from the standard model.« less

Criticality and big brake singularities in the tachyonic evolutions of closed Friedmann universes with cold dark matter

NASA Astrophysics Data System (ADS)

Horváth, Zsolt; Keresztes, Zoltán; Kamenshchik, Alexander Yu.; Gergely, László Á.

2015-05-01

The evolution of a closed Friedmann universe filled by a tachyon scalar field with a trigonometric potential and cold dark matter (CDM) is investigated. A subset of the evolutions consistent to 1 σ confidence level with the Union 2.1 supernova data set is identified. The evolutions of the tachyon field are classified. Some of them evolve into a de Sitter attractor, while others proceed through a pseudotachyonic regime into a sudden future singularity. Critical evolutions leading to big brake singularities in the presence of CDM are found and a new type of cosmological evolution characterized by singularity avoidance in the pseudotachyon regime is presented.

Anisotropies of the cosmic microwave background in nonstandard cold dark matter models

NASA Technical Reports Server (NTRS)

Vittorio, Nicola; Silk, Joseph

1992-01-01

Small angular scale cosmic microwave anisotropies in flat, vacuum-dominated, cold dark matter cosmological models which fit large-scale structure observations and are consistent with a high value for the Hubble constant are reexamined. New predictions for CDM models in which the large-scale power is boosted via a high baryon content and low H(0) are presented. Both classes of models are consistent with current limits: an improvement in sensitivity by a factor of about 3 for experiments which probe angular scales between 7 arcmin and 1 deg is required, in the absence of very early reionization, to test boosted CDM models for large-scale structure formation.

N-body simulations with a cosmic vector for dark energy

NASA Astrophysics Data System (ADS)

Carlesi, Edoardo; Knebe, Alexander; Yepes, Gustavo; Gottlöber, Stefan; Jiménez, Jose Beltrán.; Maroto, Antonio L.

2012-07-01

We present the results of a series of cosmological N-body simulations of a vector dark energy (VDE) model, performed using a suitably modified version of the publicly available GADGET-2 code. The set-ups of our simulations were calibrated pursuing a twofold aim: (1) to analyse the large-scale distribution of massive objects and (2) to determine the properties of halo structure in this different framework. We observe that structure formation is enhanced in VDE, since the mass function at high redshift is boosted up to a factor of 10 with respect to Λ cold dark matter (ΛCDM), possibly alleviating tensions with the observations of massive clusters at high redshifts and early reionization epoch. Significant differences can also be found for the value of the growth factor, which in VDE shows a completely different behaviour, and in the distribution of voids, which in this cosmology are on average smaller and less abundant. We further studied the structure of dark matter haloes more massive than 5 × 1013 h-1 M⊙, finding that no substantial difference emerges when comparing spin parameter, shape, triaxiality and profiles of structures evolved under different cosmological pictures. Nevertheless, minor differences can be found in the concentration-mass relation and the two-point correlation function, both showing different amplitudes and steeper slopes. Using an additional series of simulations of a ΛCDM scenario with the same ? and σ8 used in the VDE cosmology, we have been able to establish whether the modifications induced in the new cosmological picture were due to the particular nature of the dynamical dark energy or a straightforward consequence of the cosmological parameters. On large scales, the dynamical effects of the cosmic vector field can be seen in the peculiar evolution of the cluster number density function with redshift, in the shape of the mass function, in the distribution of voids and on the characteristic form of the growth index γ(z). On smaller scales, internal properties of haloes are almost unaffected by the change of cosmology, since no statistical difference can be observed in the characteristics of halo profiles, spin parameters, shapes and triaxialities. Only halo masses and concentrations show a substantial increase, which can, however, be attributed to the change in the cosmological parameters.

The H II galaxy Hubble diagram strongly favours Rh = ct over ΛCDM

NASA Astrophysics Data System (ADS)

Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio

2016-12-01

We continue to build support for the proposal to use H II galaxies (HIIGx) and giant extragalactic H II regions (GEHR) as standard candles to construct the Hubble diagram at redshifts beyond the current reach of Type Ia supernovae. Using a sample of 25 high-redshift HIIGx, 107 local HIIGx, and 24 GEHR, we confirm that the correlation between the emission-line luminosity and ionized-gas velocity dispersion is a viable luminosity indicator, and use it to test and compare the standard model ΛCDM and the Rh = ct universe by optimizing the parameters in each cosmology using a maximization of the likelihood function. For the flat ΛCDM model, the best fit is obtained with Ω _m= 0.40_{-0.09}^{+0.09}. However, statistical tools, such as the Akaike (AIC), Kullback (KIC) and Bayes (BIC) Information Criteria favour Rh = ct over the standard model with a likelihood of ≈94.8-98.8 per cent versus only ≈1.2-5.2 per cent. For wCDM (the version of ΛCDM with a dark-energy equation of state wde ≡ pde/ρde rather than wde = wΛ = -1), a statistically acceptable fit is realized with Ω _m=0.22_{-0.14}^{+0.16} and w_de= -0.51_{-0.25}^{+0.15} which, however, are not fully consistent with their concordance values. In this case, wCDM has two more free parameters than Rh = ct, and is penalized more heavily by these criteria. We find that Rh = ct is strongly favoured over wCDM with a likelihood of ≈92.9-99.6 per cent versus only 0.4-7.1 per cent. The current HIIGx sample is already large enough for the BIC to rule out ΛCDM/wCDM in favour of Rh = ct at a confidence level approaching 3σ.

Cosmological backreaction within the Szekeres model and emergence of spatial curvature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bolejko, Krzysztof, E-mail: krzysztof.bolejko@sydney.edu.au

This paper discusses the phenomenon of backreaction within the Szekeres model. Cosmological backreaction describes how the mean global evolution of the Universe deviates from the Friedmannian evolution. The analysis is based on models of a single cosmological environment and the global ensemble of the Szekeres models (of the Swiss-Cheese-type and Styrofoam-type). The obtained results show that non-linear growth of cosmic structures is associated with the growth of the spatial curvature Ω{sub R} (in the FLRW limit Ω{sub R} → Ω {sub k} ). If averaged over global scales the result depends on the assumed global model of the Universe. Withinmore » the Swiss-Cheese model, which does have a fixed background, the volume average follows the evolution of the background, and the global spatial curvature averages out to zero (the background model is the ΛCDM model, which is spatially flat). In the Styrofoam-type model, which does not have a fixed background, the mean evolution deviates from the spatially flat ΛCDM model, and the mean spatial curvature evolves from Ω{sub R} =0 at the CMB to Ω{sub R} ∼ 0.1 at 0 z =. If the Styrofoam-type model correctly captures evolutionary features of the real Universe then one should expect that in our Universe, the spatial curvature should build up (local growth of cosmic structures) and its mean global average should deviate from zero (backreaction). As a result, this paper predicts that the low-redshift Universe should not be spatially flat (i.e. Ω {sub k} ≠ 0, even if in the early Universe Ω {sub k} = 0) and therefore when analysing low- z cosmological data one should keep Ω {sub k} as a free parameter and independent from the CMB constraints.« less

Cosmological constraints from galaxy clusters in the 2500 square-degree SPT-SZ survey

DOE PAGES

Haan, T. de; Benson, B. A.; Bleem, L. E.; ...

2016-11-18

Here, we present cosmological parameter constraints obtained from galaxy clusters identified by their Sunyaev–Zel’dovich effect signature in the 2500 square-degree South Pole Telescope Sunyaev Zel’dovich (SPT-SZ) survey. We consider the 377 cluster candidates identified atmore » $$z\\gt 0.25$$ with a detection significance greater than five, corresponding to the 95% purity threshold for the survey. We compute constraints on cosmological models using the measured cluster abundance as a function of mass and redshift. We include additional constraints from multi-wavelength observations, including Chandra X-ray data for 82 clusters and a weak lensing-based prior on the normalization of the mass-observable scaling relations. Assuming a spatially flat ΛCDM cosmology, we combine the cluster data with a prior on H (0) and find $${\\sigma }_{8}=0.784\\pm 0.039$$ and $${{\\rm{\\Omega }}}_{m}=0.289\\pm 0.042$$, with the parameter combination $${\\sigma }_{8}{({{\\rm{\\Omega }}}_{m}/0.27)}^{0.3}=0.797\\pm 0.031$$. These results are in good agreement with constraints from the cosmic microwave background (CMB) from SPT, WMAP, and Planck, as well as with constraints from other cluster data sets. We also consider several extensions to ΛCDM, including models in which the equation of state of dark energy w, the species-summed neutrino mass, and/or the effective number of relativistic species ($${N}_{\\mathrm{eff}}$$) are free parameters. When combined with constraints from the Planck CMB, H (0), baryon acoustic oscillation, and SNe, adding the SPT cluster data improves the w constraint by 14%, to $$w=-1.023\\pm 0.042$$.« less

Cosmological backreaction within the Szekeres model and emergence of spatial curvature

NASA Astrophysics Data System (ADS)

Bolejko, Krzysztof

2017-06-01

This paper discusses the phenomenon of backreaction within the Szekeres model. Cosmological backreaction describes how the mean global evolution of the Universe deviates from the Friedmannian evolution. The analysis is based on models of a single cosmological environment and the global ensemble of the Szekeres models (of the Swiss-Cheese-type and Styrofoam-type). The obtained results show that non-linear growth of cosmic structures is associated with the growth of the spatial curvature ΩScript R (in the FLRW limit ΩScript R → Ωk). If averaged over global scales the result depends on the assumed global model of the Universe. Within the Swiss-Cheese model, which does have a fixed background, the volume average follows the evolution of the background, and the global spatial curvature averages out to zero (the background model is the ΛCDM model, which is spatially flat). In the Styrofoam-type model, which does not have a fixed background, the mean evolution deviates from the spatially flat ΛCDM model, and the mean spatial curvature evolves from ΩScript R =0 at the CMB to ΩScript R ~ 0.1 at 0z =. If the Styrofoam-type model correctly captures evolutionary features of the real Universe then one should expect that in our Universe, the spatial curvature should build up (local growth of cosmic structures) and its mean global average should deviate from zero (backreaction). As a result, this paper predicts that the low-redshift Universe should not be spatially flat (i.e. Ωk ≠ 0, even if in the early Universe Ωk = 0) and therefore when analysing low-z cosmological data one should keep Ωk as a free parameter and independent from the CMB constraints.

Towards accurate modelling of galaxy clustering on small scales: testing the standard ΛCDM + halo model

NASA Astrophysics Data System (ADS)

Sinha, Manodeep; Berlind, Andreas A.; McBride, Cameron K.; Scoccimarro, Roman; Piscionere, Jennifer A.; Wibking, Benjamin D.

2018-07-01

Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and dark matter haloes. Unfortunately, the modelling is typically not sufficiently accurate for ruling out models statistically. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. In this paper, we attempt to push halo modelling into the `accurate' regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. With our forward-modelling approach, we can incorporate clustering statistics beyond the traditional two-point statistics. We use this modelling methodology to test the standard Λ cold dark matter (ΛCDM) + halo model against the clustering of Sloan Digital Sky Survey (SDSS) seventh data release (DR7) galaxies. Specifically, we use the projected correlation function, group multiplicity function, and galaxy number density as constraints. We find that while the model fits each statistic separately, it struggles to fit them simultaneously. Adding group statistics leads to a more stringent test of the model and significantly tighter constraints on model parameters. We explore the impact of varying the adopted halo definition and cosmological model and find that changing the cosmology makes a significant difference. The most successful model we tried (Planck cosmology with Mvir haloes) matches the clustering of low-luminosity galaxies, but exhibits a 2.3σ tension with the clustering of luminous galaxies, thus providing evidence that the `standard' halo model needs to be extended. This work opens the door to adding interesting freedom to the halo model and including additional clustering statistics as constraints.

Cosmological constraints from a combination of galaxy clustering and lensing - III. Application to SDSS data

NASA Astrophysics Data System (ADS)

Cacciato, Marcello; van den Bosch, Frank C.; More, Surhud; Mo, Houjun; Yang, Xiaohu

2013-04-01

We simultaneously constrain cosmology and galaxy bias using measurements of galaxy abundances, galaxy clustering and galaxy-galaxy lensing taken from the Sloan Digital Sky Survey. We use the conditional luminosity function (which describes the halo occupation statistics as a function of galaxy luminosity) combined with the halo model (which describes the non-linear matter field in terms of its halo building blocks) to describe the galaxy-dark matter connection. We explicitly account for residual redshift-space distortions in the projected galaxy-galaxy correlation functions, and marginalize over uncertainties in the scale dependence of the halo bias and the detailed structure of dark matter haloes. Under the assumption of a spatially flat, vanilla Λ cold dark matter (ΛCDM) cosmology, we focus on constraining the matter density, Ωm, and the normalization of the matter power spectrum, σ8, and we adopt 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) priors for the spectral index, n, the Hubble parameter, h, and the baryon density, Ωb. We obtain that Ωm = 0.278+ 0.023- 0.026 and σ8 = 0.763+ 0.064- 0.049 (95 per cent CL). These results are robust to uncertainties in the radial number density distribution of satellite galaxies, while allowing for non-Poisson satellite occupation distributions results in a slightly lower value for σ8 (0.744+ 0.056- 0.047). These constraints are in excellent agreement (at the 1σ level) with the cosmic microwave background constraints from WMAP. This demonstrates that the use of a realistic and accurate model for galaxy bias, down to the smallest non-linear scales currently observed in galaxy surveys, leads to results perfectly consistent with the vanilla ΛCDM cosmology.

Cosmological constraints from galaxy clusters in the 2500 square-degree SPT-SZ survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haan, T. de; Benson, B. A.; Bleem, L. E.

Here, we present cosmological parameter constraints obtained from galaxy clusters identified by their Sunyaev–Zel’dovich effect signature in the 2500 square-degree South Pole Telescope Sunyaev Zel’dovich (SPT-SZ) survey. We consider the 377 cluster candidates identified atmore » $$z\\gt 0.25$$ with a detection significance greater than five, corresponding to the 95% purity threshold for the survey. We compute constraints on cosmological models using the measured cluster abundance as a function of mass and redshift. We include additional constraints from multi-wavelength observations, including Chandra X-ray data for 82 clusters and a weak lensing-based prior on the normalization of the mass-observable scaling relations. Assuming a spatially flat ΛCDM cosmology, we combine the cluster data with a prior on H (0) and find $${\\sigma }_{8}=0.784\\pm 0.039$$ and $${{\\rm{\\Omega }}}_{m}=0.289\\pm 0.042$$, with the parameter combination $${\\sigma }_{8}{({{\\rm{\\Omega }}}_{m}/0.27)}^{0.3}=0.797\\pm 0.031$$. These results are in good agreement with constraints from the cosmic microwave background (CMB) from SPT, WMAP, and Planck, as well as with constraints from other cluster data sets. We also consider several extensions to ΛCDM, including models in which the equation of state of dark energy w, the species-summed neutrino mass, and/or the effective number of relativistic species ($${N}_{\\mathrm{eff}}$$) are free parameters. When combined with constraints from the Planck CMB, H (0), baryon acoustic oscillation, and SNe, adding the SPT cluster data improves the w constraint by 14%, to $$w=-1.023\\pm 0.042$$.« less

Cosmological study with galaxy clusters detected by the Sunyaev-Zel'dovich effect

NASA Astrophysics Data System (ADS)

Mak, Suet-Ying

In this work, we present various studies to forecast the power of the galaxy clusters detected by the Sunyaev-Zel'dovich (SZ) effect in constraining cosmological models. The SZ effect is regarded as one of the new and promising technique to identify and study cluster physics. With the latest data being released in recent years from the SZ telescopes, it is essential to explore their potentials in providing cosmological information and investigate their relative strengths with respect to galaxy cluster data from X-ray and optical, as well as other cosmological probes such as Cosmic Microwave Background (CMB). One of the topics regard resolving the debate on the existence of an anomalous large scale bulk flow as measured from the kinetic SZ signal of galaxy clusters in the WMAP CMB data. We predict that if such measurement is done with the latest CMB data from the Planck satellite, the sensitivity will be improved by a factor of >5 and thus be able to provide an independent view of its existence. As it turns out, the Planck data, when using the technique developed in this work, find that the observed bulk flow amplitude is consistent with those expected from the LambdaCDM, which is in clear contradiction to the previous claim of a significant bulk flow detection in the WMAP data. We also forecast on the capability of the ongoing and future cluster surveys identified through thermal SZ (tSZ) in constraining three extended models to the LambdaCDM model: modified gravity f( R) model, primordial non-Gaussianity of density perturbation, and the presence of massive neutrinos. We do so by employing their effects on the cluster number count and power spectrum and using Fisher Matrix analysis to estimate the errors on the model parameters. We find that SZ cluster surveys can provide vital complementary information to those expected from non-cluster probes. Our results therefore give the confidence for pursuing these extended cosmological models with SZ clusters.

The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Cosmological implications of the configuration-space clustering wedges

NASA Astrophysics Data System (ADS)

Sánchez, Ariel G.; Scoccimarro, Román; Crocce, Martín; Grieb, Jan Niklas; Salazar-Albornoz, Salvador; Dalla Vecchia, Claudio; Lippich, Martha; Beutler, Florian; Brownstein, Joel R.; Chuang, Chia-Hsun; Eisenstein, Daniel J.; Kitaura, Francisco-Shu; Olmstead, Matthew D.; Percival, Will J.; Prada, Francisco; Rodríguez-Torres, Sergio; Ross, Ashley J.; Samushia, Lado; Seo, Hee-Jong; Tinker, Jeremy; Tojeiro, Rita; Vargas-Magaña, Mariana; Wang, Yuting; Zhao, Gong-Bo

2017-01-01

We explore the cosmological implications of anisotropic clustering measurements in configuration space of the final galaxy samples from Data Release 12 of the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey. We implement a new detailed modelling of the effects of non-linearities, bias and redshift-space distortions that can be used to extract unbiased cosmological information from our measurements for scales s ≳ 20 h-1 Mpc. We combined the information from Baryon Oscillation Spectroscopic Survey (BOSS) with the latest cosmic microwave background (CMB) observations and Type Ia supernovae samples and found no significant evidence for a deviation from the Λ cold dark matter (ΛCDM) cosmological model. In particular, these data sets can constrain the dark energy equation-of-state parameter to wDE = -0.996 ± 0.042 when to be assumed time independent, the curvature of the Universe to Ωk = -0.0007 ± 0.0030 and the sum of the neutrino masses to ∑mν < 0.25 eV at 95 per cent confidence levels. We explore the constraints on the growth rate of cosmic structures assuming f(z) = Ωm(z)γ and obtain γ = 0.609 ± 0.079, in good agreement with the predictions of general relativity of γ = 0.55. We compress the information of our clustering measurements into constraints on the parameter combinations DV(z)/rd, FAP(z) and fσ8(z) at zeff = 0.38, 0.51 and 0.61 with their respective covariance matrices and find good agreement with the predictions for these parameters obtained from the best-fitting ΛCDM model to the CMB data from the Planck satellite. This paper is part of a set that analyses the final galaxy clustering data set from BOSS. The measurements and likelihoods presented here are combined with others by Alam et al. to produce the final cosmological constraints from BOSS.

What do parameterized Om(z) diagnostics tell us in light of recent observations?

NASA Astrophysics Data System (ADS)

Qi, Jing-Zhao; Cao, Shuo; Biesiada, Marek; Xu, Teng-Peng; Wu, Yan; Zhang, Si-Xuan; Zhu, Zong-Hong

2018-06-01

In this paper, we propose a new parametrization for Om(z) diagnostics and show how the most recent and significantly improved observations concerning the H(z) and SN Ia measurements can be used to probe the consistency or tension between the ΛCDM model and observations. Our results demonstrate that H 0 plays a very important role in the consistency test of ΛCDM with H(z) data. Adopting the Hubble constant priors from Planck 2013 and Riess, one finds considerable tension between the current H(z) data and ΛCDM model and confirms the conclusions obtained previously by others. However, with the Hubble constant prior taken from WMAP9, the discrepancy between H(z) data and ΛCDM disappears, i.e., the current H(z) observations still support the cosmological constant scenario. This conclusion is also supported by the results derived from the Joint Light-curve Analysis (JLA) SN Ia sample. The best-fit Hubble constant from the combination of H(z)+JLA ({H}0={68.81}-1.49+1.50 km s‑1 Mpc‑1) is very consistent with results derived both by Planck 2013 and WMAP9, but is significantly different from the recent local measurement by Riess.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yun; Ratra, Bharat; Biesiada, Marek

We investigate two dark energy cosmological models (i.e., the ΛCDM and ϕ CDM models) with massive neutrinos assuming two different neutrino mass hierarchies in both the spatially flat and non-flat scenarios, where in the ϕ CDM model the scalar field possesses an inverse power-law potential, V ( ϕ ) ∝ ϕ {sup −} {sup α} ( α > 0). Cosmic microwave background data from Planck 2015, baryon acoustic oscillation data from 6dFGS, SDSS-MGS, BOSS-LOWZ and BOSS CMASS-DR11, the joint light-curve analysis compilation of SNe Ia apparent magnitude observations, and the Hubble Space Telescope H {sub 0} prior, are jointly employedmore » to constrain the model parameters. We first determine constraints assuming three species of degenerate massive neutrinos. In the spatially flat (non-flat) ΛCDM model, the sum of neutrino masses is bounded as Σ m {sub ν} < 0.165(0.299) eV at 95% confidence level (CL). Correspondingly, in the flat (non-flat) ϕ CDM model, we find Σ m {sub ν} < 0.164(0.301) eV at 95% CL. The inclusion of spatial curvature as a free parameter results in a significant broadening of confidence regions for Σ m {sub ν} and other parameters. In the scenario where the total neutrino mass is dominated by the heaviest neutrino mass eigenstate, we obtain similar conclusions to those obtained in the degenerate neutrino mass scenario. In addition, the results show that the bounds on Σ m {sub ν} based on two different neutrino mass hierarchies have insignificant differences in the spatially flat case for both the ΛCDM and ϕ CDM models; however, the corresponding differences are larger in the non-flat case.« less

Quintessential inflation with α-attractors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimopoulos, Konstantinos; Owen, Charlotte, E-mail: k.dimopoulos1@lancaster.ac.uk, E-mail: c.owen@lancaster.ac.uk

2017-06-01

A novel approach to quintessential inflation model building is studied, within the framework of α-attractors, motivated by supergravity theories. Inflationary observables are in excellent agreement with the latest CMB observations, while quintessence explains the dark energy observations without any fine-tuning. The model is kept intentionally minimal, avoiding the introduction of many degrees of freedom, couplings and mass scales. In stark contrast to ΛCDM, for natural values of the parameters, the model attains transient accelerated expansion, which avoids the future horizon problem, while it maintains the field displacement mildly sub-Planckian such that the flatness of the quintessential tail is not liftedmore » by radiative corrections and violations of the equivalence principle (fifth force) are under control. In particular, the required value of the cosmological constant is near the eletroweak scale. Attention is paid to the reheating of the Universe, which avoids gravitino overproduction and respects nucleosynthesis constraints. Kination is treated in a model independent way. A spike in gravitational waves, due to kination, is found not to disturb nucleosynthesis as well.« less

Quintessential inflation with α-attractors

NASA Astrophysics Data System (ADS)

Dimopoulos, Konstantinos; Owen, Charlotte

2017-06-01

A novel approach to quintessential inflation model building is studied, within the framework of α-attractors, motivated by supergravity theories. Inflationary observables are in excellent agreement with the latest CMB observations, while quintessence explains the dark energy observations without any fine-tuning. The model is kept intentionally minimal, avoiding the introduction of many degrees of freedom, couplings and mass scales. In stark contrast to ΛCDM, for natural values of the parameters, the model attains transient accelerated expansion, which avoids the future horizon problem, while it maintains the field displacement mildly sub-Planckian such that the flatness of the quintessential tail is not lifted by radiative corrections and violations of the equivalence principle (fifth force) are under control. In particular, the required value of the cosmological constant is near the eletroweak scale. Attention is paid to the reheating of the Universe, which avoids gravitino overproduction and respects nucleosynthesis constraints. Kination is treated in a model independent way. A spike in gravitational waves, due to kination, is found not to disturb nucleosynthesis as well.

Testing cold dark matter models using Hubble flow variations

NASA Astrophysics Data System (ADS)

Shi, Xiangdong

1999-05-01

COBE-normalized flat (matter plus cosmological constant) and open cold dark matter (CDM) models are tested by comparing their expected Hubble flow variations and the observed variations in a Type Ia supernova sample and a Tully-Fisher cluster sample. The test provides a probe of the CDM power spectrum on scales of 0.02h Mpc^-1<~ k<~ 0.2h Mpc^-1, free of the bias factor b. The results favour a low matter content universe, or a flat matter-dominated universe with a very low Hubble constant and/or a very small spectral index n^ps, with the best fits having Ο_0~ 0.3 to 0.4. The test is found to be more discriminative to the open CDM models than to the flat CDM models. For example, the test results are found to be compatible with those from the X-ray cluster abundance measurements at smaller length-scales, and consistent with the galaxy and cluster correlation analysis of Peacock & Dodds at similar length-scales, if our universe is flat; but the results are marginally incompatible with the X-ray cluster abundance measurements if our universe is open. The open CDM results are consistent with that of Peacock & Dodds only if the matter density of the universe is less than about 60 per cent of the critical density. The shortcoming of the test is discussed, so are ways to minimize it.

Galaxy clusters and cold dark matter - A low-density unbiased universe?

NASA Technical Reports Server (NTRS)

Bahcall, Neta A.; Cen, Renyue

1992-01-01

Large-scale simulations of a universe dominated by cold dark matter (CDM) are tested against two fundamental properties of clusters of galaxies: the cluster mass function and the cluster correlation function. We find that standard biased CDM models are inconsistent with these observations for any bias parameter b. A low-density, low-bias CDM-type model, with or without a cosmological constant, appears to be consistent with both the cluster mass function and the cluster correlations. The low-density model agrees well with the observed correlation function of the Abell, Automatic Plate Measuring Facility (APM), and Edinburgh-Durham cluster catalogs. The model is in excellent agreement with the observed dependence of the correlation strength on cluster mean separation, reproducing the measured universal dimensionless cluster correlation. The low-density model is also consistent with other large-scale structure observations, including the APM angular galaxy-correlations, and for lambda = 1-Omega with the COBE results of the microwave background radiation fluctuations.

The impact of dark energy on galaxy formation. What does the future of our Universe hold?

NASA Astrophysics Data System (ADS)

Salcido, Jaime; Bower, Richard G.; Barnes, Luke A.; Lewis, Geraint F.; Elahi, Pascal J.; Theuns, Tom; Schaller, Matthieu; Crain, Robert A.; Schaye, Joop

2018-04-01

We investigate the effect of the accelerated expansion of the Universe due to a cosmological constant, Λ, on the cosmic star formation rate. We utilise hydrodynamical simulations from the EAGLE suite, comparing a ΛCDM Universe to an Einstein-de Sitter model with Λ = 0. Despite the differences in the rate of growth of structure, we find that dark energy, at its observed value, has negligible impact on star formation in the Universe. We study these effects beyond the present day by allowing the simulations to run forward into the future (t > 13.8 Gyr). We show that the impact of Λ becomes significant only when the Universe has already produced most of its stellar mass, only decreasing the total co-moving density of stars ever formed by ≈15%. We develop a simple analytic model for the cosmic star formation rate that captures the suppression due to a cosmological constant. The main reason for the similarity between the models is that feedback from accreting black holes dramatically reduces the cosmic star formation at late times. Interestingly, simulations without feedback from accreting black holes predict an upturn in the cosmic star formation rate for t > 15 Gyr due to the rejuvenation of massive (>1011M⊙) galaxies. We briefly discuss the implication of the weak dependence of the cosmic star formation on Λ in the context of the anthropic principle.

The H0 tension in light of vacuum dynamics in the universe

NASA Astrophysics Data System (ADS)

Solà, Joan; Gómez-Valent, Adrià; de Cruz Pérez, Javier

2017-11-01

Despite the outstanding achievements of modern cosmology, the classical dispute on the precise value of H0, which is the first ever parameter of modern cosmology and one of the prime parameters in the field, still goes on and on after over half a century of measurements. Recently the dispute came to the spotlight with renewed strength owing to the significant tension (at > 3 σ c.l.) between the latest Planck determination obtained from the CMB anisotropies and the local (distance ladder) measurement from the Hubble Space Telescope (HST), based on Cepheids. In this work, we investigate the impact of the running vacuum model (RVM) and related models on such a controversy. For the RVM, the vacuum energy density ρΛ carries a mild dependence on the cosmic expansion rate, i.e. ρΛ (H), which allows to ameliorate the fit quality to the overall SNIa + BAO + H (z) + LSS + CMB cosmological observations as compared to the concordance ΛCDM model. By letting the RVM to deviate from the vacuum option, the equation of state w = - 1 continues to be favored by the overall fit. Vacuum dynamics also predicts the following: i) the CMB range of values for H0 is more favored than the local ones, and ii) smaller values for σ8 (0). As a result, a better account for the LSS structure formation data is achieved as compared to the ΛCDM, which is based on a rigid (i.e. non-dynamical) Λ term.

Modified Regge calculus as an explanation of dark energy

NASA Astrophysics Data System (ADS)

Stuckey, W. M.; McDevitt, T. J.; Silberstein, M.

2012-03-01

Using the Regge calculus, we construct a Regge differential equation for the time evolution of the scale factor a(t) in the Einstein-de Sitter cosmology model (EdS). We propose two modifications to the Regge calculus approach: (1) we allow the graphical links on spatial hypersurfaces to be large, as in direct particle interaction when the interacting particles reside in different galaxies, and (2) we assume that luminosity distance DL is related to graphical proper distance Dp by the equation D_L = (1+z)\\sqrt{\\overrightarrow{D_p}\\cdot \\overrightarrow{D_p}}, where the inner product can differ from its usual trivial form. The modified Regge calculus model (MORC), EdS and ΛCDM are compared using the data from the Union2 Compilation, i.e. distance moduli and redshifts for type Ia supernovae. We find that a best fit line through log {\\big(\\frac{D_L}{{Gpc}}\\big)} versus log z gives a correlation of 0.9955 and a sum of squares error (SSE) of 1.95. By comparison, the best fit ΛCDM gives SSE = 1.79 using Ho = 69.2 km s-1 Mpc, ΩM = 0.29 and ΩΛ = 0.71. The best fit EdS gives SSE = 2.68 using Ho = 60.9 km s-1 Mpc. The best-fit MORC gives SSE = 1.77 and Ho = 73.9 km s-1 Mpc using R = A-1 = 8.38 Gcy and m = 1.71 × 1052 kg, where R is the current graphical proper distance between nodes, A-1 is the scaling factor from our non-trivial inner product, and m is the nodal mass. Thus, the MORC improves the EdS as well as ΛCDM in accounting for distance moduli and redshifts for type Ia supernovae without having to invoke accelerated expansion, i.e. there is no dark energy and the universe is always decelerating.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stavridis, Adamantios; Arun, K. G.; Will, Clifford M.

Spin induced precessional modulations of gravitational wave signals from supermassive black hole binaries can improve the estimation of luminosity distance to the source by space based gravitational wave missions like the Laser Interferometer Space Antenna (LISA). We study how this impacts the ability of LISA to do cosmology, specifically, to measure the dark energy equation of state (EOS) parameter w. Using the {lambda}CDM model of cosmology, we show that observations of precessing binaries with mass ratio 10 ratio 1 by LISA, combined with a redshift measurement, can improve the determination of w up to an order of magnitude with respectmore » to the nonprecessing case depending on the total mass and the redshift.« less

Cold dark matter: Controversies on small scales

PubMed Central

Weinberg, David H.; Bullock, James S.; Governato, Fabio; Kuzio de Naray, Rachel; Peter, Annika H. G.

2015-01-01

The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way’s dwarf galaxy satellites. We review the current observational and theoretical status of these “small-scale controversies.” Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years. PMID:25646464

Testing Viable f(T) Models with Current Observations

NASA Astrophysics Data System (ADS)

Xu, Bing; Yu, Hongwei; Wu, Puxun

2018-03-01

We perform observational tests on the f(T) gravity with the BAO data (including the BOSS DR 12 galaxy sample, the DR12 Lyα-Forests measurement, the new eBOSS DR14 quasar sample, the 6dFGS, and the SDSS), the CMB distance priors from the Planck 2015, the SNIa data from the joint light-curve analysis, the latest H(z) data, and the local value of the Hubble constant. Six different f(T) models are investigated. Furthermore, the ΛCDM is also considered. All models are compared by using the Akaike information criteria (AIC) and the Bayesian information criteria (BIC). Our results show that the ΛCDM remains to be the most favored model by current observations. However, there are also the Hubble constant tension between the Planck measurements and the local Universe observations and the tension between the CMB data and the H(z) data in the ΛCDM. For f(T) models considered in this paper, half, which can reduce to the ΛCDM, have values of {{χ }2}\\min smaller than that of the ΛCDM and can relieve the tensions existing in the ΛCDM. However, they are punished slightly by the BIC due to one extra parameter. Two of six f(T) models, in which the crossing of the phantom divide line can be realized for the equation of state of the effective dark energy and this crossing is shown in this paper to be favored by current observations, are punished by the information criteria. In addition, we find that the logarithmic f(T) model is excluded by cosmological observations.

Computing general-relativistic effects from Newtonian N-body simulations: Frame dragging in the post-Friedmann approach

NASA Astrophysics Data System (ADS)

Bruni, Marco; Thomas, Daniel B.; Wands, David

2014-02-01

We present the first calculation of an intrinsically relativistic quantity, the leading-order correction to Newtonian theory, in fully nonlinear cosmological large-scale structure studies. Traditionally, nonlinear structure formation in standard ΛCDM cosmology is studied using N-body simulations, based on Newtonian gravitational dynamics on an expanding background. When one derives the Newtonian regime in a way that is a consistent approximation to the Einstein equations, the first relativistic correction to the usual Newtonian scalar potential is a gravitomagnetic vector potential, giving rise to frame dragging. At leading order, this vector potential does not affect the matter dynamics, thus it can be computed from Newtonian N-body simulations. We explain how we compute the vector potential from simulations in ΛCDM and examine its magnitude relative to the scalar potential, finding that the power spectrum of the vector potential is of the order 10-5 times the scalar power spectrum over the range of nonlinear scales we consider. On these scales the vector potential is up to two orders of magnitudes larger than the value predicted by second-order perturbation theory extrapolated to the same scales. We also discuss some possible observable effects and future developments.

The planes of satellite galaxies problem, suggested solutions, and open questions

NASA Astrophysics Data System (ADS)

Pawlowski, Marcel S.

2018-02-01

Satellite galaxies of the Milky Way and of the Andromeda galaxy have been found to preferentially align in significantly flattened planes of satellite galaxies, and available velocity measurements are indicative of a preference of satellites in those structures to co-orbit. There is an increasing evidence that such kinematically correlated satellite planes are also present around more distant hosts. Detailed comparisons show that similarly anisotropic phase-space distributions of sub-halos are exceedingly rare in cosmological simulations based on the ΛCDM paradigm. Analogs to the observed systems have frequencies of ≤ 0.5% in such simulations. In contrast to other small-scale problems, the satellite planes issue is not strongly affected by baryonic processes because the distribution of sub-halos on scales of hundreds of kpc is dominated by gravitational effects. This makes the satellite planes one of the most serious small-scale problems for ΛCDM. This review summarizes the observational evidence for planes of satellite galaxies in the Local Group and beyond, and provides an overview of how they compare to cosmological simulations. It also discusses scenarios which aim at explaining the coherence of satellite positions and orbits, and why they all are currently unable to satisfactorily resolve the issue.

ΛCDM Cosmology for Astronomers

NASA Astrophysics Data System (ADS)

Condon, J. J.; Matthews, A. M.

2018-07-01

The homogeneous, isotropic, and flat ΛCDM universe favored by observations of the cosmic microwave background can be described using only Euclidean geometry, locally correct Newtonian mechanics, and the basic postulates of special and general relativity. We present simple derivations of the most useful equations connecting astronomical observables (redshift, flux density, angular diameter, brightness, local space density, ...) with the corresponding intrinsic properties of distant sources (lookback time, distance, spectral luminosity, linear size, specific intensity, source counts, ...). We also present an analytic equation for lookback time that is accurate within 0.1% for all redshifts z. The exact equation for comoving distance is an elliptic integral that must be evaluated numerically, but we found a simple approximation with errors <0.2% for all redshifts up to z ≈ 50.

Composite dark energy: Cosmon models with running cosmological term and gravitational coupling

NASA Astrophysics Data System (ADS)

Grande, Javier; Solà, Joan; Štefančić, Hrvoje

2007-02-01

In the recent literature on dark energy (DE) model building we have learnt that cosmologies with variable cosmological parameters can mimic more traditional DE pictures exclusively based on scalar fields (e.g. quintessence and phantom). In a previous work we have illustrated this situation within the context of a renormalization group running cosmological term, Λ. Here we analyze the possibility that both the cosmological term and the gravitational coupling, G, are running parameters within a more general framework (a variant of the so-called “ΛXCDM models”) in which the DE fluid can be a mixture of a running Λ and another dynamical entity X (the “cosmon”) which may behave quintessence-like or phantom-like. We compute the effective EOS parameter, ω, of this composite fluid and show that the ΛXCDM can mimic to a large extent the standard ΛCDM model while retaining features hinting at its potential composite nature (such as the smooth crossing of the cosmological constant boundary ω=-1). We further argue that the ΛXCDM models can cure the cosmological coincidence problem. All in all we suggest that future experimental studies on precision cosmology should take seriously the possibility that the DE fluid can be a composite medium whose dynamical features are partially caused and renormalized by the quantum running of the cosmological parameters.

Study of the observational compatibility of an inhomogeneous cosmology with linear expansion according to SNe Ia

NASA Astrophysics Data System (ADS)

Monjo, R.

