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Sample records for dark energy eos

  1. A new class of LRS Bianchi type-II dark energy models with variable EoS parameter

    NASA Astrophysics Data System (ADS)

    Pradhan, Anirudh; Amirhashchi, Hassan; Jaiswal, Rekha

    2011-08-01

    A new class of dark energy models in a Locally Rotationally Symmetric Bianchi type-II (LRS B-II) space-time with variable equation of state (EoS) parameter and constant deceleration parameter have been investigated in the present paper. The Einstein's field equations have been solved by applying a variation law for generalized Hubble's parameter given by Berman: Nuovo Cimento 74:182 (1983) which generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential-law form. Using these two forms, Einstein's field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. The dark energy EoS parameter ω is found to be time dependent and its existing range for both models is in good agreement with the three recent observations of (i) SNe Ia data (Knop et al.: Astrophys. J. 598:102 (2003)), (ii) SNe Ia data collaborated with CMBR anisotropy and galaxy clustering statistics (Tegmark et al.: Astrophys. J. 606:702 (2004)) and latest (iii) a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift type Ia supernovae and galaxy clustering (Hinshaw et al.: Astrophys. J. Suppl. 180:225 (2009); Komatsu et al. Astrophys. J. Suppl. 180:330 (2009)). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical and geometric behaviour of the universe have also been discussed in detail.

  2. Are dark energy models with variable EoS parameter w compatible with the late inhomogeneous Universe?

    SciTech Connect

    Akarsu, Özgür; Bouhmadi-López, Mariam; Brilenkov, Maxim; Brilenkov, Ruslan; Eingorn, Maxim; Zhuk, Alexander E-mail: mbl@ubi.pt E-mail: ruslan.brilenkov@gmail.com E-mail: ai.zhuk2@gmail.com

    2015-07-01

    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 of 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.

  3. G-corrected holographic dark energy model

    NASA Astrophysics Data System (ADS)

    Malekjani, M.; Honari-Jafarpour, M.

    2013-08-01

    Here we investigate the holographic dark energy model in the framework of FRW cosmology where the Newtonian gravitational constant, G, is varying with cosmic time. Using the complementary astronomical data which support the time dependency of G, the evolutionary treatment of EoS parameter and energy density of dark energy model are calculated in the presence of time variation of G. It has been shown that in this case, the phantom regime can be achieved at the present time. We also calculate the evolution of G-corrected deceleration parameter for holographic dark energy model and show that the dependency of G on the comic time can influence on the transition epoch from decelerated expansion to the accelerated phase. Finally we perform the statefinder analysis for G-corrected holographic model and show that this model has a shorter distance from the observational point in s- r plane compare with original holographic dark energy model.

  4. Holographic Dark Energy Density

    NASA Astrophysics Data System (ADS)

    Saadat, Hassan

    2011-06-01

    In this article we consider the cosmological model based on the holographic dark energy. We study dark energy density in Universe with arbitrary spatially curvature described by the Friedmann-Robertson-Walker metric. We use Chevallier-Polarski-Linder parametrization to specify dark energy density.

  5. Inhomogeneous dark energy

    SciTech Connect

    Chamseddine, Ali H.; Mukhanov, Viatcheslav E-mail: viatcheslav.Mukhanov@lmu.de

    2016-02-01

    We modify Einstein General Relativity by adding non-dynamical scalar fields to account simultaneously for both dark matter and dark energy. The dark energy in this case can be distributed in-homogeneously even within horizon scales. Its inhomogeneities can contribute to the late time integrated Sachs-Wolfe effect, possibly removing some of the low multipole anomalies in the temperature fluctuations of the CMB spectrum. The presence of the inhomogeneous dark matter also influences structure formation in the universe.

  6. Holographic dark energy reexamined

    SciTech Connect

    Gong Yungui; Wang Bin; Zhang Yuanzhong

    2005-08-15

    We have reexamined the holographic dark energy model by considering the spatial curvature. We have refined the model parameter and observed that the holographic dark energy model does not behave as phantom model. Comparing the holographic dark energy model to the supernova observation alone, we found that the closed Universe is favored. Combining with the Wilkinson microwave anisotropy probe (WMAP) data, we obtained the reasonable value of the spatial curvature of our Universe.

  7. EOS

    NASA Astrophysics Data System (ADS)

    Asrar, Ghassem; Dozier, Jeff

    Market: Students and researchers in geophysics, astronomy, and astrophysics. This book reports on the timely Earth Observing System (EOS) Program's wide range of scientific investigations, observational capabilities, vast data and information system, and educational activities. Because its primary goal is to determine the extent, causes, and regional consequences of global climate change, this program provides the scientific knowledge needed by world leaders to formulate sound and equitable environmental policies.

  8. Metastable dark energy

    NASA Astrophysics Data System (ADS)

    Landim, Ricardo G.; Abdalla, Elcio

    2017-01-01

    We build a model of metastable dark energy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable dark energy is also embedded into a model with SU(2)R symmetry. The dark energy doublet and the dark matter doublet naturally interact with each other. A three-body decay of the dark energy particle into (cold and warm) dark matter can be as long as large fraction of the age of the universe, if the mediator is massive enough, the lower bound being at intermediate energy level some orders below the grand unification scale. Such a decay shows a different form of interaction between dark matter and dark energy, and the model opens a new window to investigate the dark sector from the point-of-view of particle physics.

  9. Analysis of dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Yongquan, Han

    2016-05-01

    As the law of unity of opposites of the Philosophy tells us, the bright material exists, the dark matter also exists. Dark matter and dark energy should allow the law of unity of opposites. The Common attributes of the matter is radiation, then common attributes of dark matter must be absorb radiation. Only the rotation speed is lower than the speed of light radiation, can the matter radiate, since the speed of the matter is lower than the speed of light, so the matter is radiate; The rotate speed of the dark matter is faster than the light , so the dark matter doesn't radiate, it absorbs radiation. The energy that the dark matter absorb radiation produced (affect the measurement of time and space distribution of variations) is dark energy, so the dark matter produce dark energy only when it absorbs radiation. Dark matter does not radiate, two dark matters does not exist inevitably forces, and also no dark energy. Called the space-time ripples, the gravitational wave is bent radiation, radiation particles should be graviton, graviton is mainly refers to the radiation particles whose wavelength is small. Dark matter, dark energy also confirms the existence of the law of symmetry.

  10. Elucidating dark energy with future 21 cm observations at the epoch of reionization

    NASA Astrophysics Data System (ADS)

    Kohri, Kazunori; Oyama, Yoshihiko; Sekiguchi, Toyokazu; Takahashi, Tomo

    2017-02-01

    We investigate how precisely we can determine the nature of dark energy such as the equation of state (EoS) and its time dependence by using future observations of 21 cm fluctuations at the epoch of reionization (06.8lesssim zlesssim1) such as Square Kilometre Array (SKA) and Omniscope in combination with those from cosmic microwave background, baryon acoustic oscillation, type Ia supernovae and direct measurement of the Hubble constant. We consider several parametrizations for the EoS and find that future 21 cm observations will be powerful in constraining models of dark energy, especially when its EoS varies at high redshifts.

  11. Fingerprinting dark energy

    SciTech Connect

    Sapone, Domenico; Kunz, Martin

    2009-10-15

    Dark energy perturbations are normally either neglected or else included in a purely numerical way, obscuring their dependence on underlying parameters like the equation of state or the sound speed. However, while many different explanations for the dark energy can have the same equation of state, they usually differ in their perturbations so that these provide a fingerprint for distinguishing between different models with the same equation of state. In this paper we derive simple yet accurate approximations that are able to characterize a specific class of models (encompassing most scalar-field models) which is often generically called 'dark energy'. We then use the approximate solutions to look at the impact of the dark energy perturbations on the dark matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background radiation.

  12. Can dark matter decay in dark energy?

    NASA Astrophysics Data System (ADS)

    Pereira, S. H.; Jesus, J. F.

    2009-02-01

    We analyze the interaction between dark energy and dark matter from a thermodynamical perspective. By assuming they have different temperatures, we study the possibility of occurring a decay from dark matter into dark energy, characterized by a negative parameter Q. We find that, if at least one of the fluids has nonvanishing chemical potential, for instance μx<0 and μdm=0 or μx=0 and μdm>0, the decay is possible, where μx and μdm are the chemical potentials of dark energy and dark matter, respectively. Using recent cosmological data, we find that, for a fairly simple interaction, the dark matter decay is favored with a probability of ˜93% over the dark energy decay. This result comes from a likelihood analysis where only background evolution has been considered.

  13. Dark Energy, or Worse

    ScienceCinema

    Professor Sean Carroll

    2016-07-12

    General relativity is inconsistent with cosmological observations unless we invoke components of dark matter and dark energy that dominate the universe. While it seems likely that these exotic substances really do exist, the alternative is worth considering: that Einstein's general relativity breaks down on cosmological scales. I will discuss models of modified gravity, tests in the solar system and elsewhere, and consequences for cosmology.

  14. Dark Energy, or Worse

    SciTech Connect

    Professor Sean Carroll

    2006-11-13

    General relativity is inconsistent with cosmological observations unless we invoke components of dark matter and dark energy that dominate the universe. While it seems likely that these exotic substances really do exist, the alternative is worth considering: that Einstein's general relativity breaks down on cosmological scales. I will discuss models of modified gravity, tests in the solar system and elsewhere, and consequences for cosmology.

  15. Dark Energy in the Dark Ages

    SciTech Connect

    Linder, Eric V.