2017-11-01

Most of current cosmological theories are built combining an isotropic and homogeneous manifold with a scale factor that depends on time. If one supposes a hyperconical universe with linear expansion, an inhomogeneous metric can be obtained by an appropriate transformation that preserves the proper time. This model locally tends to a flat Friedman-Robertson-Walker metric with linear expansion. The objective of this work is to analyze the observational compatibility of the inhomogeneous metric considered. For this purpose, the corresponding luminosity distance was obtained and was compared with the observations of 580 SNe Ia, taken from the Supernova Cosmology Project. The best fit of the hyperconical model obtains χ02=562 , the same value as the standard Λ CDM model. Finally, a possible relationship is found between both theories.

Model selection using cosmic chronometers with Gaussian Processes

NASA Astrophysics Data System (ADS)

Melia, Fulvio; Yennapureddy, Manoj K.

2018-02-01

The use of Gaussian Processes with a measurement of the cosmic expansion rate based solely on the observation of cosmic chronometers provides a completely cosmology-independent reconstruction of the Hubble constant H(z) suitable for testing different models. The corresponding dispersion σH is smaller than ~ 9% over the entire redshift range (lesssim zlesssim 20) of the observations, rivaling many kinds of cosmological measurements available today. We use the reconstructed H(z) function to test six different cosmologies, and show that it favours the Rh=ct universe, which has only one free parameter (i.e., H0) over other models, including Planck ΛCDM . The parameters of the standard model may be re-optimized to improve the fits to the reconstructed H(z) function, but the results have smaller p-values than one finds with Rh=ct.

A Solution to ``Too Big to Fail''

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-10-01

Its a tricky business to reconcile simulations of our galaxys formation with our current observations of the Milky Way and its satellites. In a recent study, scientists have addressed one discrepancy between simulations and observations: the so-called to big to fail problem.From Missing Satellites to Too Big to FailThe favored model of the universe is the lambda-cold-dark-matter (CDM) cosmological model. This model does a great job of correctly predicting the large-scale structure of the universe, but there are still a few problems with it on smaller scales.Hubble image of UGC 5497, a dwarf galaxy associated with Messier 81. In the missing satellite problem, simulations of galaxy formation predict that there should be more such satellite galaxies than we observe. [ESA/NASA]The first is the missing satellites problem: CDM cosmology predicts that galaxies like the Milky Way should have significantly more satellite galaxies than we observe. A proposed solution to this problem is the argument that there may exist many more satellites than weve observed, but these dwarf galaxies have had their stars stripped from them during tidal interactions which prevents us from being able to see them.This solution creates a new problem, though: the too big to fail problem. This problem states that many of the satellites predicted by CDM cosmology are simply so massive that theres no way they couldnt have visible stars. Another way of looking at it: the observed satellites of the Milky Way are not massive enough to be consistent with predictions from CDM.Artists illustration of a supernova, a type of stellar feedback that can modify the dark-matter distribution of a satellite galaxy. [NASA/CXC/M. Weiss]Density Profiles and Tidal StirringLed by Mihai Tomozeiu (University of Zurich), a team of scientists has published a study in which they propose a solution to the too big to fail problem. By running detailed cosmological zoom simulations of our galaxys formation, Tomozeiu and collaborators modeled the dark matter and the stellar content of the galaxy, tracking the formation and evolution of dark-matter subhalos.Based on the results of their simulations, the team argues that the too big to fail problem can be resolved by combining two effects:Stellar feedback in a satellite galaxy can modify its dark-matter distribution, lowering the dark-matter density in the galaxys center and creating a shallower density profile. Satellites with such shallow density profiles evolve differently than those typically modeled, which have a high concentration of dark matter in their centers.After these satellites fall into the Milky Ways potential, tidal effects such as shocks and stripping modify the mass distribution of both the dark matter and the baryons even further.Each curve represents a simulated satellites circular velocity (which corresponds to its total mass) at z=0. Left: results using typical dark-matter density profiles. Right: results using the shallower profiles expected when stellar feedback is included. Results from the shallower profiles are consistent with observed Milky-Way satellites(black crosses). [Adapted from Tomozeiu et al. 2016]A Match to ObservationsTomozeiu and collaborators found that when they used traditional density profiles to model the satellites, the satellites at z=0 in the simulation were much larger than those we observe around the Milky Way consistent with the too big to fail problem.When the team used shallower density profiles and took into account tidal effects, however, the simulations produced a distribution of satellites at z=0 that is consistent with what we observe.This study provides a tidy potential solution to the too big to fail problem, further strengthening the support for CDM cosmology.CitationMihai Tomozeiu et al 2016 ApJ 827 L15. doi:10.3847/2041-8205/827/1/L15

The best-fit universe. [cosmological models

NASA Technical Reports Server (NTRS)

Turner, Michael S.

1991-01-01

Inflation provides very strong motivation for a flat Universe, Harrison-Zel'dovich (constant-curvature) perturbations, and cold dark matter. However, there are a number of cosmological observations that conflict with the predictions of the simplest such model: one with zero cosmological constant. They include the age of the Universe, dynamical determinations of Omega, galaxy-number counts, and the apparent abundance of large-scale structure in the Universe. While the discrepancies are not yet serious enough to rule out the simplest and most well motivated model, the current data point to a best-fit model with the following parameters: Omega(sub B) approximately equal to 0.03, Omega(sub CDM) approximately equal to 0.17, Omega(sub Lambda) approximately equal to 0.8, and H(sub 0) approximately equal to 70 km/(sec x Mpc) which improves significantly the concordance with observations. While there is no good reason to expect such a value for the cosmological constant, there is no physical principle that would rule out such.

Search for sterile neutrinos in holographic dark energy cosmology: Reconciling Planck observation with the local measurement of the Hubble constant

NASA Astrophysics Data System (ADS)

Zhao, Ming-Ming; He, Dong-Ze; Zhang, Jing-Fei; Zhang, Xin

2017-08-01

We search for sterile neutrinos in the holographic dark energy cosmology by using the latest observational data. To perform the analysis, we employ the current cosmological observations, including the cosmic microwave background temperature power spectrum data from the Planck mission, the baryon acoustic oscillation measurements, the type Ia supernova data, the redshift space distortion measurements, the shear data of weak lensing observation, the Planck lensing measurement, and the latest direct measurement of H0 as well. We show that, compared to the Λ CDM cosmology, the holographic dark energy cosmology with sterile neutrinos can relieve the tension between the Planck observation and the direct measurement of H0 much better. Once we include the H0 measurement in the global fit, we find that the hint of the existence of sterile neutrinos in the holographic dark energy cosmology can be given. Under the constraint of the all-data combination, we obtain Neff=3.76 ±0.26 and mν,sterile eff<0.215 eV , indicating that the detection of Δ Neff>0 in the holographic dark energy cosmology is at the 2.75 σ level and the massless or very light sterile neutrino is favored by the current observations.

Measuring the universe with high-precision large-scale structure

NASA Astrophysics Data System (ADS)

Mehta, Kushal Tushar

Baryon acoustic oscillations (BAOs) are used to obtain precision measurements of cosmological parameters from large-scale surveys. While robust against most systematics, there are certain theoretical uncertainties that can affect BAO and galaxy clustering measurements. In this thesis I use data from the Sloan Digital Sky Survey (SDSS) to measure cosmological parameters and use N-body and smoothed-particle hydrodynamic (SPH) simulations to measure the effect of theoretical uncertainties by using halo occupation distributions (HODs). I investigate the effect of galaxy bias on BAO measurements by creating mock galaxy catalogs from large N-body simulations at z = 1. I find that there is no additional shift in the acoustic scale (0.10% +/- 0.10%) for the less biased HODs (b 3). I present the methodology and implementation of the simple one-step reconstruction technique introduced by Eisenstein et al. (2007) to biased tracers in N-body simulation. Reconstruction reduces the errorbars on the acoustic scale measurement by a factor of 1.5 - 2, and removes any additional shift due to galaxy bias for all HODs (0.07% +/- 0.15%) . Padmanabhan et al. (2012) and Xu et al. (2012) use this reconstruction technique in the SDSS DR7 data to measure DV (z = 0.35) (rsfidr s) = 1356 +/- 25 Mpc. Here I use this measurement in combination with measurements from the cosmic microwave background and the supernovae legacy survey to measure various cosmological parameters. I find the data consistent with the LambdaCDM Universe with a flat geometry. In particular, I measure H0 = 69.8 +/- 1.2 km/s/Mpc, w = 0.97 +/- 0.17, OK= -0.004 +/- 0.005 in the LambdaCDM, wCDM, and oCDM models respectively. Next, I measure the effect of large-scale (5 Mpc) halo environment density on the HOD by using an SPH simulation at z = 0, 0.35, 0.5, 0.75, 1.0$. I do not find any significant dependence of the HOD on the halo environment density for different galaxy mass thresholds, red and blue galaxies, and at different redshifts. I use the MultiDark N-body simualtion to measure the possible effect of environment density on the galaxy correlation function xi(r). I find that environment density enhances xi(r) by 3% at scales of 1 - 20 Mpc/h at z = 0 and up to 12% at 0.3 Mpc/h and 8% at 1 - 4 Mpc/h for z = 1.

Ground-based Opportunities for Astrometry

DTIC Science & Technology

2013-01-01

those stars (Dinescu eta/. 2005) leads to a measurement of the tangential velocity of the Sagittarius dwarf and a definitive orbit. Several other...Currently accepted Lambda cold-dark-matter (CDM) cosmological models (see also Chapter 28) predict several hundred merging dwarf galaxies within 1...nination of tations with I) diagrams. o parallaxes lial velocity tarius dwarf of possible eta/. 2005) a definitive ttion of their uti on. :Is

Reionization and Galaxy Formation in Warm Dark Matter Cosmologies

NASA Astrophysics Data System (ADS)

Dayal, Pratika; Choudhury, Tirthankar Roy; Bromm, Volker; Pacucci, Fabio

2017-02-01

We compare model results from a semi-analytic (merger-tree based) framework for high-redshift (z ≃ 5-20) galaxy formation against reionization indicators, including the Planck electron scattering optical depth (τ es) and the ionizing photon emissivity ({\\dot{n}}{ion}), to shed light on the reionization history and sources in Cold (CDM) and Warm Dark Matter (WDM; particle masses of {m}x = 1.5, 3, and 5 keV) cosmologies. This model includes all of the key processes of star formation, supernova feedback, the merger/accretion/ejection driven evolution of gas and stellar mass and the effect of the ultra-violet background (UVB), created during reionization, in photo-evaporating the gas content of galaxies in halos with M h ≲ 109 {M}⊙ . We find that the delay in the start of reionization in light (1.5 keV) WDM models can be compensated by a steeper redshift evolution of the ionizing photon escape fraction and a faster mass assembly, resulting in reionization ending at comparable redshifts (z ≃ 5.5) in all the dark matter models considered. We find that the bulk of the reionization photons come from galaxies with a halo mass of M h ≲ 109 {M}⊙ and a UV magnitude of -15 ≲ M UV ≲ -10 in CDM. The progressive suppression of low-mass halos with decreasing {m}x leads to a shift in the “reionization” population to larger halo masses of M h ≳ 109 {M}⊙ and -17 ≲ M UV ≲ -13 for 1.5 keV WDM. We find that current observations of τ es and the ultra violet luminosity function are equally compatible with all the (cold and warm) dark matter models considered in this work. Quantifying the impact of the UVB on galaxy observables (luminosity functions, stellar mass densities, and stellar to halo mass ratios) for different DM models, we propose that global indicators including the redshift evolution of the stellar mass density and the stellar mass-halo mass relation, observable with the James Webb Space Telescope, can be used to distinguish between CDM and WDM (1.5 keV) cosmologies.

Model-independent limits and constraints on extended theories of gravity from cosmic reconstruction techniques

NASA Astrophysics Data System (ADS)

de la Cruz-Dombriz, Álvaro; Dunsby, Peter K. S.; Luongo, Orlando; Reverberi, Lorenzo

2016-12-01

The onset of dark energy domination depends on the particular gravitational theory driving the cosmic evolution. Model independent techniques are crucial to test the both the present ΛCDM cosmological paradigm and alternative theories, making the least possible number of assumptions about the Universe. In this paper we investigate whether cosmography is able to distinguish between different gravitational theories, by determining bounds on model parameters for three different extensions of General Relativity, namely quintessence, F(𝒯) and f(R) gravitational theories. We expand each class of theories in powers of redshift z around the present time, making no additional assumptions. This procedure is an extension of previous work and can be seen as the most general approach for testing extended theories of gravity through the use of cosmography. In the case of F(𝒯) and f(R) theories, we show that some assumptions on model parameters often made in previous works are superfluous or even unjustified. We use data from the Union 2.1 supernovae catalogue, baryonic acoustic oscillation data and H(z) differential age compilations, which probe cosmology on different scales of the cosmological evolution. We perform a Monte Carlo analysis using a Metropolis-Hastings algorithm with a Gelman-Rubin convergence criterion, reporting 1-σ and 2-σ confidence levels. To do so, we perform two distinct fits, assuming only data within z < 1 first and then without limitations in redshift. We obtain the corresponding numerical intervals in which coefficients span, and find that the data is compatible the ΛCDM limit of all three theories at the 1-σ level, while still compatible with quite a large portion of parameter space. We compare our results to the truncated ΛCDM paradigm, demonstrating that our bounds divert from the expectations of previous works, showing that the permitted regions of coefficients are significantly modified and in general widened with respect to values usually reported in the existing literature. Finally, we test the extended theories through the Bayesian selection criteria AIC and BIC.

Model-independent limits and constraints on extended theories of gravity from cosmic reconstruction techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cruz-Dombriz, Álvaro de la; Dunsby, Peter K.S.; Luongo, Orlando

The onset of dark energy domination depends on the particular gravitational theory driving the cosmic evolution. Model independent techniques are crucial to test the both the present ΛCDM cosmological paradigm and alternative theories, making the least possible number of assumptions about the Universe. In this paper we investigate whether cosmography is able to distinguish between different gravitational theories, by determining bounds on model parameters for three different extensions of General Relativity, namely quintessence, F (Τ) and f ( R ) gravitational theories. We expand each class of theories in powers of redshift z around the present time, making no additionalmore » assumptions. This procedure is an extension of previous work and can be seen as the most general approach for testing extended theories of gravity through the use of cosmography. In the case of F (Τ) and f ( R ) theories, we show that some assumptions on model parameters often made in previous works are superfluous or even unjustified. We use data from the Union 2.1 supernovae catalogue, baryonic acoustic oscillation data and H ( z ) differential age compilations, which probe cosmology on different scales of the cosmological evolution. We perform a Monte Carlo analysis using a Metropolis-Hastings algorithm with a Gelman-Rubin convergence criterion, reporting 1-σ and 2-σ confidence levels. To do so, we perform two distinct fits, assuming only data within z < 1 first and then without limitations in redshift. We obtain the corresponding numerical intervals in which coefficients span, and find that the data is compatible the ΛCDM limit of all three theories at the 1-σ level, while still compatible with quite a large portion of parameter space. We compare our results to the truncated ΛCDM paradigm, demonstrating that our bounds divert from the expectations of previous works, showing that the permitted regions of coefficients are significantly modified and in general widened with respect to values usually reported in the existing literature. Finally, we test the extended theories through the Bayesian selection criteria AIC and BIC.« less

SIDM on FIRE: hydrodynamical self-interacting dark matter simulations of low-mass dwarf galaxies

NASA Astrophysics Data System (ADS)

Robles, Victor H.; Bullock, James S.; Elbert, Oliver D.; Fitts, Alex; González-Samaniego, Alejandro; Boylan-Kolchin, Michael; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Kereš, Dušan; Hayward, Christopher C.

2017-12-01

We compare a suite of four simulated dwarf galaxies formed in 1010 M⊙ haloes of collisionless cold dark matter (CDM) with galaxies simulated in the same haloes with an identical galaxy formation model but a non-zero cross-section for DM self-interactions. These cosmological zoom-in simulations are part of the Feedback In Realistic Environments (FIRE) project and utilize the FIRE-2 model for hydrodynamics and galaxy formation physics. We find the stellar masses of the galaxies formed in self-interacting dark matter (SIDM) with σ/m = 1 cm2 g-1 are very similar to those in CDM (spanning M⋆ ≈ 105.7-7.0M⊙) and all runs lie on a similar stellar mass-size relation. The logarithmic DM density slope (α = d log ρ/d log r) in the central 250-500 pc remains steeper than α = -0.8 for the CDM-Hydro simulations with stellar mass M⋆ ∼ 106.6 M⊙ and core-like in the most massive galaxy. In contrast, every SIDM hydrodynamic simulation yields a flatter profile, with α > -0.4. Moreover, the central density profiles predicted in SIDM runs without baryons are similar to the SIDM runs that include FIRE-2 baryonic physics. Thus, SIDM appears to be much more robust to the inclusion of (potentially uncertain) baryonic physics than CDM on this mass scale, suggesting that SIDM will be easier to falsify than CDM using low-mass galaxies. Our FIRE simulations predict that galaxies less massive than M⋆ ≲ 3 × 106 M⊙ provide potentially ideal targets for discriminating models, with SIDM producing substantial cores in such tiny galaxies and CDM producing cusps.

Isocurvature forecast in the anthropic axion window

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamann, J.; Hannestad, S.; Raffelt, G.G.

2009-06-01

We explore the cosmological sensitivity to the amplitude of isocurvature fluctuations that would be caused by axions in the ''anthropic window'' where the axion decay constant f{sub a} >> 10{sup 12} GeV and the initial misalignment angle Θ{sub i} << 1. In a minimal ΛCDM cosmology extended with subdominant scale-invariant isocurvature fluctuations, existing data constrain the isocurvature fraction to α < 0.09 at 95% C.L. If no signal shows up, Planck can improve this constraint to 0.042 while an ultimate CMB probe limited only by cosmic variance in both temperature and E-polarisation can reach 0.017, about a factor of fivemore » better than the current limit. In the parameter space of f{sub a} and H{sub I} (Hubble parameter during inflation) we identify a small region where axion detection remains within the reach of realistic cosmological probes.« less

The Atacama Cosmology Telescope: Two-season spectrum and parameters

NASA Astrophysics Data System (ADS)

Hlozek, Renée; Louis, Thibaut; Grace, Emily; Hasselfield, Matthew; Lungu, Marius; Maurin, Loic; Atacama Cosmology Telescope

2017-01-01

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope polarimeter (ACTPol) over 548 deg^2 of sky on the celestial Equator, from nighttime data collected during 2013-14 using two kilo-detector arrays at 146 GHz. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP satellite data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the ΛCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature power spectrum, including the baryon density and the acoustic peak position angle, and the derived Hubble constant. Adding the new data to Planck temperature data tightens the limits on damping tail parameters, which we present here.

Examining the evidence for dynamical dark energy.

PubMed

Zhao, Gong-Bo; Crittenden, Robert G; Pogosian, Levon; Zhang, Xinmin

2012-10-26

We apply a new nonparametric Bayesian method for reconstructing the evolution history of the equation of state w of dark energy, based on applying a correlated prior for w(z), to a collection of cosmological data. We combine the latest supernova (SNLS 3 year or Union 2.1), cosmic microwave background, redshift space distortion, and the baryonic acoustic oscillation measurements (including BOSS, WiggleZ, and 6dF) and find that the cosmological constant appears consistent with current data, but that a dynamical dark energy model which evolves from w<-1 at z~0.25 to w>-1 at higher redshift is mildly favored. Estimates of the Bayesian evidence show little preference between the cosmological constant model and the dynamical model for a range of correlated prior choices. Looking towards future data, we find that the best fit models for current data could be well distinguished from the ΛCDM model by observations such as Planck and Euclid-like surveys.

Holographic dark energy with cosmological constant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Yazhou; Li, Nan; Zhang, Zhenhui

2015-08-01

Inspired by the multiverse scenario, we study a heterotic dark energy model in which there are two parts, the first being the cosmological constant and the second being the holographic dark energy, thus this model is named the ΛHDE model. By studying the ΛHDE model theoretically, we find that the parameters d and Ω{sub hde} are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the ΛHDE model by usingmore » the recent observational data. We find the model yields χ{sup 2}{sub min}=426.27 when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant ΛCDM model (431.35). At 68.3% CL, we obtain −0.07« less

Neglecting primordial non-Gaussianity threatens future cosmological experiment accuracy

NASA Astrophysics Data System (ADS)

Camera, Stefano; Carbone, Carmelita; Fedeli, Cosimo; Moscardini, Lauro

2015-02-01

Future galaxy redshift surveys aim at probing the clustering of the cosmic large-scale structure with unprecedented accuracy, thus complementing cosmic microwave background experiments in the quest to deliver the most precise and accurate picture ever of our Universe. Analyses of such measurements are usually performed within the context of the so-called vanilla Λ CDM model—the six-parameter phenomenological model which, for instance, emerges from best fits against the recent data obtained by the Planck satellite. Here, we show that such an approach is prone to subtle systematics when the Gaussianity of primordial fluctuations is concerned. In particular, we demonstrate that, if we neglect even a tiny amount of primordial non-Gaussianity—fully consistent with current limits—we shall introduce spurious biases in the reconstruction of cosmological parameters. This is a serious issue that must be properly accounted for in view of accurate (as well as precise) cosmology.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nunes, Rafael C.; Abreu, Everton M.C.; Neto, Jorge Ananias

Based on the relationship between thermodynamics and gravity we propose, with the aid of Verlinde's formalism, an alternative interpretation of the dynamical evolution of the Friedmann-Robertson-Walker Universe. This description takes into account the entropy and temperature intrinsic to the horizon of the universe due to the information holographically stored there through non-gaussian statistical theories proposed by Tsallis and Kaniadakis. The effect of these non-gaussian statistics in the cosmological context is to change the strength of the gravitational constant. In this paper, we consider the w CDM model modified by the non-gaussian statistics and investigate the compatibility of these non-gaussian modificationmore » with the cosmological observations. In order to analyze in which extend the cosmological data constrain these non-extensive statistics, we will use type Ia supernovae, baryon acoustic oscillations, Hubble expansion rate function and the linear growth of matter density perturbations data. We show that Tsallis' statistics is favored at 1σ confidence level.« less

Measuring the lensing potential with tomographic galaxy number counts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montanari, Francesco; Durrer, Ruth, E-mail: francesco.montanari@unige.ch, E-mail: ruth.durrer@unige.ch

2015-10-01

We investigate how the lensing potential can be measured tomographically with future galaxy surveys using their number counts. Such a measurement is an independent test of the standard ΛCDM framework and can be used to discern modified theories of gravity. We perform a Fisher matrix forecast based on galaxy angular-redshift power spectra, assuming specifications consistent with future photometric Euclid-like surveys and spectroscopic SKA-like surveys. For the Euclid-like survey we derive a fitting formula for the magnification bias. Our analysis suggests that the cross correlation between different redshift bins is very sensitive to the lensing potential such that the survey canmore » measure the amplitude of the lensing potential at the same level of precision as other standard ΛCDM cosmological parameters.« less

Galactic chemical evolution in hierarchical formation models

NASA Astrophysics Data System (ADS)

Arrigoni, Matias

2010-10-01

The chemical properties and abundance ratios of galaxies provide important information about their formation histories. Galactic chemical evolution has been modelled in detail within the monolithic collapse scenario. These models have successfully described the abundance distributions in our Galaxy and other spiral discs, as well as the trends of metallicity and abundance ratios observed in early-type galaxies. In the last three decades, however, the paradigm of hierarchical assembly in a Cold Dark Matter (CDM) cosmology has revised the picture of how structure in the Universe forms and evolves. In this scenario, galaxies form when gas radiatively cools and condenses inside dark matter haloes, which themselves follow dissipationless gravitational collapse. The CDM picture has been successful at predicting many observed properties of galaxies (for example, the luminosity and stellar mass function of galaxies, color-magnitude or star formation rate vs. stellar mass distributions, relative numbers of early and late-type galaxies, gas fractions and size distributions of spiral galaxies, and the global star formation history), though many potential problems and open questions remain. It is therefore interesting to see whether chemical evolution models, when implemented within this modern cosmological context, are able to correctly predict the observed chemical properties of galaxies. With the advent of more powerfull telescopes and detectors, precise observations of chemical abundances and abundance ratios in various phases (stellar, ISM, ICM) offer the opportunity to obtain strong constraints on galaxy formation histories and the physics that shapes them. However, in order to take advantage of these observations, it is necessary to implement detailed modeling of chemical evolution into a modern cosmological model of hierarchical assembly.

Detectability of [C II] 158 μm Emission from High-Redshift Galaxies: Predictions for ALMA and SPICA

NASA Astrophysics Data System (ADS)

Nagamine, Kentaro; Wolfe, Arthur M.; Hernquist, Lars

2006-08-01

We discuss the detectability of high-redshift galaxies via [C II] 158 μm line emission by coupling an analytic model with cosmological smoothed particle hydrodynamics (SPH) simulations that are based on the concordance Λ cold dark matter (CDM) model. Our analytic model describes a multiphase interstellar medium (ISM) irradiated by the far-ultraviolet (FUV) radiation from local star-forming regions, and it calculates thermal and ionization equilibrium between cooling and heating. The model allows us to predict the mass fraction of a cold neutral medium (CNM) embedded in a warm neutral medium (WNM). Our cosmological SPH simulations include a treatment of radiative cooling/heating, star formation, and feedback effects from supernovae and galactic winds. Using our method, we make predictions for the [C II] luminosity from high-redshift galaxies that can be directly compared with upcoming observations by the Atacama Large Millimeter Array (ALMA) and the Space Infrared Telescope for Cosmology and Astrophysics (SPICA). We find that the number density of high-redshift galaxies detectable by ALMA and SPICA via [C II] emission depends significantly on the amount of neutral gas, which is highly uncertain. Our calculations suggest that, in a CDM universe, most [C II] sources at z=3 are faint objects with Sν<0.01 mJy. Lyman break galaxies (LBGs) brighter than RAB=23.5 mag are expected to have flux densities Sν=1-3 mJy depending on the strength of galactic wind feedback. The recommended observing strategy for ALMA and SPICA is to aim at very bright LBGs or star-forming DRG/BzK galaxies.

The Rh=ct universe

NASA Astrophysics Data System (ADS)

Melia, F.; Shevchuk, A. S. H.

2012-01-01

The backbone of standard cosmology is the Friedmann-Robertson-Walker solution to Einstein's equations of general relativity (GR). In recent years, observations have largely confirmed many of the properties of this model, which are based on a partitioning of the universe's energy density into three primary constituents: matter, radiation and a hypothesized dark energy which, in Λ cold dark matter (ΛCDM), is assumed to be a cosmological constant Λ. Yet with this progress, several unpalatable coincidences (perhaps even inconsistencies) have emerged along with the successful confirmation of expected features. One of these is the observed equality of our gravitational horizon Rh(t0) with the distance ct0 light has travelled since the big bang, in terms of the current age t0 of the universe. This equality is very peculiar because it need not have occurred at all and, if it did, should only have happened once (right now) in the context of ΛCDM. In this paper, we propose an explanation for why this equality may actually be required by GR, through the application of Birkhoff's theorem and the Weyl postulate, at least in the case of a flat space-time. If this proposal is correct, Rh(t) should be equal to ct for all cosmic time t, not just its present value t0. Therefore, models such as ΛCDM would be incomplete because they ascribe the cosmic expansion to variable conditions not consistent with this relativistic constraint. We show that this may be the reason why the observed galaxy correlation function is not consistent with the predictions of the standard model. We suggest that an Rh=ct universe is easily distinguishable from all other models at large redshift (i.e. in the early universe), where the latter all predict a rapid deceleration.

The serendipitous observation of a gravitationally lensed galaxy at z = 0.9057 from the Blanco Cosmology Survey: the Elliot Arc

DOE PAGES

Buckley-Geer, E. J.; Lin, H.; Drabek, E. R.; ...

2011-11-03

We report on the serendipitous discovery in the Blanco Cosmology Survey (BCS) imaging data of a z = 0.9057 galaxy that is being strongly lensed by a massive galaxy cluster at a redshift of z = 0.3838. The lens (BCS J2352-5452) was discovered while examining i- and z-band images being acquired in October 2006 during a BCS observing run. Follow-up spectroscopic observations with the GMOS instrument on the Gemini South 8m telescope confirmed the lensing nature of this system. Using weak plus strong lensing, velocity dispersion, cluster richness N 200, and fitting to an NFW cluster mass density profile, wemore » have made three independent estimates of the mass M 200 which are all very consistent with each other. The combination of the results from the three methods gives M 200 = (5.1 x 1.3) x 10 14 circle_dot, which is fully consistent with the individual measurements. The final NFW concentration c 200 from the combined fit is c 200 = 5.4 -1.1 +1.4. We have compared our measurements of M 200 and c 200 with predictions for (a) clusters from λCDM simulations, (b) lensing selected clusters from simulations, and (c) a real sample of cluster lenses. We find that we are most compatible with the predictions for λCDM simulations for lensing clusters, and we see no evidence based on this one system for an increased concentration compared to λCDM. Finally, using the flux measured from the [OII]3727 line we have determined the star formation rate (SFR) of the source galaxy and find it to be rather modest given the assumed lens magnification.« less

A 14 h-3 Gpc3 study of cosmic homogeneity using BOSS DR12 quasar sample

NASA Astrophysics Data System (ADS)

Laurent, Pierre; Le Goff, Jean-Marc; Burtin, Etienne; Hamilton, Jean-Christophe; Hogg, David W.; Myers, Adam; Ntelis, Pierros; Pâris, Isabelle; Rich, James; Aubourg, Eric; Bautista, Julian; Delubac, Timothée; du Mas des Bourboux, Hélion; Eftekharzadeh, Sarah; Palanque Delabrouille, Nathalie; Petitjean, Patrick; Rossi, Graziano; Schneider, Donald P.; Yeche, Christophe

2016-11-01

The BOSS quasar sample is used to study cosmic homogeneity with a 3D survey in the redshift range 2.2 < z < 2.8. We measure the count-in-sphere, N(< r), i.e. the average number of objects around a given object, and its logarithmic derivative, the fractal correlation dimension, D2(r). For a homogeneous distribution N(< r) propto r3 and D2(r) = 3. Due to the uncertainty on tracer density evolution, 3D surveys can only probe homogeneity up to a redshift dependence, i.e. they probe so-called ``spatial isotropy". Our data demonstrate spatial isotropy of the quasar distribution in the redshift range 2.2 < z < 2.8 in a model-independent way, independent of any FLRW fiducial cosmology, resulting in 3 - langleD2rangle < 1.7 × 10-3 (2 σ) over the range 250 < r < 1200 h-1 Mpc for the quasar distribution. If we assume that quasars do not have a bias much less than unity, this implies spatial isotropy of the matter distribution on large scales. Then, combining with the Copernican principle, we finally get homogeneity of the matter distribution on large scales. Alternatively, using a flat ΛCDM fiducial cosmology with CMB-derived parameters, and measuring the quasar bias relative to this ΛCDM model, our data provide a consistency check of the model, in terms of how homogeneous the Universe is on different scales. D2(r) is found to be compatible with our ΛCDM model on the whole 10 < r < 1200 h-1 Mpc range. For the matter distribution we obtain 3 - langleD2rangle < 5 × 10-5 (2 σ) over the range 250 < r < 1200 h-1 Mpc, consistent with homogeneity on large scales.

Another baryon miracle? Testing solutions to the `missing dwarfs' problem

NASA Astrophysics Data System (ADS)

Trujillo-Gomez, Sebastian; Schneider, Aurel; Papastergis, Emmanouil; Reed, Darren S.; Lake, George

2018-04-01

The dearth of dwarf galaxies in the local Universe is hard to reconcile with the large number of low-mass haloes expected within the concordance Λ cold dark matter (ΛCDM) paradigm. In this paper, we perform a systematic evaluation of the uncertainties affecting the measurement of dark matter halo abundance using galaxy kinematics. Using a large sample of dwarf galaxies with spatially resolved kinematics, we derive a correction to obtain the abundance of galaxies as a function of maximum circular velocity - a direct probe of halo mass - from the line-of-sight velocity function in the Local Volume. This method provides a direct means of comparing the predictions of theoretical models and simulations (including non-standard cosmologies and novel galaxy formation physics) to the observational constraints. The new `galactic Vmax' function is steeper than the line-of-sight velocity function but still shallower than the theoretical CDM expectation, implying that unaccounted baryonic physics may be necessary to reduce the predicted abundance of galaxies. Using the galactic Vmax function, we investigate the theoretical effects of feedback-powered outflows and photoevaporation of gas due to reionization. At the 3σ confidence level, we find that feedback and reionization are not effective enough to reconcile the disagreement. In the case of maximum baryonic effects, the theoretical prediction still deviates significantly from the observations for Vmax < 60 km s-1. CDM predicts at least 1.8 times more galaxies with Vmax = 50 km s-1 and 2.5 times more than observed at 30 km s-1. Recent hydrodynamic simulations seem to resolve the discrepancy but disagree with the properties of observed galaxies with spatially resolved kinematics. This abundance problem might point to the need to modify cosmological predictions at small scales.

Lensing convergence in galaxy clustering in ΛCDM and beyond

NASA Astrophysics Data System (ADS)

Villa, Eleonora; Di Dio, Enea; Lepori, Francesca

2018-04-01

We study the impact of neglecting lensing magnification in galaxy clustering analyses for future galaxy surveys, considering the ΛCDM model and two extensions: massive neutrinos and modifications of General Relativity. Our study focuses on the biases on the constraints and on the estimation of the cosmological parameters. We perform a comprehensive investigation of these two effects for the upcoming photometric and spectroscopic galaxy surveys Euclid and SKA for different redshift binning configurations. We also provide a fitting formula for the magnification bias of SKA. Our results show that the information present in the lensing contribution does improve the constraints on the modified gravity parameters whereas the lensing constraining power is negligible for the ΛCDM parameters. For photometric surveys the estimation is biased for all the parameters if lensing is not taken into account. This effect is particularly significant for the modified gravity parameters. Conversely for spectroscopic surveys the bias is below one sigma for all the parameters. Our findings show the importance of including lensing in galaxy clustering analyses for testing General Relativity and to constrain the parameters which describe its modifications.

Cosmological Studies with Galaxy Clusters, Active Galactic Nuclei, and Strongly Lensed Quasars

NASA Astrophysics Data System (ADS)

Rumbaugh, Nicholas Andrew

The large-scale structure (LSS) of the universe provides scientists with one of the best laboratories for studying Lambda Cold Dark Matter (LambdaCDM) cosmology. Especially at high redshift, we see increased rates of galaxy cluster and galaxy merging in LSS relative to the field, which is useful for studying the hierarchical merging predicted by LambdaCDM. The largest identified bound structures, superclusters, have not yet virialized. Despite the wide range of dynamical states of their constituent galaxies, groups, and clusters, they are all still actively evolving, providing an ideal laboratory in which to study cluster and galaxy evolution. In this dissertation, I present original research on several aspects of LSS and LambdaCDM cosmology. Three separate studies are included, each one focusing on a different aspect. In the first study, we use X-ray and optical observations from nine galaxy clusters at high redshift, some embedded in larger structures and some isolated, to study their evolutionary states. We extract X-ray gas temperatures and luminosities as well as optical velocity dispersions. These cluster properties are compared using low-redshift scaling relations. In addition, we employ several tests of substructure, using velocity histograms, Dressler-Shectman tests, and centroiding offsets. We conclude that two clusters out of our sample are most likely unrelaxed, and find support for deviations from self-similarity in the redshift evolution of the Lx-T relation. Our numerous complementary tests of the evolutionary state of clusters suggest potential under-estimations of systematic error in studies employing only a single such test. In the second study, we use multi-band imaging and spectroscopy to study active galactic nuclei (AGN) in high-redshift LSS. The AGN were identified using X-ray imaging and matched to optical catalogs that contained spectroscopic redshifts to identify members of the structures. AGN host galaxies tended to be associated with the transitional `green valley' on a color-magnitude diagram. Spectral analysis of the AGN hosts showed that the average host galaxy had either on-going or recent star formation, and was younger than the average galaxy, across all LSS in our sample. We further subdivided our sample in two based on the average evolutionary state of the LSS. The AGN in the more evolved structures had lower X-ray luminosities and longer times since last starburst. These results provide some evidence for merger-based AGN triggering, although other mechanisms, and possibly more than one, could be responsible. In the third study, we probed LambdaCDM cosmology from a different angle. An important part of the model is the cosmological parameters that define our universe. As such, probes that can more accurately and precisely measure these parameters, such as H0 and the dark energy equation of state, w, can allow us to more closely inspect the model. Strongly-lensed quasars provide one such probe, and we sought to perform the first step in using them for cosmological inference, which is to measure the time delays between strongly lensed images. We performed radio monitoring campaigns on six strongly lensed quasars using the Very Large Array. Lightcurves were extracted for each lensed image and analyzed for intrinsic variability. Two lensed quasars showed strong time variations, but the variations were linear in time, preventing precise time delay measurements due to a degeneracy with the magnifications. These results suggest most of the systems should be targeted for followup monitoring, and we estimate that time delays can be measured for the most variable systems with precision of 0.5 to 3.5 days with two more seasons of monitoring. In a joint fit with previously studied systems, these measurements could tighten constraints on H 0 by up to ~1.4.

Are There Rotation Measure Gradients Across Active Galactic Nuclei Jets?

DTIC Science & Technology

2010-10-20

transverse RM gradient exists. We assume H0 = 71 km s−1 Mpc−1 and a ΛCDM cosmology with Ωλ = 0.7 and Ωm = 0.3 (e.g., Eisenstein et al. 2005; Hinshaw...O’Sullivan, S. P., & Gabuzda, D. C. 2010, MNRAS, 402, 259 Denn, G. R., Mutel, R. L., & Marscher, A. P. 2000, ApJS, 129, 61 Eisenstein , D. J., et al. 2005

How to Reconcile the Observed Velocity Function of Galaxies with Theory

NASA Astrophysics Data System (ADS)

Brooks, Alyson M.; Papastergis, Emmanouil; Christensen, Charlotte R.; Governato, Fabio; Stilp, Adrienne; Quinn, Thomas R.; Wadsley, James

2017-11-01

Within a Λ cold dark matter (ΛCDM) scenario, we use high-resolution cosmological simulations spanning over four orders of magnitude in galaxy mass to understand the deficit of dwarf galaxies in observed velocity functions (VFs). We measure velocities in as similar a way as possible to observations, including generating mock H I data cubes for our simulated galaxies. We demonstrate that this apples-to-apples comparison yields an “observed” VF in agreement with observations, reconciling the large number of low-mass halos expected in a ΛCDM cosmological model with the low number of observed dwarfs at a given velocity. We then explore the source of the discrepancy between observations and theory and conclude that the dearth of observed dwarf galaxies is primarily explained by two effects. The first effect is that galactic rotational velocities derived from the H I linewidth severely underestimate the maximum halo velocity. The second effect is that a large fraction of halos at the lowest masses are too faint to be detected by current galaxy surveys. We find that cored DM density profiles can contribute to the lower observed velocity of galaxies but only for galaxies in which the velocity is measured interior to the size of the core (˜3 kpc).