    2006-04-11

    Non-negligible dark energy density at high redshifts would indicate dark energy physics distinct from a cosmological constant or"reasonable'" canonical scalar fields. Such dark energy can be constrained tightly through investigation of the growth of structure, with limits of<~;;2percent of total energy density at z>> 1 for many models. Intermediate dark energy can have effects distinct from its energy density; the dark ages acceleration can be constrained to last less than 5percent of a Hubble e-fold time, exacerbating the coincidence problem. Both the total linear growth, or equivalently sigma 8, and the shape and evolution of the nonlinear mass power spectrum for z<2 (using the Linder-White nonlinear mapping prescription) provide important windows. Probes of growth, such as weak gravitational lensing, can interact with supernovae and CMB distance measurements to scan dark energy behavior over the entire range z=0-1100.

  16. Is dark energy evolving?

    SciTech Connect

    Nair, Remya; Jhingan, Sanjay E-mail: sanjay.jhingan@gmail.com

    2013-02-01

    We look for evidence for the evolution in dark energy density by employing Principal Component Analysis (PCA). Distance redshift data from supernovae and baryon acoustic oscillations (BAO) along with WMAP7 distance priors are used to put constraints on curvature parameter Ω{sub k} and dark energy parameters. The data sets are consistent with a flat Universe. The constraints on the dark energy evolution parameters obtained from supernovae (including CMB distance priors) are consistent with a flat ΛCDM Universe. On the other hand, in the parameter estimates obtained from the addition of BAO data the second principal component, which characterize a non-constant contribution from dark energy, is non-zero at 1σ. This could be a systematic effect and future BAO data holds key to making more robust claims.

  17. Is Dark Energy Falsifiable?

    NASA Astrophysics Data System (ADS)

    Gibson, C. H.; Schild, R. E.

    2011-11-01

    Is the accelerating expansion of the Universe true, inferred through observations of distant supernovae, and is the implied existence of an enormous amount of anti- gravitational dark energy material driving the accelerating expansion of the universe also true? To be physically useful these propositions must be falsifiable; that is, subject to observational tests that could render them false, and both fail when viscous, diffusive, astro-biological and turbulence effects are included in the interpretation of observations. A more plausible explanation of negative stresses producing the big bang is turbulence at Planck temperatures. Inflation results from gluon viscous stresses at the strong force transition. Anti-gravitational (dark energy) turbulence stresses are powerful but only temporary. No permanent dark energy is needed. At the plasma-gas transition, viscous stresses cause fragmentation of plasma proto-galaxies into dark matter clumps of primordial gas planets, each of which falsifies dark-energy cold-dark-matter cosmologies. Clumps of these planets form all stars, and explain the alleged accelerating expansion of the universe as a systematic dimming error of Supernovae Ia by light scattered in the hot turbulent atmospheres of evaporated planets surrounding central white dwarf stars.

  18. Cosmological study in loop quantum cosmology through dark energy model

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Rani, Shamaila; Salako, Ines G.; Gulshan, Faiza

    The interacting generalized ghost version of pilgrim dark energy (GGPDE) is discussed in the framework of loop quantum cosmology (LQC). We analyze the behavior of cosmological parameters (Hubble, equation of state (EoS), deceleration) and cosmological planes (ωD ‑ ωD‧ and r-s) in the present scenario (ωD represents the EoS parameter and ωD‧ indicates the evolution of the EoS parameter, r,s are statefinder parameters). It is observed that the deceleration parameter corresponds to the accelerated expansion of the universe. The EoS parameter lies in vacuum and phantom regions for all cases of u (pilgrim dark energy (PDE) parameter). The ωD ‑ ωD‧ plane lies in thawing region for all cases of u. The r ‑ s plane corresponds to Λ cold dark matter (CDM) and Chaplygin gas model. We have also mentioned the constraints on calculated cosmological parameters and found that all the trajectories of cosmological parameters and planes show the consistence behavior with the observational schemes.

  19. Big Mysteries: Dark Energy

    SciTech Connect

    Lincoln, Don

    2014-04-15

    Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.

  20. Big Mysteries: Dark Energy

    ScienceCinema

    Lincoln, Don

    2016-07-12

    Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.

  1. The Dark Energy Survey

    SciTech Connect

    Flaugher, Brenna; /Fermilab

    2004-11-01

    Dark Energy is the dominant constituent of the universe and they have little understanding of it. They describe a new project aimed at measuring the dark energy equation of state parameter, w, to a statistical precision of {approx} 5%, with four separate techniques. The survey will image 5000 deg{sup 2} in the southern sky and collect 300 million galaxies, 30,000 galaxy clusters, and 2000 Type Ia supernovae. The survey will be carried out using a new 3 deg{sup 2} mosaic camera mounted at the prime focus of the 4m Blanco telescope at CTIO.

  2. Dark Energy simulations

    NASA Astrophysics Data System (ADS)

    Baldi, Marco

    2012-11-01

    Cosmology is presently facing the deep mystery of the origin of the observed accelerated expansion of the Universe. Be it a cosmological constant, a homogeneous scalar field, or a more complex inhomogeneous field possibly inducing effective modifications of the laws of gravity, such elusive physical entity is indicated with the general term of “Dark Energy”. The growing role played by numerical N-body simulations in cosmological studies as a fundamental connection between theoretical modeling and direct observations has led to impressive advancements also in the development and application of specific algorithms designed to probe a wide range of Dark Energy scenarios. Over the last decade, a large number of independent and complementary investigations have been carried out in the field of Dark Energy N-body simulations, starting from the simplest case of homogeneous Dark Energy models up to the recent development of highly sophisticated iterative solvers for a variety of Modified Gravity theories. In this review -which is meant to be complementary to the general Review by Kuhlen et al. (2012) [1] published in this Volume - I will discuss the range of scenarios for the cosmic acceleration that have been successfully investigated by means of dedicated N-body simulations, and I will provide a broad summary of the main results that have been obtained in this rather new research field. I will focus the discussion on a few selected studies that have led to particularly significant advancements in the field, and I will provide a comprehensive list of references for a larger number of related works. Due to the vastness of the topic, the discussion will not enter into the finest details of the different implementations and will mainly focus on the outcomes of the various simulations studies. Although quite recent, the field of Dark Energy simulations has witnessed huge developments in the last few years, and presently stands as a reliable approach to the investigation

  3. Dark-energy thermodynamic models

    SciTech Connect

    Besprosvany, Jaime; Izquierdo, German

    2010-12-07

    We study cosmological consequences of dark-energy thermodynamic models. The assumption that dark energy is conformed of quanta, and an extensivity argument generalize its equation of state. This implies that dark energy and another key component exchange energy. The energy densities of dark energy and the other component then tend asymptotically to a constant, thus explaining the coincidence of dark matter and dark energy today. On the other hand, a model of non-relativistic particles in a Bose-Einstein condensate, with a short-range attractive interaction, produces acceleration. It is shown that the phantom-acceleration regime, at the beginning of the universe, solves the horizon problem.

  4. Improved constraints on the dark energy equation of state using Gaussian processes

    NASA Astrophysics Data System (ADS)

    Wang, Deng; Meng, Xin-He

    2017-01-01

    We perform a comprehensive study of the dark energy equation of state (EoS) utilizing the model-independent Gaussian processes (GP). Using a combination of the Union 2.1 data set, the 30 newly added H(z) cosmic chronometer data points and Planck's shift parameter, we modify the usual GaPP code and provide a tighter constraint on the dark energy EoS than the previous literature about GP reconstructions. Subsequently, we take the "controlling variable method " to investigate directly the effects of the variable matter density parameter Ωm 0, variable cosmic curvature Ωk 0, and variable Hubble constant H0 on the dark energy EoS. We find that too small or large Ωm 0, Ωk 0, and H0 are all disfavored by our GP reconstructions based on current cosmological observations. Subsequently, we find that variables Ωm 0 and Ωk 0 affect the reconstructions of the dark energy EoS but hardly affect the reconstructions of the normalized comoving distance D (z ) and its derivatives D'(z ) and D''(z ). However, variable H0 affects the reconstructions of the dark energy EoS by affecting obviously those of D (z ) , D'(z ) , and D''(z ). Furthermore, we find that the results of our reconstructions support substantially the recent local measurement of H0 reported by Riess et al.

  5. Dark Energy. What the ...?

    SciTech Connect

    Wechsler, Risa

    2007-10-30

    What is the Universe made of? This question has been asked as long as humans have been questioning, and astronomers and physicists are finally converging on an answer. The picture which has emerged from numerous complementary observations over the past decade is a surprising one: most of the matter in the Universe isn't visible, and most of the Universe isn't even made of matter. In this talk, I will explain what the rest of this stuff, known as 'Dark Energy' is, how it is related to the so-called 'Dark Matter', how it impacts the evolution of the Universe, and how we can study the dark universe using observations of light from current and future telescopes.

  6. Unparticle dark energy

    SciTech Connect

    Dai, D.-C.; Stojkovic, Dejan; Dutta, Sourish

    2009-09-15

    We examine a dark energy model where a scalar unparticle degree of freedom plays the role of quintessence. In particular, we study a model where the unparticle degree of freedom has a standard kinetic term and a simple mass potential, the evolution is slowly rolling and the field value is of the order of the unparticle energy scale ({lambda}{sub u}). We study how the evolution of w depends on the parameters B (a function of unparticle scaling dimension d{sub u}), the initial value of the field {phi}{sub i} (or equivalently, {lambda}{sub u}) and the present matter density {omega}{sub m0}. We use observational data from type Ia supernovae, baryon acoustic oscillations and the cosmic microwave background to constrain the model parameters and find that these models are not ruled out by the observational data. From a theoretical point of view, unparticle dark energy model is very attractive, since unparticles (being bound states of fundamental fermions) are protected from radiative corrections. Further, coupling of unparticles to the standard model fields can be arbitrarily suppressed by raising the fundamental energy scale M{sub F}, making the unparticle dark energy model free of most of the problems that plague conventional scalar field quintessence models.