Estimating the weak-lensing rotation signal in radio cosmic shear surveys

NASA Astrophysics Data System (ADS)

Thomas, Daniel B.; Whittaker, Lee; Camera, Stefano; Brown, Michael L.

2017-09-01

Weak lensing has become an increasingly important tool in cosmology and the use of galaxy shapes to measure cosmic shear has become routine. The weak-lensing distortion tensor contains two other effects in addition to the two components of shear: the convergence and rotation. The rotation mode is not measurable using the standard cosmic shear estimators based on galaxy shapes, as there is no information on the original shapes of the images before they were lensed. Due to this, no estimator has been proposed for the rotation mode in cosmological weak-lensing surveys, and the rotation mode has never been constrained. Here, we derive an estimator for this quantity, which is based on the use of radio polarization measurements of the intrinsic position angles of galaxies. The rotation mode can be sourced by physics beyond Λ cold dark matter (ΛCDM), and also offers the chance to perform consistency checks of ΛCDM and of weak-lensing surveys themselves. We present simulations of this estimator and show that, for the pedagogical example of cosmic string spectra, this estimator could detect a signal that is consistent with the constraints from Planck. We examine the connection between the rotation mode and the shear B modes and thus how this estimator could help control systematics in future radio weak-lensing surveys.

Model independent inference of the expansion history and implications for the growth of structure

NASA Astrophysics Data System (ADS)

Joudaki, Shahab; Kaplinghat, Manoj; Keeley, Ryan; Kirkby, David

2018-06-01

We model the expansion history of the Universe as a Gaussian process and find constraints on the dark energy density and its low-redshift evolution using distances inferred from the Luminous Red Galaxy and Lyman-alpha data sets of the Baryon Oscillation Spectroscopic Survey, supernova data from the Joint Light-Curve Analysis sample, cosmic microwave background data from the Planck satellite, and local measurement of the Hubble parameter from the Hubble Space Telescope (H 0 ). Our analysis shows that the cosmic microwave background, Luminous Red Galaxy, Lyman-alpha, and Joint Light-Curve Analysis data are consistent with each other and with a Λ CDM cosmology, but the H 0 data are inconsistent at moderate significance. Including the presence of dark radiation does not alleviate the H 0 tension in our analysis. While some of these results have been noted previously, the strength here lies in that we do not assume a particular cosmological model. We calculate the growth of the gravitational potential in General Relativity corresponding to these general expansion histories and show that they are well approximated by Ωm0.55 given the current precision. We assess the prospects for upcoming surveys to measure deviations from Λ CDM using this model-independent approach.

Dark matter component decaying after recombination: Sensitivity to baryon acoustic oscillation and redshift space distortion probes

NASA Astrophysics Data System (ADS)

Chudaykin, A.; Gorbunov, D.; Tkachev, I.

2018-04-01

It has been recently suggested [1] that a subdominant fraction of dark matter decaying after recombination may alleviate tension between high-redshift (CMB anisotropy) and low-redshift (Hubble constant, cluster counts) measurements. In this report, we continue our previous study [2] of the decaying dark matter (DDM) model adding all available recent baryon acoustic oscillation (BAO) and redshift space distortions (RSD) measurements. We find that the BAO/RSD measurements generically prefer the standard Λ CDM and combined with other cosmological measurements impose an upper limit on the DDM fraction at the level of ˜5 %, strengthening by a factor of 1.5 limits obtained in [2] mostly from CMB data. However, the numbers vary from one analysis to other based on the same Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 (DR12) galaxy sample. Overall, the model with a few percent DDM fraction provides a better fit to the combined cosmological data as compared to the Λ CDM : the cluster counting and direct measurements of the Hubble parameter are responsible for that. The improvement can be as large as 1.5 σ and grows to 3.3 σ when the CMB lensing power amplitude AL is introduced as a free fitting parameter.

Demise of faint satellites around isolated early-type galaxies

NASA Astrophysics Data System (ADS)

Park, Changbom; Hwang, Ho Seong; Park, Hyunbae; Lee, Jong Chul

2018-02-01

The hierarchical galaxy formation scenario in the Cold Dark Matter cosmology with a non-vanishing cosmological constant Λ and geometrically flat space (ΛCDM) has been very successful in explaining the large-scale distribution of galaxies. However, there have been claims that ΛCDM over-predicts the number of satellite galaxies associated with massive galaxies compared with observations—the missing satellite galaxy problem1-3. Isolated groups of galaxies hosted by passively evolving massive early-type galaxies are ideal laboratories for identifying the missing physics in the current theory4-11. Here, we report—based on a deep spectroscopic survey—that isolated massive and passive early-type galaxies without any signs of recent wet mergers or accretion episodes have almost no satellite galaxies fainter than the r-band absolute magnitude of about Mr = -14. If only early-type satellites are used, the cutoff is at the somewhat brighter magnitude of about Mr = -15. Such a cutoff has not been found in other nearby satellite galaxy systems hosted by late-type galaxies or those with merger features. Various physical properties of satellites depend strongly on the host-centric distance. Our observations indicate that the satellite galaxy luminosity function is largely determined by the interaction of satellites with the environment provided by their host.

The impact of dark energy on galaxy formation. What does the future of our Universe hold?

NASA Astrophysics Data System (ADS)

Salcido, Jaime; Bower, Richard G.; Barnes, Luke A.; Lewis, Geraint F.; Elahi, Pascal J.; Theuns, Tom; Schaller, Matthieu; Crain, Robert A.; Schaye, Joop

2018-07-01

We investigate the effect of the accelerated expansion of the Universe due to a cosmological constant, Λ, on the cosmic star formation rate. We utilize hydrodynamical simulations from the EAGLE suite, comparing a ΛCDM (cold dark matter) Universe to an Einstein-de Sitter model with Λ = 0. Despite the differences in the rate of growth of structure, we find that dark energy, at its observed value, has negligible impact on star formation in the Universe. We study these effects beyond the present day by allowing the simulations to run forward into the future (t > 13.8 Gyr). We show that the impact of Λ becomes significant only when the Universe has already produced most of its stellar mass, only decreasing the total comoving density of stars ever formed by ≈ 15 per cent. We develop a simple analytic model for the cosmic star formation rate that captures the suppression due to a cosmological constant. The main reason for the similarity between the models is that feedback from accreting black holes dramatically reduces the cosmic star formation at late times. Interestingly, simulations without feedback from accreting black holes predict an upturn in the cosmic star formation rate for t > 15 Gyr due to the rejuvenation of massive (>1011 M⊙) galaxies. We briefly discuss the implication of the weak dependence of the cosmic star formation on Λ in the context of the anthropic principle.

Cosmological consistency tests of gravity theory and cosmic acceleration

NASA Astrophysics Data System (ADS)

Ishak-Boushaki, Mustapha B.

2017-01-01

Testing general relativity at cosmological scales and probing the cause of cosmic acceleration are among the important objectives targeted by incoming and future astronomical surveys and experiments. I present our recent results on consistency tests that can provide insights about the underlying gravity theory and cosmic acceleration using cosmological data sets. We use statistical measures, the rate of cosmic expansion, the growth rate of large scale structure, and the physical consistency of these probes with one another.

Relativistic initial conditions for N-body simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fidler, Christian; Tram, Thomas; Crittenden, Robert

2017-06-01

Initial conditions for (Newtonian) cosmological N-body simulations are usually set by re-scaling the present-day power spectrum obtained from linear (relativistic) Boltzmann codes to the desired initial redshift of the simulation. This back-scaling method can account for the effect of inhomogeneous residual thermal radiation at early times, which is absent in the Newtonian simulations. We analyse this procedure from a fully relativistic perspective, employing the recently-proposed Newtonian motion gauge framework. We find that N-body simulations for ΛCDM cosmology starting from back-scaled initial conditions can be self-consistently embedded in a relativistic space-time with first-order metric potentials calculated using a linear Boltzmann code.more » This space-time coincides with a simple ''N-body gauge'' for z < 50 for all observable modes. Care must be taken, however, when simulating non-standard cosmologies. As an example, we analyse the back-scaling method in a cosmology with decaying dark matter, and show that metric perturbations become large at early times in the back-scaling approach, indicating a breakdown of the perturbative description. We suggest a suitable ''forwards approach' for such cases.« less

Holographic dark energy with cosmological constant

NASA Astrophysics Data System (ADS)

Hu, Yazhou; Li, Miao; Li, Nan; Zhang, Zhenhui

2015-08-01

Inspired by the multiverse scenario, we study a heterotic dark energy model in which there are two parts, the first being the cosmological constant and the second being the holographic dark energy, thus this model is named the ΛHDE model. By studying the ΛHDE model theoretically, we find that the parameters d and Ωhde are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the ΛHDE model by using the recent observational data. We find the model yields χ2min=426.27 when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant ΛCDM model (431.35). At 68.3% CL, we obtain -0.07<ΩΛ0<0.68 and correspondingly 0.04<Ωhde0<0.79, implying at present there is considerable degeneracy between the holographic dark energy and cosmological constant components in the ΛHDE model.

Competing explanations for cosmic acceleration or why is the expansion of the universe accelerating?

NASA Astrophysics Data System (ADS)

Ishak, Mustapha

2012-06-01

For more than a decade, a number of cosmological observations have been indicating that the expansion of the universe is accelerating. Cosmic acceleration and the questions associated with it have become one of the most challenging and puzzling problems in cosmology and physics. Cosmic acceleration can be caused by (i) a repulsive dark energy pervading the universe, (ii) an extension to General Relativity that takes effect at cosmological scales of distance, or (iii) the acceleration may be an apparent effect due to the fact that the expansion rate of space-time is uneven from one region to another in the universe. I will review the basics of these possibilities and provide some recent results including ours on these questions.

The little sibling of the big rip singularity

NASA Astrophysics Data System (ADS)

Bouhmadi-López, Mariam; Errahmani, Ahmed; Martín-Moruno, Prado; Ouali, Taoufik; Tavakoli, Yaser

2015-07-01

In this paper, we present a new cosmological event, which we named the little sibling of the big rip. This event is much smoother than the big rip singularity. When the little sibling of the big rip is reached, the Hubble rate and the scale factor blow up, but the cosmic derivative of the Hubble rate does not. This abrupt event takes place at an infinite cosmic time where the scalar curvature explodes. We show that a doomsday à la little sibling of the big rip is compatible with an accelerating universe, indeed at present it would mimic perfectly a ΛCDM scenario. It turns out that, even though the event seems to be harmless as it takes place in the infinite future, the bound structures in the universe would be unavoidably destroyed on a finite cosmic time from now. The model can be motivated by considering that the weak energy condition should not be strongly violated in our universe, and it could give us some hints about the status of recently formulated nonlinear energy conditions.

THE DIMENSIONLESS AGE OF THE UNIVERSE: A RIDDLE FOR OUR TIME

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avelino, Arturo; Kirshner, Robert P., E-mail: aavelino@cfa.harvard.edu

We present the interesting coincidence of cosmology and astrophysics that points toward a dimensionless age of the Universe H {sub 0} t {sub 0} that is close to one. Despite cosmic deceleration for 9 Gyr and acceleration since then, we find H {sub 0} t {sub 0} = 0.96 ± 0.01 for the ΛCDM model that fits SN Ia data from Pan-STARRS, CMB power spectra, and baryon acoustic oscillations. Similarly, astrophysical measures of stellar ages and the Hubble constant derived from redshifts and distances point to H {sub 0} t ∼ 1.0 ± 0.1. The wide range of possible valuesmore » for H {sub 0} t {sub 0} realized during cosmic evolution means that we live at what appears to be a special time. This “synchronicity problem” is not precisely the same as the usual coincidence problem , because there are combinations of Ω{sub M} and Ω{sub Λ} for which the usual coincidence problem holds but for which H {sub 0} t {sub 0} is not close to 1.« less

Reconstruction, thermodynamics and stability of the ΛCDM model in f(T,{ T }) gravity

NASA Astrophysics Data System (ADS)

Junior, Ednaldo L. B.; Rodrigues, Manuel E.; Salako, Ines G.; Houndjo, Mahouton J. S.

2016-06-01

We reconstruct the ΛCDM model for f(T,{ T }) theory, where T is the torsion scalar and { T } the trace of the energy-momentum tensor. The result shows that the action of ΛCDM is a combination of a linear term, a constant (-2{{Λ }}) and a nonlinear term given by the product \\sqrt{-T}{F}g[({T}1/3/16π G) (16π G{ T }+T+8{{Λ }})], with F g being a generic function. We show that to maintain conservation of the energy-momentum tensor, we should impose that {F}g[y] must be linear on the trace { T }. This reconstruction decays in f (T) theory for {F}g\\equiv Q, with Q a constant. Our reconstruction describes the cosmological eras to the present time. The model present stability within the geometric and matter perturbations for the choice {F}g=y, where y=({T}1/3/16π G)(16π G{ T }+T+8{{Λ }}), except for the geometric part in the de Sitter model. We impose the first and second laws of thermodynamics to ΛCDM and find the condition where they are satisfied, that is, {T}A,{G}{{eff}}\\gt 0, however where this is not possible in the cases that we choose, this leads to a breakdown of positive entropy and Misner-Sharp energy.

Angular Baryon Acoustic Oscillation measure at z=2.225 from the SDSS quasar survey

NASA Astrophysics Data System (ADS)

de Carvalho, E.; Bernui, A.; Carvalho, G. C.; Novaes, C. P.; Xavier, H. S.

2018-04-01

Following a quasi model-independent approach we measure the transversal BAO mode at high redshift using the two-point angular correlation function (2PACF). The analyses done here are only possible now with the quasar catalogue from the twelfth data release (DR12Q) from the Sloan Digital Sky Survey, because it is spatially dense enough to allow the measurement of the angular BAO signature with moderate statistical significance and acceptable precision. Our analyses with quasars in the redshift interval z in [2.20,2.25] produce the angular BAO scale θBAO = 1.77° ± 0.31° with a statistical significance of 2.12 σ (i.e., 97% confidence level), calculated through a likelihood analysis performed using the theoretical covariance matrix sourced by the analytical power spectra expected in the ΛCDM concordance model. Additionally, we show that the BAO signal is robust—although with less statistical significance—under diverse bin-size choices and under small displacements of the quasars' angular coordinates. Finally, we also performed cosmological parameter analyses comparing the θBAO predictions for wCDM and w(a)CDM models with angular BAO data available in the literature, including the measurement obtained here, jointly with CMB data. The constraints on the parameters ΩM, w0 and wa are in excellent agreement with the ΛCDM concordance model.

Signatures of Higgs dilaton and critical Higgs inflation.

PubMed

García-Bellido, Juan

2018-03-06

We test the Higgs dilaton inflation model (HDM) using the latest cosmological datasets, including the cosmic microwave background temperature, polarization and lensing data from the Planck satellite (2015), the BICEP and Keck Array experiments, the type Ia supernovae from the JLA catalogue, the baryon acoustic oscillations from CMASS, LOWZ and 6dF, the weak lensing data from the CFHTLenS survey and the matter power spectrum measurements from the latest SDSS data release. We find that the values of all cosmological parameters allowed by the HDM are well within the Planck satellite (2015) constraints. In particular, we determine [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] (at 95.5% c.l.). We also place new stringent constraints on the couplings of the HDM, ξ χ <0.00328 and [Formula: see text] (at 95.5% c.l.). We find that the HDM is only slightly better than the w 0 w a CDM model, with [Formula: see text] Given that the HDM has two fewer parameters, we find Bayesian evidence favouring the HDM over the w 0 w a CDM model. We also study the critical Higgs inflation model, taking into account the running of both the self-coupling λ( μ ) and the non-minimal coupling to gravity ξ ( μ ). We find peaks in the curvature power spectrum at scales corresponding to the critical value μ that re-enter during the radiation era and collapse to form a broad distribution of clustered primordial black holes, which could constitute today the main component of dark matter.This article is part of the Theo Murphy meeting issue 'Higgs cosmology'. © 2018 The Author(s).

Testing core creation in hydrodynamical simulations using the HI kinematics of field dwarfs

NASA Astrophysics Data System (ADS)

Papastergis, E.; Ponomareva, A. A.

2017-05-01

The majority of recent hydrodynamical simulations indicate the creation of central cores in the mass profiles of low-mass halos, a process that is attributed to star formation-related baryonic feedback. Core creation is regarded as one of the most promising solutions to potential issues faced by lambda cold dark matter (ΛCDM) cosmology on small scales. For example, the reduced dynamical mass enclosed by cores can explain the low rotational velocities measured for nearby dwarf galaxies, thus possibly lifting the seeming contradiction with the ΛCDM expectations (the so-called "too big to fail" problem). Here we test core creation as a solution of cosmological issues by using a sample of dwarfs with measurements of their atomic hydrogen (HI) kinematics extending to large radii. Using the NIHAO hydrodynamical simulation as an example, we show that core creation can successfully reproduce the kinematics of dwarfs with small kinematic radii, R ≲ 1.5 kpc. However, the agreement with observations becomes poor once galaxies with kinematic measurements extending beyond the core region, R ≈ 1.5-4 kpc, are considered. This result illustrates the importance of testing the predictions of hydrodynamical simulations that are relevant for cosmology against a broad range of observational samples. We would like to stress that our result is valid only under the following set of assumptions: I) that our sample of dwarfs with HI kinematics is representative of the overall population of field dwarfs; II) that there are no severe measurement biases in the observational parameters of our HI dwarfs (e.g., related to inclination estimates); and III) that the HI velocity fields of dwarfs are regular enough to allow the recovery of the true enclosed dynamical mass.

Planck 2015 results. XXIV. Cosmology from Sunyaev-Zeldovich cluster counts

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Battye, R.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chiang, H. C.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Melin, J.-B.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Roman, M.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Weller, J.; White, S. D. M.; Yvon, D.; Zacchei, A.; Zonca, A.

2016-09-01

We present cluster counts and corresponding cosmological constraints from the Planck full mission data set. Our catalogue consists of 439 clusters detected via their Sunyaev-Zeldovich (SZ) signal down to a signal-to-noise ratio of 6, and is more than a factor of 2 larger than the 2013 Planck cluster cosmology sample. The counts are consistent with those from 2013 and yield compatible constraints under the same modelling assumptions. Taking advantage of the larger catalogue, we extend our analysis to the two-dimensional distribution in redshift and signal-to-noise. We use mass estimates from two recent studies of gravitational lensing of background galaxies by Planck clusters to provide priors on the hydrostatic bias parameter, (1-b). In addition, we use lensing of cosmic microwave background (CMB) temperature fluctuations by Planck clusters as an independent constraint on this parameter. These various calibrations imply constraints on the present-day amplitude of matter fluctuations in varying degrees of tension with those from the Planck analysis of primary fluctuations in the CMB; for the lowest estimated values of (1-b) the tension is mild, only a little over one standard deviation, while it remains substantial (3.7σ) for the largest estimated value. We also examine constraints on extensions to the base flat ΛCDM model by combining the cluster and CMB constraints. The combination appears to favour non-minimal neutrino masses, but this possibility does little to relieve the overall tension because it simultaneously lowers the implied value of the Hubble parameter, thereby exacerbating the discrepancy with most current astrophysical estimates. Improving the precision of cluster mass calibrations from the current 10%-level to 1% would significantly strengthen these combined analyses and provide a stringent test of the base ΛCDM model.

Planck 2015 results: XXIV. Cosmology from Sunyaev-Zeldovich cluster counts

DOE PAGES

Ade, P. A. R.; Aghanim, N.; Arnaud, M.; ...

2016-09-20

In this work, we present cluster counts and corresponding cosmological constraints from the Planck full mission data set. Our catalogue consists of 439 clusters detected via their Sunyaev-Zeldovich (SZ) signal down to a signal-to-noise ratio of 6, and is more than a factor of 2 larger than the 2013 Planck cluster cosmology sample. The counts are consistent with those from 2013 and yield compatible constraints under the same modelling assumptions. Taking advantage of the larger catalogue, we extend our analysis to the two-dimensional distribution in redshift and signal-to-noise. We use mass estimates from two recent studies of gravitational lensing ofmore » background galaxies by Planck clusters to provide priors on the hydrostatic bias parameter, (1-b). In addition, we use lensing of cosmic microwave background (CMB) temperature fluctuations by Planck clusters as an independent constraint on this parameter. These various calibrations imply constraints on the present-day amplitude of matter fluctuations in varying degrees of tension with those from the Planck analysis of primary fluctuations in the CMB; for the lowest estimated values of (1-b) the tension is mild, only a little over one standard deviation, while it remains substantial (3.7σ) for the largest estimated value. We also examine constraints on extensions to the base flat ΛCDM model by combining the cluster and CMB constraints. The combination appears to favour non-minimal neutrino masses, but this possibility does little to relieve the overall tension because it simultaneously lowers the implied value of the Hubble parameter, thereby exacerbating the discrepancy with most current astrophysical estimates. In conclusion, improving the precision of cluster mass calibrations from the current 10%-level to 1% would significantly strengthen these combined analyses and provide a stringent test of the base ΛCDM model.« less

Planck 2015 results: XXIV. Cosmology from Sunyaev-Zeldovich cluster counts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ade, P. A. R.; Aghanim, N.; Arnaud, M.

In this work, we present cluster counts and corresponding cosmological constraints from the Planck full mission data set. Our catalogue consists of 439 clusters detected via their Sunyaev-Zeldovich (SZ) signal down to a signal-to-noise ratio of 6, and is more than a factor of 2 larger than the 2013 Planck cluster cosmology sample. The counts are consistent with those from 2013 and yield compatible constraints under the same modelling assumptions. Taking advantage of the larger catalogue, we extend our analysis to the two-dimensional distribution in redshift and signal-to-noise. We use mass estimates from two recent studies of gravitational lensing ofmore » background galaxies by Planck clusters to provide priors on the hydrostatic bias parameter, (1-b). In addition, we use lensing of cosmic microwave background (CMB) temperature fluctuations by Planck clusters as an independent constraint on this parameter. These various calibrations imply constraints on the present-day amplitude of matter fluctuations in varying degrees of tension with those from the Planck analysis of primary fluctuations in the CMB; for the lowest estimated values of (1-b) the tension is mild, only a little over one standard deviation, while it remains substantial (3.7σ) for the largest estimated value. We also examine constraints on extensions to the base flat ΛCDM model by combining the cluster and CMB constraints. The combination appears to favour non-minimal neutrino masses, but this possibility does little to relieve the overall tension because it simultaneously lowers the implied value of the Hubble parameter, thereby exacerbating the discrepancy with most current astrophysical estimates. In conclusion, improving the precision of cluster mass calibrations from the current 10%-level to 1% would significantly strengthen these combined analyses and provide a stringent test of the base ΛCDM model.« less

Rotation curves of high-resolution LSB and SPARC galaxies with fuzzy and multistate (ultralight boson) scalar field dark matter

NASA Astrophysics Data System (ADS)

Bernal, T.; Fernández-Hernández, L. M.; Matos, T.; Rodríguez-Meza, M. A.

2018-04-01

Cold dark matter (CDM) has shown to be an excellent candidate for the dark matter (DM) of the Universe at large scales; however, it presents some challenges at the galactic level. The scalar field dark matter (SFDM), also called fuzzy, wave, Bose-Einstein condensate, or ultralight axion DM, is identical to CDM at cosmological scales but different at the galactic ones. SFDM forms core haloes, it has a natural cut-off in its matter power spectrum, and it predicts well-formed galaxies at high redshifts. In this work we reproduce the rotation curves of high-resolution low surface brightness (LSB) and SPARC galaxies with two SFDM profiles: (1) the soliton+NFW profile in the fuzzy DM (FDM) model, arising empirically from cosmological simulations of real, non-interacting scalar field (SF) at zero temperature, and (2) the multistate SFDM (mSFDM) profile, an exact solution to the Einstein-Klein-Gordon equations for a real, self-interacting SF, with finite temperature into the SF potential, introducing several quantum states as a realistic model for an SFDM halo. From the fits with the soliton+NFW profile, we obtained for the boson mass 0.212 < mψ/(10-23 eV/c2) < 27.0 and for the core radius 0.326 < rc/kpc < 8.96. From the combined analysis with the LSB galaxies, we obtained mψ = 0.554 × 10-23 eV, a result in tension with the severe cosmological constraints. Also, we show the analytical mSFDM model fits the observations as well as or better than the empirical soliton+NFW profile, and it reproduces naturally the wiggles present in some galaxies, being a theoretically motivated framework additional or alternative to the FDM profile.

Order statistics applied to the most massive and most distant galaxy clusters

NASA Astrophysics Data System (ADS)

Waizmann, J.-C.; Ettori, S.; Bartelmann, M.

2013-06-01

In this work, we present an analytic framework for calculating the individual and joint distributions of the nth most massive or nth highest redshift galaxy cluster for a given survey characteristic allowing us to formulate Λ cold dark matter (ΛCDM) exclusion criteria. We show that the cumulative distribution functions steepen with increasing order, giving them a higher constraining power with respect to the extreme value statistics. Additionally, we find that the order statistics in mass (being dominated by clusters at lower redshifts) is sensitive to the matter density and the normalization of the matter fluctuations, whereas the order statistics in redshift is particularly sensitive to the geometric evolution of the Universe. For a fixed cosmology, both order statistics are efficient probes of the functional shape of the mass function at the high-mass end. To allow a quick assessment of both order statistics, we provide fits as a function of the survey area that allow percentile estimation with an accuracy better than 2 per cent. Furthermore, we discuss the joint distributions in the two-dimensional case and find that for the combination of the largest and the second largest observation, it is most likely to find them to be realized with similar values with a broadly peaked distribution. When combining the largest observation with higher orders, it is more likely to find a larger gap between the observations and when combining higher orders in general, the joint probability density function peaks more strongly. Having introduced the theory, we apply the order statistical analysis to the Southpole Telescope (SPT) massive cluster sample and metacatalogue of X-ray detected clusters of galaxies catalogue and find that the 10 most massive clusters in the sample are consistent with ΛCDM and the Tinker mass function. For the order statistics in redshift, we find a discrepancy between the data and the theoretical distributions, which could in principle indicate a deviation from the standard cosmology. However, we attribute this deviation to the uncertainty in the modelling of the SPT survey selection function. In turn, by assuming the ΛCDM reference cosmology, order statistics can also be utilized for consistency checks of the completeness of the observed sample and of the modelling of the survey selection function.

The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological analysis of the DR12 galaxy sample

NASA Astrophysics Data System (ADS)

Alam, Shadab; Ata, Metin; Bailey, Stephen; Beutler, Florian; Bizyaev, Dmitry; Blazek, Jonathan A.; Bolton, Adam S.; Brownstein, Joel R.; Burden, Angela; Chuang, Chia-Hsun; Comparat, Johan; Cuesta, Antonio J.; Dawson, Kyle S.; Eisenstein, Daniel J.; Escoffier, Stephanie; Gil-Marín, Héctor; Grieb, Jan Niklas; Hand, Nick; Ho, Shirley; Kinemuchi, Karen; Kirkby, David; Kitaura, Francisco; Malanushenko, Elena; Malanushenko, Viktor; Maraston, Claudia; McBride, Cameron K.; Nichol, Robert C.; Olmstead, Matthew D.; Oravetz, Daniel; Padmanabhan, Nikhil; Palanque-Delabrouille, Nathalie; Pan, Kaike; Pellejero-Ibanez, Marcos; Percival, Will J.; Petitjean, Patrick; Prada, Francisco; Price-Whelan, Adrian M.; Reid, Beth A.; Rodríguez-Torres, Sergio A.; Roe, Natalie A.; Ross, Ashley J.; Ross, Nicholas P.; Rossi, Graziano; Rubiño-Martín, Jose Alberto; Saito, Shun; Salazar-Albornoz, Salvador; Samushia, Lado; Sánchez, Ariel G.; Satpathy, Siddharth; Schlegel, David J.; Schneider, Donald P.; Scóccola, Claudia G.; Seo, Hee-Jong; Sheldon, Erin S.; Simmons, Audrey; Slosar, Anže; Strauss, Michael A.; Swanson, Molly E. C.; Thomas, Daniel; Tinker, Jeremy L.; Tojeiro, Rita; Magaña, Mariana Vargas; Vazquez, Jose Alberto; Verde, Licia; Wake, David A.; Wang, Yuting; Weinberg, David H.; White, Martin; Wood-Vasey, W. Michael; Yèche, Christophe; Zehavi, Idit; Zhai, Zhongxu; Zhao, Gong-Bo

2017-09-01

We present cosmological results from the final galaxy clustering data set of the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. Our combined galaxy sample comprises 1.2 million massive galaxies over an effective area of 9329 deg2 and volume of 18.7 Gpc3, divided into three partially overlapping redshift slices centred at effective redshifts 0.38, 0.51 and 0.61. We measure the angular diameter distance DM and Hubble parameter H from the baryon acoustic oscillation (BAO) method, in combination with a cosmic microwave background prior on the sound horizon scale, after applying reconstruction to reduce non-linear effects on the BAO feature. Using the anisotropic clustering of the pre-reconstruction density field, we measure the product DMH from the Alcock-Paczynski (AP) effect and the growth of structure, quantified by fσ8(z), from redshift-space distortions (RSD). We combine individual measurements presented in seven companion papers into a set of consensus values and likelihoods, obtaining constraints that are tighter and more robust than those from any one method; in particular, the AP measurement from sub-BAO scales sharpens constraints from post-reconstruction BAOs by breaking degeneracy between DM and H. Combined with Planck 2016 cosmic microwave background measurements, our distance scale measurements simultaneously imply curvature ΩK = 0.0003 ± 0.0026 and a dark energy equation-of-state parameter w = -1.01 ± 0.06, in strong affirmation of the spatially flat cold dark matter (CDM) model with a cosmological constant (ΛCDM). Our RSD measurements of fσ8, at 6 per cent precision, are similarly consistent with this model. When combined with supernova Ia data, we find H0 = 67.3 ± 1.0 km s-1 Mpc-1 even for our most general dark energy model, in tension with some direct measurements. Adding extra relativistic species as a degree of freedom loosens the constraint only slightly, to H0 = 67.8 ± 1.2 km s-1 Mpc-1. Assuming flat ΛCDM, we find Ωm = 0.310 ± 0.005 and H0 = 67.6 ± 0.5 km s-1 Mpc-1, and we find a 95 per cent upper limit of 0.16 eV c-2 on the neutrino mass sum.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nersisyan, Henrik; Cid, Adrian Fernandez; Amendola, Luca, E-mail: h.nersisyan@thphys.uni-heidelberg.de, E-mail: fernandez@thphys.uni-heidelberg.de, E-mail: l.amendola@thphys.uni-heidelberg.de

In this work, we extend previous analyses of the structure formation in the f (□{sup −1} R ) model of nonlocal gravity proposed by Deser and Woodard (DW), which reproduces the background expansion of ΛCDM with no need of a cosmological constant nor of any dimensional constant beside Newton's one. A previous analysis based on redshift-space distortions (RSD) data concluded that the model was ruled out. In this work we revisit the issue and find that, when recast in a localized model, the DW model is not ruled out and actually gives a better fit to RSD data than ΛCDM.more » In fact, the DW model presents a suppressed growth of matter perturbations with respect to ΛCDM and a slightly lower value of σ{sub 8}, as favored by observations. We also produce analytical approximations of the two modified gravity functions, i.e. the anisotropic stress η and the relative change of Newton's constant Y , and of f σ{sub 8}( z ) as a function of redshift. Finally, we also show how much the fit depends on initial conditions when these are generalized with respect to a standard matter-dominated era.« less

Distinguishing cold dark matter dwarfs from self-interacting dark matter dwarfs in baryonic simulations

NASA Astrophysics Data System (ADS)

Strickland, Emily; Fitts, Alex; Boylan-Kolchin, Michael

2018-01-01

Our collaboration has simulated several high-resolution (mbaryon = 500Mo, mdm = 2500Mo) cosmological zoom-in simulations of isolated dwarf galaxies. We simulate each galaxy in standard cold dark matter (ΛCDM) as well as a self-interacting dark matter (SIDM) (with a cross section of σ/m ~ 1 cm2/g), both with and without baryons, to identify distinguishing characteristics between the two. The simulations are run using GIZMO, a meshless-finite-mass (MFM) hydrodynamical code, and are part of the Feedback in Realistic Environments (FIRE) project. By analyzing both the global properties and inner structure of the dwarfs in varying dark matter prescriptions, we provide a side-by-side comparison of isolated, dark matter dominated galaxies at the mass scale where differences in the two models of dark matter are thought to be the most obvious. We find that the edge of classical dwarfs and ultra-faint dwarfs (UFDs) (at ~105 Mo) provides the clearest window for distinguishing between the two theories. Here our SIDM galaxies continue to display a cored inner profile unlike their CDM counterparts. The SIDM versions of each galaxy also have measurably lower stellar velocity dispersions than their CDM counterparts.

Indications of a late-time interaction in the dark sector.

PubMed

Salvatelli, Valentina; Said, Najla; Bruni, Marco; Melchiorri, Alessandro; Wands, David

2014-10-31

We show that a general late-time interaction between cold dark matter and vacuum energy is favored by current cosmological data sets. We characterize the strength of the coupling by a dimensionless parameter q(V) that is free to take different values in four redshift bins from the primordial epoch up to today. This interacting scenario is in agreement with measurements of cosmic microwave background temperature anisotropies from the Planck satellite, supernovae Ia from Union 2.1 and redshift space distortions from a number of surveys, as well as with combinations of these different data sets. Our analysis of the 4-bin interaction shows that a nonzero interaction is likely at late times. We then focus on the case q(V)≠0 in a single low-redshift bin, obtaining a nested one parameter extension of the standard ΛCDM model. We study the Bayesian evidence, with respect to ΛCDM, of this late-time interaction model, finding moderate evidence for an interaction starting at z=0.9, dependent upon the prior range chosen for the interaction strength parameter q(V). For this case the null interaction (q(V)=0, i.e., ΛCDM) is excluded at 99% C.L.

The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

NASA Technical Reports Server (NTRS)

Louis, Thibaut; Grace, Emily; Hasselfield, Matthew; Lungu, Marius; Maurin, Loic; Addison, Graeme E.; Adem Peter A. R.; Aiola, Simone; Allison, Rupert; Amiri, Mandana;

The Atacama Cosmology Telescope: two-season ACTPol spectra and parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Louis, Thibaut; Grace, Emily; Aiola, Simone

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013–14 using two detector arrays at 149 GHz, from 548 deg{sup 2} of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008–10, in combination with planck and wmap data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the ΛCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters thanmore » the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. The new ACTPol data provide information on damping tail parameters. The joint uncertainty on the number of neutrino species and the primordial helium fraction is reduced by 20% when adding ACTPol to Planck temperature data alone.« less

The Atacama Cosmology Telescope: two-season ACTPol spectra and parameters

NASA Astrophysics Data System (ADS)

Louis, Thibaut; Grace, Emily; Hasselfield, Matthew; Lungu, Marius; Maurin, Loïc; Addison, Graeme E.; Ade, Peter A. R.; Aiola, Simone; Allison, Rupert; Amiri, Mandana; Angile, Elio; Battaglia, Nicholas; Beall, James A.; de Bernardis, Francesco; Bond, J. Richard; Britton, Joe; Calabrese, Erminia; Cho, Hsiao-mei; Choi, Steve K.; Coughlin, Kevin; Crichton, Devin; Crowley, Kevin; Datta, Rahul; Devlin, Mark J.; Dicker, Simon R.; Dunkley, Joanna; Dünner, Rolando; Ferraro, Simone; Fox, Anna E.; Gallardo, Patricio; Gralla, Megan; Halpern, Mark; Henderson, Shawn; Hill, J. Colin; Hilton, Gene C.; Hilton, Matt; Hincks, Adam D.; Hlozek, Renée; Ho, S. P. Patty; Huang, Zhiqi; Hubmayr, Johannes; Huffenberger, Kevin M.; Hughes, John P.; Infante, Leopoldo; Irwin, Kent; Muya Kasanda, Simon; Klein, Jeff; Koopman, Brian; Kosowsky, Arthur; Li, Dale; Madhavacheril, Mathew; Marriage, Tobias A.; McMahon, Jeff; Menanteau, Felipe; Moodley, Kavilan; Munson, Charles; Naess, Sigurd; Nati, Federico; Newburgh, Laura; Nibarger, John; Niemack, Michael D.; Nolta, Michael R.; Nuñez, Carolina; Page, Lyman A.; Pappas, Christine; Partridge, Bruce; Rojas, Felipe; Schaan, Emmanuel; Schmitt, Benjamin L.; Sehgal, Neelima; Sherwin, Blake D.; Sievers, Jon; Simon, Sara; Spergel, David N.; Staggs, Suzanne T.; Switzer, Eric R.; Thornton, Robert; Trac, Hy; Treu, Jesse; Tucker, Carole; Van Engelen, Alexander; Ward, Jonathan T.; Wollack, Edward J.

2017-06-01

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013-14 using two detector arrays at 149 GHz, from 548 deg2 of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with planck and wmap data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the ΛCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. The new ACTPol data provide information on damping tail parameters. The joint uncertainty on the number of neutrino species and the primordial helium fraction is reduced by 20% when adding ACTPol to Planck temperature data alone.

νΛMDM: A model for sterile neutrino and dark matter reconciles cosmological and neutrino oscillation data after BICEP2

NASA Astrophysics Data System (ADS)

Ko, P.; Tang, Yong

2014-12-01

We propose an ultraviolet complete theory for cold dark matter (CDM) and sterile neutrinos that can accommodate both cosmological data and neutrino oscillation experiments within 1σ level. We assume a new U(1)X dark gauge symmetry which is broken at ∼ O (MeV) scale resulting light dark photon. Such a light mediator for DM's self-scattering and scattering-off sterile neutrinos can resolve three controversies for cold DM on small cosmological scales: cusp vs. core, too-big-to-fail and missing satellites. We can also accommodate ∼ O (1) eV scale sterile neutrinos as the hot dark matter (HDM) and can fit some neutrino anomalies from neutrino oscillation experiments within 1σ. Finally, the right amount of HDM can make a sizable contribution to dark radiation, and also helps to reconcile the tension between the data on the tensor-to-scalar ratio reported by Planck and BICEP2 Collaborations.

Impact of theoretical priors in cosmological analyses: The case of single field quintessence

NASA Astrophysics Data System (ADS)

Peirone, Simone; Martinelli, Matteo; Raveri, Marco; Silvestri, Alessandra

2017-09-01

We investigate the impact of general conditions of theoretical stability and cosmological viability on dynamical dark energy models. As a powerful example, we study whether minimally coupled, single field quintessence models that are safe from ghost instabilities, can source the Chevallier-Polarski-Linder (CPL) expansion history recently shown to be mildly favored by a combination of cosmic microwave background (Planck) and weak lensing (KiDS) data. We find that in their most conservative form, the theoretical conditions impact the analysis in such a way that smooth single field quintessence becomes significantly disfavored with respect to the standard Λ CDM cosmological model. This is due to the fact that these conditions cut a significant portion of the (w0,wa) parameter space for CPL, in particular, eliminating the region that would be favored by weak lensing data. Within the scenario of a smooth dynamical dark energy parametrized with CPL, weak lensing data favors a region that would require multiple fields to ensure gravitational stability.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petiteau, Antoine; Babak, Stanislav; Sesana, Alberto

Gravitational wave (GW) signals from coalescing massive black hole (MBH) binaries could be used as standard sirens to measure cosmological parameters. The future space-based GW observatory Laser Interferometer Space Antenna (LISA) will detect up to a hundred of those events, providing very accurate measurements of their luminosity distances. To constrain the cosmological parameters, we also need to measure the redshift of the galaxy (or cluster of galaxies) hosting the merger. This requires the identification of a distinctive electromagnetic event associated with the binary coalescence. However, putative electromagnetic signatures may be too weak to be observed. Instead, we study here themore » possibility of constraining the cosmological parameters by enforcing statistical consistency between all the possible hosts detected within the measurement error box of a few dozen of low-redshift (z < 3) events. We construct MBH populations using merger tree realizations of the dark matter hierarchy in a {Lambda}CDM universe, and we use data from the Millennium simulation to model the galaxy distribution in the LISA error box. We show that, assuming that all the other cosmological parameters are known, the parameter w describing the dark energy equation of state can be constrained to a 4%-8% level (2{sigma} error), competitive with current uncertainties obtained by type Ia supernovae measurements, providing an independent test of our cosmological model.« less

Cosmological implications of primordial black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luis Bernal, José; Bellomo, Nicola; Raccanelli, Alvise

The possibility that a relevant fraction of the dark matter might be comprised of Primordial Black Holes (PBHs) has been seriously reconsidered after LIGO's detection of a ∼ 30 M {sub ⊙} binary black holes merger. Despite the strong interest in the model, there is a lack of studies on possible cosmological implications and effects on cosmological parameters inference. We investigate correlations with the other standard cosmological parameters using cosmic microwave background observations, finding significant degeneracies, especially with the tilt of the primordial power spectrum and the sound horizon at radiation drag. However, these degeneracies can be greatly reduced withmore » the inclusion of small scale polarization data. We also explore if PBHs as dark matter in simple extensions of the standard ΛCDM cosmological model induces extra degeneracies, especially between the additional parameters and the PBH's ones. Finally, we present cosmic microwave background constraints on the fraction of dark matter in PBHs, not only for monochromatic PBH mass distributions but also for popular extended mass distributions. Our results show that extended mass distribution's constraints are tighter, but also that a considerable amount of constraining power comes from the high-ℓ polarization data. Moreover, we constrain the shape of such mass distributions in terms of the correspondent constraints on the PBH mass fraction.« less

Smoot Cosmology Group

Science.gov Websites

Links We bring the universe to you! University of California Berkeley Cosmology Group Lawrence Computational Cosmology Center Institute for Nuclear & Particle Astrophysics Supernova Acceleration Probe

Cosmology with decaying cosmological constant—exact solutions and model testing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szydłowski, Marek; Stachowski, Aleksander, E-mail: marek.szydlowski@uj.edu.pl, E-mail: aleksander.stachowski@uj.edu.pl

We study dynamics of Λ(t) cosmological models which are a natural generalization of the standard cosmological model (the ΛCDM model). We consider a class of models: the ones with a prescribed form of Λ(t)=Λ{sub bare}+α{sup 2}/t{sup 2}. This type of a Λ(t) parametrization is motivated by different cosmological approaches. We interpret the model with running Lambda (Λ(t)) as a special model of an interacting cosmology with the interaction term −dΛ(t)/dt in which energy transfer is between dark matter and dark energy sectors. For the Λ(t) cosmology with a prescribed form of Λ(t) we have found the exact solution in themore » form of Bessel functions. Our model shows that fractional density of dark energy Ω{sub e} is constant and close to zero during the early evolution of the universe. We have also constrained the model parameters for this class of models using the astronomical data such as SNIa data, BAO, CMB, measurements of H(z) and the Alcock-Paczyński test. In this context we formulate a simple criterion of variability of Λ with respect to t in terms of variability of the jerk or sign of estimator (1−Ω{sub m},0−Ω{sub Λ,0}). The case study of our model enable us to find an upper limit α{sup 2} < 0.012 (2σ C.L.) describing the variation from the cosmological constant while the LCDM model seems to be consistent with various data.« less

Large-scale clustering of galaxies in the CfA Redshift Survey

NASA Technical Reports Server (NTRS)

Vogeley, Michael S.; Park, Changbom; Geller, Margaret J.; Huchra, John P.

1992-01-01

The power spectrum of the galaxy distribution in the Center for Astrophysics Redshift Survey (de Lapparent et al., 1986; Geller and Huchra, 1989; and Huchra et al., 1992) is measured up to wavelengths of 200/h Mpc. Results are compared with several cosmological simulations with Gaussian initial conditions. It is shown that the power spectrum of the standard CDM model is inconsistent with the observed power spectrum at the 99 percent confidence level.

Impact of large-scale tides on cosmological distortions via redshift-space power spectrum

NASA Astrophysics Data System (ADS)

Akitsu, Kazuyuki; Takada, Masahiro

2018-03-01

Although large-scale perturbations beyond a finite-volume survey region are not direct observables, these affect measurements of clustering statistics of small-scale (subsurvey) perturbations in large-scale structure, compared with the ensemble average, via the mode-coupling effect. In this paper we show that a large-scale tide induced by scalar perturbations causes apparent anisotropic distortions in the redshift-space power spectrum of galaxies in a way depending on an alignment between the tide, wave vector of small-scale modes and line-of-sight direction. Using the perturbation theory of structure formation, we derive a response function of the redshift-space power spectrum to large-scale tide. We then investigate the impact of large-scale tide on estimation of cosmological distances and the redshift-space distortion parameter via the measured redshift-space power spectrum for a hypothetical large-volume survey, based on the Fisher matrix formalism. To do this, we treat the large-scale tide as a signal, rather than an additional source of the statistical errors, and show that a degradation in the parameter is restored if we can employ the prior on the rms amplitude expected for the standard cold dark matter (CDM) model. We also discuss whether the large-scale tide can be constrained at an accuracy better than the CDM prediction, if the effects up to a larger wave number in the nonlinear regime can be included.

The cosmic transparency measured with Type Ia supernovae: implications for intergalactic dust

NASA Astrophysics Data System (ADS)

Goobar, Ariel; Dhawan, Suhail; Scolnic, Daniel

2018-04-01

Observations of high-redshift Type Ia supernovae (SNe Ia) are used to study the cosmic transparency at optical wavelengths. Assuming a flat ΛCDM cosmological model based on BAO and CMB results, redshift dependent deviations of SN Ia distances are used to constrain mechanisms that would dim light. The analysis is based on the most recent Pantheon SN compilation, for which there is a 0.03± 0.01 {(stat)} mag discrepancy in the distant supernova distance moduli relative to the ΛCDM model anchored by supernovae at z < 0.05. While there are known systematic uncertainties that combined could explain the observed offset, here we entertain the possibility that the discrepancy may instead be explained by scattering of supernova light in the intergalactic medium (IGM). We focus on two effects: Compton scattering by free electrons and extinction by dust in the IGM. We find that if the discrepancy is due entirely to dimming by dust, the measurements can be modeled with a cosmic dust density Ω _IGM^dust = 8 \\cdot 10^{-5} (1+z)^{-1}, corresponding to an average attenuation of 2 . 10-5 mag Mpc-1 in V-band. Forthcoming SN Ia studies may provide a definitive measurement of the IGM dust properties, while still providing an unbiased estimate of cosmological parameters by introducing additional parameters in the global fits to the observations.

Measuring the hydrostatic mass bias in galaxy clusters by combining Sunyaev-Zel'dovich and CMB lensing data

NASA Astrophysics Data System (ADS)

Hurier, G.; Angulo, R. E.

2018-02-01

The cosmological parameters preferred by the cosmic microwave background (CMB) primary anisotropies predict many more galaxy clusters than those that have been detected via the thermal Sunyaev-Zeldovich (tSZ) effect. This discrepancy has attracted considerable attention since it might be evidence of physics beyond the simplest ΛCDM model. However, an accurate and robust calibration of the mass-observable relation for clusters is necessary for the comparison, which has been proven difficult to obtain so far. Here, we present new constraints on the mass-pressure relation by combining tSZ and CMB lensing measurements of optically selected clusters. Consequently, our galaxy cluster sample is independent of the data employed to derive cosmological constrains. We estimate an average hydrostatic mass bias of b = 0.26 ± 0.07, with no significant mass or redshift evolution. This value greatly reduces the discrepancy between the predictions of ΛCDM and the observed abundance of tSZ clusters but agrees with recent estimates from tSZ clustering. On the other hand, our value for b is higher than the predictions from hydrodynamical simulations. This suggests mechanisms that drive large departures from hydrostatic equilibrium and that are not included in the latest simulations, and/or unaccounted systematic errors such as biases in the cluster catalogue that are due to the optical selection.

The cosmic transparency measured with Type Ia supernovae: implications for intergalactic dust

NASA Astrophysics Data System (ADS)

Goobar, Ariel; Dhawan, Suhail; Scolnic, Daniel

2018-06-01

Observations of high-redshift Type Ia supernovae (SNe Ia) are used to study the cosmic transparency at optical wavelengths. Assuming a flat Λ cold dark matter (ΛCDM) cosmological model based on baryon acoustic oscillations and cosmic microwave background measurements, redshift dependent deviations of SN Ia distances are used to constrain mechanisms that would dim light. The analysis is based on the most recent Pantheon SN compilation, for which there is a 0.03 ± 0.01 {({stat})} mag discrepancy in the distant supernova distance moduli relative to the ΛCDM model anchored by supernovae at z < 0.05. While there are known systematic uncertainties that combined could explain the observed offset, here we entertain the possibility that the discrepancy may instead be explained by scattering of supernova light in the intergalactic medium (IGM). We focus on two effects: Compton scattering by free electrons and extinction by dust in the IGM. We find that if the discrepancy is entirely due to dimming by dust, the measurements can be modelled with a cosmic dust density Ω _IGM^dust = 8 × 10^{-5} (1+z)^{-1}, corresponding to an average attenuation of 2 × 10-5 mag Mpc-1 in V band. Forthcoming SN Ia studies may provide a definitive measurement of the IGM dust properties, while still providing an unbiased estimate of cosmological parameters by introducing additional parameters in the global fits to the observations.

Cosmological implications of baryon acoustic oscillation measurements

DOE PAGES

Aubourg, Eric

2015-12-01

Here, we derive constraints on cosmological parameters and tests of dark energy models from the combination of baryon acoustic oscillation (BAO) measurements with cosmic microwave background (CMB) data and a recent reanalysis of Type Ia supernova (SN) data. Particularly, we take advantage of high-precision BAO measurements from galaxy clustering and the Lyman-α forest (LyaF) in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). Treating the BAO scale as an uncalibrated standard ruler, BAO data alone yield a high confidence detection of dark energy; in combination with the CMB angular acoustic scale they further imply a nearly flat universe. Adding the CMB-calibratedmore » physical scale of the sound horizon, the combination of BAO and SN data into an “inverse distance ladder” yields a measurement of H 0=67.3±1.1 km s -1 Mpc -1, with 1.7% precision. This measurement assumes standard prerecombination physics but is insensitive to assumptions about dark energy or space curvature, so agreement with CMB-based estimates that assume a flat ΛCDM cosmology is an important corroboration of this minimal cosmological model. For constant dark energy (Λ), our BAO+SN+CMB combination yields matter density Ω m=0.301±0.008 and curvature Ω k=-0.003±0.003. When we allow more general forms of evolving dark energy, the BAO+SN+CMB parameter constraints are always consistent with flat ΛCDM values at ≈1σ. And while the overall χ 2 of model fits is satisfactory, the LyaF BAO measurements are in moderate (2–2.5σ) tension with model predictions. Models with early dark energy that tracks the dominant energy component at high redshift remain consistent with our expansion history constraints, and they yield a higher H 0 and lower matter clustering amplitude, improving agreement with some low redshift observations. Expansion history alone yields an upper limit on the summed mass of neutrino species, Σm ν<0.56 eV (95% confidence), improving to Σm ν<0.25 eV if we include the lensing signal in the Planck CMB power spectrum. In a flat ΛCDM model that allows extra relativistic species, our data combination yields N eff=3.43±0.26; while the LyaF BAO data prefer higher Neff when excluding galaxy BAO, the galaxy BAO alone favor N eff≈3. Finally, when structure growth is extrapolated forward from the CMB to low redshift, standard dark energy models constrained by our data predict a level of matter clustering that is high compared to most, but not all, observational estimates.« less

Fully Characterizing Axially Symmetric Szekeres Models with Three Data Sets

NASA Astrophysics Data System (ADS)

Célérier, Marie-Nöelle Mishra, Priti; Singh, Tejinder P.

2015-01-01

Inhomogeneous exact solutions of General Relativity with zero cosmological constant have been used in the literature to challenge the ΛCDM model. From one patch Lemaître-Tolman-Bondi (LTB) models to axially symmetric quasi-spherical Szekeres (QSS) Swiss-cheese models, some of them are able to reproduce to a good accuracy the cosmological data. It has been shown in the literature that a zero Λ LTB model with a central observer can be fully determined by two data sets. We demonstrate that an axially symmetric zero Λ QSS model with an observer located at the origin can be fully reconstructed from three data sets, number counts, luminosity distance and redshift drift. This is a first step towards a future demonstration involving five data sets and the most general Szekeres model.

Limits on cold dark matter cosmologies from new anisotropy bounds on the cosmic microwave background

NASA Technical Reports Server (NTRS)

Vittorio, Nicola; Meinhold, Peter; Lubin, Philip; Muciaccia, Pio Francesco; Silk, Joseph

1991-01-01

A self-consistent method is presented for comparing theoretical predictions of and observational upper limits on CMB anisotropy. New bounds on CDM cosmologies set by the UCSB South Pole experiment on the 1 deg angular scale are presented. An upper limit of 4.0 x 10 to the -5th is placed on the rms differential temperature anisotropy to a 95 percent confidence level and a power of the test beta = 55 percent. A lower limit of about 0.6/b is placed on the density parameter of cold dark matter universes with greater than about 3 percent baryon abundance and a Hubble constant of 50 km/s/Mpc, where b is the bias factor, equal to unity only if light traces mass.

Super-Eddington accreting massive black holes explore high-z cosmology: Monte-Carlo simulations

NASA Astrophysics Data System (ADS)

Cai, Rong-Gen; Guo, Zong-Kuan; Huang, Qing-Guo; Yang, Tao

2018-06-01

In this paper, we simulate Super-Eddington accreting massive black holes (SEAMBHs) as the candles to probe cosmology for the first time. SEAMBHs have been demonstrated to be able to provide a new tool for estimating cosmological distance. Thus, we create a series of mock data sets of SEAMBHs, especially in the high redshift region, to check their abilities to probe the cosmology. To fulfill the potential of the SEAMBHs on the cosmology, we apply the simulated data to three projects. The first is the exploration of their abilities to constrain the cosmological parameters, in which we combine different data sets of current observations such as the cosmic microwave background from Planck and type Ia supernovae from Joint Light-curve Analysis (JLA). We find that the high redshift SEAMBHs can help to break the degeneracies of the background cosmological parameters constrained by Planck and JLA, thus giving much tighter constraints of the cosmological parameters. The second uses the high redshift SEAMBHs as the complements of the low redshift JLA to constrain the early expansion rate and the dark energy density evolution in the cold dark matter frame. Our results show that these high redshift SEAMBHs are very powerful on constraining the early Hubble rate and the evolution of the dark energy density; thus they can give us more information about the expansion history of our Universe, which is also crucial for testing the Λ CDM model in the high redshift region. Finally, we check the SEAMBH candles' abilities to reconstruct the equation of state for dark energy at high redshift. In summary, our results show that the SEAMBHs, as the rare candles in the high redshift region, can provide us a new and independent observation to probe cosmology in the future.

A simple model of universe describing the early inflation and the late accelerated expansion in a symmetric manner

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chavanis, Pierre-Henri

We construct a simple model of universe which 'unifies' vacuum energy and radiation on the one hand, and matter and dark energy on the other hand in the spirit of a generalized Chaplygin gas model. Specifically, the phases of early inflation and late accelerated expansion are described by a generalized equation of state p/c{sup 2} = αρ+kρ{sup 1+1/n} having a linear component p = αρc{sup 2} and a polytropic component p = kρ{sup 1+1/n}c{sup 2}. For α= 1/3, n= 1 and k=−4/(3ρ{sub P}), where ρ{sub P}= 5.1610{sup 99} g/m{sup 3} is the Planck density, this equation of state describes themore » transition between the vacuum energy era and the radiation era. For t≥ 0, the universe undergoes an inflationary expansion that brings it from the Planck size l{sub P}= 1.6210{sup −35} m to a size a{sub 1}= 2.6110{sup −6} m on a timescale of about 23.3 Planck times t{sub P}= 5.3910{sup −44} s (early inflation). When t > t{sub 1}= 23.3t{sub P}, the universe decelerates and enters in the radiation era. We interpret the transition from the vacuum energy era to the radiation era as a second order phase transition where the Planck constant ℏ plays the role of finite size effects (the standard Big Bang theory is recovered for ℏ= 0). For α= 0, n=−1 and k=−ρ{sub Λ}, where ρ{sub Λ}= 7.0210{sup −24} g/m{sup 3} is the cosmological density, the equation of state p/c{sup 2} = αρ+kρ{sup 1+1/n} describes the transition from a decelerating universe dominated by pressureless matter (baryonic and dark matter) to an accelerating universe dominated by dark energy (late inflation). This transition takes place at a size a{sub 2}= 0.204l{sub Λ}. corresponding to a time t{sub 2}= 0.203t{sub Λ} where l{sub Λ}= 4.38 10{sup 26} m is the cosmological length and t{sub Λ}= 1.46 10{sup 18} s the cosmological time. The present universe turns out to be just at the transition between these two periods (t{sub 0}∼t{sub 2}). Our model gives the same results as the standard ΛCDM model for t≫t{sub P} and completes it by incorporating a phase of early inflation for t < 23.3t{sub P} in a very natural manner. Furthermore, it reveals a nice 'symmetry' between the early and the late evolution of the universe. The early universe is modeled by a polytrope n=+ 1 and the late universe by a polytrope n=−1. Furthermore, the cosmological constant Λ in the late universe plays a role similar to the Planck constant ℏ in the early universe. The mathematical formulae in the early and in the late universe are then strikingly symmetric. We interpret the cosmological constant as a fundamental constant of Nature describing the 'cosmophysics' just like the Planck constant describes the 'microphysics'. The Planck density and the cosmological density represent fundamental upper and lower bounds differing by 122 orders of magnitude. The cosmological constant 'problem' may be a false problem. Finally, we show that our model admits a scalar field interpretation based on a quintessence field or a tachyon field.« less

Imprint of thawing scalar fields on the large scale galaxy overdensity

NASA Astrophysics Data System (ADS)

Dinda, Bikash R.; Sen, Anjan A.

2018-04-01

We investigate the observed galaxy power spectrum for the thawing class of scalar field models taking into account various general relativistic corrections that occur on very large scales. We consider the full general relativistic perturbation equations for the matter as well as the dark energy fluid. We form a single autonomous system of equations containing both the background and the perturbed equations of motion which we subsequently solve for different scalar field potentials. First we study the percentage deviation from the Λ CDM model for different cosmological parameters as well as in the observed galaxy power spectra on different scales in scalar field models for various choices of scalar field potentials. Interestingly the difference in background expansion results from the enhancement of power from Λ CDM on small scales, whereas the inclusion of general relativistic (GR) corrections results in the suppression of power from Λ CDM on large scales. This can be useful to distinguish scalar field models from Λ CDM with future optical/radio surveys. We also compare the observed galaxy power spectra for tracking and thawing types of scalar field using some particular choices for the scalar field potentials. We show that thawing and tracking models can have large differences in observed galaxy power spectra on large scales and for smaller redshifts due to different GR effects. But on smaller scales and for larger redshifts, the difference is small and is mainly due to the difference in background expansion.

Distinguishing CDM dwarfs from SIDM dwarfs in baryonic simulations

NASA Astrophysics Data System (ADS)

Strickland, Emily; Fitts, Alex B.; Boylan-Kolchin, Michael

2017-06-01

Dwarf galaxies in the nearby Universe are the most dark-matter-dominated systems known. They are therefore natural probes of the nature of dark matter, which remains unknown. Our collaboration has performed several high-resolution cosmological zoom-in simulations of isolated dwarf galaxies. We simulate each galaxy in standard cold dark matter (ΛCDM) as well as self-interacting dark matter (SIDM, with a cross section of σ/m ~ 1 cm2/g), both with and without baryons, in order to identify distinguishing characteristics between the two. The simulations are run using GIZMO, a meshless-finite-mass hydrodynamical code, and are part of the Feedback in Realistic Environments (FIRE) project. By analyzing both the global properties and inner structure of the dwarfs in varying dark matter prescriptions, we provide a side-by-side comparison of isolated, dark-matter-dominated galaxies at the mass scale where differences in the two models of dark matter are thought to be the most obvious. We find that the edge of classical dwarfs and ultra-faint dwarfs (at stellar masses of ~105 solar masses) provides the clearest window for distinguishing between the two theories. At these low masses, our SIDM galaxies have a cored inner density profile, while their CDM counterparts have “cuspy” centers. The SIDM versions of each galaxy also have measurably lower stellar velocity dispersions than their CDM counterparts. Future observations of ultra faint dwarfs with JWST and 30-m telescopes will be able to discern whether such alternate theories of dark matter are viable.

Cosmic acceleration from a single fluid description

NASA Astrophysics Data System (ADS)

Capozziello, Salvatore; D'Agostino, Rocco; Luongo, Orlando

2018-06-01

We here propose a new class of barotropic factor for matter, motivated by properties of isotropic deformations of crystalline solids. Our approach is dubbed Anton-Schmidt's equation of state and provides a non-vanishing, albeit small, pressure term for matter. The corresponding pressure is thus proportional to the logarithm of universe's volume, i.e. to the density itself since V ∝ρ-1. In the context of solid state physics, we demonstrate that by only invoking standard matter with such a property, we are able to frame the universe speed up in a suitable way, without invoking a dark energy term by hand. Our model extends a recent class of dark energy paradigms named logotropic dark fluids and depends upon two free parameters, namely n and B. Within the Debye approximation, we find that n and B are related to the Grüneisen parameter and the bulk modulus of crystals. We thus show the main differences between our model and the logotropic scenario, and we highlight the most relevant properties of our new equation of state on the background cosmology. Discussions on both kinematics and dynamics of our new model have been presented. We demonstrate that the ΛCDM model is inside our approach, as limiting case. Comparisons with CPL parametrization have been also reported in the text. Finally, a Monte Carlo analysis on the most recent low-redshift cosmological data allowed us to place constraints on n and B. In particular, we found n = - 0 . 147-0.107+0.113 and B = 3.54 × 10-3.

Thermodynamics and cosmological reconstruction in f(T , B) gravity

NASA Astrophysics Data System (ADS)

Bahamonde, Sebastian; Zubair, M.; Abbas, G.

2018-03-01

Recently, it was formulated a teleparallel theory called f(T , B) gravity which connects both f(T) and f(R) under suitable limits. In this theory, the function in the action is assumed to depend on the torsion scalar T and also on a boundary term related with the divergence of torsion, B = 2∇μTμ. In this work, we study different features of a flat Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology in this theory. First, we show that the FLRW equations can be transformed to the form of Clausius relation TˆhSeff = - dE + WdV, where Tˆh is the horizon temperature and Seff is the entropy which contains contributions both from horizon entropy and an additional entropy term introduced due to the non-equilibrium. We also formulate the constraint for the validity of the generalised second law of thermodynamics (GSLT). Additionally, using a cosmological reconstruction technique, we show that both f(T , B) and - T + F(B) gravity can mimic power-law, de-Sitter and ΛCDM models. Finally, we formulate the perturbed evolution equations and analyse the stability of some important cosmological solutions.

Statistical Hierarchy of Varying Speed of Light Cosmologies

NASA Astrophysics Data System (ADS)

Salzano, Vincenzo; Da¸browski, Mariusz P.

2017-12-01

Many varying speed of light (VSL) theories have been developed recently. Here we address the issue of their observational verification in a fully comprehensive way. By using the most updated cosmological probes, we test three different candidates for a VSL theory (Barrow & Magueijo, Avelino & Martins, and Moffat). We consider many different Ansätze for both the functional form of c(z) and the dark energy dynamics. We compare these results using a reliable statistical tool such as the Bayesian evidence. We find that the present cosmological data are perfectly compatible with any of these VSL scenarios, but for the Moffat model there is a higher Bayesian evidence ratio in favor of VSL rather than the c = constant ΛCDM scenario. Moreover, in such a scenario, the VSL signal can help to strengthen constraints on the spatial curvature (with indication toward an open universe), to clarify some properties of dark energy (exclusion of a cosmological constant at 2σ level), and is also falsifiable in the near future owing to peculiar issues that differentiate this model from the standard one. Finally, we apply an information prior and entropy prior in order to put physical constraints on the models, though still in favor Moffat’s proposal.

THE MIRA–TITAN UNIVERSE: PRECISION PREDICTIONS FOR DARK ENERGY SURVEYS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heitmann, Katrin; Habib, Salman; Biswas, Rahul

2016-04-01

Large-scale simulations of cosmic structure formation play an important role in interpreting cosmological observations at high precision. The simulations must cover a parameter range beyond the standard six cosmological parameters and need to be run at high mass and force resolution. A key simulation-based task is the generation of accurate theoretical predictions for observables using a finite number of simulation runs, via the method of emulation. Using a new sampling technique, we explore an eight-dimensional parameter space including massive neutrinos and a variable equation of state of dark energy. We construct trial emulators using two surrogate models (the linear powermore » spectrum and an approximate halo mass function). The new sampling method allows us to build precision emulators from just 26 cosmological models and to systematically increase the emulator accuracy by adding new sets of simulations in a prescribed way. Emulator fidelity can now be continuously improved as new observational data sets become available and higher accuracy is required. Finally, using one ΛCDM cosmology as an example, we study the demands imposed on a simulation campaign to achieve the required statistics and accuracy when building emulators for investigations of dark energy.« less

The mira-titan universe. Precision predictions for dark energy surveys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heitmann, Katrin; Bingham, Derek; Lawrence, Earl

2016-03-28

Large-scale simulations of cosmic structure formation play an important role in interpreting cosmological observations at high precision. The simulations must cover a parameter range beyond the standard six cosmological parameters and need to be run at high mass and force resolution. A key simulation-based task is the generation of accurate theoretical predictions for observables using a finite number of simulation runs, via the method of emulation. Using a new sampling technique, we explore an eight-dimensional parameter space including massive neutrinos and a variable equation of state of dark energy. We construct trial emulators using two surrogate models (the linear powermore » spectrum and an approximate halo mass function). The new sampling method allows us to build precision emulators from just 26 cosmological models and to systematically increase the emulator accuracy by adding new sets of simulations in a prescribed way. Emulator fidelity can now be continuously improved as new observational data sets become available and higher accuracy is required. Finally, using one ΛCDM cosmology as an example, we study the demands imposed on a simulation campaign to achieve the required statistics and accuracy when building emulators for investigations of dark energy.« less

Cosmology with CLASS

NASA Astrophysics Data System (ADS)

Watts, Duncan; CLASS Collaboration

2018-01-01

The Cosmology Large Angular Scale Surveyor (CLASS) will use large-scale measurements of the polarized cosmic microwave background (CMB) to constrain the physics of inflation, reionization, and massive neutrinos. The experiment is designed to characterize the largest scales, which are inaccessible to most ground-based experiments, and remove Galactic foregrounds from the CMB maps. In this dissertation talk, I present simulations of CLASS data and demonstrate their ability to constrain the simplest single-field models of inflation and to reduce the uncertainty of the optical depth to reionization, τ, to near the cosmic variance limit, significantly improving on current constraints. These constraints will bring a qualitative shift in our understanding of standard ΛCDM cosmology. In particular, CLASS's measurement of τ breaks cosmological parameter degeneracies. Probes of large scale structure (LSS) test the effect of neutrino free-streaming at small scales, which depends on the mass of the neutrinos. CLASS's τ measurement, when combined with next-generation LSS and BAO measurements, will enable a 4σ detection of neutrino mass, compared with 2σ without CLASS data.. I will also briefly discuss the CLASS experiment's measurements of circular polarization of the CMB and the implications of the first-such near-all-sky map.

A 14 h {sup −3} Gpc{sup 3} study of cosmic homogeneity using BOSS DR12 quasar sample

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laurent, Pierre; Goff, Jean-Marc Le; Burtin, Etienne

2016-11-01

The BOSS quasar sample is used to study cosmic homogeneity with a 3D survey in the redshift range 2.2 < z < 2.8. We measure the count-in-sphere, N (< r ), i.e. the average number of objects around a given object, and its logarithmic derivative, the fractal correlation dimension, D {sub 2}( r ). For a homogeneous distribution N (< r ) ∝ r {sup 3} and D {sub 2}( r ) = 3. Due to the uncertainty on tracer density evolution, 3D surveys can only probe homogeneity up to a redshift dependence, i.e. they probe so-called ''spatial isotropy'. Ourmore » data demonstrate spatial isotropy of the quasar distribution in the redshift range 2.2 < z < 2.8 in a model-independent way, independent of any FLRW fiducial cosmology, resulting in 3 − ( D {sub 2}) < 1.7 × 10{sup −3} (2 σ) over the range 250 < r < 1200 h {sup −1} Mpc for the quasar distribution. If we assume that quasars do not have a bias much less than unity, this implies spatial isotropy of the matter distribution on large scales. Then, combining with the Copernican principle, we finally get homogeneity of the matter distribution on large scales. Alternatively, using a flat ΛCDM fiducial cosmology with CMB-derived parameters, and measuring the quasar bias relative to this ΛCDM model, our data provide a consistency check of the model, in terms of how homogeneous the Universe is on different scales. D {sub 2}( r ) is found to be compatible with our ΛCDM model on the whole 10 < r < 1200 h {sup −1} Mpc range. For the matter distribution we obtain 3 − ( D {sub 2}) < 5 × 10{sup −5} (2 σ) over the range 250 < r < 1200 h {sup −1} Mpc, consistent with homogeneity on large scales.« less

A Comparison of Cosmological Parameters Determined from CMB Temperature Power Spectra from the South Pole Telescope and the Planck Satellite

DOE PAGES

Aylor, K.; Hou, Z.; Knox, L.; ...

2017-11-20

The Planck cosmic microwave background temperature data are best fit with a ΛCDM model that mildly contradicts constraints from other cosmological probes. The South Pole Telescope (SPT) 2540more » $${\\deg }^{2}$$ SPT-SZ survey offers measurements on sub-degree angular scales (multipoles $$650\\leqslant {\\ell }\\leqslant 2500$$) with sufficient precision to use as an independent check of the Planck data. Here we build on the recent joint analysis of the SPT-SZ and Planck data in Hou et al. by comparing ΛCDM parameter estimates using the temperature power spectrum from both data sets in the SPT-SZ survey region. We also restrict the multipole range used in parameter fitting to focus on modes measured well by both SPT and Planck, thereby greatly reducing sample variance as a driver of parameter differences and creating a stringent test for systematic errors. We find no evidence of systematic errors from these tests. When we expand the maximum multipole of SPT data used, we see low-significance shifts in the angular scale of the sound horizon and the physical baryon and cold dark matter densities, with a resulting trend to higher Hubble constant. When we compare SPT and Planck data on the SPT-SZ sky patch to Planck full-sky data but keep the multipole range restricted, we find differences in the parameters n s and $${A}_{s}{e}^{-2\\tau }$$. We perform further checks, investigating instrumental effects and modeling assumptions, and we find no evidence that the effects investigated are responsible for any of the parameter shifts. Taken together, these tests reveal no evidence for systematic errors in SPT or Planck data in the overlapping sky coverage and multipole range and at most weak evidence for a breakdown of ΛCDM or systematic errors influencing either the Planck data outside the SPT-SZ survey area or the SPT data at $${\\ell }\\gt 2000$$.« less

Structure and dynamics of Andromeda's stellar disk

NASA Astrophysics Data System (ADS)

Dorman, Claire Elise

2015-10-01

Lambda cold dark matter (LambdaCDM) cosmology predicts that the disks of Milky Way-mass galaxies should have undergone at least one merger with a large (mass ratio 1:10) satellite in the last several Gyr. However, the stellar disk in the solar neighborhood of the Milky Way is too thin and dynamically cold to have experienced such an impact. The dynamics of the nearby Andromeda galaxy can serve as a second data point, and help us understand whether the Milky Way may simply have had an unusually quiescent merger history, or whether LambdaCDM theory needs to be revisited. Over the last few years, we have carried out a detailed study of the resolved stellar populations in the disk of the Andromeda galaxy using data from two surveys: six-filter Hubble Space Telescope photometry from the recently-completed Panchromatic Hubble Andromeda Treasury (PHAT) survey, and radial velocities derived from Keck/DEIMOS optical spectra obtained as part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar 0Halo (SPLASH) program. These detailed, multidimensional data sets allow us to decouple the structural subcomponents and characterize them individually. We find that an old, dynamically hot (velocity dispersion 150 km/s) RGB population extends out to 20 kpc (the edge of the visible disk) but has a disk-like surface brightness profile and luminosity function. This population may have originated in the disk but been kicked out subsequently in impacts with satellite galaxies. We also study the kinematics of the disk as a function of the age of stellar tracers, and find a direct correlation between age and velocity dispersion, indicating that Andromeda has undergone a continuous heating or disk settling process throughout its lifetime. Overall, both the velocity dispersion of Andromeda's disk and the slope of the velocity dispersion vs. stellar age curve are several times those of the Milky Way's, suggesting a more active merger history more in line with LambdaCDM cosmological predictions.

A Comparison of Cosmological Parameters Determined from CMB Temperature Power Spectra from the South Pole Telescope and the Planck Satellite

NASA Astrophysics Data System (ADS)

Aylor, K.; Hou, Z.; Knox, L.; Story, K. T.; Benson, B. A.; Bleem, L. E.; Carlstrom, J. E.; Chang, C. L.; Cho, H.-M.; Chown, R.; Crawford, T. M.; Crites, A. T.; de Haan, T.; Dobbs, M. A.; Everett, W. B.; George, E. M.; Halverson, N. W.; Harrington, N. L.; Holder, G. P.; Holzapfel, W. L.; Hrubes, J. D.; Keisler, R.; Lee, A. T.; Leitch, E. M.; Luong-Van, D.; Marrone, D. P.; McMahon, J. J.; Meyer, S. S.; Millea, M.; Mocanu, L. M.; Mohr, J. J.; Natoli, T.; Omori, Y.; Padin, S.; Pryke, C.; Reichardt, C. L.; Ruhl, J. E.; Sayre, J. T.; Schaffer, K. K.; Shirokoff, E.; Staniszewski, Z.; Stark, A. A.; Vanderlinde, K.; Vieira, J. D.; Williamson, R.

2017-11-01

The Planck cosmic microwave background temperature data are best fit with a ΛCDM model that mildly contradicts constraints from other cosmological probes. The South Pole Telescope (SPT) 2540 {\\deg }2 SPT-SZ survey offers measurements on sub-degree angular scales (multipoles 650≤slant {\\ell }≤slant 2500) with sufficient precision to use as an independent check of the Planck data. Here we build on the recent joint analysis of the SPT-SZ and Planck data in Hou et al. by comparing ΛCDM parameter estimates using the temperature power spectrum from both data sets in the SPT-SZ survey region. We also restrict the multipole range used in parameter fitting to focus on modes measured well by both SPT and Planck, thereby greatly reducing sample variance as a driver of parameter differences and creating a stringent test for systematic errors. We find no evidence of systematic errors from these tests. When we expand the maximum multipole of SPT data used, we see low-significance shifts in the angular scale of the sound horizon and the physical baryon and cold dark matter densities, with a resulting trend to higher Hubble constant. When we compare SPT and Planck data on the SPT-SZ sky patch to Planck full-sky data but keep the multipole range restricted, we find differences in the parameters n s and {A}s{e}-2τ . We perform further checks, investigating instrumental effects and modeling assumptions, and we find no evidence that the effects investigated are responsible for any of the parameter shifts. Taken together, these tests reveal no evidence for systematic errors in SPT or Planck data in the overlapping sky coverage and multipole range and at most weak evidence for a breakdown of ΛCDM or systematic errors influencing either the Planck data outside the SPT-SZ survey area or the SPT data at {\\ell }> 2000.