  7. Effects of EoS in viscous hydro + cascade model for the RHIC Beam Energy Scan

    NASA Astrophysics Data System (ADS)

    Karpenko, Iu.; Bleicher, M.; Huovinen, P.; Petersen, H.

    2016-12-01

    A state-of-the-art 3+1 dimensional cascade + viscous hydro + cascade model vHLLE+UrQMD has been applied to heavy ion collisions in RHIC Beam Energy Scan range √{sNN} = 7.7 , … , 200 GeV. Based on comparison to available experimental data it was estimated that an effective value of shear viscosity over entropy density ratio η / s in hydrodynamic stage has to decrease from η / s = 0.2 to 0.08 as collision energy increases from √{sNN} = 7.7 to 39 GeV, and to stay at η / s = 0.08 for 39 ≤√{ s} ≤ 200 GeV. In this work we show how an equation of state with first order phase transition affects the hydrodynamic evolution at those collision energies and changes the results of the model as compared to "default scenario" with a crossover type EoS from chiral model.

  8. Natural Neutrino Dark Energy

    SciTech Connect

    Gurwich, Ilya

    2010-06-23

    1 construct a general description for neutrino dark energy models, that do not require exotic particles or strange couplings. With the help of the above, this class of models is reduced to a single function with several constraints. It is shown that these models lead to some concrete predictions that can be verified (or disproved) within the next decade, using results from PLANK, EUCLID and JDEM.

  9. Dynamics of Dark Energy

    SciTech Connect

    Copeland, Edmund J.

    2007-11-20

    I briefly review attempts that have been made to model dark energy. These include models of a cosmological constant, dynamical models where a scalar field may be responsible for the observed late time acceleration through to the possibility that we are not fully in control of the gravity sector and the acceleration may be some manifestation of modified gravity. In all cases we will see some degree of fine tuning is required with the current models.

  10. On dark energy isocurvature perturbation

    SciTech Connect

    Liu, Jie; Zhang, Xinmin; Li, Mingzhe E-mail: limz@nju.edu.cn

    2011-06-01

    Determining the equation of state of dark energy with astronomical observations is crucially important to understand the nature of dark energy. In performing a likelihood analysis of the data, especially of the cosmic microwave background and large scale structure data the dark energy perturbations have to be taken into account both for theoretical consistency and for numerical accuracy. Usually, one assumes in the global fitting analysis that the dark energy perturbations are adiabatic. In this paper, we study the dark energy isocurvature perturbation analytically and discuss its implications for the cosmic microwave background radiation and large scale structure. Furthermore, with the current astronomical observational data and by employing Markov Chain Monte Carlo method, we perform a global analysis of cosmological parameters assuming general initial conditions for the dark energy perturbations. The results show that the dark energy isocurvature perturbations are very weakly constrained and that purely adiabatic initial conditions are consistent with the data.

  11. Constraining Dark Energy

    NASA Astrophysics Data System (ADS)

    Abrahamse, Augusta

    2010-12-01

    Future advances in cosmology will depend on the next generation of cosmological observations and how they shape our theoretical understanding of the universe. Current theoretical ideas, however, have an important role to play in guiding the design of such observational programs. The work presented in this thesis concerns the intersection of observation and theory, particularly as it relates to advancing our understanding of the accelerated expansion of the universe (or the dark energy). Chapters 2 - 4 make use of the simulated data sets developed by the Dark Energy Task Force (DETF) for a number of cosmological observations currently in the experimental pipeline. We use these forecast data in the analysis of four quintessence models of dark energy: the PNGB, Exponential, Albrecht-Skordis and Inverse Power Law (IPL) models. Using Markov Chain Monte Carlo sampling techniques we examine the ability of each simulated data set to constrain the parameter space of these models. We examine the potential of the data for differentiating time-varying models from a pure cosmological constant. Additionally, we introduce an abstract parameter space to facilitate comparison between models and investigate the ability of future data to distinguish between these quintessence models. In Chapter 5 we present work towards understanding the effects of systematic errors associated with photometric redshift estimates. Due to the need to sample a vast number of deep and faint galaxies, photometric redshifts will be used in a wide range of future cosmological observations including gravitational weak lensing, baryon accoustic oscillations and type 1A supernovae observations. The uncertainty in the redshift distributions of galaxies has a significant potential impact on the cosmological parameter values inferred from such observations. We introduce a method for parameterizing uncertainties in modeling assumptions affecting photometric redshift calculations and for propagating these

  12. The dark side of cosmology: dark matter and dark energy.

    PubMed

    Spergel, David N

    2015-03-06

    A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales. Copyright © 2015, American Association for the Advancement of Science.

  13. The Dark Energy Camera

    SciTech Connect

    Flaugher, B.

    2015-04-11

    The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250-μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. The CCDs have 15μm x 15μm pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

  14. The Dark Energy Camera

    DOE PAGES

    Flaugher, B.

    2015-04-11

    The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250-μm thick fully depleted CCDs cooled inside a vacuum Dewar.more » The 570 Mpixel focal plane comprises 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. The CCDs have 15μm x 15μm pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.« less

  15. The Dark Energy Camera

    NASA Astrophysics Data System (ADS)

    Flaugher, B.; Diehl, H. T.; Honscheid, K.; Abbott, T. M. C.; Alvarez, O.; Angstadt, R.; Annis, J. T.; Antonik, M.; Ballester, O.; Beaufore, L.; Bernstein, G. M.; Bernstein, R. A.; Bigelow, B.; Bonati, M.; Boprie, D.; Brooks, D.; Buckley-Geer, E. J.; Campa, J.; Cardiel-Sas, L.; Castander, F. J.; Castilla, J.; Cease, H.; Cela-Ruiz, J. M.; Chappa, S.; Chi, E.; Cooper, C.; da Costa, L. N.; Dede, E.; Derylo, G.; DePoy, D. L.; de Vicente, J.; Doel, P.; Drlica-Wagner, A.; Eiting, J.; Elliott, A. E.; Emes, J.; Estrada, J.; Fausti Neto, A.; Finley, D. A.; Flores, R.; Frieman, J.; Gerdes, D.; Gladders, M. D.; Gregory, B.; Gutierrez, G. R.; Hao, J.; Holland, S. E.; Holm, S.; Huffman, D.; Jackson, C.; James, D. J.; Jonas, M.; Karcher, A.; Karliner, I.; Kent, S.; Kessler, R.; Kozlovsky, M.; Kron, R. G.; Kubik, D.; Kuehn, K.; Kuhlmann, S.; Kuk, K.; Lahav, O.; Lathrop, A.; Lee, J.; Levi, M. E.; Lewis, P.; Li, T. S.; Mandrichenko, I.; Marshall, J. L.; Martinez, G.; Merritt, K. W.; Miquel, R.; Muñoz, F.; Neilsen, E. H.; Nichol, R. C.; Nord, B.; Ogando, R.; Olsen, J.; Palaio, N.; Patton, K.; Peoples, J.; Plazas, A. A.; Rauch, J.; Reil, K.; Rheault, J.-P.; Roe, N. A.; Rogers, H.; Roodman, A.; Sanchez, E.; Scarpine, V.; Schindler, R. H.; Schmidt, R.; Schmitt, R.; Schubnell, M.; Schultz, K.; Schurter, P.; Scott, L.; Serrano, S.; Shaw, T. M.; Smith, R. C.; Soares-Santos, M.; Stefanik, A.; Stuermer, W.; Suchyta, E.; Sypniewski, A.; Tarle, G.; Thaler, J.; Tighe, R.; Tran, C.; Tucker, D.; Walker, A. R.; Wang, G.; Watson, M.; Weaverdyck, C.; Wester, W.; Woods, R.; Yanny, B.; DES Collaboration

    2015-11-01

    The Dark Energy Camera is a new imager with a 2.°2 diameter field of view mounted at the prime focus of the Victor M. Blanco 4 m telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five-element optical corrector, seven filters, a shutter with a 60 cm aperture, and a charge-coupled device (CCD) focal plane of 250 μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 megapixel focal plane comprises 62 2k × 4k CCDs for imaging and 12 2k × 2k CCDs for guiding and focus. The CCDs have 15 μm × 15 μm pixels with a plate scale of 0.″263 pixel-1. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 s with 6-9 electron readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

  16. THE DARK ENERGY CAMERA

    SciTech Connect

    Flaugher, B.; Diehl, H. T.; Alvarez, O.; Angstadt, R.; Annis, J. T.; Buckley-Geer, E. J.; Honscheid, K.; Abbott, T. M. C.; Bonati, M.; Antonik, M.; Brooks, D.; Ballester, O.; Cardiel-Sas, L.; Beaufore, L.; Bernstein, G. M.; Bernstein, R. A.; Bigelow, B.; Boprie, D.; Campa, J.; Castander, F. J.; Collaboration: DES Collaboration; and others

    2015-11-15

    The Dark Energy Camera is a new imager with a 2.°2 diameter field of view mounted at the prime focus of the Victor M. Blanco 4 m telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five-element optical corrector, seven filters, a shutter with a 60 cm aperture, and a charge-coupled device (CCD) focal plane of 250 μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 megapixel focal plane comprises 62 2k × 4k CCDs for imaging and 12 2k × 2k CCDs for guiding and focus. The CCDs have 15 μm × 15 μm pixels with a plate scale of 0.″263 pixel{sup −1}. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 s with 6–9 electron readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

  17. Dark energy and extended dark matter halos

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.