THE SERENDIPITOUS OBSERVATION OF A GRAVITATIONALLY LENSED GALAXY AT z = 0.9057 FROM THE BLANCO COSMOLOGY SURVEY: THE ELLIOT ARC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buckley-Geer, E. J.; Lin, H.; Drabek, E. R.

2011-11-20

We report on the serendipitous discovery in the Blanco Cosmology Survey (BCS) imaging data of a z = 0.9057 galaxy that is being strongly lensed by a massive galaxy cluster at a redshift of z = 0.3838. The lens (BCS J2352-5452) was discovered while examining i- and z-band images being acquired in 2006 October during a BCS observing run. Follow-up spectroscopic observations with the Gemini Multi-Object Spectrograph instrument on the Gemini-South 8 m telescope confirmed the lensing nature of this system. Using weak-plus-strong lensing, velocity dispersion, cluster richness N{sub 200}, and fitting to a Navarro-Frenk-White (NFW) cluster mass density profile,more » we have made three independent estimates of the mass M{sub 200} which are all very consistent with each other. The combination of the results from the three methods gives M{sub 200} = (5.1 {+-} 1.3) Multiplication-Sign 10{sup 14} M{sub Sun }, which is fully consistent with the individual measurements. The final NFW concentration c{sub 200} from the combined fit is c{sub 200} = 5.4{sup +1.4}{sub -1.1}. We have compared our measurements of M{sub 200} and c{sub 200} with predictions for (1) clusters from {Lambda}CDM simulations, (2) lensing-selected clusters from simulations, and (3) a real sample of cluster lenses. We find that we are most compatible with the predictions for {Lambda}CDM simulations for lensing clusters, and we see no evidence based on this one system for an increased concentration compared to {Lambda}CDM. Finally, using the flux measured from the [O II]3727 line we have determined the star formation rate of the source galaxy and find it to be rather modest given the assumed lens magnification.« less

Particle Accelerators Test Cosmological Theory.

ERIC Educational Resources Information Center

Schramm, David N.; Steigman, Gary

1988-01-01

Discusses the symbiotic relationship of cosmology and elementary-particle physics. Presents a brief overview of particle physics. Explains how cosmological considerations set limits on the number of types of elementary particles. (RT)

MOSAIC--A Modular Approach to Data Management in Epidemiological Studies.

PubMed

Bialke, M; Bahls, T; Havemann, C; Piegsa, J; Weitmann, K; Wegner, T; Hoffmann, W

2015-01-01

In the context of an increasing number of multi-centric studies providing data from different sites and sources the necessity for central data management (CDM) becomes undeniable. This is exacerbated by a multiplicity of featured data types, formats and interfaces. In relation to methodological medical research the definition of central data management needs to be broadened beyond the simple storage and archiving of research data. This paper highlights typical requirements of CDM for cohort studies and registries and illustrates how orientation for CDM can be provided by addressing selected data management challenges. Therefore in the first part of this paper a short review summarises technical, organisational and legal challenges for CDM in cohort studies and registries. A deduced set of typical requirements of CDM in epidemiological research follows. In the second part the MOSAIC project is introduced (a modular systematic approach to implement CDM). The modular nature of MOSAIC contributes to manage both technical and organisational challenges efficiently by providing practical tools. A short presentation of a first set of tools, aiming for selected CDM requirements in cohort studies and registries, comprises a template for comprehensive documentation of data protection measures, an interactive reference portal for gaining insights and sharing experiences, supplemented by modular software tools for generation and management of generic pseudonyms, for participant management and for sophisticated consent management. Altogether, work within MOSAIC addresses existing challenges in epidemiological research in the context of CDM and facilitates the standardized collection of data with pre-programmed modules and provided document templates. The necessary effort for in-house programming is reduced, which accelerates the start of data collection.

A tale of two modes: neutrino free-streaming in the early universe

NASA Astrophysics Data System (ADS)

Lancaster, Lachlan; Cyr-Racine, Francis-Yan; Knox, Lloyd; Pan, Zhen

2017-07-01

We present updated constraints on the free-streaming nature of cosmological neutrinos from cosmic microwave background (CMB) temperature and polarization power spectra, baryonic acoustic oscillation data, and distance ladder measurements of the Hubble constant. Specifically, we consider a Fermi-like four-fermion interaction between massless neutrinos, characterized by an effective coupling constant Geff, and resulting in a neutrino opacity dot tauνpropto Geff2 Tν5. Using a conservative flat prior on the parameter log10( Geff MeV2), we find a bimodal posterior distribution with two clearly separated regions of high probability. The first of these modes is consistent with the standard ΛCDM cosmology and corresponds to neutrinos decoupling at redshift zν,dec > 1.3×105, that is before the Fourier modes probed by the CMB damping tail enter the causal horizon. The other mode of the posterior, dubbed the "interacting neutrino mode", corresponds to neutrino decoupling occurring within a narrow redshift window centered around zν,dec~8300. This mode is characterized by a high value of the effective neutrino coupling constant, log10( Geff MeV2) = -1.72 ± 0.10 (68% C.L.), together with a lower value of the scalar spectral index and amplitude of fluctuations, and a higher value of the Hubble parameter. Using both a maximum likelihood analysis and the ratio of the two mode's Bayesian evidence, we find the interacting neutrino mode to be statistically disfavored compared to the standard ΛCDM cosmology, and determine this result to be largely driven by the low-l CMB temperature data. Interestingly, the addition of CMB polarization and direct Hubble constant measurements significantly raises the statistical significance of this secondary mode, indicating that new physics in the neutrino sector could help explain the difference between local measurements of H0, and those inferred from CMB data. A robust consequence of our results is that neutrinos must be free streaming long before the epoch of matter-radiation equality in order to fit current cosmological data.

Expansion and growth of structure observables in a macroscopic gravity averaged universe

NASA Astrophysics Data System (ADS)

Wijenayake, Tharake; Ishak, Mustapha

2015-03-01

We investigate the effect of averaging inhomogeneities on expansion and large-scale structure growth observables using the exact and covariant framework of macroscopic gravity (MG). It is well known that applying the Einstein's equations and spatial averaging do not commute and lead to the averaging problem and backreaction terms. For the MG formalism applied to the Friedman-Lemaitre-Robertson-Walker (FLRW) metric, the extra term can be encapsulated as an averaging density parameter denoted ΩA . An exact isotropic cosmological solution of MG for the flat FLRW metric is already known in the literature; we derive here an anisotropic exact solution. Using the isotropic solution, we compare the expansion history to current available data of distances to supernovae, baryon acoustic oscillations, cosmic microwave background last scattering surface data, and Hubble constant measurements, and find -0.05 ≤ΩA≤0.07 (at the 95% confidence level). For the flat metric case this reduces to -0.03 ≤ΩA≤0.05 . The positive part of the intervals can be rejected if a mathematical (and physical) prior is taken into account. We also find that the inclusion of this term in the fits can shift the values of the usual cosmological parameters by a few to several percents. Next, we derive an equation for the growth rate of large-scale structure in MG that includes a term due to the averaging and assess its effect on the evolution of the growth compared to that of the Lambda cold dark matter (Λ CDM ) concordance model. We find that an ΩA term of an amplitude range of [-0.04 ,-0.02 ] lead to a relative deviation of the growth from that of the Λ CDM of up to 2%-4% at late times. Thus, the shift in the growth could be of comparable amplitude to that caused by similar changes in cosmological parameters like the dark energy density parameter or its equation of state. The effect could also be comparable in amplitude to some systematic effects considered for future surveys. This indicates that the averaging term and its possible effect need to be tightly constrained in future precision cosmological studies.

Anisotropic ghost dark energy cosmological model with hybrid expansion law

NASA Astrophysics Data System (ADS)

Mahanta, Chandra Rekha; Sarma, Nitin

2017-11-01

In this paper, we study the anisotropic Bianchi type-VI0 metric filled with dark matter and anisotropic ghost dark energy. We have solved the Einstein's field equations by considering hybrid expansion law (HEL) for the average scale factor. It is found that at later times the universe becomes spatially homogeneous, isotropic and flat. From a state finder diagnosis, it is found that our model is having similar behavior like ɅCDM model at late phase of cosmic time.

Beasts in Lambda-CDM zoo

NASA Astrophysics Data System (ADS)

Dolgov, A. D.

2017-09-01

Recent astronomical discoveries of supermassive black holes (quasars), gamma-bursters, super-novae, and dust at high redshifts, z = (5-10), are reviewed. Such a dense population of the early universe is at odds with the conventional mechanisms of its possible origin. Similar data from the contemporary universe, which are also in conflict with natural expectations, are considered too. Two possible mechanisms are suggested, at least one of which can potentially solve all these problems. As a by-product of the last model, an abundant cosmological antimatter may be created.

Final Scientific/Technical Report-Quantum Field Theories for Cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nicolis, Alberto

The research funded by this award spanned a wide range of subjects in theoretical cosmology and in field theory. In the first part, the PI and his collaborators applied effective field theory techniques to the study of macroscopic media and of cosmological perturbations. Such an approach—now standard in particle physics—is quite unconventional for theoretical cosmology. They addressed several concrete questions where this formalism proved valuable, both within and outside the cosmological context, concerning for instance macroscopic physical phenomena for fluids, superfluids, and solids, and their relationship to the dynamics of cosmological perturbations. A particularly successful outcome of this line ofmore » research has been the development of “solid inflation”: a cosmological model for primordial inflation where the expansion of the universe is driven by an exotic solid substance. In the second part, the PI and his collaborators investigated more fundamental questions and ideas, for the present universe as well as for the very early one, using quantum field theory as a guide. The questions addressed include: Is the present cosmic acceleration due to a new, ‘dark’ form of energy, or are we instead observing a breakdown of Einstein’s general relativity at cosmological distances? Is the cosmic acceleration accelerating? Is the Big Bang unavoidable? Related to this, is early inflation the only sensible cure for the shortcomings of the standard Big Bang model, and the only possible source for the observed scale-invariant cosmological perturbations?« less

One hundred years of the cosmological constant: from "superfluous stunt" to dark energy

NASA Astrophysics Data System (ADS)

O'Raifeartaigh, Cormac; O'Keeffe, Michael; Nahm, Werner; Mitton, Simon

2018-05-01

We present a centennial review of the history of the term known as the cosmological constant. First introduced to the general theory of relativity by Einstein in 1917 in order to describe a universe that was assumed to be static, the term fell from favour in the wake of the discovery of the expanding universe, only to make a dramatic return in recent times. We consider historical and philosophical aspects of the cosmological constant over four main epochs; (i) the use of the term in static cosmologies (both Newtonian and relativistic): (ii) the marginalization of the term following the discovery of cosmic expansion: (iii) the use of the term to address specific cosmic puzzles such as the timespan of expansion, the formation of galaxies and the redshifts of the quasars: (iv) the re-emergence of the term in today's Λ-CDM cosmology. We find that the cosmological constant was never truly banished from theoretical models of the universe, but was marginalized by astronomers for reasons of convenience. We also find that the return of the term to the forefront of modern cosmology did not occur as an abrupt paradigm shift due to one particular set of observations, but as the result of a number of empirical advances such as the measurement of present cosmic expansion using the Hubble Space Telescope, the measurement of past expansion using type SN Ia supernovae as standard candles, and the measurement of perturbations in the cosmic microwave background by balloon and satellite. We give a brief overview of contemporary interpretations of the physics underlying the cosmic constant and conclude with a synopsis of the famous cosmological constant problem.

The Atacama Cosmology Telescope: Cosmology from Galaxy Clusters Detected Via the Sunyaev-Zel'dovich Effect

NASA Technical Reports Server (NTRS)

Sehgal, Neelima; Trac, Hy; Acquaviva, Viviana; Ade, Peter A. R.; Aguirre, Paula; Amiri, Mandana; Appel, John W.; Barrientos, L. Felipe; Battistelli, Elia S.; Bond, J. Richard;

One hundred years of the cosmological constant: from "superfluous stunt" to dark energy

NASA Astrophysics Data System (ADS)

O'Raifeartaigh, Cormac; O'Keeffe, Michael; Nahm, Werner; Mitton, Simon

2018-03-01

We present a centennial review of the history of the term known as the cosmological constant. First introduced to the general theory of relativity by Einstein in 1917 in order to describe a universe that was assumed to be static, the term fell from favour in the wake of the discovery of the expanding universe, only to make a dramatic return in recent times. We consider historical and philosophical aspects of the cosmological constant over four main epochs; (i) the use of the term in static cosmologies (both Newtonian and relativistic): (ii) the marginalization of the term following the discovery of cosmic expansion: (iii) the use of the term to address specific cosmic puzzles such as the timespan of expansion, the formation of galaxies and the redshifts of the quasars: (iv) the re-emergence of the term in today's Λ-CDM cosmology. We find that the cosmological constant was never truly banished from theoretical models of the universe, but was marginalized by astronomers for reasons of convenience. We also find that the return of the term to the forefront of modern cosmology did not occur as an abrupt paradigm shift due to one particular set of observations, but as the result of a number of empirical advances such as the measurement of present cosmic expansion using the Hubble Space Telescope, the measurement of past expansion using type SN Ia supernovae as standard candles, and the measurement of perturbations in the cosmic microwave background by balloon and satellite. We give a brief overview of contemporary interpretations of the physics underlying the cosmic constant and conclude with a synopsis of the famous cosmological constant problem.

Ultralight scalars as cosmological dark matter

NASA Astrophysics Data System (ADS)

Hui, Lam; Ostriker, Jeremiah P.; Tremaine, Scott; Witten, Edward

2017-02-01

Many aspects of the large-scale structure of the Universe can be described successfully using cosmological models in which 27 ±1 % of the critical mass-energy density consists of cold dark matter (CDM). However, few—if any—of the predictions of CDM models have been successful on scales of ˜10 kpc or less. This lack of success is usually explained by the difficulty of modeling baryonic physics (star formation, supernova and black-hole feedback, etc.). An intriguing alternative to CDM is that the dark matter is an extremely light (m ˜10-22 eV ) boson having a de Broglie wavelength λ ˜1 kpc , often called fuzzy dark matter (FDM). We describe the arguments from particle physics that motivate FDM, review previous work on its astrophysical signatures, and analyze several unexplored aspects of its behavior. In particular, (i) FDM halos or subhalos smaller than about 1 07(m /10-22 eV )-3 /2 M⊙ do not form, and the abundance of halos smaller than a few times 1 010(m /10-22 eV )-4 /3 M⊙ is substantially smaller in FDM than in CDM. (ii) FDM halos are comprised of a central core that is a stationary, minimum-energy solution of the Schrödinger-Poisson equation, sometimes called a "soliton," surrounded by an envelope that resembles a CDM halo. The soliton can produce a distinct signature in the rotation curves of FDM-dominated systems. (iii) The transition between soliton and envelope is determined by a relaxation process analogous to two-body relaxation in gravitating N-body systems, which proceeds as if the halo were composed of particles with mass ˜ρ λ3 where ρ is the halo density. (iv) Relaxation may have substantial effects on the stellar disk and bulge in the inner parts of disk galaxies, but has negligible effect on disk thickening or globular cluster disruption near the solar radius. (v) Relaxation can produce FDM disks but a FDM disk in the solar neighborhood must have a half-thickness of at least ˜300 (m /10-22 eV )-2/3 pc and a midplane density less than 0.2 (m /10-22 eV )2/3 times the baryonic disk density. (vi) Solitonic FDM subhalos evaporate by tunneling through the tidal radius and this limits the minimum subhalo mass inside ˜30 kpc of the Milky Way to a few times 1 08(m /10-22 eV )-3 /2 M⊙ . (vii) If the dark matter in the Fornax dwarf galaxy is composed of CDM, most of the globular clusters observed in that galaxy should have long ago spiraled to its center, and this problem is resolved if the dark matter is FDM. (viii) FDM delays galaxy formation relative to CDM but its galaxy-formation history is consistent with current observations of high-redshift galaxies and the late reionization observed by Planck. If the dark matter is composed of FDM, most observations favor a particle mass ≳10-22 eV and the most significant observational consequences occur if the mass is in the range 1 - 10 ×10-22 eV . There is tension with observations of the Lyman-α forest, which favor m ≳10 - 20 ×10-22 eV and we discuss whether more sophisticated models of reionization may resolve this tension.

A hydrodynamic approach to cosmology: The mixed dark matter cosmological scenario

NASA Technical Reports Server (NTRS)

Cen, Renyue; Ostriker, Jeremiah P.

1994-01-01

We compute the evolution of spatially flat, mixed cold and hot dark matter models containing both baryonic matter and two kinds of dark matter. Hydrodynamics is treated with a highly developed Eulerian hydrodynamic code (see Cen 1992). A standard particle-mesh (PM) code is also used in parallel to calculate the motion of the dark matter components. We adopt the following parameters: h equivalent to (sub 0)/100 km/s Mpc(exp -1) = 0.5, OMEGA(sub C) = 0.3, and OMEGA(sub B) = 0.06, with amplitude of the perturbation spectrum fixed by the Cosmic Background Explorer Satellite (COBE) Dark Matter Radiation (DMR) measurements (Smoot et al. 1992) being sigma (sub 8) = 0.67. Four different boxes are simulated with box sizes of L = (64, 16, 4, 1) h(exp -1) Mpc, respectively, the two small boxes providing good resolution but little valid information due to absence of large-scale power. We use 128(exp 3) approximate 10(exp 6.3) baryonic cells, 128(exp .3) cold dark matter particles, and 2 x 128(exp 3) hot dark matter particles. In addition to the dark matter we follow separately six baryonic species (H, H(+), He, He(+), He(++), e(-)) with allowance for both (nonequilibrium) collisional and radiative ionization in every cell. The background radiation field is also followed in detail with allowance made for both continuum and line processes, to allow nonequilibrium heating and cooling processes to be followed in detail. The mean final Zeldovich-Sunyaev y parameter is estimated to be y Bar = (5.4 + or - 2.7) x 10(exp -7) below currently attainable observations, with a rms fluctuation of approximately delta bar y = (0.6 + or - 3.0) x 10(exp -7) on arcminute scales. The rate of galaxy formation peaks at an even later epoch (z approximate 0.3) than in the standard (OMEGA = 1, sigma sub 8 = 0.67) cold dark matter (CDM) model (z approximate 0.5) and, at a redshift of z = 4, is nearly a factor of 100 lower than for the CDM model with the same value of sigma sub 8. With regard to mass function, the smallest objects are stabilized against collapse by thermal energy: the mass-weighted mass spectrum has a broad peak in the vicinity of M(sub B) = 10(exp 9.5) solar mass with a reasonable fit to the Schechter luminosity function if the ratio of baryon mass to blue light is approximately 4. In addition, one very large PM simulation was made in a box with size (320 h(exp - 1) Mpc) containing 3 x 200(exp 3) = 10(exp 7.4) particles. Utilizing this simulation we find that the model yields a cluster mass function which is about a factor of 4 higher than observed, but a cluster-cluster correlation length marginally lower than observed, but that both are closer to observations than in the (COBE) normalized CDM model. The one-dimensional pairwise velocity dispersion is 605 + or - 8 km/s at 1/h separation, lower than that of the DCM model normalized to COBE, but still significant higher than observations (Davis & Peebles 1983). A plausible velocity bias b(sub v) = 0.8 + or - 0.1 on this scale will reduce but not remove the discrepancy. The velocity auto-correlat ion function has a coherence length of 40/h Mpc, which is somewhat lower than the observed counterpart. In all these respects the model would be improved by decreasing the cold fraction of the dark OMEGA(sub CDM)/ (OMEGA(sub CDM) + OMEGA(sub HDB). But formation of galaxies and clusters of galaxies is much later in this model than in COBE-normalized CDM, perhaps too late. To improve on these constraints a larger ratio of OMEGA(sub CDM)/ (OMEGA(sub CDM) + OMEGA(sub HDM)) is required than the value of 0.67 adopted here. It does not seem possible to find a value for this ratio which would satisfy all tests. Overall, the model is similar both on large and intermediate scales to the standard CDM model normalized to the same value of sigma(sub B), but the problem with regard to late formation of galaxies is more severe in this model than in that CDM model. Adding hot dark matter, significantly improves the ability of the COBE-normalized CDM scenario to fit existing observations, but the model is in fact not as good as the CDM model with the same sigma(sub 8) and is still probably unsatisfactory with regard to several critical tests.

Cosmological signatures of ultralight dark matter with an axionlike potential

NASA Astrophysics Data System (ADS)

Cedeño, Francisco X. Linares; González-Morales, Alma X.; Ureña-López, L. Arturo

2017-09-01

Nonlinearities in a realistic axion field potential may play an important role in the cosmological dynamics. In this paper we use the Boltzmann code class to solve the background and linear perturbations evolution of an axion field and contrast our results with those of CDM and the free axion case. We conclude that there is a slight delay in the onset of the axion field oscillations when nonlinearities in the axion potential are taken into account. Besides, we identify a tachyonic instability of linear modes resulting in the presence of a bump in the power spectrum at small scales. Some comments are in turn about the true source of the tachyonic instability, how the parameters of the axionlike potential can be constrained by Ly-α observations, and the consequences in the stability of self-gravitating objects made of axions.

The intrinsic matter bispectrum in ΛCDM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tram, Thomas; Crittenden, Robert; Koyama, Kazuya

2016-05-01

We present a fully relativistic calculation of the matter bispectrum at second order in cosmological perturbation theory assuming a Gaussian primordial curvature perturbation. For the first time we perform a full numerical integration of the bispectrum for both baryons and cold dark matter using the second-order Einstein-Boltzmann code, SONG. We review previous analytical results and provide an improved analytic approximation for the second-order kernel in Poisson gauge which incorporates Newtonian nonlinear evolution, relativistic initial conditions, the effect of radiation at early times and the cosmological constant at late times. Our improved kernel provides a percent level fit to the fullmore » numerical result at late times for most configurations, including both equilateral shapes and the squeezed limit. We show that baryon acoustic oscillations leave an imprint in the matter bispectrum, making a significant impact on squeezed shapes.« less

Extending the ΛCDM model through shear-free anisotropies

NASA Astrophysics Data System (ADS)

Pereira, Thiago S.; Pabon, Davincy T.

2016-07-01

If the spacetime metric has anisotropic spatial curvature, one can still expand the universe as if it were isotropic, provided that the energy-momentum tensor satisfies a certain constraint. This leads to the so-called shear-free (SF) metrics, which have the interesting property of violating the cosmological principle while still preserving the isotropy of the cosmic microwave background (CMB) radiation. In this work, we show that SF cosmologies correspond to an attractor solution in the space of models with anisotropic spatial curvature. Through a rigorous definition of linear perturbation theory in these spacetimes, we show that SF models represent a viable alternative to explain the large-scale evolution of the universe, leading, in particular to a kinematically equivalent Sachs-Wolfe (SW) effect. Alternatively, we discuss some specific signatures that SF models would imprint on the temperature spectrum of CMB.

Are dark energy models with variable EoS parameter w compatible with the late inhomogeneous Universe?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akarsu, Özgür; Bouhmadi-López, Mariam; Brilenkov, Maxim

We study the late-time evolution of the Universe where dark energy (DE) is presented by a barotropic fluid on top of cold dark matter (CDM) . We also take into account the radiation content of the Universe. Here by the late stage of the evolution we refer to the epoch where CDM is already clustered into inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies). Under this condition the mechanical approach is an adequate tool to study the Universe deep inside the cell of uniformity. More precisely, we study scalar perturbations of the FLRW metric due to inhomogeneities ofmore » CDM as well as fluctuations of radiation and DE. For an arbitrary equation of state for DE we obtain a system of equations for the scalar perturbations within the mechanical approach. First, in the case of a constant DE equation of state parameter w, we demonstrate that our method singles out the cosmological constant as the only viable dark energy candidate. Then, we apply our approach to variable equation of state parameters in the form of three different linear parametrizations of w, e.g., the Chevallier-Polarski-Linder perfect fluid model. We conclude that all these models are incompatible with the theory of scalar perturbations in the late Universe.« less

Exploring cosmic homogeneity with the BOSS DR12 galaxy sample

NASA Astrophysics Data System (ADS)

Ntelis, Pierros; Hamilton, Jean-Christophe; Le Goff, Jean-Marc; Burtin, Etienne; Laurent, Pierre; Rich, James; Guillermo Busca, Nicolas; Tinker, Jeremy; Aubourg, Eric; du Mas des Bourboux, Hélion; Bautista, Julian; Palanque Delabrouille, Nathalie; Delubac, Timothée; Eftekharzadeh, Sarah; Hogg, David W.; Myers, Adam; Vargas-Magaña, Mariana; Pâris, Isabelle; Petitjean, Partick; Rossi, Graziano; Schneider, Donald P.; Tojeiro, Rita; Yeche, Christophe

2017-06-01

In this study, we probe the transition to cosmic homogeneity in the Large Scale Structure (LSS) of the Universe using the CMASS galaxy sample of BOSS spectroscopic survey which covers the largest effective volume to date, 3 h-3 Gpc3 at 0.43 <= z <= 0.7. We study the scaled counts-in-spheres, N(2.97 for r>RH, we find RH = (63.3±0.7) h-1 Mpc, in agreement at the percentage level with the predictions of the ΛCDM model RH=62.0 h-1 Mpc. Thanks to the large cosmic depth of the survey, we investigate the redshift evolution of the transition to homogeneity scale and find agreement with the ΛCDM prediction. Finally, we find that Script D2 is compatible with 3 at scales larger than 300 h-1 Mpc in all redshift bins. These results consolidate the Cosmological Principle and represent a precise consistency test of the ΛCDM model.

EDGES result versus CMB and low-redshift constraints on ionization histories

NASA Astrophysics Data System (ADS)

Witte, Samuel; Villanueva-Domingo, Pablo; Gariazzo, Stefano; Mena, Olga; Palomares-Ruiz, Sergio

2018-05-01

We examine the results from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), which has recently claimed the detection of a strong absorption in the 21 cm hyperfine transition line of neutral hydrogen, at redshifts demarcating the early stages of star formation. More concretely, we study the compatibility of the shape of the EDGES absorption profile, centered at a redshift of z ˜17.2 , with measurements of the reionization optical depth, the Gunn-Peterson optical depth, and Lyman-α emission from star-forming galaxies, for a variety of possible reionization models within the standard Λ CDM framework (that is, a Universe with a cosmological constant Λ and cold dark matter CDM). When, conservatively, we only try to accommodate the location of the absorption dip, we identify a region in the parameter space of the astrophysical parameters that successfully explains all of the aforementioned observations. However, one of the most abnormal features of the EDGES measurement is the absorption amplitude, which is roughly a factor of 2 larger than the maximum allowed value in the Λ CDM framework. We point out that the simple considered astrophysical models that produce the largest absorption amplitudes are unable to explain the depth of the dip and of reproducing the observed shape of the absorption profile.

Particle Astrophysics after COBE- Blois 92- Summary Talk

NASA Astrophysics Data System (ADS)

Primack, J. R.

The IV Rencontres de Blois, on Particle Astrophysics, held at the Ch\\^ateau de Blois, June 15-20, 1992, was a meeting well-timed for a reconsideration of the issues in particle astrophysics in the light of the COBE discovery of the cosmic microwave background (CMB) fluctuations. This is a summary of what I thought were the most interesting things discussed at Blois: (1) The near-success of Cold Dark Matter (CDM) in predicting the COBE fluctuation amplitude, which favors the hypothesis that structure formed in the universe through gravitational collapse. (2) The indications that $\\Omega\\approx1$ and that the power spectrum has a little more power on supercluster and larger scales than CDM. These are suggested by the IRAS and CfA redshift surveys and POTENT galaxy peculiar velocity analysis, and also by the COBE data. (3) The consequent demise of CDM and the rise of hybrid schemes such as Cold+Hot Dark Matter (C+HDM). (4) The possible implications for neutrino masses and mixings, and for cosmology, of the recent results on solar neutrinos. (5) The first discovery of TeV $\\gamma$ rays from an extragalactic source, which was announced at Blois. I also summarize here a number of the exciting ongoing and planned experiments and observations discussed at Blois: CERN experiments on $\

Effects of coupled dark energy on the Milky Way and its satellites

NASA Astrophysics Data System (ADS)

Penzo, Camilla; Macciò, Andrea V.; Baldi, Marco; Casarini, Luciano; Oñorbe, Jose; Dutton, Aaron A.

2016-09-01

We present the first numerical simulations in coupled dark energy cosmologies with high enough resolution to investigate the effects of the coupling on galactic and subgalactic scales. We choose two constant couplings and a time-varying coupling function and we run simulations of three Milky Way-sized haloes (˜1012 M⊙), a lower mass halo (6 × 1011 M⊙) and a dwarf galaxy halo (5 × 109 M⊙). We resolve each halo with several million dark matter particles. On all scales, the coupling causes lower halo concentrations and a reduced number of substructures with respect to Λ cold dark matter (ΛCDM). We show that the reduced concentrations are not due to different formation times. We ascribe them to the extra terms that appear in the equations describing the gravitational dynamics. On the scale of the Milky Way satellites, we show that the lower concentrations can help in reconciling observed and simulated rotation curves, but the coupling values necessary to have a significant difference from ΛCDM are outside the current observational constraints. On the other hand, if other modifications to the standard model allowing a higher coupling (e.g. massive neutrinos) are considered, coupled dark energy can become an interesting scenario to alleviate the small-scale issues of the ΛCDM model.

Inflationary features and shifts in cosmological parameters from Planck 2015 data

NASA Astrophysics Data System (ADS)

Obied, Georges; Dvorkin, Cora; Heinrich, Chen; Hu, Wayne; Miranda, Vinicius

2017-10-01

We explore the relationship between features in the Planck 2015 temperature and polarization data, shifts in the cosmological parameters, and features from inflation. Residuals in the temperature data from the best-fit power-law Λ CDM model at low multipole ℓ≲40 are mainly responsible for the high H0 and low σ8Ωm1 /2 values when comparing the ℓ<1000 portion to the full data set. These same residuals are better fit to inflationary features with a 1.9 σ preference for running of the running of the tilt or a stronger 99% C.L. local significance preference for a sharp drop in power around k =0.004 Mpc-1, relieving the internal tension with H0. At ℓ>1000 , the same in-phase acoustic residuals that drive the global H0 constraints and appear as a lensing anomaly also favor running parameters which allow even lower H0, but not once lensing reconstruction is considered. Polarization spectra are intrinsically highly sensitive to these parameter shifts, and even more so in the Planck 2015 TE data due to an anomalous suppression in power at ℓ≈165 , which disfavors the best-fit H0 Λ CDM solution by more than 2 σ , and high H0 value at almost 3 σ . Current polarization data also slightly enhance the significance of a sharp suppression of large-scale power but leave room for large improvements in the future with cosmic variance limited E -mode measurements.

A cosmological solution to the Impossibly Early Galaxy Problem

NASA Astrophysics Data System (ADS)

Yennapureddy, Manoj K.; Melia, Fulvio

2018-06-01

To understand the formation and evolution of galaxies at redshifts 0 ≲ z ≲ 10, one must invariably introduce specific models (e.g., for the star formation) in order to fully interpret the data. Unfortunately, this tends to render the analysis compliant to the theory and its assumptions, so consensus is still somewhat elusive. Nonetheless, the surprisingly early appearance of massive galaxies challenges the standard model, and the halo mass function estimated from galaxy surveys at z ≳ 4 appears to be inconsistent with the predictions of ΛCDM, giving rise to what has been termed "The Impossibly Early Galaxy Problem" by some workers in the field. A simple resolution to this question may not be forthcoming. The situation with the halos themselves, however, is more straightforward and, in this paper, we use linear perturbation theory to derive the halo mass function over the redshift range 0 ≲ z ≲ 10 for the Rh = ct universe. We use this predicted halo distribution to demonstrate that both its dependence on mass and its very weak dependence on redshift are compatible with the data. The difficulties with ΛCDM may eventually be overcome with refinements to the underlying theory of star formation and galaxy evolution within the halos. For now, however, we demonstrate that the unexpected early formation of structure may also simply be due to an incorrect choice of the cosmology, rather than to yet unknown astrophysical issues associated with the condensation of mass fluctuations and subsequent galaxy formation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ata, Metin; Baumgarten, Falk; Bautista, Julian

We present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshiftsmore » $0.8 < z < 2.2$ and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.5$$\\sigma$$. We determine the spherically averaged BAO distance to $z = 1.52$ to 4.4 per cent precision: $$D_V(z=1.52)=3855\\pm170 \\left(r_{\\rm d}/r_{\\rm d, fid}\\right)\\ $$Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat $$\\Lambda$$CDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Using these BAO data alone and marginalizing over the length of the standard ruler, we find $$\\Omega_{\\Lambda} > 0$$ at 6.5$$\\sigma$$ significance when testing a $$\\Lambda$$CDM model with free curvature.« less

Hints on the nature of dark matter from the properties of Milky Way satellites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderhalden, Donnino; Diemand, Juerg; Schneider, Aurel

2013-03-01

The nature of dark matter is still unknown and one of the most fundamental scientific mysteries. Although successfully describing large scales, the standard cold dark matter model (CDM) exhibits possible shortcomings on galactic and sub-galactic scales. It is exactly at these highly non-linear scales where strong astrophysical constraints can be set on the nature of the dark matter particle. While observations of the Lyman-α forest probe the matter power spectrum in the mildly non-linear regime, satellite galaxies of the Milky Way provide an excellent laboratory as a test of the underlying cosmology on much smaller scales. Here we present resultsmore » from a set of high resolution simulations of a Milky Way sized dark matter halo in eight distinct cosmologies: CDM, warm dark matter (WDM) with a particle mass of 2 keV and six different cold plus warm dark matter (C+WDM) models, varying the fraction, f{sub wdm}, and the mass, m{sub wdm}, of the warm component. We used three different observational tests based on Milky Way satellite observations: the total satellite abundance, their radial distribution and their mass profile. We show that the requirement of simultaneously satisfying all three constraints sets very strong limits on the nature of dark matter. This shows the power of a multi-dimensional small scale approach in ruling out models which would be still allowed by large scale observations.« less

The New Era of Precision Cosmology: Testing Gravity at Large Scales

NASA Technical Reports Server (NTRS)

Prescod-Weinstein, Chanda

2011-01-01

Cosmic acceleration may be the biggest phenomenological mystery in cosmology today. Various explanations for its cause have been proposed, including the cosmological constant, dark energy and modified gravities. Structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy ore modified gravity implement the Press & Schechter formalism (PGF). However, does the PGF apply in all cosmologies? The search is on for a better understanding of universality in the PGF In this talk, I explore the potential for universality and talk about what dark matter haloes may be able to tell us about cosmology. I will also discuss the implications of this and new cosmological experiments for better understanding our theory of gravity.

Singular F(R) cosmology unifying early- and late-time acceleration with matter and radiation domination era

NASA Astrophysics Data System (ADS)

Odintsov, S. D.; Oikonomou, V. K.

2016-06-01

We present some cosmological models which unify the late- and early-time acceleration eras with the radiation and the matter domination era, and we realize the cosmological models by using the theoretical framework of F(R) gravity. Particularly, the first model unifies the late- and early-time acceleration with the matter domination era, and the second model unifies all the evolution eras of our Universe. The two models are described in the same way at early and late times, and only the intermediate stages of the evolution have some differences. Each cosmological model contains two Type IV singularities which are chosen to occur one at the end of the inflationary era and one at the end of the matter domination era. The cosmological models at early times are approximately identical to the R 2 inflation model, so these describe a slow-roll inflationary era which ends when the slow-roll parameters become of order one. The inflationary era is followed by the radiation era and after that the matter domination era follows, which lasts until the second Type IV singularity, and then the late-time acceleration era follows. The models have two appealing features: firstly they produce a nearly scale invariant power spectrum of primordial curvature perturbations and a scalar-to-tensor ratio which are compatible with the most recent observational data and secondly, it seems that the deceleration-acceleration transition is crucially affected by the presence of the second Type IV singularity which occurs at the end of the matter domination era. As we demonstrate, the Hubble horizon at early times shrinks, as expected for an initially accelerating Universe, then during the matter domination era, it expands and finally after the Type IV singularity, the Hubble horizon starts to shrink again, during the late-time acceleration era. Intriguingly enough, the deceleration-acceleration transition, occurs after the second Type IV singularity. In addition, we investigate which F(R) gravity can successfully realize each of the four cosmological epochs.

Spreading out and staying sharp - creating diverse rotation curves via baryonic and self-interaction effects

NASA Astrophysics Data System (ADS)

Creasey, Peter; Sameie, Omid; Sales, Laura V.; Yu, Hai-Bo; Vogelsberger, Mark; Zavala, Jesús

2017-06-01

Galactic rotation curves are a fundamental constraint for any cosmological model. We use controlled N-body simulations of galaxies to study the gravitational effect of baryons in a scenario with collisionless cold dark matter (CDM) versus one with a self-interacting dark matter (SIDM) component. In particular, we examine the inner profiles of the rotation curves in the velocity range Vmax = [30-250] km s-1, whose diversity has been found to be greater than predicted by the ΛCDM scenario. We find that the scatter in the observed rotation curves exceeds that predicted by dark matter only mass-concentration relations in either the CDM nor SIDM models. Allowing for realistic baryonic content and spatial distributions, however, helps create a large variety of rotation curve shapes, which is in a better agreement with observations in the case of self-interactions due to the characteristic cored profiles being more accommodating to the slowly rising rotation curves than CDM. We find individual fits to model two of the most remarkable outliers of similar Vmax, UGC 5721 and IC 2574 - the former a cusp-like rotation curve and the latter a seemingly 8-kpc-cored profile. This diversity in SIDM arises as permutations of overly concentrated haloes with compact baryonic distributions versus underdense haloes with extended baryonic discs. The SIDM solution is promising and its feasibility ultimately depends on the sampling of the halo mass-concentration relation and its interplay with the baryonic profiles, emphasizing the need for a better understanding of the frequency of extreme outliers present in current observational samples.