    2012-03-01

    The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even

  18. Explosive Products EOS: Adjustment for detonation speed and energy release

    SciTech Connect

    Menikoff, Ralph

    2014-09-05

    Propagating detonation waves exhibit a curvature effect in which the detonation speed decreases with increasing front curvature. The curvature effect is due to the width of the wave profile. Numerically, the wave profile depends on resolution. With coarse resolution, the wave width is too large and results in a curvature effect that is too large. Consequently, the detonation speed decreases as the cell size is increased. We propose a modification to the products equation of state (EOS) to compensate for the effect of numerical resolution; i.e., to increase the CJ pressure in order that a simulation propagates a detonation wave with a speed that is on average correct. The EOS modification also adjusts the release isentrope to correct the energy release.

  19. Assisted dark energy

    SciTech Connect

    Ohashi, Junko; Tsujikawa, Shinji

    2009-11-15

    Cosmological scaling solutions, which give rise to a scalar-field density proportional to a background fluid density during radiation and matter eras, are attractive to alleviate the energy scale problem of dark energy. In the presence of multiple scalar fields, the scaling solution can exit to the epoch of cosmic acceleration through the so-called assisted inflation mechanism. We study cosmological dynamics of a multifield system in details with a general Lagrangian density p={sub i=1}{sup n}X{sub i}g(X{sub i}e{sup {lambda}{sub i}}{sup {phi}{sub i}}), where X{sub i}=-({nabla}{phi}{sub i}){sup 2}/2 is the kinetic energy of the ith field {phi}{sub i}, {lambda}{sub i} is a constant, and g is an arbitrary function in terms of Y{sub i}=X{sub i}e{sup {lambda}{sub i}}{sup {phi}{sub i}}. This covers most of the scalar-field models of dark energy proposed in literature that possess scaling solutions. Using the bound coming from big-bang nucleosynthesis and the condition under which each field cannot drive inflation as a single component of the universe, we find the following features: (i) a transient or eternal cosmic acceleration can be realized after the scaling matter era, (ii) a thawing property of assisting scalar fields is crucial to determine the evolution of the field equation of state w{sub {phi}}, and (iii) the field equation of state today can be consistent with the observational bound w{sub {phi}}<-0.8 in the presence of multiple scalar fields.

  20. Light thoughts on dark energy

    SciTech Connect

    Linder, Eric V.

    2004-04-01

    The physical process leading to the acceleration of the expansion of the universe is unknown. It may involve new high energy physics or extensions to gravitation. Calling this generically dark energy, we examine the consistencies and relations between these two approaches, showing that an effective equation of state function w(z) is broadly useful in describing the properties of the dark energy. A variety of cosmological observations can provide important information on the dynamics of dark energy and the future looks bright for constraining dark energy, though both the measurements and the interpretation will be challenging. We also discuss a more direct relation between the spacetime geometry and acceleration, via ''geometric dark energy'' from the Ricci scalar, and superacceleration or phantom energy where the fate of the universe may be more gentle than the Big Rip.

  1. Reconstructing and deconstructing dark energy

    SciTech Connect

    Linder, Eric V.

    2004-06-07

    The acceleration of the expansion of the universe, ascribed to a dark energy, is one of the most intriguing discoveries in science. In addition to precise, systematics controlled data, clear, robust interpretation of the observations is required to reveal the nature of dark energy. Even for the simplest question: is the data consistent with the cosmological constant? there are important subtleties in the reconstruction of the dark energy properties. We discuss the roles of analysis both in terms of the Hubble expansion rate or dark energy density {rho}DE(z) and in terms of the dark energy equation of state w(z), arguing that each has its carefully defined place. Fitting the density is best for learning about the density, but using it to probe the equation of state can lead to instability and bias.

  2. New holographic dark energy model inspired by the DGP braneworld

    NASA Astrophysics Data System (ADS)

    Sheykhi, A.; Dehghani, M. H.; Ghaffari, S.

    2016-11-01

    The energy density of the holographic dark energy (HDE) is based on the area law of entropy, and thus any modification of the area law leads to a modified holographic energy density. Inspired by the entropy expression associated with the apparent horizon of a Friedmann-Robertson-Walker (FRW) universe in DGP braneworld, we propose a new model for the HDE in the framework of DGP brane cosmology. We investigate the cosmological consequences of this new model and calculate the equation of state (EoS) parameter by choosing the Hubble radius, L = H-1, as the system’s IR cutoff. Our study show that, due to the effects of the extra dimension (bulk), the identification of IR cutoff with Hubble radius, can reproduce the present acceleration of the universe expansion. This is in contrast to the ordinary HDE in standard cosmology which leads to the zero EoS parameter in the case of choosing the Hubble radius as system’s IR cutoff in the absence of interaction between dark matter (DM) and dark energy (DE).

  3. Optimizing New Dark Energy Experiments

    SciTech Connect

    Tyson, J. Anthony

    2013-08-26

    Next generation “Stage IV” dark energy experiments under design during this grant, and now under construction, will enable the determination of the properties of dark energy and dark matter to unprecedented precision using multiple complementary probes. The most pressing challenge in these experiments is the characterization and understanding of the systematic errors present within any given experimental configuration and the resulting impact on the accuracy of our constraints on dark energy physics. The DETF and the P5 panel in their reports recommended “Expanded support for ancillary measurements required for the long-term program and for projects that will improve our understanding and reduction of the dominant systematic measurement errors.” Looking forward to the next generation Stage IV experiments we have developed a program to address the most important potential systematic errors within these experiments. Using data from current facilities it has been feasible and timely to undertake a detailed investigation of the systematic errors. In this DOE grant we studied of the source and impact of the dominant systematic effects in dark energy measurements, and developed new analysis tools and techniques to minimize their impact. Progress under this grant is briefly reviewed in this technical report. This work was a necessary precursor to the coming generations of wide-deep probes of the nature of dark energy and dark matter. The research has already had an impact on improving the efficiencies of all Stage III and IV dark energy experiments.

  4. Inflation, dark matter, and dark energy in the string landscape.

    PubMed

    Liddle, Andrew R; Ureña-López, L Arturo

    2006-10-20

    We consider the conditions needed to unify the description of dark matter, dark energy, and inflation in the context of the string landscape. We find that incomplete decay of the inflaton field gives the possibility that a single field is responsible for all three phenomena. By contrast, unifying dark matter and dark energy into a single field, separate from the inflaton, appears rather difficult.

  5. Beyond two dark energy parameters.

    PubMed

    Sarkar, Devdeep; Sullivan, Scott; Joudaki, Shahab; Amblard, Alexandre; Holz, Daniel E; Cooray, Asantha

    2008-06-20

    Our ignorance of dark energy is generally described by a two-parameter equation of state. In these approaches, a particular ad hoc functional form is assumed, and only two independent parameters are incorporated. We propose a model-independent, multiparameter approach to fitting dark energy and show that next-generation surveys will constrain the equation of state in three or more independent redshift bins to better than 10%. Future knowledge of dark energy will surpass two numbers (e.g., [w{0},w{1}] or [w{0},w{a}]), and we propose a more flexible approach to the analysis of present and future data.

  6. Dark matter and dark energy: The critical questions

    SciTech Connect

    Michael S. Turner

    2002-11-19

    Stars account for only about 0.5% of the content of the Universe; the bulk of the Universe is optically dark. The dark side of the Universe is comprised of: at least 0.1% light neutrinos; 3.5% {+-} 1% baryons; 29% {+-} 4% cold dark matter; and 66% {+-} 6% dark energy. Now that we have characterized the dark side of the Universe, the challenge is to understand it. The critical questions are: (1) What form do the dark baryons take? (2) What is (are) the constituent(s) of the cold dark matter? (3) What is the nature of the mysterious dark energy that is causing the Universe to speed up.

  7. Understanding Dark Energy

    NASA Astrophysics Data System (ADS)

    Greyber, Howard

    2009-11-01

    By careful analysis of the data from the WMAP satellite, scientists were surprised to determine that about 70% of the matter in our universe is in some unknown form, and labeled it Dark Energy. Earlier, in 1998, two separate international groups of astronomers studying Ia supernovae were even more surprised to be forced to conclude that an amazing smooth transition occurred, from the expected slowing down of the expansion of our universe (due to normal positive gravitation) to an accelerating expansion of the universe that began at at a big bang age of the universe of about nine billion years. In 1918 Albert Einstein stated that his Lambda term in his theory of general relativity was ees,``the energy of empty space,'' and represented a negative pressure and thus a negative gravity force. However my 2004 ``Strong'' Magnetic Field model (SMF) for the origin of magnetic fields at Combination Time (Astro-ph0509223 and 0509222) in our big bang universe produces a unique topology for Superclusters, having almost all the mass, visible and invisible, i.e. from clusters of galaxies down to particles with mass, on the surface of an ellipsoid surrounding a growing very high vacuum. If I hypothesize, with Einstein, that there exists a constant ees force per unit volume, then, gradually, as the universe expands from Combination Time, two effects occur (a) the volume of the central high vacuum region increases, and (b) the density of positive gravity particles in the central region of each Supercluster in our universe decreases dramatically. Thus eventually Einstein's general relativity theory's repulsive gravity of the central very high vacuum region becomes larger than the positive gravitational attraction of all the clusters of galaxies, galaxies, quasars, stars and plasma on the Supercluster shell, and the observed accelerating expansion of our universe occurs. This assumes that our universe is made up mostly of such Superclusters. It is conceivable that the high vacuum

  8. 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.

  9. Holographic dark energy with the sign-changeable interaction term

    NASA Astrophysics Data System (ADS)

    Zadeh, M. Abdollahi; Sheykhi, A.; Moradpour, H.

    We use three infrared (IR) cutoffs, including the future event horizon, the Hubble and Granda-Oliveros (GO) cutoffs, to construct three holographic models of dark energy (DE). Additionally, we consider a Friedmann-Robertson-Walker (FRW) universe filled by a dark matter (DM) and a DE that interact with each other through a mutual sign-changeable interaction with positive coupling constant. Thereinafter, we address the evolution of the some cosmological parameters, such as the equation of state (EoS) and dimensionless density parameters of DE as well as the deceleration parameter, during the cosmic evolution from the matter-dominated era until the late-time acceleration. We observe that a holographic dark energy (HDE) model with Hubble cutoff interacting with DM cannot be in line with the current universe. Our study shows that models with the future event horizon as the IR cutoff or the GO cutoff are in good agreement with the observational data. In fact, we find out that these two recent models can predict the universe transition from a deceleration phase to the acceleration one in a compatible way with observations. The three obtained models may also allow the EoS parameter to cross the phantom line, a result which depends on the values of the system’s constants such as the value of the interaction coupling constant.

  10. Dark Energy Rules the Universe

    SciTech Connect

    Linder, Eric

    2008-01-01

    Berkeley Lab theoretical physicist Eric Linder previews his Nov. 24, 2008 talk on the mystery of dark energy. Catch his full lecture here: http://www.osti.gov/sciencecinema/servlets/purl/1007511?format=mp4

  11. Direct reconstruction of dark energy.

    PubMed

    Clarkson, Chris; Zunckel, Caroline

    2010-05-28

    An important issue in cosmology is reconstructing the effective dark energy equation of state directly from observations. With so few physically motivated models, future dark energy studies cannot only be based on constraining a dark energy parameter space. We present a new nonparametric method which can accurately reconstruct a wide variety of dark energy behavior with no prior assumptions about it. It is simple, quick and relatively accurate, and involves no expensive explorations of parameter space. The technique uses principal component analysis and a combination of information criteria to identify real features in the data, and tailors the fitting functions to pick up trends and smooth over noise. We find that we can constrain a large variety of w(z) models to within 10%-20% at redshifts z≲1 using just SNAP-quality data.

  12. Throwing light on dark energy.

    PubMed

    Kirshner, Robert P

    2003-06-20

    Supernova observations show that the expansion of the universe has been speeding up. This unexpected acceleration is ascribed to a dark energy that pervades space. Supernova data, combined with other observations, indicate that the universe is about 14 billion years old and is composed of about 30%matter and 70%dark energy. New observational programs can trace the history of cosmic expansion more precisely and over a larger span of time than has been done to date to learn whether the dark energy is a modern version of Einstein's cosmological constant or another form of dark energy that changes with time. Either conclusion is an enigma that points to gaps in our fundamental understanding of gravity.

  13. Holographic Ricci Dark Energy Model

    NASA Astrophysics Data System (ADS)

    Saadat, Hassan

    2012-03-01

    In this paper, we consider holographic Ricci dark energy model, and by using general relativity equations obtain time-dependent density of the Universe. We show that the resulting density in independent of space curvature.

  14. Constraints on parameterized dark energy properties from new observations with principal component analysis

    NASA Astrophysics Data System (ADS)

    Zheng, Wei; Li, Hong

    2017-01-01

    For dark energy, the equation of state (EoS) is a critical parameter to depict its physical properties. In this paper, we mainly give constraints on the EoS of dark energy w with the latest observations of cosmic microwave background radiation (CMB) from Planck satellite, JLA Type Ia supernovae (SNIa) sample, baryon acoustic oscillation (BAO) and Hubble parameter measurements. We introduce a kind of parameterized dark energy model called "constant bin - w ", in which the whole redshift range is divided into several bins, and EoS w in each bin is assumed as an independent constant. The results show that EoS in all of the redshift bins are comparable with ΛCDM in the 2σ confidence regions, but some weak deviations from w = - 1 are still indicated. In particular, in the framework of 7 bins, a slight oscillation behavior is shown in the redshift 0 < z < 0.75, especially around the range of 4th bin (0.25 < z < 0.35) and 5th bin (0.35 < z < 0.51). Additionally, we adopt the principal component analysis (PCA) method to do the model-independent analysis, which includes normal PCA and localized PCA methods. By implementing so called normal PCA method, the original oscillation behavior of EoS indicated in the framework of 7 bins becomes more significant after the best reconstruction, but such result still supports ΛCDM within the margin of 2σ errors. To further reduce the errors of constraints on EoS, and confirm such deviations from the cosmological constant scenario, we hope for more precise observational data in the future.

  15. Cosmological evolution with interaction between dark energy and dark matter

    NASA Astrophysics Data System (ADS)

    Bolotin, Yuri L.; Kostenko, Alexander; Lemets, Oleg A.; Yerokhin, Danylo A.

    2015-12-01

    In this review we consider in detail different theoretical topics associated with interaction in the dark sector. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities. We consider a number of different models (including the holographic dark energy and dark energy in a fractal universe), with interacting dark energy and dark matter, have done a thorough analysis of these models. The main task of this review was not only to give an idea about the modern set of different models of dark energy, but to show how much can be diverse dynamics of the universe in these models. We find that the dynamics of a universe that contains interaction in the dark sector can differ significantly from the Standard Cosmological Model.

  16. Cold Fusion Dark Matter and Dark Energy

    NASA Astrophysics Data System (ADS)

    Levi, Mark

    2009-05-01

    Explanation of Cold Fusion [1] ``It is k-capture forming dineutrons followed by absorption by palladium.'' with excess heat energy no more than about .15 MeV per nucleon. Experimentally [1], ^1H and electrons are at high pressure at the center of a palladium wire sample, ``After hours of loading with ^1H, bubbles were present on the wire surface and the wire's resistance had stopped increasing, there was a fizz of hydrogen from the wire within a few seconds after loading current and large bubbles were stopped.'' a repeatable cycle. K-capture rate is affected by environment at the 1/10000 level has has been known since 1946 ( ref. [6]in [1]); and recently has been seen at the 0.35% level for 7Be in C60 [2]. Neutron halos have been seen recently in 8He [3], 6He [4] and others long ago. Conclusions: 1) the evidence for dineutrons is fairly good and as in all K-captures is accompanied by a neutrino emission. collapse of a star to a neutron star has a succession of K-captures in conditions like cold fusion i.e. high pressure. 2)Dark matter is dineutrons from formation of neutron stars and black holes, and dark energy of neutrinos generated in neutron stars, ordinary stars and black holes. If in the latter, then their mass must be zero for an infinite horizon. References: [1] M. Levi, DAMOP Meeting poster paper, session WP, 16-19 May,1995 [2]T. Ohtsuku et al., Phys. Rev. Lett. 98, 252501 (2007) [3] V. I. Ryjkov et al., Phys. Rev. Lett. 101, 01901 (2008) [4] L. B. Wang et al., Phys. Rev. Lett. 93 ,142501 (2004).

  17. 2-loop quantum Yang Mills condensate as dark energy

    NASA Astrophysics Data System (ADS)

    Xia, T. Y.; Zhang, Y.

    2007-11-01

    In seeking a model solving the coincidence problem, the effective Yang Mills condensate (YMC) is an alternative candidate for dark energy. A study is made for the model up to the 2-loop order of quantum corrections. It is found that, like in the 1-loop model, for generic initial conditions during the radiation era, there is always a desired tracking solution, yielding the current status Ω≃0.73 and Ω≃0.27. As the time t→∞ the dynamics is a stable attractor. Thus the model naturally solves the coincidence problem of dark energy. Moreover, if YMC decays into matter, its equation of state (EoS) crosses -1 and takes w˜-1.1, as indicated by the recent observations.

  18. Anisotropic Generalized Ghost Pilgrim Dark Energy Model in General Relativity

    NASA Astrophysics Data System (ADS)

    Santhi, M. Vijaya; Rao, V. U. M.; Aditya, Y.

    2017-02-01

    A spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi type- I Universe filled with matter and generalized ghost pilgrim dark energy (GGPDE) has been studied in general theory of relativity. To obtain determinate solution of the field equations we have used scalar expansion proportional to the shear scalar which leads to a relation between the metric potentials. Some well-known cosmological parameters (equation of state (EoS) parameter ( ω Λ), deceleration parameter ( q) and squared speed of sound {vs2}) and planes (ω _{Λ }-dot {ω }_{Λ } and statefinder) are constructed for obtained model. The discussion and significance of these parameters is totally done through pilgrim dark energy parameter ( β) and cosmic time ( t).