The ISW effect and the lack of large-angle CMB temperature correlations

NASA Astrophysics Data System (ADS)

Copi, Craig J.; O'Dwyer, Márcio; Starkman, Glenn D.

2016-12-01

It is by now well established that the magnitude of the two-point angular-correlation function of the cosmic microwave background temperature anisotropies is anomalously low for angular separations greater than about 60°. Physics explanations of this anomaly typically focus on the properties of the Universe at the surface of last scattering, relying on the fact that large-angle temperature fluctuations are dominated by the Sachs-Wolfe effect (SW). However, these fluctuations also receive important contributions from the integrated Sachs-Wolfe effect (ISW) at both early (eISW) and late (ℓISW) times. Here, we study the correlations in those large-angle temperature fluctuations and their relative contributions to S1/2- the standard measure of the correlations on large angular scales. We find that in the best-fitting lambda cold dark matter (ΛCDM) cosmology, while the autocorrelation of the early contributions (SW plus eISW) dominates S1/2, there are also significant contributions originating from cross-terms between the early and late contributions. In particular, realizations of ΛCDM with low S1/2 are typically produced from a combination of somewhat low pure-early correlations and accidental cancellations among early-late correlations. We also find that if the pure ℓISW autocorrelations were the only contribution to S1/2 in ΛCDM, then the p-value of the observed cut-sky S1/2 would be unremarkable. This suggests that the physical mechanisms operating only at or near the last scattering surface could explain the observed lack of large-angle correlations, though this is not the typical resolution within ΛCDM.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernal, José Luis; Cuesta, Antonio J.; Verde, Licia, E-mail: joseluis.bernal@icc.ub.edu, E-mail: liciaverde@icc.ub.edu, E-mail: ajcuesta@icc.ub.edu

We perform an empirical consistency test of General Relativity/dark energy by disentangling expansion history and growth of structure constraints. We replace each late-universe parameter that describes the behavior of dark energy with two meta-parameters: one describing geometrical information in cosmological probes, and the other controlling the growth of structure. If the underlying model (a standard wCDM cosmology with General Relativity) is correct, that is under the null hypothesis, the two meta-parameters coincide. If they do not, it could indicate a failure of the model or systematics in the data. We present a global analysis using state-of-the-art cosmological data sets whichmore » points in the direction that cosmic structures prefer a weaker growth than that inferred by background probes. This result could signify inconsistencies of the model, the necessity of extensions to it or the presence of systematic errors in the data. We examine all these possibilities. The fact that the result is mostly driven by a specific sub-set of galaxy clusters abundance data, points to the need of a better understanding of this probe.« less

Cosmology from a gauge induced gravity

NASA Astrophysics Data System (ADS)

Falciano, F. T.; Sadovski, G.; Sobreiro, R. F.; Tomaz, A. A.

2017-09-01

The main goal of the present work is to analyze the cosmological scenario of the induced gravity theory developed in previous works. Such a theory consists on a Yang-Mills theory in a four-dimensional Euclidian spacetime with { SO}(m,n) such that m+n=5 and m\\in {0,1,2} as its gauge group. This theory undergoes a dynamical gauge symmetry breaking via an Inönü-Wigner contraction in its infrared sector. As a consequence, the { SO}(m,n) algebra is deformed into a Lorentz algebra with the emergency of the local Lorentz symmetries and the gauge fields being identified with a vierbein and a spin connection. As a result, gravity is described as an effective Einstein-Cartan-like theory with ultraviolet correction terms and a propagating torsion field. We show that the cosmological model associated with this effective theory has three different regimes. In particular, the high curvature regime presents a de Sitter phase which tends towards a Λ CDM model. We argue that { SO}(m,n) induced gravities are promising effective theories to describe the early phase of the universe.

The Atacama Cosmology Telescope: temperature and gravitational lensing power spectrum measurements from three seasons of data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Sudeep; Louis, Thibaut; Calabrese, Erminia

2014-04-01

We present the temperature power spectra of the cosmic microwave background (CMB) derived from the three seasons of data from the Atacama Cosmology Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. We detect and correct for contamination due to the Galactic cirrus in our equatorial maps. We present the results of a number of tests for possible systematic error and conclude that any effects are not significant compared to the statistical errors we quote. Where they overlap, we cross-correlate the ACT and the South Pole Telescope (SPT) maps and showmore » they are consistent. The measurements of higher-order peaks in the CMB power spectrum provide an additional test of the ΛCDM cosmological model, and help constrain extensions beyond the standard model. The small angular scale power spectrum also provides constraining power on the Sunyaev-Zel'dovich effects and extragalactic foregrounds. We also present a measurement of the CMB gravitational lensing convergence power spectrum at 4.6σ detection significance.« less

The Atacama Cosmology Telescope: Temperature and Gravitational Lensing Power Spectrum Measurements from Three Seasons of Data

NASA Technical Reports Server (NTRS)

Das, Sudeep; Louis, Thibaut; Nolta, Michael R.; Addison, Graeme E.; Battisetti, Elia S.; Bond, J. Richard; Calabrese, Erminia; Crichton, Devin; Devlin, Mark J.; Dicker, Simon;

QCD nature of dark energy at finite temperature: Cosmological implications

NASA Astrophysics Data System (ADS)

Azizi, K.; Katırcı, N.

2016-05-01

The Veneziano ghost field has been proposed as an alternative source of dark energy, whose energy density is consistent with the cosmological observations. In this model, the energy density of the QCD ghost field is expressed in terms of QCD degrees of freedom at zero temperature. We extend this model to finite temperature to search the model predictions from late time to early universe. We depict the variations of QCD parameters entering the calculations, dark energy density, equation of state, Hubble and deceleration parameters on temperature from zero to a critical temperature. We compare our results with the observations and theoretical predictions existing at different eras. It is found that this model safely defines the universe from quark condensation up to now and its predictions are not in tension with those of the standard cosmology. The EoS parameter of dark energy is dynamical and evolves from -1/3 in the presence of radiation to -1 at late time. The finite temperature ghost dark energy predictions on the Hubble parameter well fit to those of Λ CDM and observations at late time.

Beyond H {sub 0} and q {sub 0}: Cosmology is no longer just two numbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neben, Abraham R.; Turner, Michael S., E-mail: abrahamn@mit.edu

2013-06-01

For decades, H {sub 0} and q {sub 0} were the quest of cosmology, as they promised to characterize our 'world model' without reference to a specific cosmological framework. Using Monte Carlo simulations, we show that q {sub 0} cannot be directly measured using distance indicators with both accuracy (without offset away from its true value) and precision (small error bar). While H {sub 0} can be measured with accuracy and precision, to avoid a small bias in its direct measurement (of order 5%) we demonstrate that the pair H {sub 0} and Ω {sub M} (assuming flatness and wmore » = –1) is a better choice of two parameters, even if our world model is not precisely ΛCDM. We illustrate this with analysis of the Constitution set of supernovae and indirectly infer q {sub 0} = –0.57 ± –0.04. Finally, we show that it may be possible to directly determine q {sub 0} with both accuracy and precision using the time dependence of redshifts ('redshift drift').« less

Apparent cosmic acceleration from Type Ia supernovae

NASA Astrophysics Data System (ADS)

Dam, Lawrence H.; Heinesen, Asta; Wiltshire, David L.

2017-11-01

Parameters that quantify the acceleration of cosmic expansion are conventionally determined within the standard Friedmann-Lemaître-Robertson-Walker (FLRW) model, which fixes spatial curvature to be homogeneous. Generic averages of Einstein's equations in inhomogeneous cosmology lead to models with non-rigidly evolving average spatial curvature, and different parametrizations of apparent cosmic acceleration. The timescape cosmology is a viable example of such a model without dark energy. Using the largest available supernova data set, the JLA catalogue, we find that the timescape model fits the luminosity distance-redshift data with a likelihood that is statistically indistinguishable from the standard spatially flat Λ cold dark matter cosmology by Bayesian comparison. In the timescape case cosmic acceleration is non-zero but has a marginal amplitude, with best-fitting apparent deceleration parameter, q_{0}=-0.043^{+0.004}_{-0.000}. Systematic issues regarding standardization of supernova light curves are analysed. Cuts of data at the statistical homogeneity scale affect light-curve parameter fits independent of cosmology. A cosmological model dependence of empirical changes to the mean colour parameter is also found. Irrespective of which model ultimately fits better, we argue that as a competitive model with a non-FLRW expansion history, the timescape model may prove a useful diagnostic tool for disentangling selection effects and astrophysical systematics from the underlying expansion history.

The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological analysis of the DR12 galaxy sample

DOE PAGES

Alam, Shadab; Ata, Metin; Bailey, Stephen; ...

2017-03-28

Here we present cosmological results from the final galaxy clustering data set of the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. Our combined galaxy sample comprises 1.2 million massive galaxies over an effective area of 9329 deg 2 and volume of 18.7 Gpc 3, divided into three partially overlapping redshift slices centred at effective redshifts 0.38, 0.51 and 0.61. We measure the angular diameter distance DM and Hubble parameter H from the baryon acoustic oscillation (BAO) method, in combination with a cosmic microwave background prior on the sound horizon scale, after applying reconstruction to reducemore » non-linear effects on the BAO feature. Using the anisotropic clustering of the pre-reconstruction density field, we measure the product DMH from the Alcock–Paczynski (AP) effect and the growth of structure, quantified by fσ8(z), from redshift-space distortions (RSD). We combine individual measurements presented in seven companion papers into a set of consensus values and likelihoods, obtaining constraints that are tighter and more robust than those from any one method; in particular, the AP measurement from sub-BAO scales sharpens constraints from post-reconstruction BAOs by breaking degeneracy between DM and H. Combined with Planck 2016 cosmic microwave background measurements, our distance scale measurements simultaneously imply curvature ΩK = 0.0003 ± 0.0026 and a dark energy equation-of-state parameter w = -1.01 ± 0.06, in strong affirmation of the spatially flat cold dark matter (CDM) model with a cosmological constant (ΛCDM). Our RSD measurements of fσ8, at 6 per cent precision, are similarly consistent with this model. When combined with supernova Ia data, we find H0 = 67.3 ± 1.0 km s -1 Mpc -1 even for our most general dark energy model, in tension with some direct measurements. Adding extra relativistic species as a degree of freedom loosens the constraint only slightly, to H0 = 67.8 ± 1.2km s -1 Mpc -1. Assuming flat ΛCDM, we find Ωm = 0.310 ± 0.005 and H0 = 67.6 ± 0.5 km s -1 Mpc -1, and we find a 95 per cent upper limit of 0.16 eV c -2 on the neutrino mass sum.« less

The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological analysis of the DR12 galaxy sample

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alam, Shadab; Ata, Metin; Bailey, Stephen

Here we present cosmological results from the final galaxy clustering data set of the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. Our combined galaxy sample comprises 1.2 million massive galaxies over an effective area of 9329 deg 2 and volume of 18.7 Gpc 3, divided into three partially overlapping redshift slices centred at effective redshifts 0.38, 0.51 and 0.61. We measure the angular diameter distance DM and Hubble parameter H from the baryon acoustic oscillation (BAO) method, in combination with a cosmic microwave background prior on the sound horizon scale, after applying reconstruction to reducemore » non-linear effects on the BAO feature. Using the anisotropic clustering of the pre-reconstruction density field, we measure the product DMH from the Alcock–Paczynski (AP) effect and the growth of structure, quantified by fσ8(z), from redshift-space distortions (RSD). We combine individual measurements presented in seven companion papers into a set of consensus values and likelihoods, obtaining constraints that are tighter and more robust than those from any one method; in particular, the AP measurement from sub-BAO scales sharpens constraints from post-reconstruction BAOs by breaking degeneracy between DM and H. Combined with Planck 2016 cosmic microwave background measurements, our distance scale measurements simultaneously imply curvature ΩK = 0.0003 ± 0.0026 and a dark energy equation-of-state parameter w = -1.01 ± 0.06, in strong affirmation of the spatially flat cold dark matter (CDM) model with a cosmological constant (ΛCDM). Our RSD measurements of fσ8, at 6 per cent precision, are similarly consistent with this model. When combined with supernova Ia data, we find H0 = 67.3 ± 1.0 km s -1 Mpc -1 even for our most general dark energy model, in tension with some direct measurements. Adding extra relativistic species as a degree of freedom loosens the constraint only slightly, to H0 = 67.8 ± 1.2km s -1 Mpc -1. Assuming flat ΛCDM, we find Ωm = 0.310 ± 0.005 and H0 = 67.6 ± 0.5 km s -1 Mpc -1, and we find a 95 per cent upper limit of 0.16 eV c -2 on the neutrino mass sum.« less

Mass calibration and cosmological analysis of the SPT-SZ galaxy cluster sample using velocity dispersion σ v and x-ray Y X measurements

DOE PAGES

Bocquet, S.; Saro, A.; Mohr, J. J.; ...

2015-01-30

Here, we present a velocity-dispersion-based mass calibration of the South Pole Telescope Sunyaev-Zel'dovich effect survey (SPT-SZ) galaxy cluster sample. Using a homogeneously selected sample of 100 cluster candidates from 720 deg 2 of the survey along with 63 velocity dispersion (σ v) and 16 X-ray Y X measurements of sample clusters, we simultaneously calibrate the mass-observable relation and constrain cosmological parameters. Our method accounts for cluster selection, cosmological sensitivity, and uncertainties in the mass calibrators. The calibrations using σ v and Y X are consistent at the 0.6σ level, with the σ v calibration preferring ~16% higher masses. We usemore » the full SPTCL data set (SZ clusters+σ v+Y X) to measure σ 8(Ωm/0.27) 0.3 = 0.809 ± 0.036 within a flat ΛCDM model. The SPT cluster abundance is lower than preferred by either the WMAP9 or Planck+WMAP9 polarization (WP) data, but assuming that the sum of the neutrino masses is m ν = 0.06 eV, we find the data sets to be consistent at the 1.0σ level for WMAP9 and 1.5σ for Planck+WP. Allowing for larger Σm ν further reconciles the results. When we combine the SPTCL and Planck+WP data sets with information from baryon acoustic oscillations and Type Ia supernovae, the preferred cluster masses are 1.9σ higher than the Y X calibration and 0.8σ higher than the σ v calibration. Given the scale of these shifts (~44% and ~23% in mass, respectively), we execute a goodness-of-fit test; it reveals no tension, indicating that the best-fit model provides an adequate description of the data. Using the multi-probe data set, we measure Ω m = 0.299 ± 0.009 and σ8 = 0.829 ± 0.011. Within a νCDM model we find Σm ν = 0.148 ± 0.081 eV. We present a consistency test of the cosmic growth rate using SPT clusters. Allowing both the growth index γ and the dark energy equation-of-state parameter w to vary, we find γ = 0.73 ± 0.28 and w = –1.007 ± 0.065, demonstrating that the eΣxpansion and the growth histories are consistent with a ΛCDM universe (γ = 0.55; w = –1).« less

Mass Calibration and Cosmological Analysis of the SPT-SZ Galaxy Cluster Sample Using Velocity Dispersion σ v and X-Ray Y X Measurements

NASA Astrophysics Data System (ADS)

Bocquet, S.; Saro, A.; Mohr, J. J.; Aird, K. A.; Ashby, M. L. N.; Bautz, M.; Bayliss, M.; Bazin, G.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; Carlstrom, J. E.; Chang, C. L.; Chiu, I.; Cho, H. M.; Clocchiatti, A.; Crawford, T. M.; Crites, A. T.; Desai, S.; de Haan, T.; Dietrich, J. P.; Dobbs, M. A.; Foley, R. J.; Forman, W. R.; Gangkofner, D.; George, E. M.; Gladders, M. D.; Gonzalez, A. H.; Halverson, N. W.; Hennig, C.; Hlavacek-Larrondo, J.; Holder, G. P.; Holzapfel, W. L.; Hrubes, J. D.; Jones, C.; Keisler, R.; Knox, L.; Lee, A. T.; Leitch, E. M.; Liu, J.; Lueker, M.; Luong-Van, D.; Marrone, D. P.; McDonald, M.; McMahon, J. J.; Meyer, S. S.; Mocanu, L.; Murray, S. S.; Padin, S.; Pryke, C.; Reichardt, C. L.; Rest, A.; Ruel, J.; Ruhl, J. E.; Saliwanchik, B. R.; Sayre, J. T.; Schaffer, K. K.; Shirokoff, E.; Spieler, H. G.; Stalder, B.; Stanford, S. A.; Staniszewski, Z.; Stark, A. A.; Story, K.; Stubbs, C. W.; Vanderlinde, K.; Vieira, J. D.; Vikhlinin, A.; Williamson, R.; Zahn, O.; Zenteno, A.

2015-02-01

We present a velocity-dispersion-based mass calibration of the South Pole Telescope Sunyaev-Zel'dovich effect survey (SPT-SZ) galaxy cluster sample. Using a homogeneously selected sample of 100 cluster candidates from 720 deg2 of the survey along with 63 velocity dispersion (σ v ) and 16 X-ray Y X measurements of sample clusters, we simultaneously calibrate the mass-observable relation and constrain cosmological parameters. Our method accounts for cluster selection, cosmological sensitivity, and uncertainties in the mass calibrators. The calibrations using σ v and Y X are consistent at the 0.6σ level, with the σ v calibration preferring ~16% higher masses. We use the full SPTCL data set (SZ clusters+σ v +Y X) to measure σ8(Ωm/0.27)0.3 = 0.809 ± 0.036 within a flat ΛCDM model. The SPT cluster abundance is lower than preferred by either the WMAP9 or Planck+WMAP9 polarization (WP) data, but assuming that the sum of the neutrino masses is ∑m ν = 0.06 eV, we find the data sets to be consistent at the 1.0σ level for WMAP9 and 1.5σ for Planck+WP. Allowing for larger ∑m ν further reconciles the results. When we combine the SPTCL and Planck+WP data sets with information from baryon acoustic oscillations and Type Ia supernovae, the preferred cluster masses are 1.9σ higher than the Y X calibration and 0.8σ higher than the σ v calibration. Given the scale of these shifts (~44% and ~23% in mass, respectively), we execute a goodness-of-fit test; it reveals no tension, indicating that the best-fit model provides an adequate description of the data. Using the multi-probe data set, we measure Ωm = 0.299 ± 0.009 and σ8 = 0.829 ± 0.011. Within a νCDM model we find ∑m ν = 0.148 ± 0.081 eV. We present a consistency test of the cosmic growth rate using SPT clusters. Allowing both the growth index γ and the dark energy equation-of-state parameter w to vary, we find γ = 0.73 ± 0.28 and w = -1.007 ± 0.065, demonstrating that the expansion and the growth histories are consistent with a ΛCDM universe (γ = 0.55; w = -1).

Cosmology with a stiff matter era

NASA Astrophysics Data System (ADS)

Chavanis, Pierre-Henri

2015-11-01

We consider the possibility that the Universe is made of a dark fluid described by a quadratic equation of state P =K ρ2 , where ρ is the rest-mass density and K is a constant. The energy density ɛ =ρ c2+K ρ2 is the sum of two terms: a rest-mass term ρ c2 that mimics "dark matter" (P =0 ) and an internal energy term u =K ρ2=P that mimics a "stiff fluid" (P =ɛ ) in which the speed of sound is equal to the speed of light. In the early universe, the internal energy dominates and the dark fluid behaves as a stiff fluid (P ˜ɛ , ɛ ∝a-6). In the late universe, the rest-mass energy dominates and the dark fluid behaves as pressureless dark matter (P ≃0 , ɛ ∝a-3). We provide a simple analytical solution of the Friedmann equations for a universe undergoing a stiff matter era, a dark matter era, and a dark energy era due to the cosmological constant. This analytical solution generalizes the Einstein-de Sitter solution describing the dark matter era, and the Λ CDM model describing the dark matter era and the dark energy era. Historically, the possibility of a primordial stiff matter era first appeared in the cosmological model of Zel'dovich where the primordial universe is assumed to be made of a cold gas of baryons. A primordial stiff matter era also occurs in recent cosmological models where dark matter is made of relativistic self-gravitating Bose-Einstein condensates (BECs). When the internal energy of the dark fluid mimicking stiff matter is positive, the primordial universe is singular like in the standard big bang theory. It expands from an initial state with a vanishing scale factor and an infinite density. We consider the possibility that the internal energy of the dark fluid is negative (while, of course, its total energy density is positive), so that it mimics anti-stiff matter. This happens, for example, when the BECs have an attractive self-interaction with a negative scattering length. In that case, the primordial universe is nonsingular and bouncing like in loop quantum cosmology. At t =0 , the scale factor is finite and the energy density is equal to zero. The universe first has a phantom behavior where the energy density increases with the scale factor, then a normal behavior where the energy density decreases with the scale factor. For the sake of generality, we consider a cosmological constant of arbitrary sign. When the cosmological constant is positive, the Universe asymptotically reaches a de Sitter regime where the scale factor increases exponentially rapidly with time. This can account for the accelerating expansion of the Universe that we observe at present. When the cosmological constant is negative (anti-de Sitter), the evolution of the Universe is cyclic. Therefore, depending on the sign of the internal energy of the dark fluid and on the sign of the cosmological constant, we obtain analytical solutions of the Friedmann equations describing singular and nonsingular expanding, bouncing, or cyclic universes.

Cosmology and astrophysics from relaxed galaxy clusters - V. Consistency with cold dark matter structure formation

NASA Astrophysics Data System (ADS)

Mantz, A. B.; Allen, S. W.; Morris, R. G.

2016-10-01

This is the fifth in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Our sample comprises 40 clusters identified as being dynamically relaxed and hot in Papers I and II of this series. Here we use constraints on cluster mass profiles from X-ray data to test some of the basic predictions of cosmological structure formation in the cold dark matter (CDM) paradigm. We present constraints on the concentration-mass relation for massive clusters, finding a power-law mass dependence with a slope of κm = -0.16 ± 0.07, in agreement with CDM predictions. For this relaxed sample, the relation is consistent with a constant as a function of redshift (power-law slope with 1 + z of κζ = -0.17 ± 0.26), with an intrinsic scatter of σln c = 0.16 ± 0.03. We investigate the shape of cluster mass profiles over the radial range probed by the data (typically ˜50 kpc-1 Mpc), and test for departures from the simple Navarro-Frenk-White (NFW) form, for which the logarithmic slope of the density profile tends to -1 at small radii. Specifically, we consider as alternatives the generalized NFW (GNFW) and Einasto parametrizations. For the GNFW model, we find an average value of (minus) the logarithmic inner slope of β = 1.02 ± 0.08, with an intrinsic scatter of σβ = 0.22 ± 0.07, while in the Einasto case we constrain the average shape parameter to be α = 0.29 ± 0.04 with an intrinsic scatter of σα = 0.12 ± 0.04. Our results are thus consistent with the simple NFW model on average, but we clearly detect the presence of intrinsic, cluster-to-cluster scatter about the average.

THE LOCAL GROUP IN THE COSMIC WEB

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forero-Romero, J. E.; González, R., E-mail: je.forero@uniandes.edu.co, E-mail: regonzar@astro.puc.cl

We explore the characteristics of the cosmic web around Local-Group (LG)-like pairs using a cosmological simulation in the ΛCDM cosmology. We use the Hessian of the gravitational potential to classify regions on scales of ∼2 Mpc as a peak, sheet, filament, or void. The sample of LG counterparts is represented by two samples of halo pairs. The first is a general sample composed of pairs with similar masses and isolation criteria as observed for the LG. The second is a subset with additional observed kinematic constraints such as relative pair velocity and separation. We find that the pairs in the LGmore » sample with all constraints are: (1) preferentially located in filaments and sheets, (2) located in a narrow range of local overdensity 0 < δ < 2, web ellipticity 0.1 < e < 1.0, and prolateness –0.4 < p < 0.4, (3) strongly aligned with the cosmic web. The alignments are such that the pair orbital angular momentum tends to be perpendicular to the smallest tidal eigenvector, e-hat {sub 3}, which lies along the filament direction or the sheet plane. A stronger alignment is present for the vector linking the two halos with the vector e-hat {sub 3}. Additionally, we fail to find a strong correlation between the spin of each halo in the pair with the cosmic web. All of these trends are expected to a great extent from the selection of LG total mass in the general sample. Applied to the observed LG, there is a potential conflict between the alignments of the different satellite planes and the numerical evidence for satellite accretion along filaments; the direction defined by e-hat {sub 3}. This highlights the relevance of achieving a precise characterization for the location of the LG in the cosmic web in the cosmological context provided by ΛCDM.« less

Extensive investigation of the generalized dark matter model

NASA Astrophysics Data System (ADS)

Kopp, Michael; Skordis, Constantinos; Thomas, Dan B.

2016-08-01

The cold dark matter (CDM) model, wherein the dark matter is treated as a pressureless perfect fluid, provides a good fit to galactic and cosmological data. With the advent of precision cosmology, it should be asked whether this simplest model needs to be extended, and whether doing so could improve our understanding of the properties of dark matter. One established parametrization for generalizing the CDM fluid is the generalized dark matter (GDM) model, in which dark matter is an imperfect fluid with pressure and shear viscosity that fulfill certain postulated closure equations. We investigate these closure equations and the three new parametric functions they contain: the background equation of state w , the speed of sound cs2 and the viscosity cvis2. Taking these functions to be constant parameters, we analyze an exact solution of the perturbed Einstein equations in a flat GDM-dominated universe and discuss the main effects of the three parameters on the cosmic microwave background (CMB). Our analysis suggests that the CMB alone is not able to distinguish between the GDM sound speed and viscosity parameters, but that other observables, such as the matter power spectrum, are required to break this degeneracy. In order to elucidate further the meaning of the GDM closure equations, we also consider other descriptions of imperfect fluids that have a nonperturbative definition and relate these to the GDM model. In particular, we consider scalar fields, an effective field theory (EFT) of fluids, an EFT of large-scale structure, nonequilibrium thermodynamics and tightly coupled fluids. These descriptions could be used to extend the GDM model into the nonlinear regime of structure formation, which is necessary if the wealth of data available on those scales is to be employed in constraining the model. We also derive the initial conditions for adiabatic and isocurvature perturbations in the presence of GDM and standard cosmological fluids and provide the result in a form ready for implementation in Einstein-Boltzmann solvers.

Stage 4 Cosmic Microwave Background Experiment

NASA Astrophysics Data System (ADS)

Carlstrom, John

2016-03-01

Measurements of the CMB have driven our understanding of the universe and the physics that govern its evolution from quantum fluctuations to its present state. They provide the foundation for the remarkable 6-parameter cosmological model, ΛCDM, which fits all cosmological data, although there are some tensions which may hint at new physics, or simply unaccounted systematics. Far from being the last word in cosmology, the model raises deep questions: Is Inflation correct? What is its energy scale? What is the dark matter? What is the nature of dark energy? There is still a lot to learn from the CMB measurements. We are searching for the unique B-mode polarization that would be induced on the CMB by inflationary gravitational waves. We are able to detect the impact of the neutrino background on the CMB, which can be used to provide precise constraints on the number and masses of the neutrinos. We are untangling the correlations in the CMB induced by gravitational lensing to make maps of all the mass in the universe. We are measuring the scattering of the CMB by ionized structures, the Sunyaev-Zel'dovich effects, to detect clusters of galaxies and soon to map the momentum of the universe in addition to its density. To realize the enormous potential of these CMB tools we need to greatly increase the sensitivity of CMB measurements. We can expect significant advances in the next few years as the ongoing experiments deploy of order 10,000 detectors (Stage III), but to achieve critical threshold crossing goals we need to go further. The CMB community is therefore planning CMB-S4, an ambitious next generation (Stage IV) ground-based program with order of 500,000 detectors with science goals that include detecting or ruling out large field inflationary models, determining the number and masses of the neutrinos, providing precision constraints on dark energy through its impact on structure formation, as well as searching for cracks in the ΛCDM model.

Dark Energy and the Cosmological Constant: A Brief Introduction

ERIC Educational Resources Information Center

Harvey, Alex

2009-01-01

The recently observed acceleration of the expansion of the universe is a topic of intense interest. The favoured causes are the "cosmological constant" or "dark energy". The former, which appears in the Einstein equations as the term [lambda]g[subscript [mu]v], provides an extremely simple, well-defined mechanism for the acceleration. However,…

Reconstructing matter profiles of spherically compensated cosmic regions in ΛCDM cosmology

NASA Astrophysics Data System (ADS)

de Fromont, Paul; Alimi, Jean-Michel

2018-02-01

The absence of a physically motivated model for large-scale profiles of cosmic voids limits our ability to extract valuable cosmological information from their study. In this paper, we address this problem by introducing the spherically compensated cosmic regions, named CoSpheres. Such cosmic regions are identified around local extrema in the density field and admit a unique compensation radius R1 where the internal spherical mass is exactly compensated. Their origin is studied by extending the standard peak model and implementing the compensation condition. Since the compensation radius evolves as the Universe itself, R1(t) ∝ a(t), CoSpheres behave as bubble Universes with fixed comoving volume. Using the spherical collapse model, we reconstruct their profiles with a very high accuracy until z = 0 in N-body simulations. CoSpheres are symmetrically defined and reconstructed for both central maximum (seeding haloes and galaxies) and minimum (identified with cosmic voids). We show that the full non-linear dynamics can be solved analytically around this particular compensation radius, providing useful predictions for cosmology. This formalism highlights original correlations between local extremum and their large-scale cosmic environment. The statistical properties of these spherically compensated cosmic regions and the possibilities to constrain efficiently both cosmology and gravity will be investigated in companion papers.

The effect of interacting dark energy on local measurements of the Hubble constant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Odderskov, Io; Baldi, Marco; Amendola, Luca, E-mail: isho07@phys.au.dk, E-mail: marco.baldi5@unibo.it, E-mail: l.amendola@thphys.uni-heidelberg.de

2016-05-01

In the current state of cosmology, where cosmological parameters are being measured to percent accuracy, it is essential to understand all sources of error to high precision. In this paper we present the results of a study of the local variations in the Hubble constant measured at the distance scale of the Coma Cluster, and test the validity of correcting for the peculiar velocities predicted by gravitational instability theory. The study is based on N-body simulations, and includes models featuring a coupling between dark energy and dark matter, as well as two ΛCDM simulations with different values of σ{sub 8}.more » It is found that the variance in the local flows is significantly larger in the coupled models, which increases the uncertainty in the local measurements of the Hubble constant in these scenarios. By comparing the results from the different simulations, it is found that most of the effect is caused by the higher value of σ{sub 8} in the coupled cosmologies, though this cannot account for all of the additional variance. Given the discrepancy between different estimates of the Hubble constant in the universe today, cosmological models causing a greater cosmic variance is something that we should be aware of.« less

Constraints on modified gravity from Planck 2015: when the health of your theory makes the difference

NASA Astrophysics Data System (ADS)

Salvatelli, Valentina; Piazza, Federico; Marinoni, Christian

2016-09-01

We use the effective field theory of dark energy (EFT of DE) formalism to constrain dark energy models belonging to the Horndeski class with the recent Planck 2015 CMB data. The space of theories is spanned by a certain number of parameters determining the linear cosmological perturbations, while the expansion history is set to that of a standard ΛCDM model. We always demand that the theories be free of fatal instabilities. Additionally, we consider two optional conditions, namely that scalar and tensor perturbations propagate with subliminal speed. Such criteria severely restrict the allowed parameter space and are thus very effective in shaping the posteriors. As a result, we confirm that no theory performs better than ΛCDM when CMB data alone are analysed. Indeed, the healthy dark energy models considered here are not able to reproduce those phenomenological behaviours of the effective Newton constant and gravitational slip parameters that, according to previous studies, best fit the data.

Possible signals of vacuum dynamics in the Universe

NASA Astrophysics Data System (ADS)

Peracaula, Joan Solà; de Cruz Pérez, Javier; Gómez-Valent, Adrià

2018-05-01

We study a generic class of time-evolving vacuum models which can provide a better phenomenological account of the overall cosmological observations as compared to the ΛCDM. Among these models, the running vacuum model (RVM) appears to be the most motivated and favored one, at a confidence level of ˜3σ. We further support these results by computing the Akaike and Bayesian information criteria. Our analysis also shows that we can extract fair signals of dynamical dark energy (DDE) by confronting the same set of data to the generic XCDM and CPL parametrizations. In all cases we confirm that the combined triad of modern observations on Baryonic Acoustic Oscillations, Large Scale Structure formation, and the Cosmic Microwave Background, provide the bulk of the signal sustaining a possible vacuum dynamics. In the absence of any of these three crucial data sources, the DDE signal can not be perceived at a significant confidence level. Its possible existence could be a cure for some of the tensions existing in the ΛCDM when confronted to observations.

Constraints on modified gravity from Planck 2015: when the health of your theory makes the difference

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salvatelli, Valentina; Piazza, Federico; Marinoni, Christian, E-mail: Valentina.Salvatelli@cpt.univ-mrs.fr, E-mail: Federico.Piazza@cpt.univ-mrs.fr, E-mail: Christian.Marinoni@cpt.univ-mrs.fr

We use the effective field theory of dark energy (EFT of DE) formalism to constrain dark energy models belonging to the Horndeski class with the recent Planck 2015 CMB data. The space of theories is spanned by a certain number of parameters determining the linear cosmological perturbations, while the expansion history is set to that of a standard ΛCDM model. We always demand that the theories be free of fatal instabilities. Additionally, we consider two optional conditions, namely that scalar and tensor perturbations propagate with subliminal speed. Such criteria severely restrict the allowed parameter space and are thus very effectivemore » in shaping the posteriors. As a result, we confirm that no theory performs better than ΛCDM when CMB data alone are analysed. Indeed, the healthy dark energy models considered here are not able to reproduce those phenomenological behaviours of the effective Newton constant and gravitational slip parameters that, according to previous studies, best fit the data.« less

Declining Rotation Curves at z = 2 in ΛCDM Galaxy Formation Simulations

NASA Astrophysics Data System (ADS)

Teklu, Adelheid F.; Remus, Rhea-Silvia; Dolag, Klaus; Arth, Alexander; Burkert, Andreas; Obreja, Aura; Schulze, Felix

2018-02-01

Selecting disk galaxies from the cosmological, hydrodynamical simulation Magneticum Pathfinder, we show that almost half of our poster child disk galaxies at z = 2 show significantly declining rotation curves and low dark matter fractions, very similar to recently reported observations. These galaxies do not show any anomalous behavior, they reside in standard dark matter halos, and they typically grow significantly in mass until z = 0, where they span all morphological classes, including disk galaxies matching present-day rotation curves and observed dark matter fractions. Our findings demonstrate that declining rotation curves and low dark matter fractions in rotation-dominated galaxies at z = 2 appear naturally within the ΛCDM paradigm and reflect the complex baryonic physics, which plays a role at the peak epoch of star formation. In addition, we find some dispersion-dominated galaxies at z = 2 that host a significant gas disk and exhibit similar shaped rotation curves as the disk galaxy population, rendering it difficult to differentiate between these two populations with currently available observation techniques.

Baryon acoustic oscillations in the Ly α forest of BOSS quasars

DOE PAGES

Busca, N. G.; Delubac, T.; Rich, J.; ...

2013-04-04

In this paper, we report a detection of the baryon acoustic oscillation (BAO) feature in the three-dimensional correlation function of the transmitted flux fraction in the Lyα forest of high-redshift quasars. The study uses 48,640 quasars in the redshift rangemore » $$2.1\\le z \\le 3.5$$ from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third generation of the Sloan Digital Sky Survey (SDSS-III). At a mean redshift $z=2.3$, we measure the monopole and quadrupole components of the correlation function for separations in the range 20 h -1 Mpc < r < 200 h -1. A peak in the correlation function is seen at a separation equal to $$(1.01\\pm0.03)$$ times the distance expected for the BAO peak within a concordance $$\\Lambda$$CDM cosmology. This first detection of the BAO peak at high redshift, when the universe was strongly matter dominated, results in constraints on the angular diameter distance D A and the expansion rate $H$ at $z=2.3$ that, combined with priors on $$H_0$$ and the baryon density, require the existence of dark energy. Combined with constraints derived from Cosmic Microwave Background (CMB) observations, this result implies $$H(z=2.3)=(224\\pm8){\\rm km\\,s^{-1}Mpc^{-1}}$$, indicating that the time derivative of the cosmological scale parameter $$\\dot{a}=H(z=2.3)/(1+z)$$ is significantly greater than that measured with BAO at $$z\\sim0.5$$. This demonstrates that the expansion was decelerating in the range 0.7 < z < 2.3 , as expected from the matter domination during this epoch. Finally, combined with measurements of H 0, one sees the pattern of deceleration followed by acceleration characteristic of a dark-energy dominated universe.« less

Reconstruction of the Dark Energy Equation of State from the Latest Observations

NASA Astrophysics Data System (ADS)

Dai, Ji-Ping; Yang, Yang; Xia, Jun-Qing

2018-04-01

Since the discovery of the accelerating expansion of our universe in 1998, studying the features of dark energy has remained a hot topic in modern cosmology. In the literature, dark energy is usually described by w ≡ P/ρ, where P and ρ denote its pressure and energy density. Therefore, exploring the evolution of w is the key approach to understanding dark energy. In this work, we adopt three different methods, polynomial expansion, principal component analysis, and the correlated prior method, to reconstruct w with a collection of the latest observations, including the type-Ia supernova, cosmic microwave background, large-scale structure, Hubble measurements, and baryon acoustic oscillations (BAOs), and find that the concordance cosmological constant model (w = ‑1) is still safely consistent with these observational data at the 68% confidence level. However, when we add the high-redshift BAO measurement from the Lyα forest (Lyα FB) of BOSS DR11 quasars into the calculation, there is a significant impact on the reconstruction result. In the standard ΛCDM model, since the Lyα FB data slightly prefer a negative dark energy density, in order to avoid this problem, a dark energy model with a w significantly smaller than ‑1 is needed to explain this Lyα FB data. In this work, we find the consistent conclusion that there is a strong preference for the time-evolving behavior of dark energy w at high redshifts, when including the Lyα FB data. Therefore, we think that this Lyα FB data needs to be watched carefully attention when studying the evolution of the dark energy equation of state.

Calculating the Sachs-Wolfe Effect from Solutions of Null Geodesics in Perturbed FRW Spacetime

NASA Astrophysics Data System (ADS)

Arroyo-Cárdenas, C. A.; Muñoz-Cuartas, J. C.

2017-07-01

In the upcoming precision era in cosmology, fine grained effects will be measured accurately. In particular, the late integrated Sachs-Wolfe (ISW) effect measurements will be improved to levels of unprecedented precision. The ISW consists on temperature fluctuations in the CMB due to gravitational redshift induced by the evolving potential well of large scale structure in the Universe. Currently there is large controversy related to the actual observability of the ISW effect. In principle, it is expected that, as an effect of the late accelerated expansion of the universe motivated by the current amount of dark energy, large scale structures may evolve rapidly, inducing an observable signature in the CMB photons in the way of a ISW anisotropy in the CMB. Tension arises since using galaxy redshift surveys some works report a temperature fluctuations with amplitude smaller than predicted by the Lambda-CDM. We argue that these discrepancies may be originated in the approximation that one has to make to get the classic Sachs-Wolfe effect. In this work, we compare the classic Sachs-Wolfe approximation with an exact solution to the propagation of photons in a dynamical background. We solve numerically the null geodesics on a perturbed FRW spacetime in the Newtonian gauge. From null geodesics, temperature fluctuations in the CMB due to the evolving potential has been calculated. Since solving geodesics accounts for more terms than solving the Sachs-Wolfe (approximated) integral, our results are more accurate. We have been able to substract the background cosmological redshift with the information provided by null geodesics, which allows to get an estimate of the integrated Sachs-Wolfe effect contribution to the temperature of the CMB.

A COMPARATIVE ANALYSIS OF THE SUPERNOVA LEGACY SURVEY SAMPLE WITH ΛCDM AND THE R{sub h}=ct UNIVERSE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio

The use of Type Ia supernovae (SNe Ia) has thus far produced the most reliable measurement of the expansion history of the universe, suggesting that ΛCDM offers the best explanation for the redshift–luminosity distribution observed in these events. However, analysis of other kinds of sources, such as cosmic chronometers, gamma-ray bursts, and high-z quasars, conflicts with this conclusion, indicating instead that the constant expansion rate implied by the R{sub h} = ct universe is a better fit to the data. The central difficulty with the use of SNe Ia as standard candles is that one must optimize three or fourmore » nuisance parameters characterizing supernova (SN) luminosities simultaneously with the parameters of an expansion model. Hence, in comparing competing models, one must reduce the data independently for each. We carry out such a comparison of ΛCDM and the R{sub h} = ct universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. However, since R{sub h} = ct has only one free parameter (the Hubble constant), it follows from a standard model selection technique that it is to be preferred over ΛCDM, the minimalist version of which has three (the Hubble constant, the scaled matter density, and either the spatial curvature constant or the dark energy equation-of-state parameter). We estimate using the Bayes Information Criterion that in a pairwise comparison, the likelihood of R{sub h} = ct is ∼90%, compared with only ∼10% for a minimalist form of ΛCDM, in which dark energy is simply a cosmological constant. Compared to R{sub h} = ct, versions of the standard model with more elaborate parametrizations of dark energy are judged to be even less likely.« less

Beta Function Quintessence Cosmological Parameters and Fundamental Constants I: Power and Inverse Power Law Dark Energy Potentials

NASA Astrophysics Data System (ADS)

Thompson, Rodger I.

2018-04-01

This investigation explores using the beta function formalism to calculate analytic solutions for the observable parameters in rolling scalar field cosmologies. The beta function in this case is the derivative of the scalar ϕ with respect to the natural log of the scale factor a, β (φ )=d φ /d ln (a). Once the beta function is specified, modulo a boundary condition, the evolution of the scalar ϕ as a function of the scale factor is completely determined. A rolling scalar field cosmology is defined by its action which can contain a range of physically motivated dark energy potentials. The beta function is chosen so that the associated "beta potential" is an accurate, but not exact, representation of the appropriate dark energy model potential. The basic concept is that the action with the beta potential is so similar to the action with the model potential that solutions using the beta action are accurate representations of solutions using the model action. The beta function provides an extra equation to calculate analytic functions of the cosmologies parameters as a function of the scale factor that are that are not calculable using only the model action. As an example this investigation uses a quintessence cosmology to demonstrate the method for power and inverse power law dark energy potentials. An interesting result of the investigation is that the Hubble parameter H is almost completely insensitive to the power of the potentials and that ΛCDM is part of the family of quintessence cosmology power law potentials with a power of zero.

Constraints on running vacuum model with H(z) and f σ8

NASA Astrophysics Data System (ADS)

Geng, Chao-Qiang; Lee, Chung-Chi; Yin, Lu

2017-08-01

We examine the running vacuum model with Λ (H) = 3 ν H2 + Λ0, where ν is the model parameter and Λ0 is the cosmological constant. From the data of the cosmic microwave background radiation, weak lensing and baryon acoustic oscillation along with the time dependent Hubble parameter H(z) and weighted linear growth f (z)σ8(z) measurements, we find that ν=(1.37+0.72-0.95)× 10-4 with the best fitted χ2 value slightly smaller than that in the ΛCDM model.

Evolution of the distribution of baryons in a simulated Local Group Universe

NASA Astrophysics Data System (ADS)

Peirani, S.

2012-12-01

Using hydrodynamical zoom simulations in the standard ΛCDM cosmology, we have investigated the evolution of the distribution of baryons (gas and stars) in a local group-type universe. We found that physical mechanisms able to drive the gas out of the virial radius at high redshifts (such as AGN) will have a stronger impact on the deficit of baryons in the mass budget of Milky Way type-galaxies at present times than those that expel the gas in the longer, late phases of galaxy formation.

COSMOLOGY OF CHAMELEONS WITH POWER-LAW COUPLINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mota, David F.; Winther, Hans A.

2011-05-20

In chameleon field theories, a scalar field can couple to matter with gravitational strength and still evade local gravity constraints due to a combination of self-interactions and the couplings to matter. Originally, these theories were proposed with a constant coupling to matter; however, the chameleon mechanism also extends to the case where the coupling becomes field dependent. We study the cosmology of chameleon models with power-law couplings and power-law potentials. It is found that these generalized chameleons, when viable, have a background expansion very close to {Lambda}CDM, but can in some special cases enhance the growth of the linear perturbationsmore » at low redshifts. For the models we consider, it is found that this region of the parameter space is ruled out by local gravity constraints. Imposing a coupling to dark matter only, the local constraints are avoided, and it is possible to have observable signatures on the linear matter perturbations.« less

Entropy in universes evolving from initial to final de Sitter eras

NASA Astrophysics Data System (ADS)

Mimoso, José P.; Pavón, Diego

2014-05-01

This work studies the behavior of entropy in recent cosmological models that start with an initial de Sitter expansion phase, go through the conventional radiation and matter dominated eras to be followed by a final de Sitter epoch. In spite of their seemingly similarities (observationally they are close to the Λ-CDM model), different models deeply differ in their physics. The second law of thermodynamics encapsulates the underlying microscopic, statistical description, and hence we investigate it in the present work. Our study reveals that the entropy of the apparent horizon plus that of matter and radiation inside it, increases and is a concave function of the scale factor. Thus thermodynamic equilibrium is approached in the last de Sitter era, and this class of models is thermodynamically correct. Cosmological models that do not approach equilibrium appear in conflict with the second law of thermodynamics. (Based on Mimoso & Pavon 2013)

Visser's massive graviton bimetric theory revisited

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roany, Alain de; Chauvineau, Bertrand; Freitas Pacheco, Jose A. de

2011-10-15

A massive gravity theory was proposed by Visser in the late 1990s. This theory, based on a background metric b{sub {alpha}{beta}} and on an usual dynamical metric g{sub {alpha}{beta}} has the advantage of being free of ghosts as well as discontinuities present in other massive theories proposed in the past. In the present investigation, the equations of Visser's theory are revisited with particular care on the related conservation laws. It will be shown that a multiplicative factor is missing in the graviton tensor originally derived by Visser, which has no incidence on the weak field approach but becomes important inmore » the strong field regime when, for instance, cosmological applications are considered. In this case, contrary to some previous claims found in the literature, we conclude that a nonstatic background metric is required in order to obtain a solution able to mimic the {Lambda}CDM cosmology.« less

Bulk viscous cosmology with causal transport theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piattella, Oliver F.; Fabris, Júlio C.; Zimdahl, Winfried, E-mail: oliver.piattella@gmail.com, E-mail: fabris@pq.cnpq.br, E-mail: winfried.zimdahl@pq.cnpq.br

2011-05-01

We consider cosmological scenarios originating from a single imperfect fluid with bulk viscosity and apply Eckart's and both the full and the truncated Müller-Israel-Stewart's theories as descriptions of the non-equilibrium processes. Our principal objective is to investigate if the dynamical properties of Dark Matter and Dark Energy can be described by a single viscous fluid and how such description changes when a causal theory (Müller-Israel-Stewart's, both in its full and truncated forms) is taken into account instead of Eckart's non-causal one. To this purpose, we find numerical solutions for the gravitational potential and compare its behaviour with the corresponding ΛCDMmore » case. Eckart's and the full causal theory seem to be disfavoured, whereas the truncated theory leads to results similar to those of the ΛCDM model for a bulk viscous speed in the interval 10{sup −11} || cb{sup 2} ∼< 10{sup −8}.« less

Modifying gravity: you cannot always get what you want.

PubMed

Starkman, Glenn D

2011-12-28

The combination of general relativity (GR) and the Standard Model of particle physics disagrees with numerous observations on scales from our Solar System up. In the canonical concordance model of Lambda cold dark matter (ΛCDM) cosmology, many of these contradictions between theory and data are removed or alleviated by the introduction of three completely independent new components of stress energy--the inflaton, dark matter and dark energy. Each of these in its turn is meant to have dominated (or to currently dominate) the dynamics of the Universe. There is, until now, no non-gravitational evidence for any of these dark sectors, nor is there evidence (though there may be motivation) for the required extension of the Standard Model. An alternative is to imagine that it is GR that must be modified to account for some or all of these disagreements. Certain coincidences of scale even suggest that one might expect not to make independent modifications of the theory to replace each of the three dark sectors. Because they must address the most different types of data, attempts to replace dark matter with modified gravity are the most controversial. A phenomenological model (or family of models), modified Newtonian dynamics, has, over the last few years, seen several covariant realizations. We discuss a number of challenges that any model that seeks to replace dark matter with modified gravity must face: the loss of Birkhoff's theorem, and the calculational simplifications it implies; the failure to explain clusters, whether static or interacting, and the consequent need to introduce dark matter of some form, whether hot dark matter neutrinos or dark fields that arise in new sectors of the modified gravity theory; the intrusion of cosmological expansion into the modified force law, which arises precisely because of the coincidence in scale between the centripetal acceleration at which Newtonian gravity fails in galaxies and the cosmic acceleration. We conclude with the observation that, although modified gravity may indeed manage to replace dark matter, it is likely to do so by becoming or at least incorporating a dark matter theory itself.

Can the Λ CDM model reproduce MOND-like behavior?

NASA Astrophysics Data System (ADS)

Dai, De-Chang; Lu, Chunyu

2017-12-01

It is usually believed that MOND can describe the galactic rotational curves with only baryonic matter and without any dark matter very well, while the Λ CDM model is expected to have difficulty in reproducing MOND-like behavior. Here, we use EAGLE's data to learn whether the Λ CDM model can reproduce MOND-like behavior. EAGLE's simulation result clearly reproduces the MOND-like behavior for ab⪆10-12 m/s 2 at z =0 , although the acceleration constant, a0, is a little larger than the observational data indicate. We find that a0 increases with the redshift in a way different from what Milgrom proposed (a0∝H ). Therefore, while galaxy rotation curves can be fitted by MOND's empirical function in the Λ CDM model, there is no clear connection between a0 and the Hubble constant. We also find that a0 at z ⪆1 is well separated from a0 at z =0 . Once we have enough galaxies observed at high redshifts, we will be able to rule out the modified gravity model based on MOND-like empirical function with a z -independent a0.

Power spectrum, correlation function, and tests for luminosity bias in the CfA redshift survey

NASA Astrophysics Data System (ADS)

Park, Changbom; Vogeley, Michael S.; Geller, Margaret J.; Huchra, John P.

1994-08-01

We describe and apply a method for directly computing the power spectrum for the galaxy distribution in the extension of the Center for Astrophysics Redshift Survey. Tests show that our technique accurately reproduces the true power spectrum for k greater than 0.03 h Mpc-1. The dense sampling and large spatial coverage of this survey allow accurate measurement of the redshift-space power spectrum on scales from 5 to approximately 200 h-1 Mpc. The power spectrum has slope n approximately equal -2.1 on small scales (lambda less than or equal 25 h-1 Mpc) and n approximately -1.1 on scales 30 less than lambda less than 120 h-1 Mpc. On larger scales the power spectrum flattens somewhat, but we do not detect a turnover. Comparison with N-body simulations of cosmological models shows that an unbiased, open universe CDM model (OMEGA h = 0.2) and a nonzero cosmological constant (CDM) model (OMEGA h = 0.24, lambdazero = 0.6, b = 1.3) match the CfA power spectrum over the wavelength range we explore. The standard biased CDM model (OMEGA h = 0.5, b = 1.5) fails (99% significance level) because it has insufficient power on scales lambda greater than 30 h-1 Mpc. Biased CDM with a normalization that matches the Cosmic Microwave Background (CMB) anisotropy (OMEGA h = 0.5, b = 1.4, sigma8 (mass) = 1) has too much power on small scales to match the observed galaxy power spectrum. This model with b = 1 matches both Cosmic Background Explorer Satellite (COBE) and the small-scale power spect rum but has insufficient power on scales lambda approximately 100 h-1 Mpc. We derive a formula for the effect of small-scale peculiar velocities on the power spectrum and combine this formula with the linear-regime amplification described by Kaiser to compute an estimate of the real-space power spectrum. Two tests reveal luminosity bias in the galaxy distribution: First, the amplitude of the power spectrum is approximately 40% larger for the brightest 50% of galaxies in volume-limited samples that have Mlim greater than M*. This bias in the power spectrum is independent of scale, consistent with the peaks-bias paradigm for galaxy formation. Second, the distribution of local density around galaxies shows that regions of moderate and high density contain both very bright (M less than M* = -19.2 + 5 log h) and fainter galaxies, but that voids preferentially harbor fainter galaxies (approximately 2 sigma significance level).

New Kinematical Constraints on Cosmic Acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rapetti, David; Allen, Steve W.; Amin, Mustafa A.

2007-05-25

We present and employ a new kinematical approach to ''dark energy'' studies. We construct models in terms of the dimensionless second and third derivatives of the scale factor a(t) with respect to cosmic time t, namely the present-day value of the deceleration parameter q{sub 0} and the cosmic jerk parameter, j(t). An elegant feature of this parameterization is that all {Lambda}CDM models have j(t)=1 (constant), which facilitates simple tests for departures from the {Lambda}CDM paradigm. Applying our model to redshift-independent distance measurements, from type Ia supernovae and X-ray cluster gas mass fraction measurements, we obtain clear statistical evidence for amore » late time transition from a decelerating to an accelerating phase. For a flat model with constant jerk, j(t)=j, we measure q{sub 0}=-0.81 {+-} 0.14 and j=2.16 +0.81 -0.75, results that are consistent with {Lambda}CDM at about the 1{sigma} confidence level. In comparison to dynamical analyses, the kinematical approach uses a different model set and employs a minimum of prior information, being independent of any particular gravity theory. The results obtained with this new approach therefore provide important additional information and we argue that both kinematical and dynamical techniques should be employed in future dark energy studies, where possible.« less

Did Cosmology Trigger the Origin of the Solar System?

NASA Technical Reports Server (NTRS)

Blome, H.-J.; Wilson, T. L.

2011-01-01

It is a matter of curious coincidence that the Solar System formed 4.6 billion years ago around the same epoch that the Friedmann-Lemaitre (FL) universe became -dominated or dark-energy-dominated, where is the cosmological constant. This observation was made in the context of known gravitational anomalies that affect spacecraft orbits during planetary flyby's and the Pioneer anomaly, both possibly having connections with cosmology. In addition, it has been known for some time that the Universe is not only expanding but accelerating as well. Hence one must add the onset of cosmological acceleration in the FL universe as having a possible influence on the origin of the Solar System. These connections will now be examined in greater detail.

Dark energy two decades after: observables, probes, consistency tests.

PubMed

Huterer, Dragan; Shafer, Daniel L

2018-01-01

The discovery of the accelerating universe in the late 1990s was a watershed moment in modern cosmology, as it indicated the presence of a fundamentally new, dominant contribution to the energy budget of the universe. Evidence for dark energy, the new component that causes the acceleration, has since become extremely strong, owing to an impressive variety of increasingly precise measurements of the expansion history and the growth of structure in the universe. Still, one of the central challenges of modern cosmology is to shed light on the physical mechanism behind the accelerating universe. In this review, we briefly summarize the developments that led to the discovery of dark energy. Next, we discuss the parametric descriptions of dark energy and the cosmological tests that allow us to better understand its nature. We then review the cosmological probes of dark energy. For each probe, we briefly discuss the physics behind it and its prospects for measuring dark energy properties. We end with a summary of the current status of dark energy research.

The Q continuum simulation: Harnessing the power of GPU accelerated supercomputers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heitmann, Katrin; Frontiere, Nicholas; Sewell, Chris

2015-08-01

Modeling large-scale sky survey observations is a key driver for the continuing development of high-resolution, large-volume, cosmological simulations. We report the first results from the "Q Continuum" cosmological N-body simulation run carried out on the GPU-accelerated supercomputer Titan. The simulation encompasses a volume of (1300 Mpc)(3) and evolves more than half a trillion particles, leading to a particle mass resolution of m(p) similar or equal to 1.5 . 10(8) M-circle dot. At thismass resolution, the Q Continuum run is currently the largest cosmology simulation available. It enables the construction of detailed synthetic sky catalogs, encompassing different modeling methodologies, including semi-analyticmore » modeling and sub-halo abundance matching in a large, cosmological volume. Here we describe the simulation and outputs in detail and present first results for a range of cosmological statistics, such as mass power spectra, halo mass functions, and halo mass-concentration relations for different epochs. We also provide details on challenges connected to running a simulation on almost 90% of Titan, one of the fastest supercomputers in the world, including our usage of Titan's GPU accelerators.« less

Imprints of dark energy on cosmic structure formation - I. Realistic quintessence models and the non-linear matter power spectrum

NASA Astrophysics Data System (ADS)

Alimi, J.-M.; Füzfa, A.; Boucher, V.; Rasera, Y.; Courtin, J.; Corasaniti, P.-S.

2010-01-01

Quintessence has been proposed to account for dark energy (DE) in the Universe. This component causes a typical modification of the background cosmic expansion, which, in addition to its clustering properties, can leave a potentially distinctive signature on large-scale structures. Many previous studies have investigated this topic, particularly in relation to the non-linear regime of structure formation. However, no careful pre-selection of viable quintessence models with high precision cosmological data was performed. Here we show that this has led to a misinterpretation (and underestimation) of the imprint of quintessence on the distribution of large-scale structures. To this purpose, we perform a likelihood analysis of the combined Supernova Ia UNION data set and Wilkinson Microwave Anisotropy Probe 5-yr data to identify realistic quintessence models. These are specified by different model parameter values, but still statistically indistinguishable from the vanilla Λ cold dark matter (ΛCDM). Differences are especially manifest in the predicted amplitude and shape of the linear matter power spectrum though these remain within the uncertainties of the Sloan Digital Sky Survey data. We use these models as a benchmark for studying the clustering properties of dark matter haloes by performing a series of high-resolution N-body simulations. In this first paper, we specifically focus on the non-linear matter power spectrum. We find that realistic quintessence models allow for relevant differences of the dark matter distribution with respect to the ΛCDM scenario well into the non-linear regime, with deviations of up to 40 per cent in the non-linear power spectrum. Such differences are shown to depend on the nature of DE, as well as the scale and epoch considered. At small scales (k ~ 1-5hMpc-1, depending on the redshift), the structure formation process is about 20 per cent more efficient than in ΛCDM. We show that these imprints are a specific record of the cosmic structure formation history in DE cosmologies and therefore cannot be accounted for in standard fitting functions of the non-linear matter power spectrum.

The COBE normalization for standard cold dark matter

NASA Technical Reports Server (NTRS)

Bunn, Emory F.; Scott, Douglas; White, Martin

1995-01-01

The Cosmic Background Explorer Satellite (COBE) detection of microwave anisotropies provides the best way of fixing the amplitude of cosmological fluctuations on the largest scales. This normalization is usually given for an n = 1 spectrum, including only the anisotropy caused by the Sachs-Wolfe effect. This is certainly not a good approximation for a model containing any reasonable amount of baryonic matter. In fact, even tilted Sachs-Wolfe spectra are not a good fit to models like cold dark matter (CDM). Here, we normalize standard CDM (sCDM) to the two-year COBE data and quote the best amplitude in terms of the conventionally used measures of power. We also give normalizations for some specific variants of this standard model, and we indicate how the normalization depends on the assumed values on n, Omega(sub B) and H(sub 0). For sCDM we find the mean value of Q = 19.9 +/- 1.5 micro-K, corresponding to sigma(sub 8) = 1.34 +/- 0.10, with the normalization at large scales being B = (8.16 +/- 1.04) x 10(exp 5)(Mpc/h)(exp 4), and other numbers given in the table. The measured rms temperature fluctuation smoothed on 10 deg is a little low relative to this normalization. This is mainly due to the low quadrupole in the data: when the quadrupole is removed, the measured value of sigma(10 deg) is quite consistent with the best-fitting the mean value of Q. The use of the mean value of Q should be preferred over sigma(10 deg), when its value can be determined for a particular theory, since it makes full use of the data.

Probing the nature of dark matter through the metal enrichment of the intergalactic medium

NASA Astrophysics Data System (ADS)

Bremer, Jonas; Dayal, Pratika; Ryan-Weber, Emma V.

2018-06-01

We focus on exploring the metal enrichment of the intergalactic medium (IGM) in cold and warm (1.5 and 3 keV) dark matter (DM) cosmologies, and the constraints this yields on the DM particle mass, using a semi-analytic model, DELPHI, that jointly tracks the DM and baryonic assembly of galaxies at z ≃ 4-20 including both supernova (SN) and (a range of) reionization feedback (models). We find that while M_{UV}≳ -15 galaxies contribute half of all IGM metals in the cold dark matter (CDM) model by z ≃ 4.5, given the suppression of low-mass haloes, larger haloes with M_{UV}≲ -15 provide about 80 per cent of the IGM metal budget in 1.5 keV warm dark matter (WDM) models using two different models for the metallicity of the interstellar medium. Our results also show that the only models compatible with two different high-redshift data sets, provided by the evolving ultraviolet luminosity function (UV LF) at z ≃ 6-10 and IGM metal density, are standard CDM and 3 keV WDM that do not include any reionization feedback; a combination of the UV LF and the Díaz et al. point provides a weaker constraint, allowing CDM and 3 and 1.5 keV WDM models with SN feedback only, as well as CDM with complete gas suppression of all haloes with v_{circ} ≲ 30 km s^{-1}. Tightening the error bars on the IGM metal enrichment, future observations, at z ≳ 5.5, could therefore represent an alternative way of shedding light on the nature of DM.

Unveiling acoustic physics of the CMB using nonparametric estimation of the temperature angular power spectrum for Planck

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aghamousa, Amir; Shafieloo, Arman; Arjunwadkar, Mihir

2015-02-01

Estimation of the angular power spectrum is one of the important steps in Cosmic Microwave Background (CMB) data analysis. Here, we present a nonparametric estimate of the temperature angular power spectrum for the Planck 2013 CMB data. The method implemented in this work is model-independent, and allows the data, rather than the model, to dictate the fit. Since one of the main targets of our analysis is to test the consistency of the ΛCDM model with Planck 2013 data, we use the nuisance parameters associated with the best-fit ΛCDM angular power spectrum to remove foreground contributions from the data atmore » multipoles ℓ ≥50. We thus obtain a combined angular power spectrum data set together with the full covariance matrix, appropriately weighted over frequency channels. Our subsequent nonparametric analysis resolves six peaks (and five dips) up to ℓ ∼1850 in the temperature angular power spectrum. We present uncertainties in the peak/dip locations and heights at the 95% confidence level. We further show how these reflect the harmonicity of acoustic peaks, and can be used for acoustic scale estimation. Based on this nonparametric formalism, we found the best-fit ΛCDM model to be at 36% confidence distance from the center of the nonparametric confidence set—this is considerably larger than the confidence distance (9%) derived earlier from a similar analysis of the WMAP 7-year data. Another interesting result of our analysis is that at low multipoles, the Planck data do not suggest any upturn, contrary to the expectation based on the integrated Sachs-Wolfe contribution in the best-fit ΛCDM cosmology.« less

A tale of two modes: neutrino free-streaming in the early universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lancaster, Lachlan; Cyr-Racine, Francis-Yan; Knox, Lloyd

2017-07-01

We present updated constraints on the free-streaming nature of cosmological neutrinos from cosmic microwave background (CMB) temperature and polarization power spectra, baryonic acoustic oscillation data, and distance ladder measurements of the Hubble constant. Specifically, we consider a Fermi-like four-fermion interaction between massless neutrinos, characterized by an effective coupling constant G {sub eff}, and resulting in a neutrino opacity τ-dot {sub ν∝} G {sub eff}{sup 2} T {sub ν}{sup 5}. Using a conservative flat prior on the parameter log{sub 10}( G {sub eff} MeV{sup 2}), we find a bimodal posterior distribution with two clearly separated regions of high probability. The firstmore » of these modes is consistent with the standard ΛCDM cosmology and corresponds to neutrinos decoupling at redshift z {sub ν,dec} > 1.3×10{sup 5}, that is before the Fourier modes probed by the CMB damping tail enter the causal horizon. The other mode of the posterior, dubbed the 'interacting neutrino mode', corresponds to neutrino decoupling occurring within a narrow redshift window centered around z {sub ν,dec}∼8300. This mode is characterized by a high value of the effective neutrino coupling constant, log{sub 10}( G {sub eff} MeV{sup 2}) = −1.72 ± 0.10 (68% C.L.), together with a lower value of the scalar spectral index and amplitude of fluctuations, and a higher value of the Hubble parameter. Using both a maximum likelihood analysis and the ratio of the two mode's Bayesian evidence, we find the interacting neutrino mode to be statistically disfavored compared to the standard ΛCDM cosmology, and determine this result to be largely driven by the low- l CMB temperature data. Interestingly, the addition of CMB polarization and direct Hubble constant measurements significantly raises the statistical significance of this secondary mode, indicating that new physics in the neutrino sector could help explain the difference between local measurements of H {sub 0}, and those inferred from CMB data. A robust consequence of our results is that neutrinos must be free streaming long before the epoch of matter-radiation equality in order to fit current cosmological data.« less

Exploring cosmic homogeneity with the BOSS DR12 galaxy sample

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ntelis, Pierros; Hamilton, Jean-Christophe; Busca, Nicolas Guillermo

2017-06-01

In this study, we probe the transition to cosmic homogeneity in the Large Scale Structure (LSS) of the Universe using the CMASS galaxy sample of BOSS spectroscopic survey which covers the largest effective volume to date, 3 h {sup −3} Gpc{sup 3} at 0.43 ≤ z ≤ 0.7. We study the scaled counts-in-spheres, N(< r ), and the fractal correlation dimension, D{sub 2}( r ), to assess the homogeneity scale of the universe using a Landy and Szalay inspired estimator. Defining the scale of transition to homogeneity as the scale at which D{sub 2}( r ) reaches 3 within 1%,more » i.e. D{sub 2}( r )>2.97 for r >R {sub H} , we find R {sub H} = (63.3±0.7) h {sup −1} Mpc, in agreement at the percentage level with the predictions of the ΛCDM model R {sub H} =62.0 h {sup −1} Mpc. Thanks to the large cosmic depth of the survey, we investigate the redshift evolution of the transition to homogeneity scale and find agreement with the ΛCDM prediction. Finally, we find that D{sub 2} is compatible with 3 at scales larger than 300 h {sup −1} Mpc in all redshift bins. These results consolidate the Cosmological Principle and represent a precise consistency test of the ΛCDM model.« less

Halo abundance and assembly history with extreme-axion wave dark matter at z ≥ 4

NASA Astrophysics Data System (ADS)

Schive, Hsi-Yu; Chiueh, Tzihong

2018-01-01

Wave dark matter (ψDM) composed of extremely light bosons (mψ ˜ 10 - 22 eV), with quantum pressure suppressing structures below a kpc-scale de Broglie wavelength, has become a viable dark matter candidate. Compared to the conventional free-particle ψDM (FPψDM), the extreme-axion ψDM model (EAψDM) proposed by Zhang & Chiueh features a larger cut-off wavenumber and a broad spectral bump in the matter transfer function. Here, we conduct cosmological simulations to compare the halo abundances and assembly histories at z = 4-11 between three different scenarios: FPψDM, EAψDM and cold dark matter (CDM). We show that EAψDM produces significantly more abundant low-mass haloes than FPψDM with the same mψ, and therefore could alleviate the tension in mψ required by the Lyα forest data and by the kpc-scale dwarf galaxy cores. We also find that, compared to the CDM counterparts, massive EAψDM haloes are, on average, 3-4 times more massive at z = 10-11 due to their earlier formation, undergo a slower mass accretion at 7 ≲ z ≲ 11, and then show a rapidly rising major merger rate exceeding CDM by ˜ 50 per cent at 4 ≲ z ≲ 7. This fact suggests that EAψDM haloes may exhibit more prominent starbursts at z ≲ 7.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dirian, Yves; Foffa, Stefano; Kunz, Martin

We study the cosmological consequences of a recently proposed nonlocal modification of general relativity, obtained by adding a term m{sup 2}R □{sup −2}R to the Einstein-Hilbert action. The model has the same number of parameters as ΛCDM, with m replacing Ω{sub Λ}. At the background level, after fixing m so to reproduce the observed value of Ω{sub M}, we get a pure prediction for the equation of state of dark energy as a function of redshift, w{sub DE}(z), with w{sub DE}(0) in the range [−1.165,−1.135] as Ω{sub M} varies over the broad range Ω{sub M} element of [0.20,0.36]. We find thatmore » the cosmological perturbations are well-behaved, and the model fully fixes the dark energy perturbations as a function of redshift z and wavenumber k. The nonlocal model provides a good fit to supernova data and predicts deviations from General Relativity in structure formation and in weak lensing at the level of 3-4%, therefore consistent with existing data but readily detectable by future surveys. For the logarithmic growth factor we obtain γ ≅ 0.53, to be compared with γ ≅ 0.55 in ΛCDM. For the Newtonian potential on subhorizon scales our results are well fitted by Ψ(a;k) = [1+μ{sub s}a{sup s}]Ψ{sub GR}(a;k) with a scale-independent μ{sub s} ≅ 0.09 and s ≅ 2, while the anisotropic stress is negligibly small.« less

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: First measurement of Baryon Acoustic Oscillations between redshift 0.8 and 2.2

DOE PAGES

Ata, Metin

2017-06-20

Here, we present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts 0.8 < z < 2.2 and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.5σ . We determine the spherically averaged BAO distance to z = 1.52 to 4.4 per cent precision: D V (zmore » = 1:52) = 3855 170 (r d/r d,fid) Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat CDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Bu using these BAO data alone and marginalizing over the length of the standard ruler, we find Ω Λ > 0 at 6.5σ significance when testing a CDM model with free curvature.« less

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: First measurement of Baryon Acoustic Oscillations between redshift 0.8 and 2.2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ata, Metin

Here, we present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts 0.8 < z < 2.2 and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.5σ . We determine the spherically averaged BAO distance to z = 1.52 to 4.4 per cent precision: D V (zmore » = 1:52) = 3855 170 (r d/r d,fid) Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat CDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Bu using these BAO data alone and marginalizing over the length of the standard ruler, we find Ω Λ > 0 at 6.5σ significance when testing a CDM model with free curvature.« less

Conjoined constraints on modified gravity from the expansion history and cosmic growth

NASA Astrophysics Data System (ADS)

Basilakos, Spyros; Nesseris, Savvas

2017-09-01

In this paper we present conjoined constraints on several cosmological models from the expansion history H (z ) and cosmic growth f σ8. The models we study include the CPL w0wa parametrization, the holographic dark energy (HDE) model, the time-varying vacuum (ΛtCDM ) model, the Dvali, Gabadadze and Porrati (DGP) and Finsler-Randers (FRDE) models, a power-law f (T ) model, and finally the Hu-Sawicki f (R ) model. In all cases we perform a simultaneous fit to the SnIa, CMB, BAO, H (z ) and growth data, while also following the conjoined visualization of H (z ) and f σ8 as in Linder (2017). Furthermore, we introduce the figure of merit (FoM) in the H (z )-f σ8 parameter space as a way to constrain models that jointly fit both probes well. We use both the latest H (z ) and f σ8 data, but also LSST-like mocks with 1% measurements, and we find that the conjoined method of constraining the expansion history and cosmic growth simultaneously is able not only to place stringent constraints on these parameters, but also to provide an easy visual way to discriminate cosmological models. Finally, we confirm the existence of a tension between the growth-rate and Planck CMB data, and we find that the FoM in the conjoined parameter space of H (z )-f σ8(z ) can be used to discriminate between the Λ CDM model and certain classes of modified gravity models, namely the DGP and f (T ).

Addressing the too big to fail problem with baryon physics and sterile neutrino dark matter

NASA Astrophysics Data System (ADS)

Lovell, Mark R.; Gonzalez-Perez, Violeta; Bose, Sownak; Boyarsky, Alexey; Cole, Shaun; Frenk, Carlos S.; Ruchayskiy, Oleg

2017-07-01

N-body dark matter simulations of structure formation in the Λ cold dark matter (ΛCDM) model predict a population of subhaloes within Galactic haloes that have higher central densities than inferred for the Milky Way satellites, a tension known as the 'too big to fail' problem. Proposed solutions include baryonic effects, a smaller mass for the Milky Way halo and warm dark matter (WDM). We test these possibilities using a semi-analytic model of galaxy formation to generate luminosity functions for Milky Way halo-analogue satellite populations, the results of which are then coupled to the Jiang & van den Bosch model of subhalo stripping to predict the subhalo Vmax functions for the 10 brightest satellites. We find that selecting the brightest satellites (as opposed to the most massive) and modelling the expulsion of gas by supernovae at early times increases the likelihood of generating the observed Milky Way satellite Vmax function. The preferred halo mass is 6 × 1011 M⊙, which has a 14 per cent probability to host a Vmax function like that of the Milky Way satellites. We conclude that the Milky Way satellite Vmax function is compatible with a CDM cosmology, as previously found by Sawala et al. using hydrodynamic simulations. Sterile neutrino-WDM models achieve a higher degree of agreement with the observations, with a maximum 50 per cent chance of generating the observed Milky Way satellite Vmax function. However, more work is required to check that the semi-analytic stripping model is calibrated correctly for each sterile neutrino cosmology.

Dark matter self-interactions and small scale structure

NASA Astrophysics Data System (ADS)

Tulin, Sean; Yu, Hai-Bo

2018-02-01

We review theories of dark matter (DM) beyond the collisionless paradigm, known as self-interacting dark matter (SIDM), and their observable implications for astrophysical structure in the Universe. Self-interactions are motivated, in part, due to the potential to explain long-standing (and more recent) small scale structure observations that are in tension with collisionless cold DM (CDM) predictions. Simple particle physics models for SIDM can provide a universal explanation for these observations across a wide range of mass scales spanning dwarf galaxies, low and high surface brightness spiral galaxies, and clusters of galaxies. At the same time, SIDM leaves intact the success of ΛCDM cosmology on large scales. This report covers the following topics: (1) small scale structure issues, including the core-cusp problem, the diversity problem for rotation curves, the missing satellites problem, and the too-big-to-fail problem, as well as recent progress in hydrodynamical simulations of galaxy formation; (2) N-body simulations for SIDM, including implications for density profiles, halo shapes, substructure, and the interplay between baryons and self-interactions; (3) semi-analytic Jeans-based methods that provide a complementary approach for connecting particle models with observations; (4) merging systems, such as cluster mergers (e.g., the Bullet Cluster) and minor infalls, along with recent simulation results for mergers; (5) particle physics models, including light mediator models and composite DM models; and (6) complementary probes for SIDM, including indirect and direct detection experiments, particle collider searches, and cosmological observations. We provide a summary and critical look for all current constraints on DM self-interactions and an outline for future directions.

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: first measurement of baryon acoustic oscillations between redshift 0.8 and 2.2

NASA Astrophysics Data System (ADS)

Ata, Metin; Baumgarten, Falk; Bautista, Julian; Beutler, Florian; Bizyaev, Dmitry; Blanton, Michael R.; Blazek, Jonathan A.; Bolton, Adam S.; Brinkmann, Jonathan; Brownstein, Joel R.; Burtin, Etienne; Chuang, Chia-Hsun; Comparat, Johan; Dawson, Kyle S.; de la Macorra, Axel; Du, Wei; du Mas des Bourboux, Hélion; Eisenstein, Daniel J.; Gil-Marín, Héctor; Grabowski, Katie; Guy, Julien; Hand, Nick; Ho, Shirley; Hutchinson, Timothy A.; Ivanov, Mikhail M.; Kitaura, Francisco-Shu; Kneib, Jean-Paul; Laurent, Pierre; Le Goff, Jean-Marc; McEwen, Joseph E.; Mueller, Eva-Maria; Myers, Adam D.; Newman, Jeffrey A.; Palanque-Delabrouille, Nathalie; Pan, Kaike; Pâris, Isabelle; Pellejero-Ibanez, Marcos; Percival, Will J.; Petitjean, Patrick; Prada, Francisco; Prakash, Abhishek; Rodríguez-Torres, Sergio A.; Ross, Ashley J.; Rossi, Graziano; Ruggeri, Rossana; Sánchez, Ariel G.; Satpathy, Siddharth; Schlegel, David J.; Schneider, Donald P.; Seo, Hee-Jong; Slosar, Anže; Streblyanska, Alina; Tinker, Jeremy L.; Tojeiro, Rita; Vargas Magaña, Mariana; Vivek, M.; Wang, Yuting; Yèche, Christophe; Yu, Liang; Zarrouk, Pauline; Zhao, Cheng; Zhao, Gong-Bo; Zhu, Fangzhou

2018-02-01

We present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147 000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts 0.8 < z < 2.2 and measure their spherically averaged clustering in both configuration and Fourier space. Our observational data set and the 1400 simulated realizations of the data set allow us to detect a preference for BAO that is greater than 2.8σ. We determine the spherically averaged BAO distance to z = 1.52 to 3.8 per cent precision: DV(z = 1.52) = 3843 ± 147(rd/rd, fid)Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat ΛCDM best-fitting cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Using these BAO data alone and marginalizing over the length of the standard ruler, we find ΩΛ > 0 at 6.6σ significance when testing a ΛCDM model with free curvature.