  19. Anisotropic universe with magnetized dark energy

    NASA Astrophysics Data System (ADS)

    Goswami, G. K.; Dewangan, R. N.; Yadav, Anil Kumar

    2016-04-01

    In the present work we have searched the existence of the late time acceleration of the Universe filled with cosmic fluid and uniform magnetic field as source of matter in anisotropic Heckmann-Schucking space-time. The observed acceleration of universe has been explained by introducing a positive cosmological constant Λ in the Einstein's field equation which is mathematically equivalent to vacuum energy with equation of state (EOS) parameter set equal to -1. The present values of the matter and the dark energy parameters (Ωm)0 & (Ω_{Λ})0 are estimated in view of the latest 287 high red shift (0.3 ≤ z ≤1.4) SN Ia supernova data's of observed apparent magnitude along with their possible error taken from Union 2.1 compilation. It is found that the best fit value for (Ωm)0 & (Ω_{Λ})0 are 0.2820 & 0.7177 respectively which are in good agreement with recent astrophysical observations in the latest surveys like WMAP [2001-2013], Planck [latest 2015] & BOSS. Various physical parameters such as the matter and dark energy densities, the present age of the universe and deceleration parameter have been obtained on the basis of the values of (Ωm)0 & (Ω_{Λ})0. Also we have estimated that the acceleration would have begun in the past at z = 0.71131 ˜6.2334 Gyrs before from present.

  20. Dark Energy Stars

    SciTech Connect

    Chapline, G

    2005-03-08

    Event horizons and closed time-like curves cannot exist in the real world for the simple reason that they are inconsistent with quantum mechanics. Following ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago, and the speaker it is now possible to describe in some detail what happens physically when one approaches and crosses a region of space-time where classical general relativity predicts there should be an infinite red shift surface. This quantum critical physics provides a new perspective on a variety of enigmatic astrophysical phenomena including supernovae explosions, gamma ray bursts, positron emission, and dark matter.

  1. Dark energy and dark matter haloes

    NASA Astrophysics Data System (ADS)

    Kuhlen, Michael; Strigari, Louis E.; Zentner, Andrew R.; Bullock, James S.; Primack, Joel R.

    2005-02-01

    We investigate the effect of dark energy on the density profiles of dark matter haloes with a suite of cosmological N-body simulations and use our results to test analytic models. We consider constant equation of state models, and allow both w>=-1 and w < -1. Using five simulations with w ranging from -1.5 to -0.5, and with more than ~1600 well-resolved haloes each, we show that the halo concentration model of Bullock et al. accurately predicts the median concentrations of haloes over the range of w, halo masses and redshifts that we are capable of probing. We find that the Bullock et al. model works best when halo masses and concentrations are defined relative to an outer radius set by a cosmology-dependent virial overdensity. For a fixed power spectrum normalization and fixed-mass haloes, larger values of w lead to higher concentrations and higher halo central densities, both because collapse occurs earlier and because haloes have higher virial densities. While precise predictions of halo densities are quite sensitive to various uncertainties, we make broad comparisons to galaxy rotation curve data. At fixed power spectrum normalization (fixed σ8), w > -1 quintessence models seem to exacerbate the central density problem relative to the standard w=-1 model. For example, models with w~=- 0.5 seem disfavoured by the data, which can be matched only by allowing extremely low normalizations, σ8<~ 0.6. Meanwhile w < -1 models help to reduce the apparent discrepancy. We confirm that the halo mass function of Jenkins et al. provides an excellent approximation to the abundance of haloes in our simulations and extend its region of validity to include models with w < -1.

  2. Measuring the speed of dark: Detecting dark energy perturbations

    SciTech Connect

    Putter, Roland de; Huterer, Dragan; Linder, Eric V.

    2010-05-15

    The nature of dark energy can be probed not only through its equation of state but also through its microphysics, characterized by the sound speed of perturbations to the dark energy density and pressure. As the sound speed drops below the speed of light, dark energy inhomogeneities increase, affecting both cosmic microwave background and matter power spectra. We show that current data can put no significant constraints on the value of the sound speed when dark energy is purely a recent phenomenon, but can begin to show more interesting results for early dark energy models. For example, the best fit model for current data has a slight preference for dynamics [w(a){ne}-1], degrees of freedom distinct from quintessence (c{sub s{ne}}1), and early presence of dark energy [{Omega}{sub de}(a<<1){ne}0]. Future data may open a new window on dark energy by measuring its spatial as well as time variation.

  3. 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.

  4. Dark Energy Camera for Blanco

    SciTech Connect

    Binder, Gary A.; /Caltech /SLAC

    2010-08-25

    In order to make accurate measurements of dark energy, a system is needed to monitor the focus and alignment of the Dark Energy Camera (DECam) to be located on the Blanco 4m Telescope for the upcoming Dark Energy Survey. One new approach under development is to fit out-of-focus star images to a point spread function from which information about the focus and tilt of the camera can be obtained. As a first test of a new algorithm using this idea, simulated star images produced from a model of DECam in the optics software Zemax were fitted. Then, real images from the Mosaic II imager currently installed on the Blanco telescope were used to investigate the algorithm's capabilities. A number of problems with the algorithm were found, and more work is needed to understand its limitations and improve its capabilities so it can reliably predict camera alignment and focus.

  5. How many dark energy parameters?

    SciTech Connect

    Linder, Eric V.; Huterer, Dragan

    2005-05-16

    For exploring the physics behind the accelerating universe a crucial question is how much we can learn about the dynamics through next generation cosmological experiments. For example, in defining the dark energy behavior through an effective equation of state, how many parameters can we realistically expect to tightly constrain? Through both general and specific examples (including new parametrizations and principal component analysis) we argue that the answer is 42 - no, wait, two. Cosmological parameter analyses involving a measure of the equation of state value at some epoch (e.g., w_0) and a measure of the change in equation of state (e.g., w') are therefore realistic in projecting dark energy parameter constraints. More elaborate parametrizations could have some uses (e.g., testing for bias or comparison with model features), but do not lead to accurately measured dark energy parameters.

  6. Dark energy and dark matter from primordial QGP

    SciTech Connect

    Vaidya, Vaishali Upadhyaya, G. K.

    2015-07-31

    Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.

  7. Dark energy and dark matter from primordial QGP

    NASA Astrophysics Data System (ADS)

    Vaidya, Vaishali; Upadhyaya, G. K.

    2015-07-01

    Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.

  8. Field Flows of Dark Energy

    SciTech Connect

    Cahn, Robert N.; de Putter, Roland; Linder, Eric V.

    2008-07-08

    Scalar field dark energy evolving from a long radiation- or matter-dominated epoch has characteristic dynamics. While slow-roll approximations are invalid, a well defined field expansion captures the key aspects of the dark energy evolution during much of the matter-dominated epoch. Since this behavior is determined, it is not faithfully represented if priors for dynamical quantities are chosen at random. We demonstrate these features for both thawing and freezing fields, and for some modified gravity models, and unify several special cases in the literature.

  9. Observing dark energy with SNAP

    SciTech Connect

    Linder, Eric V.; SNAP Collaboration

    2004-06-07

    The nature of dark energy is of such fundamental importance -- yet such a mystery -- that a dedicated dark energy experiment should be as comprehensive and powerfully incisive as possible. The Supernova/Acceleration Probe robustly controls for a wide variety of systematic uncertainties, employing the Type Ia supernova distance method, with high signal to noise light curves and spectra over the full redshift range from z=0.1-1.7, and the weak gravitational lensing method with an accurate and stable point spread function.

  10. Measuring Dark Energy with CHIME

    NASA Astrophysics Data System (ADS)

    Newburgh, Laura; Chime Collaboration

    2015-04-01

    The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a new radio transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use the 21 cm emission line of neutral hydrogen to map baryon acoustic oscillations between 400-800 MHz across 3/4 of the sky. These measurements will yield sensitive constraints on the dark energy equation of state between redshifts 0.8 - 2.5, a fascinating but poorly probed era corresponding to when dark energy began to impact the expansion history of the Universe. I will describe theCHIME instrument, the analysis challenges, the calibration requirements, and current status.

  11. Dark energy survey and camera

    SciTech Connect

    William Wester

    2004-08-16

    The authors describe the Dark Energy Survey and Camera. The survey will image 5000 sq. deg. in the southern sky to collect 300 million galaxies, 30,000 galaxy clusters and 2000 Type Ia supernovae. They expect to derive a value for the dark energy equation of state parameters, w, to a precision of 5% by combining four distinct measurement techniques. They describe the mosaic camera that will consist of CCDs with enhanced sensitivity in the near infrared. The camera will be mounted at the prime focus of the 4m Blanco telescope.

  12. Dark energy from gravitational corrections

    NASA Astrophysics Data System (ADS)

    Abe, Yugo; Horikoshi, Masaatsu; Kawamura, Yoshiharu

    2017-03-01

    We study physics concerning the cosmological constant problem in the framework of effective field theory and suggest that a dominant part of dark energy can originate from gravitational corrections of vacuum energy, under the assumption that the classical gravitational fields do not couple to a large portion of the vacuum energy effectively, in spite of the coupling between graviton and matters at a microscopic level. Our speculation is excellent with terascale supersymmetry.

  13. Generalized ghost pilgrim dark energy in F(T,TG) cosmology

    NASA Astrophysics Data System (ADS)

    Sharif, M.; Nazir, Kanwal

    2016-07-01

    This paper is devoted to study the generalized ghost pilgrim dark energy (PDE) model in F(T,TG) gravity with flat Friedmann-Robertson-Walker (FRW) universe. In this scenario, we reconstruct F(T,TG) models and evaluate the corresponding equation of state (EoS) parameter for different choices of the scale factors. We assume power-law scale factor, scale factor for unification of two phases, intermediate and bouncing scale factor. We study the behavior of reconstructed models and EoS parameters graphically. It is found that all the reconstructed models show decreasing behavior for PDE parameter u = -2. On the other hand, the EoS parameter indicates transition from dust-like matter to phantom era for all choices of the scale factor except intermediate for which this is less than - 1. We conclude that all the results are in agreement with PDE phenomenon.