The Mira-Titan Universe. II. Matter Power Spectrum Emulation

NASA Astrophysics Data System (ADS)

Lawrence, Earl; Heitmann, Katrin; Kwan, Juliana; Upadhye, Amol; Bingham, Derek; Habib, Salman; Higdon, David; Pope, Adrian; Finkel, Hal; Frontiere, Nicholas

2017-09-01

We introduce a new cosmic emulator for the matter power spectrum covering eight cosmological parameters. Targeted at optical surveys, the emulator provides accurate predictions out to a wavenumber k˜ 5 Mpc-1 and redshift z≤slant 2. In addition to covering the standard set of ΛCDM parameters, massive neutrinos and a dynamical dark energy of state are included. The emulator is built on a sample set of 36 cosmological models, carefully chosen to provide accurate predictions over the wide and large parameter space. For each model, we have performed a high-resolution simulation, augmented with 16 medium-resolution simulations and TimeRG perturbation theory results to provide accurate coverage over a wide k-range; the data set generated as part of this project is more than 1.2Pbytes. With the current set of simulated models, we achieve an accuracy of approximately 4%. Because the sampling approach used here has established convergence and error-control properties, follow-up results with more than a hundred cosmological models will soon achieve ˜ 1 % accuracy. We compare our approach with other prediction schemes that are based on halo model ideas and remapping approaches. The new emulator code is publicly available.

Cosmological implications of the transition from the false vacuum to the true vacuum state

NASA Astrophysics Data System (ADS)

Stachowski, Aleksander; Szydłowski, Marek; Urbanowski, Krzysztof

2017-06-01

We study cosmology with running dark energy. The energy density of dark energy is obtained from the quantum process of transition from the false vacuum state to the true vacuum state. We use the Breit-Wigner energy distribution function to model the quantum unstable systems and obtain the energy density of the dark energy parametrization ρ _ {de}(t). We also use Krauss and Dent's idea linking properties of the quantum mechanical decay of unstable states with the properties of the observed Universe. In the cosmological model with this parametrization there is an energy transfer between dark matter and dark energy. The intensity of this process, measured by a parameter α , distinguishes two scenarios. As the Universe starts from the false vacuum state, for the small value of α (0<α <0.4) it goes through an intermediate oscillatory (quantum) regime of the density of dark energy, while for α > 0.4 the density of the dark energy jumps down. In both cases the present value of the density of dark energy is reached. From a statistical analysis we find this model to be in good agreement with the astronomical data and practically indistinguishable from the Λ CDM model.

The Mira-Titan Universe. II. Matter Power Spectrum Emulation

DOE PAGES

Lawrence, Earl; Heitmann, Katrin; Kwan, Juliana; ...

2017-09-20

We introduce a new cosmic emulator for the matter power spectrum covering eight cosmological parameters. Targeted at optical surveys, the emulator provides accurate predictions out to a wavenumber k ~ 5Mpc -1 and redshift z ≤ 2. Besides covering the standard set of CDM parameters, massive neutrinos and a dynamical dark energy of state are included. The emulator is built on a sample set of 36 cosmological models, carefully chosen to provide accurate predictions over the wide and large parameter space. For each model, we have performed a high-resolution simulation, augmented with sixteen medium-resolution simulations and TimeRG perturbation theory resultsmore » to provide accurate coverage of a wide k-range; the dataset generated as part of this project is more than 1.2Pbyte. With the current set of simulated models, we achieve an accuracy of approximately 4%. Because the sampling approach used here has established convergence and error-control properties, follow-on results with more than a hundred cosmological models will soon achieve ~1% accuracy. We compare our approach with other prediction schemes that are based on halo model ideas and remapping approaches. The new emulator code is publicly available.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Audren, Benjamin; Lesgourgues, Julien; Benabed, Karim

Models for the latest stages of the cosmological evolution rely on a less solid theoretical and observational ground than the description of earlier stages like BBN and recombination. As suggested in a previous work by Vonlanthen et al., it is possible to tweak the analysis of CMB data in such way to avoid making assumptions on the late evolution, and obtain robust constraints on ''early cosmology parameters''. We extend this method in order to marginalise the results over CMB lensing contamination, and present updated results based on recent CMB data. Our constraints on the minimal early cosmology model are weakermore » than in a standard ΛCDM analysis, but do not conflict with this model. Besides, we obtain conservative bounds on the effective neutrino number and neutrino mass, showing no hints for extra relativistic degrees of freedom, and proving in a robust way that neutrinos experienced their non-relativistic transition after the time of photon decoupling. This analysis is also an occasion to describe the main features of the new parameter inference code MONTE PYTHON, that we release together with this paper. MONTE PYTHON is a user-friendly alternative to other public codes like COSMOMC, interfaced with the Boltzmann code CLASS.« less

The Mira-Titan Universe. II. Matter Power Spectrum Emulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lawrence, Earl; Heitmann, Katrin; Kwan, Juliana

We introduce a new cosmic emulator for the matter power spectrum covering eight cosmological parameters. Targeted at optical surveys, the emulator provides accurate predictions out to a wavenumber k similar to 5 Mpc(-1) and redshift z <= 2. In addition to covering the standard set of Lambda CDM parameters, massive neutrinos and a dynamical dark energy of state are included. The emulator is built on a sample set of 36 cosmological models, carefully chosen to provide accurate predictions over the wide and large parameter space. For each model, we have performed a high-resolution simulation, augmented with 16 medium-resolution simulations andmore » TimeRG perturbation theory results to provide accurate coverage over a wide k-range; the data set generated as part of this project is more than 1.2Pbytes. With the current set of simulated models, we achieve an accuracy of approximately 4%. Because the sampling approach used here has established convergence and error-control properties, follow-up results with more than a hundred cosmological models will soon achieve similar to 1% accuracy. We compare our approach with other prediction schemes that are based on halo model ideas and remapping approaches.« less

The Mira-Titan Universe. II. Matter Power Spectrum Emulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lawrence, Earl; Heitmann, Katrin; Kwan, Juliana

We introduce a new cosmic emulator for the matter power spectrum covering eight cosmological parameters. Targeted at optical surveys, the emulator provides accurate predictions out to a wavenumber k ~ 5Mpc -1 and redshift z ≤ 2. Besides covering the standard set of CDM parameters, massive neutrinos and a dynamical dark energy of state are included. The emulator is built on a sample set of 36 cosmological models, carefully chosen to provide accurate predictions over the wide and large parameter space. For each model, we have performed a high-resolution simulation, augmented with sixteen medium-resolution simulations and TimeRG perturbation theory resultsmore » to provide accurate coverage of a wide k-range; the dataset generated as part of this project is more than 1.2Pbyte. With the current set of simulated models, we achieve an accuracy of approximately 4%. Because the sampling approach used here has established convergence and error-control properties, follow-on results with more than a hundred cosmological models will soon achieve ~1% accuracy. We compare our approach with other prediction schemes that are based on halo model ideas and remapping approaches. The new emulator code is publicly available.« less

How does pressure gravitate? Cosmological constant problem confronts observational cosmology

NASA Astrophysics Data System (ADS)

Narimani, Ali; Afshordi, Niayesh; Scott, Douglas

2014-08-01

An important and long-standing puzzle in the history of modern physics is the gross inconsistency between theoretical expectations and cosmological observations of the vacuum energy density, by at least 60 orders of magnitude, otherwise known as the cosmological constant problem. A characteristic feature of vacuum energy is that it has a pressure with the same amplitude, but opposite sign to its energy density, while all the precision tests of General Relativity are either in vacuum, or for media with negligible pressure. Therefore, one may wonder whether an anomalous coupling to pressure might be responsible for decoupling vacuum from gravity. We test this possibility in the context of the Gravitational Aether proposal, using current cosmological observations, which probe the gravity of relativistic pressure in the radiation era. Interestingly, we find that the best fit for anomalous pressure coupling is about half-way between General Relativity (GR), and Gravitational Aether (GA), if we include Planck together with WMAP and BICEP2 polarization cosmic microwave background (CMB) observations. Taken at face value, this data combination excludes both GR and GA at around the 3 σ level. However, including higher resolution CMB observations (``highL'') or baryonic acoustic oscillations (BAO) pushes the best fit closer to GR, excluding the Gravitational Aether solution to the cosmological constant problem at the 4- 5 σ level. This constraint effectively places a limit on the anomalous coupling to pressure in the parametrized post-Newtonian (PPN) expansion, ζ4 = 0.105 ± 0.049 (+highL CMB), or ζ4 = 0.066 ± 0.039 (+BAO). These represent the most precise measurement of this parameter to date, indicating a mild tension with GR (for ΛCDM including tensors, with 0ζ4=), and also among different data sets.

Statistical analysis of ALFALFA galaxies: Insights in galaxy formation & near-field cosmology

NASA Astrophysics Data System (ADS)

Papastergis, Emmanouil

2013-03-01

The Arecibo Legacy Fast ALFA (ALFALFA) survey is a blind, extragalactic survey in the 21cm emission line of atomic hydrogen (HI). Presently, sources have been cataloged over ≈4,000 deg2 of sky (~60% of its final area), resulting in the largest HI-selected sample to date. We use the rich ALFALFA dataset to measure the statistical properties of HI-bearing galaxies, such as their mass distribution and clustering characteristics. These statistical distributions are determined by the properties of darkmatter on galactic scales, and by the complex baryonic processes through which galaxies form over cosmic time. As a result, detailed studies of these distributions can lead to important insights in galaxy formation & evolution and near-field cosmology. In particular, we measure the space density of HI-bearing galaxies as a function of the width of their HI profile (i.e. the velocity width function of galaxies), and find substantial disagreement with the distribution expected in a lambda cold dark matter (ΛCDM) universe. In particular, the number of galaxies with maximum rotational velocities upsilonrot ≈ 35 kms--1 (as judged by their HI velocity width) is about an order of magnitude lower than what predicted based on populating ΛCDM halos with modeled galaxies. We identify two possible solutions to the discrepancy: First, an alternative dark matter scenario in which the formation of low-mass halos is heavily suppressed (e.g. a warm dark matter universe with keV-scale dark matter particles). Secondly, we consider the possibility that rotational velocitites of dwarf galaxies derived from HI velocity widths may systematically underestimate the true mass of the host halo, due to the shape of their rotation curves. In this latter scenario, quantitative predictions for the internal kinematics of dwarf galaxies can be made, which can be checked in the future to probe the nature of dark matter. Furthermore, we take advantage of the overlap of ALFALFA with the Sloan Digital Sky Survey (SDSS), to measure the number density of galaxies as a function of their "baryonic" mass (stars + atomic gas). In the context of a ΛCDM cosmological model, the measured distribution reveals that low-mass halos are heavily "baryon depleted", i.e. their baryonic-to-dark mass ratio is much lower than the cosmological value. These baryon deficits are usually attributed to stellar feedback (e.g. supernova-driven gas outflows), but the efficiency implied by our measurement is extremely high. Whether such efficient feedback can be accommodated in a consistent picture of galaxy formation is an open question, and remains one of the principle scientific drivers for hydrodynamic simulations of galaxy formation. Lastly, we measure the clustering properties of HI-selected samples, through the two-point correlation function of ALFALFA galaxies. We find no compelling evidence for a dependence of clustering on HI mass, suggesting that the relationship between galactic gas mass and host halo mass is not tight. We furthermore find that HI galaxies cluster more weakly than optically selected ones, when no color selection is applied. However, SDSS galaxies with blue colors have very similar clustering characteristics with ALFALFA galaxies, both in real as well as in redshift space. On the other hand, HI galaxies cluster much more weakly than optical galaxies with red colors, and in fact "avoid" being located within ≈3 Mpc from the latter. By considering the clustering properties of ΛCDM halos, we confirm our previous intuition for an MHI-Mh relation with large scatter, and find that spin parameter may be a key halo property related to the gas content of present-day galaxies.

Cosmological test using strong gravitational lensing systems

NASA Astrophysics Data System (ADS)

Yuan, C. C.; Wang, F. Y.

2015-09-01

As one of the probes of universe, strong gravitational lensing systems allow us to compare different cosmological models and constrain vital cosmological parameters. This purpose can be reached from the dynamic and geometry properties of strong gravitational lensing systems, for instance, time-delay Δτ of images, the velocity dispersion σ of the lensing galaxies and the combination of these two effects, Δτ/σ2. In this paper, in order to carry out one-on-one comparisons between ΛCDM universe and Rh = ct universe, we use a sample containing 36 strong lensing systems with the measurement of velocity dispersion from the Sloan Lens Advanced Camera for Surveys (SLACS) and Lens Structure and Dynamic survey (LSD) survey. Concerning the time-delay effect, 12 two-image lensing systems with Δτ are also used. In addition, Monte Carlo simulations are used to compare the efficiency of the three methods as mentioned above. From simulations, we estimate the number of lenses required to rule out one model at the 99.7 per cent confidence level. Comparing with constraints from Δτ and the velocity dispersion σ, we find that using Δτ/σ2 can improve the discrimination between cosmological models. Despite the independence tests of these methods reveal a correlation between Δτ/σ2 and σ, Δτ/σ2 could be considered as an improved method of σ if more data samples are available.

Determination of the cosmological rate of change of G and the tidal accelerations of earth and moon from ancient and modern astronomical data

NASA Technical Reports Server (NTRS)

Muller, P. M.

1976-01-01

The theory and numerical analysis of ancient astronomical observations (1374 to 1715) are combined with modern data in a simultaneous solution for: the tidal acceleration of the lunar longitude; the observed apparent acceleration of the earth's rotation; the true nontidal geophysical part of this acceleration; and the rate of change in the gravitational constant. Provided are three independent determinations of a rate of change of G consistent with the Hubble Constant and a near zero nontidal rotational acceleration of the earth. The tidal accelerations are shown to have remained constant during the historical period within uncertainties. Ancient and modern solar system data, and extragalactic observations provided a completely consistent astronomical and cosmological scheme.

Probing gravity theory and cosmic acceleration using (in)consistency tests between cosmological data sets

NASA Astrophysics Data System (ADS)

Ishak-Boushaki, Mustapha B.

2018-06-01

Testing general relativity at cosmological scales and probing the cause of cosmic acceleration are among important objectives targeted by incoming and future astronomical surveys and experiments. I present our recent results on (in)consistency tests that can provide insights about the underlying gravity theory and cosmic acceleration using cosmological data sets. We use new statistical measures that can detect discordances between data sets when present. We use an algorithmic procedure based on these new measures that is able to identify in some cases whether an inconsistency is due to problems related to systematic effects in the data or to the underlying model. Some recent published tensions between data sets are also examined using our formalism, including the Hubble constant measurements, Planck and Large-Scale-Structure. (Work supported in part by NSF under Grant No. AST-1517768).

Experiment-specific cosmic microwave background calculations made easier - Approximation formula for smoothed delta T/T windows

NASA Technical Reports Server (NTRS)

Gorski, Krzysztof M.

1993-01-01

Simple and easy to implement elementary function approximations are introduced to the spectral window functions needed in calculations of model predictions of the cosmic microwave backgrond (CMB) anisotropy. These approximations allow the investigator to obtain model delta T/T predictions in terms of single integrals over the power spectrum of cosmological perturbations and to avoid the necessity of performing the additional integrations. The high accuracy of these approximations is demonstrated here for the CDM theory-based calculations of the expected delta T/T signal in several experiments searching for the CMB anisotropy.

MASS CALIBRATION AND COSMOLOGICAL ANALYSIS OF THE SPT-SZ GALAXY CLUSTER SAMPLE USING VELOCITY DISPERSION σ {sub v} AND X-RAY Y {sub X} MEASUREMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bocquet, S.; Saro, A.; Mohr, J. J.

2015-02-01

We present a velocity-dispersion-based mass calibration of the South Pole Telescope Sunyaev-Zel'dovich effect survey (SPT-SZ) galaxy cluster sample. Using a homogeneously selected sample of 100 cluster candidates from 720 deg{sup 2} of the survey along with 63 velocity dispersion (σ {sub v}) and 16 X-ray Y {sub X} measurements of sample clusters, we simultaneously calibrate the mass-observable relation and constrain cosmological parameters. Our method accounts for cluster selection, cosmological sensitivity, and uncertainties in the mass calibrators. The calibrations using σ {sub v} and Y {sub X} are consistent at the 0.6σ level, with the σ {sub v} calibration preferring ∼16% highermore » masses. We use the full SPT{sub CL} data set (SZ clusters+σ {sub v}+Y {sub X}) to measure σ{sub 8}(Ω{sub m}/0.27){sup 0.3} = 0.809 ± 0.036 within a flat ΛCDM model. The SPT cluster abundance is lower than preferred by either the WMAP9 or Planck+WMAP9 polarization (WP) data, but assuming that the sum of the neutrino masses is ∑m {sub ν} = 0.06 eV, we find the data sets to be consistent at the 1.0σ level for WMAP9 and 1.5σ for Planck+WP. Allowing for larger ∑m {sub ν} further reconciles the results. When we combine the SPT{sub CL} and Planck+WP data sets with information from baryon acoustic oscillations and Type Ia supernovae, the preferred cluster masses are 1.9σ higher than the Y {sub X} calibration and 0.8σ higher than the σ {sub v} calibration. Given the scale of these shifts (∼44% and ∼23% in mass, respectively), we execute a goodness-of-fit test; it reveals no tension, indicating that the best-fit model provides an adequate description of the data. Using the multi-probe data set, we measure Ω{sub m} = 0.299 ± 0.009 and σ{sub 8} = 0.829 ± 0.011. Within a νCDM model we find ∑m {sub ν} = 0.148 ± 0.081 eV. We present a consistency test of the cosmic growth rate using SPT clusters. Allowing both the growth index γ and the dark energy equation-of-state parameter w to vary, we find γ = 0.73 ± 0.28 and w = –1.007 ± 0.065, demonstrating that the expansion and the growth histories are consistent with a ΛCDM universe (γ = 0.55; w = –1)« less

A simple cosmology with a varying fine structure constant.

PubMed

Sandvik, Håvard Bunes; Barrow, John D; Magueijo, João

2002-01-21

We investigate the cosmological consequences of a theory in which the electric charge e can vary. In this theory the fine structure "constant," alpha, remains almost constant in the radiation era, undergoes a small increase in the matter era, but approaches a constant value when the universe starts accelerating because of a positive cosmological constant. This model satisfies geonuclear, nucleosynthesis, and cosmic microwave background constraints on time variation in alpha, while fitting the observed accelerating Universe and evidence for small alpha variations in quasar spectra. It also places specific restrictions on the nature of the dark matter. Further tests, involving stellar spectra and Eötvös experiments, are proposed.

Isotropic vs. anisotropic components of BAO data: a tool for model selection

NASA Astrophysics Data System (ADS)

Haridasu, Balakrishna S.; Luković, Vladimir V.; Vittorio, Nicola

2018-05-01

We conduct a selective analysis of the isotropic (DV) and anisotropic (AP) components of the most recent Baryon Acoustic Oscillations (BAO) data. We find that these components provide significantly different constraints and could provide strong diagnostics for model selection, also in view of more precise data to arrive. For instance, in the ΛCDM model we find a mild tension of ~ 2 σ for the Ωm estimates obtained using DV and AP separately. Considering both Ωk and w as free parameters, we find that the concordance model is in tension with the best-fit values provided by the BAO data alone at 2.2σ. We complemented the BAO data with the Supernovae Ia (SNIa) and Observational Hubble datasets to perform a joint analysis on the ΛCDM model and its standard extensions. By assuming ΛCDM scenario, we find that these data provide H0 = 69.4 ± 1.7 km/s Mpc‑1 as the best-fit value for the present expansion rate. In the kΛCDM scenario we find that the evidence for acceleration using the BAO data alone is more than ~ 5.8σ, which increases to 8.4 σ in our joint analysis.

Accelerating universe with time variation of G and Λ

NASA Astrophysics Data System (ADS)

Darabi, F.

2012-03-01

We study a gravitational model in which scale transformations play the key role in obtaining dynamical G and Λ. We take a non-scale invariant gravitational action with a cosmological constant and a gravitational coupling constant. Then, by a scale transformation, through a dilaton field, we obtain a new action containing cosmological and gravitational coupling terms which are dynamically dependent on the dilaton field with Higgs type potential. The vacuum expectation value of this dilaton field, through spontaneous symmetry breaking on the basis of anthropic principle, determines the time variations of G and Λ. The relevance of these time variations to the current acceleration of the universe, coincidence problem, Mach's cosmological coincidence and those problems of standard cosmology addressed by inflationary models, are discussed. The current acceleration of the universe is shown to be a result of phase transition from radiation toward matter dominated eras. No real coincidence problem between matter and vacuum energy densities exists in this model and this apparent coincidence together with Mach's cosmological coincidence are shown to be simple consequences of a new kind of scale factor dependence of the energy momentum density as ρ˜ a -4. This model also provides the possibility for a super fast expansion of the scale factor at very early universe by introducing exotic type matter like cosmic strings.

Cosmology of a Friedmann-Lamaître-Robertson-Walker 3-brane, late-time cosmic acceleration, and the cosmic coincidence.

PubMed

Doolin, Ciaran; Neupane, Ishwaree P

2013-04-05

A late epoch cosmic acceleration may be naturally entangled with cosmic coincidence--the observation that at the onset of acceleration the vacuum energy density fraction nearly coincides with the matter density fraction. In this Letter we show that this is indeed the case with the cosmology of a Friedmann-Lamaître-Robertson-Walker (FLRW) 3-brane in a five-dimensional anti-de Sitter spacetime. We derive the four-dimensional effective action on a FLRW 3-brane, from which we obtain a mass-reduction formula, namely, M(P)(2) = ρ(b)/|Λ(5)|, where M(P) is the effective (normalized) Planck mass, Λ(5) is the five-dimensional cosmological constant, and ρ(b) is the sum of the 3-brane tension V and the matter density ρ. Although the range of variation in ρ(b) is strongly constrained, the big bang nucleosynthesis bound on the time variation of the effective Newton constant G(N) = (8πM(P)(2))(-1) is satisfied when the ratio V/ρ ≳ O(10(2)) on cosmological scales. The same bound leads to an effective equation of state close to -1 at late epochs in accordance with astrophysical and cosmological observations.

Gauss-Bonnet cosmology unifying late and early-time acceleration eras with intermediate eras

NASA Astrophysics Data System (ADS)

Oikonomou, V. K.

2016-07-01

In this paper we demonstrate that with vacuum F(G) gravity it is possible to describe the unification of late and early-time acceleration eras with the radiation and matter domination era. The Hubble rate of the unified evolution contains two mild singularities, so called Type IV singularities, and the evolution itself has some appealing features, such as the existence of a deceleration-acceleration transition at late times. We also address quantitatively a fundamental question related to modified gravity models description of cosmological evolution: Is it possible for all modified gravity descriptions of our Universe evolution, to produce a nearly scale invariant spectrum of primordial curvature perturbations? As we demonstrate, the answer for the F(G) description is no, since the resulting power spectrum is not scale invariant, in contrast to the F(R) description studied in the literature. Therefore, although the cosmological evolution can be realized in the context of vacuum F(G) gravity, the evolution is not compatible with the observational data, in contrast to the F(R) gravity description of the same cosmological evolution.

Cosmological parameters, shear maps and power spectra from CFHTLenS using Bayesian hierarchical inference

NASA Astrophysics Data System (ADS)

Alsing, Justin; Heavens, Alan; Jaffe, Andrew H.

2017-04-01

We apply two Bayesian hierarchical inference schemes to infer shear power spectra, shear maps and cosmological parameters from the Canada-France-Hawaii Telescope (CFHTLenS) weak lensing survey - the first application of this method to data. In the first approach, we sample the joint posterior distribution of the shear maps and power spectra by Gibbs sampling, with minimal model assumptions. In the second approach, we sample the joint posterior of the shear maps and cosmological parameters, providing a new, accurate and principled approach to cosmological parameter inference from cosmic shear data. As a first demonstration on data, we perform a two-bin tomographic analysis to constrain cosmological parameters and investigate the possibility of photometric redshift bias in the CFHTLenS data. Under the baseline ΛCDM (Λ cold dark matter) model, we constrain S_8 = σ _8(Ω _m/0.3)^{0.5} = 0.67+0.03-0.03 (68 per cent), consistent with previous CFHTLenS analyses but in tension with Planck. Adding neutrino mass as a free parameter, we are able to constrain ∑mν < 4.6 eV (95 per cent) using CFHTLenS data alone. Including a linear redshift-dependent photo-z bias Δz = p2(z - p1), we find p_1=-0.25+0.53-0.60 and p_2 = -0.15+0.17-0.15, and tension with Planck is only alleviated under very conservative prior assumptions. Neither the non-minimal neutrino mass nor photo-z bias models are significantly preferred by the CFHTLenS (two-bin tomography) data.

The ΩDE-ΩM Plane in Dark Energy Cosmology

NASA Astrophysics Data System (ADS)

Qiang, Yuan; Zhang, Tong-Jie

The dark energy cosmology with the equation of state w=const. is considered in this paper. The ΩDE-ΩM plane has been used to study the present state and expansion history of the universe. Through the mathematical analysis, we give the theoretical constraint of cosmological parameters. Together with some observations such as the transition redshift from deceleration to acceleration, more precise constraint on cosmological parameters can be acquired.

Earth’s gravity and the cosmological constant: a worked example

NASA Astrophysics Data System (ADS)

Pereira, J. A. M.

2016-03-01

The cosmological constant regained the attention of the scientific community following the recent discovery of the accelerated expansion of the Universe. Consequently, interest in the subject increased amongst the public such that it now often appears in the classroom and popular science publications. The purpose of this article is to use basic concepts of Newtonian mechanics, like dynamics, kinetic energy and potential energy diagrams, in a scenario where the cosmological constant’s action, considered as being an inertial force driven by the accelerated expansion of the Universe, could counteract Earth’s gravity. The effect that the cosmological constant might have near the Earth’s surface is discussed showing how everyday life would change. This is done in such a way that makes it accessible to students in their first year of college. Finally, the modern interpretation of the cosmological constant, associated with the existence of dark energy, is briefly discussed along with upper limit estimations for its value based on the anthropic principle.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aurich, R.; Lustig, S., E-mail: ralf.aurich@uni-ulm.de, E-mail: sven.lustig@uni-ulm.de

Early-matter-like dark energy is defined as a dark energy component whose equation of state approaches that of cold dark matter (CDM) at early times. Such a component is an ingredient of unified dark matter (UDM) models, which unify the cold dark matter and the cosmological constant of the ΛCDM concordance model into a single dark fluid. Power series expansions in conformal time of the perturbations of the various components for a model with early-matter-like dark energy are provided. They allow the calculation of the cosmic microwave background (CMB) anisotropy from the primordial initial values of the perturbations. For a phenomenologicalmore » UDM model, which agrees with the observations of the local Universe, the CMB anisotropy is computed and compared with the CMB data. It is found that a match to the CMB observations is possible if the so-called effective velocity of sound c{sub eff} of the early-matter-like dark energy component is very close to zero. The modifications on the CMB temperature and polarization power spectra caused by varying the effective velocity of sound are studied.« less

Dark degeneracy and interacting cosmic components

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aviles, Alejandro; Cervantes-Cota, Jorge L.

2011-10-15

We study some properties of the dark degeneracy, which is the fact that what we measure in gravitational experiments is the energy-momentum tensor of the total dark sector, and any split into components (as in dark matter and dark energy) is arbitrary. In fact, just one dark fluid is necessary to obtain exactly the same cosmological and astrophysical phenomenology as the {Lambda}CDM model. We work explicitly the first-order perturbation theory and show that beyond the linear order the dark degeneracy is preserved under some general assumptions. Then we construct the dark fluid from a collection of interacting fluids. Finally, wemore » try to break the degeneracy with a general class of couplings to baryonic matter. Nonetheless, we show that these interactions can also be understood in the context of the {Lambda}CDM model as between dark matter and baryons. For this last investigation we choose two independent parametrizations for the interactions, one inspired by electromagnetism and the other by chameleon theories. Then, we constrain them with a joint analysis of CMB and supernovae observational data.« less

Gravitational vacuum energy in our recently accelerating universe

NASA Astrophysics Data System (ADS)

Bludman, Sidney

2009-04-01

We review current observations of the homogeneous cosmological expansion which, because they measure only kinematic variables, cannot determine the dynamics driving the recent accelerated expansion. The minimal fit to the data, the flat ACDM model, consisting of cold dark matter and a cosmological constant, interprets 4? geometrically as a classical spacetime curvature constant of nature, avoiding any reference to quantum vacuum energy. (The observed Uehling and Casimir effects measure forces due to QED vacuum polarization, but not any quantum material vacuum energies.) An Extended Anthropic Principle, that Dark Energy and Dark Gravity be indistinguishable, selects out flat ACDM. Prospective cosmic shear and galaxy clustering observations of the growth of fluctuations are intended to test whether the 'dark energy' driving the recent cosmological acceleration is static or moderately dynamic. Even if dynamic, observational differences between an additional negative-pressure material component within general relativity (Dark Energy) and low-curvature modifications of general relativity (Dark Gravity) will be extremely small.

Power spectrum estimation from peculiar velocity catalogues

NASA Astrophysics Data System (ADS)

Macaulay, E.; Feldman, H. A.; Ferreira, P. G.; Jaffe, A. H.; Agarwal, S.; Hudson, M. J.; Watkins, R.

2012-09-01

The peculiar velocities of galaxies are an inherently valuable cosmological probe, providing an unbiased estimate of the distribution of matter on scales much larger than the depth of the survey. Much research interest has been motivated by the high dipole moment of our local peculiar velocity field, which suggests a large-scale excess in the matter power spectrum and can appear to be in some tension with the Λ cold dark matter (ΛCDM) model. We use a composite catalogue of 4537 peculiar velocity measurements with a characteristic depth of 33 h-1 Mpc to estimate the matter power spectrum. We compare the constraints with this method, directly studying the full peculiar velocity catalogue, to results by Macaulay et al., studying minimum variance moments of the velocity field, as calculated by Feldman, Watkins & Hudson. We find good agreement with the ΛCDM model on scales of k > 0.01 h Mpc-1. We find an excess of power on scales of k < 0.01 h Mpc-1 with a 1σ uncertainty which includes the ΛCDM model. We find that the uncertainty in excess at these scales is larger than an alternative result studying only moments of the velocity field, which is due to the minimum variance weights used to calculate the moments. At small scales, we are able to clearly discriminate between linear and non-linear clustering in simulated peculiar velocity catalogues and find some evidence (although less clear) for linear clustering in the real peculiar velocity data.

Is LambdaCDM consistent with the Tully-Fisher relation?

NASA Astrophysics Data System (ADS)

Reyes, Reinabelle; Gunn, J. E.; Mandelbaum, R.

2013-07-01

We consider the question of the origin of the Tully-Fisher relation in LambdaCDM cosmology. Reproducing the observed tight relation between stellar masses and rotation velocities of disk galaxies presents a challenge for semi-analytical models and hydrodynamic simulations of galaxy formation. Here, our goal is to construct a suite of galaxy mass models that is fully consistent with observations, and that also reproduces the observed Tully-Fisher relation. We take advantage of a well-defined sample of disk galaxies in SDSS with measured rotation velocities (from long-slit spectroscopy of H-alpha), stellar bulge and disk profiles (from fits to SDSS images), and average dark matter halo masses (from stacked weak lensing of a larger, similarly-selected sample). The primary remaining freedom in the mass models come from the final dark matter halo profile (after contraction from baryon infall and, possibly, feedback) and the stellar IMF. We find that the observed velocities are reproduced by models with Kroupa IMF and NFW (i.e., unmodified) dark matter haloes for galaxies with stellar masses 10^9-10^10 M_sun. For higher stellar masses, models with contracted NFW haloes are favored. A scenario in which the amount of halo contraction varies with stellar mass is able to reproduce the observed Tully-Fisher relation over the full stellar mass range of our sample from 10^9 to 10^11 M_sun. We present this as a proof-of-concept for consistency between LambdaCDM and the Tully-Fisher relation.

Reionization in sterile neutrino cosmologies

NASA Astrophysics Data System (ADS)

Bose, Sownak; Frenk, Carlos S.; Hou, Jun; Lacey, Cedric G.; Lovell, Mark R.

2016-12-01

We investigate the process of reionization in a model in which the dark matter is a warm elementary particle such as a sterile neutrino. We focus on models that are consistent with the dark matter decay interpretation of the recently detected line at 3.5 keV in the X-ray spectra of galaxies and clusters. In warm dark matter models, the primordial spectrum of density perturbations has a cut-off on the scale of dwarf galaxies. Structure formation therefore begins later than in the standard cold dark matter (CDM) model and very few objects form below the cut-off mass scale. To calculate the number of ionizing photons, we use the Durham semi-analytic model of galaxy formation, GALFORM. We find that even the most extreme 7 keV sterile neutrino we consider is able to reionize the Universe early enough to be compatible with the bounds on the epoch of reionization from Planck. This, perhaps surprising, result arises from the rapid build-up of high redshift galaxies in the sterile neutrino models which is also reflected in a faster evolution of their far-UV luminosity function between 10 > z > 7 than in CDM. The dominant sources of ionizing photons are systematically more massive in the sterile neutrino models than in CDM. As a consistency check on the models, we calculate the present-day luminosity function of satellites of Milky Way-like galaxies. When the satellites recently discovered in the Dark Energy Survey are taken into account, strong constraints are placed on viable sterile neutrino models.

Planes of satellite galaxies and the cosmic web

NASA Astrophysics Data System (ADS)

Libeskind, Noam I.; Hoffman, Yehuda; Tully, R. Brent; Courtois, Helene M.; Pomarède, Daniel; Gottlöber, Stefan; Steinmetz, Matthias

2015-09-01

Recent observational studies have demonstrated that the majority of satellite galaxies tend to orbit their hosts on highly flattened, vast, possibly corotating planes. Two nearly parallel planes of satellites have been confirmed around the M31 galaxy and around the Centaurus A galaxy, while the Milky Way also sports a plane of satellites. It has been argued that such an alignment of satellites on vast planes is unexpected in the standard Λ cold dark matter (ΛCDM) model of cosmology if not even in contradiction to its generic predictions. Guided by ΛCDM numerical simulations, which suggest that satellites are channelled towards hosts along the axis of the slowest collapse as dictated by the ambient velocity shear tensor, we re-examine the planes of local satellites systems within the framework of the local shear tensor derived from the Cosmicflows-2 data set. The analysis reveals that the Local Group and Centaurus A reside in a filament stretched by the Virgo cluster and compressed by the expansion of the Local Void. Four out of five thin planes of satellite galaxies are indeed closely aligned with the axis of compression induced by the Local Void. Being the less massive system, the moderate misalignment of the Milky Way's satellite plane can likely be ascribed to its greater susceptibility to tidal torques, as suggested by numerical simulations. The alignment of satellite systems in the local Universe with the ambient shear field is thus in general agreement with predictions of the ΛCDM model.

Distinguishing modified gravity models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brax, Philippe; Davis, Anne-Christine, E-mail: philippe.brax@cea.fr, E-mail: A.C.Davis@damtp.cam.ac.uk

2015-10-01

Modified gravity models with screening in local environments appear in three different guises: chameleon, K-mouflage and Vainshtein mechanisms. We propose to look for differences between these classes of models by considering cosmological observations at low redshift. In particular, we analyse the redshift dependence of the fine structure constant and the proton to electron mass ratio in each of these scenarios. When the absorption lines belong to unscreened regions of space such as dwarf galaxies, a time variation would be present for chameleons. For both K-mouflage and Vainshtein mechanisms, the cosmological time variation of the scalar field is not suppressed inmore » both unscreened and screened environments, therefore enhancing the variation of constants and their detection prospect. We also consider the time variation of the redshift of distant objects using their spectrocopic velocities. We find that models of the K-mouflage and Vainshtein types have very different spectroscopic velocities as a function of redshift and that their differences with the Λ-CDM template should be within reach of the future ELT-HIRES observations.« less

Baryonic matter perturbations in decaying vacuum cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marttens, R.F. vom; Zimdahl, W.; Hipólito-Ricaldi, W.S., E-mail: rodrigovonmarttens@gmail.com, E-mail: wiliam.ricaldi@ufes.br, E-mail: winfried.zimdahl@pq.cnpq.br

2014-08-01

We consider the perturbation dynamics for the cosmic baryon fluid and determine the corresponding power spectrum for a Λ(t)CDM model in which a cosmological term decays into dark matter linearly with the Hubble rate. The model is tested by a joint analysis of data from supernovae of type Ia (SNIa) (Constitution and Union 2.1), baryonic acoustic oscillations (BAO), the position of the first peak of the anisotropy spectrum of the cosmic microwave background (CMB) and large-scale-structure (LSS) data (SDSS DR7). While the homogeneous and isotropic background dynamics is only marginally influenced by the baryons, there are modifications on the perturbativemore » level if a separately conserved baryon fluid is included. Considering the present baryon fraction as a free parameter, we reproduce the observed abundance of the order of 5% independently of the dark-matter abundance which is of the order of 32% for this model. Generally, the concordance between background and perturbation dynamics is improved if baryons are explicitly taken into account.« less