  14. Dynamics of dark energy with a coupling to dark matter

    SciTech Connect

    Boehmer, Christian G.; Caldera-Cabral, Gabriela; Maartens, Roy; Lazkoz, Ruth

    2008-07-15

    Dark energy and dark matter are the dominant sources in the evolution of the late universe. They are currently only indirectly detected via their gravitational effects, and there could be a coupling between them without violating observational constraints. We investigate the background dynamics when dark energy is modeled as exponential quintessence and is coupled to dark matter via simple models of energy exchange. We introduce a new form of dark sector coupling, which leads to a more complicated dynamical phase space and has a better physical motivation than previous mathematically similar couplings.

  15. Dark Energy Coupled with Dark Matter in the Accelerating Universe

    NASA Astrophysics Data System (ADS)

    Zhang, Yang

    2004-06-01

    To model the observed Universe containing both dark energy and dark matter, we study the effective Yang Mills condensate model of dark energy and add a non-relativistic matter component as the dark matter, which is generated out of the decaying dark energy at a constant rate Gamma, a parameter of our model. For the Universe driven by these two components, the dynamic evolution still has asymptotic behaviour: the expansion of the Universe is accelerating with an asymptotically constant rate H, and the densities of both components approach to finite constant values. Moreover, OmegaLambdasimeq0.7 for dark energy and Omegamsimeq0.3 for dark matter are achieved if the decay rate Gamma is chosen such that Gamma/H~1.

  16. Cosmic Visions Dark Energy: Science

    SciTech Connect

    Dodelson, S.; Slosar, A.; Heitmann, K.; Hirata, C.; Honscheid, K.; Roodman, A.; Seljak, U.; Trodden, M.

    2016-04-26

    Cosmic surveys provide crucial information about high energy physics including strong evidence for dark energy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of dark energy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV can fully exploit this regime. These ideas flow to potential projects that could start construction in the 2020's.

  17. Cosmic Visions Dark Energy. Science

    SciTech Connect

    Dodelson, Scott; Heitmann, Katrin; Hirata, Chris; Honscheid, Klaus; Roodman, Aaron; Seljak, Uroš; Slosar, Anže; Trodden, Mark

    2016-04-26

    Cosmic surveys provide crucial information about high energy physics including strong evidence for dark energy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of dark energy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV can fully exploit this regime. These ideas flow to potential projects that could start construction in the 2020's.

  18. Dark matter and dark energy: summary and future directions.

    PubMed

    Ellis, John

    2003-11-15

    This paper reviews the progress reported at the Discussion Meeting and advertises some possible future directions in our drive to understand dark matter and dark energy. Additionally, a first attempt is made to place in context the exciting new results from the Wilkinson Microwave Anisotropy Probe satellite, which were published shortly after this meeting. In the first part of this paper, pieces of observational evidence shown here that bear on the amounts of dark matter and dark energy are reviewed. Subsequently, particle candidates for dark matter are mentioned, and detection strategies are discussed. Finally, ideas are presented for calculating the amounts of dark matter and dark energy, and possibly relating them to laboratory data.

  19. Unified dark energy-dark matter model with inverse quintessence

    SciTech Connect

    Ansoldi, Stefano; Guendelman, Eduardo I. E-mail: guendel@bgu.ac.il

    2013-05-01

    We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-canonical kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the dark energy vanishes in the early universe and then grows with time. This constitutes an ''inverse quintessence scenario'', where the universe starts from a zero vacuum energy density state, instead of approaching it in the future.

  20. Dark energy from discrete spacetime.

    PubMed

    Trout, Aaron D

    2013-01-01

    Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, [Formula: see text] in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies.

  1. Dark Energy from Discrete Spacetime

    PubMed Central

    Trout, Aaron D.

    2013-01-01

    Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies. PMID:24312502

  2. σCDM coupled to radiation: Dark energy and Universe acceleration

    NASA Astrophysics Data System (ADS)

    Abbyazov, Renat R.; Chervon, Sergey V.; Müller, Volker

    2015-07-01

    Recently, the Chiral Cosmological Model (CCM) coupled to cold dark matter (CDM) has been investigated as σCDM model to study the observed accelerated expansion of the Universe. Dark sector fields (as Dark Energy content) coupled to cosmic dust were considered as the source of Einstein gravity in Friedmann-Robertson-Walker (FRW) cosmology. Such model had a beginning at the matter-dominated era. The purposes of our present investigation are two-fold: To extend “life” of the σCDM for earlier times to radiation-dominated era and to take into account variation of the exponential potential V = V0exp -λ φ MP + V0exp -λ χ MP via variation of the interaction parameter λ. We use Markov Chain Monte Carlo (MCMC) procedure to investigate possible values of initial conditions constrained by the measured amount of the dark matter, dark energy and radiation component today. Our analysis includes dark energy contribution to critical density, the ratio of the kinetic and potential energies, deceleration parameter, effective equation of state (EoS) and evolution of DE EoS with variation of coupling constant λ. A comparison with the ΛCDM model was performed. A new feature of the model is the existence of some values of potential coupling constant, leading to a σCDM solution without transition into accelerated expansion epoch.

  3. New interactions in the dark sector mediated by dark energy

    SciTech Connect

    Brookfield, Anthony W.; Bruck, Carsten van de; Hall, Lisa M. H.

    2008-02-15

    Cosmological observations have revealed the existence of a dark matter sector, which is commonly assumed to be made up of one particle species only. However, this sector might be more complicated than we currently believe: there might be more than one dark matter species (for example, two components of cold dark matter or a mixture of hot and cold dark matter) and there may be new interactions between these particles. In this paper we study the possibility of multiple dark matter species and interactions mediated by a dark energy field. We study both the background and the perturbation evolution in these scenarios. We find that the background evolution of a system of multiple dark matter particles (with constant couplings) mimics a single fluid with a time-varying coupling parameter. However, this is no longer true on the perturbative level. We study the case of attractive and repulsive forces as well as a mixture of cold and hot dark matter particles.

  4. Condensates as components of dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Capolupo, Antonio

    2017-08-01

    We report on recent results according to which the vacuum condensate characterizing many physical systems can give contributions to dark energy and dark matter of the universe. In particular, it is shown that thermal states of the intercluster medium, the vacuum energy of fields in curved space-time and of mixed neutrinos contribute to the dark matter. The vacuum condensates generated by the mixing of axions and photons and the one produced by superpartners of neutrinos may represent a component of the dark energy.

  5. Some issues concerning holographic dark energy

    SciTech Connect

    Li, Miao; Lin, Chunshan; Wang, Yi E-mail: lics@mail.ustc.edu.cn

    2008-05-15

    We study the perturbation of holographic dark energy and find it to be stable. We study the fate of the universe when interacting holographic dark energy is present, and discuss a simple phenomenological classification of the interacting holographic dark energy models. We also discuss the cosmic coincidence problem in the context of holographic dark energy. We find that the coincidence problem cannot be completely solved by adding an interacting term. Inflation may provide a better solution of the coincidence problem.

  6. Cosmology of q-deformed dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Di˙l, Emre

    2017-06-01

    In this study, we propose a novel dark cosmology consisting an interacting q-deformed spinor field dark matter and scalar field dark energy. We investigate the proposed deformed dark cosmology in metric-affine Einstein- Cartan-Sciama-Kibble theory. Firstly, we construct the action integral of the model, in order to obtain the energy-momentum tensor of the deformed dark matter and dark energy, from which the energy density and pressure of the deformed dark matter and dark energy can be obtained, respectively. After obtaining the deformed energy densities and pressures, we set up the Friedmann equations, continuity equations and equation of motions for this dark model. Then, we obtain the attractor solutions and stability analysis of the model for the accelerated expansion phase of the universe. We also investigate the effect of deformation parameter on the stable accelerated expansion behavior. Consequently, by mapping the interaction term and the field potentials we present the relationship between them and obtain the constraint on the interaction term in order to obtain a stable attractor solution.

  7. Dark energy view of inflation

    SciTech Connect

    Ilic, Stephane; Kunz, Martin; Liddle, Andrew R.; Frieman, Joshua A.

    2010-05-15

    Traditionally, inflationary models are analyzed in terms of parameters such as the scalar spectral index n{sub s} and the tensor to scalar ratio r, while dark energy models are studied in terms of the equation of state parameter w. Motivated by the fact that both deal with periods of accelerated expansion, we study the evolution of w during inflation, in order to derive observational constraints on its value during an earlier epoch likely dominated by a dynamic form of dark energy. We find that the cosmic microwave background and large-scale structure data is consistent with w{sub inflation}=-1 and provides an upper limit of 1+w < or approx. 0.02. Nonetheless, an exact de Sitter expansion with a constant w=-1 is disfavored since this would result in n{sub s}=1.

  8. Dark energy versus modified gravity.

    PubMed

    Kunz, Martin; Sapone, Domenico

    2007-03-23

    There is now strong observational evidence that the expansion of the Universe is accelerating. The standard explanation invokes an unknown "dark energy" component. But such scenarios are faced with serious theoretical problems, which has led to increased interest in models where instead general relativity is modified in a way that leads to the observed accelerated expansion. The question then arises whether the two scenarios can be distinguished. Here we show that this may not be so easy, demonstrating explicitly that a generalized dark energy model can match the growth rate of the Dvali-Gabadadze-Porrati model and reproduce the 3+1 dimensional metric perturbations. Cosmological observations are then unable to distinguish the two cases.

  9. Foreword: Dark energy and CMB

    NASA Astrophysics Data System (ADS)

    Dodelson, Scott; Huterer, Dragan

    2015-03-01

    Maps of the Universe when it was 400,000 years old from observations of the cosmic microwave background and over the last ten billion years from galaxy surveys point to a compelling cosmological model. This model requires a very early epoch of accelerated expansion, inflation, during which the seeds of structure were planted via quantum mechanical fluctuations. These seeds began to grow via gravitational instability during the epoch in which dark matter dominated the energy density of the universe, transforming small perturbations laid down during inflation into nonlinear structures such as million light-year sized clusters, galaxies, stars, planets, and people. Over the past few billion years, we have entered a new phase, during which the expansion of the Universe is accelerating presumably driven by yet another substance, dark energy.

  10. Holographic Dark Energy Density and JBP Parametrization

    NASA Astrophysics Data System (ADS)

    Saadat, Hassan; Mousavi, S. N.; Saadat, A. M.

    2011-09-01

    In this article we consider the holographic dark energy density. We study dark energy density in Universe with arbitrary spatially curvature described by the Friedmann-Robertson-Walker metric. We use Jassal-Bagla-Padmanabhan parametrization to specify dark energy density.

  11. Tracing dark energy with quasars

    NASA Astrophysics Data System (ADS)

    Šredzińska, Justyna; Czerny, Bożena; Bilicki, M.; Hryniewicz, K.; Krupa, M.; Kurcz, A.; Marziani, P.; Pollo, A.; Pych, W.; Udalski, A.

    2016-06-01

    The nature of dark energy, driving the accelerated expansion of the Universe, is one of the most important issues in modern astrophysics. In order to understand this phenomenon, we need precise astrophysical probes of the universal expansion spanning wide redshift ranges. Quasars have recently emerged as such a probe, thanks to their high intrinsic luminosities and, most importantly, our ability to measure their luminosity distances independently of redshifts. Here we report our ongoing work on observational reverberation mapping using the time delay of the Mg II line, performed with the South African Large Telescope (SALT). The concept of dark energy was introduced in the process of understanding the evolution of the Universe. This is one of the most interesting topic in modern astronomy followed by the discovery of the accelerated expansion of the Universe. Precise measurement of this effect is a key to understand the nature of this medium, and we need good probes to do that. Quasars appears as an ideal candidate for this purpose as these objects are highly luminous and detected in wide range of redshift. From Big Bang to present time a lot of things happened and we are able to see amazing structures of galaxies and stars. In the beginning of Universe everything was blurred in space and the concept of dark energy was introduced in the process of understanding its evolution. The discovery of the accelerated expansion of the Universe gives us possibility to define new interesting topics in modern astronomy. Although there are some theoretical explanation for the existence of dark energy, yet it has remained the biggest puzzle among the astronomers and physicist.

  12. Modeling Dark Energy Through AN Ising Fluid with Network Interactions

    NASA Astrophysics Data System (ADS)

    Luongo, Orlando; Tommasini, Damiano

    2014-12-01

    We show that the dark energy (DE) effects can be modeled by using an Ising perfect fluid with network interactions, whose low redshift equation of state (EoS), i.e. ω0, becomes ω0 = -1 as in the ΛCDM model. In our picture, DE is characterized by a barotropic fluid on a lattice in the equilibrium configuration. Thus, mimicking the spin interaction by replacing the spin variable with an occupational number, the pressure naturally becomes negative. We find that the corresponding EoS mimics the effects of a variable DE term, whose limiting case reduces to the cosmological constant Λ. This permits us to avoid the introduction of a vacuum energy as DE source by hand, alleviating the coincidence and fine tuning problems. We find fairly good cosmological constraints, by performing three tests with supernovae Ia (SNeIa), baryonic acoustic oscillation (BAO) and cosmic microwave background (CMB) measurements. Finally, we perform the Akaike information criterion (AIC) and Bayesian information criterion (BIC) selection criteria, showing that our model is statistically favored with respect to the Chevallier-Polarsky-Linder (CPL) parametrization.

  13. Holographic dark-energy models

    NASA Astrophysics Data System (ADS)

    Del Campo, Sergio; Fabris, Júlio. C.; Herrera, Ramón; Zimdahl, Winfried

    2011-06-01

    Different holographic dark-energy models are studied from a unifying point of view. We compare models for which the Hubble scale, the future event horizon or a quantity proportional to the Ricci scale are taken as the infrared cutoff length. We demonstrate that the mere definition of the holographic dark-energy density generally implies an interaction with the dark-matter component. We discuss the relation between the equation-of-state parameter and the energy density ratio of both components for each of the choices, as well as the possibility of noninteracting and scaling solutions. Parameter estimations for all three cutoff options are performed with the help of a Bayesian statistical analysis, using data from supernovae type Ia and the history of the Hubble parameter. The ΛCDM model is the clear winner of the analysis. According to the Bayesian information criterion (BIC), all holographic models should be considered as ruled out, since the difference ΔBIC to the corresponding ΛCDM value is >10. According to the Akaike information criterion (AIC), however, we find ΔAIC<2 for models with Hubble-scale and Ricci-scale cutoffs, indicating, that they may still be competitive. As we show for the example of the Ricci-scale case, also the use of certain priors, reducing the number of free parameters to that of the ΛCDM model, may result in a competitive holographic model.

  14. The Dark Energy Survey: More than dark energy - An overview

    DOE PAGES

    Abbott, T.

    2016-03-21

    This overview article describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae andmore » other transients. The main goals of DES are to characterise dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the solar system, the Milky Way, galaxy evolution, quasars, and other topics. In addition, we show that if the cosmological model is assumed to be Lambda+ Cold Dark Matter (LCDM) then important astrophysics can be deduced from the primary DES probes. Lastly, highlights from DES early data include the discovery of 34 Trans Neptunian Objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).« less

  15. The Dark Energy Survey: more than dark energy - an overview

    SciTech Connect

    Vikram, Vinu; Abbott, T; Abdalla, F. B.; Allam, S.; Aleksic, J.; Amara, A.; Bacon, D.; Balbinot, E.; Banerji, M.; Bechtol, K.; Benoit-Levy, A.

    2016-08-01

    This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from ‘Science Verification’, and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be Λ+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).

  16. The Dark Energy Survey: more than dark energy - an overview

    NASA Astrophysics Data System (ADS)

    Dark Energy Survey Collaboration; Abbott, T.; Abdalla, F. B.; Aleksić, J.; Allam, S.; Amara, A.; Bacon, D.; Balbinot, E.; Banerji, M.; Bechtol, K.; Benoit-Lévy, A.; Bernstein, G. M.; Bertin, E.; Blazek, J.; Bonnett, C.; Bridle, S.; Brooks, D.; Brunner, R. J.; Buckley-Geer, E.; Burke, D. L.; Caminha, G. B.; Capozzi, D.; Carlsen, J.; Carnero-Rosell, A.; Carollo, M.; Carrasco-Kind, M.; Carretero, J.; Castander, F. J.; Clerkin, L.; Collett, T.; Conselice, C.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Davis, T. M.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Dodelson, S.; Doel, P.; Drlica-Wagner, A.; Estrada, J.; Etherington, J.; Evrard, A. E.; Fabbri, J.; Finley, D. A.; Flaugher, B.; Foley, R. J.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Giannantonio, T.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Guarnieri, P.; Gutierrez, G.; Hartley, W.; Honscheid, K.; Jain, B.; James, D. J.; Jeltema, T.; Jouvel, S.; Kessler, R.; King, A.; Kirk, D.; Kron, R.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Lima, M.; Lin, H.; Maia, M. A. G.; Makler, M.; Manera, M.; Maraston, C.; Marshall, J. L.; Martini, P.; McMahon, R. G.; Melchior, P.; Merson, A.; Miller, C. J.; Miquel, R.; Mohr, J. J.; Morice-Atkinson, X.; Naidoo, K.; Neilsen, E.; Nichol, R. C.; Nord, B.; Ogando, R.; Ostrovski, F.; Palmese, A.; Papadopoulos, A.; Peiris, H. V.; Peoples, J.; Percival, W. J.; Plazas, A. A.; Reed, S. L.; Refregier, A.; Romer, A. K.; Roodman, A.; Ross, A.; Rozo, E.; Rykoff, E. S.; Sadeh, I.; Sako, M.; Sánchez, C.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Sheldon, E.; Smith, M.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Soumagnac, M.; Suchyta, E.; Sullivan, M.; Swanson, M.; Tarle, G.; Thaler, J.; Thomas, D.; Thomas, R. C.; Tucker, D.; Vieira, J. D.; Vikram, V.; Walker, A. R.; Wechsler, R. H.; Weller, J.; Wester, W.; Whiteway, L.; Wilcox, H.; Yanny, B.; Zhang, Y.; Zuntz, J.

    2016-08-01

    This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be Λ+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).

  17. The Dark Energy Survey: More than dark energy - An overview

    SciTech Connect

    Abbott, T.

    2016-03-21

    This overview article describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterise dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the solar system, the Milky Way, galaxy evolution, quasars, and other topics. In addition, we show that if the cosmological model is assumed to be Lambda+ Cold Dark Matter (LCDM) then important astrophysics can be deduced from the primary DES probes. Lastly, highlights from DES early data include the discovery of 34 Trans Neptunian Objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).

  18. Dark Energy Coupled with Relativistic Dark Matter in Accelerating Universe

    NASA Astrophysics Data System (ADS)

    Zhang, Yang

    2003-10-01

    Recent observations favour an accelerating Universe dominated by the dark energy. We take the effective Yang-Mills condensate as the dark energy and couple it to a relativistic matter which is created by the decaying condensate. The dynamic evolution has asymptotic behaviour with finite constant energy densities, and the fractional densities OmegaLambda~0.7 for dark energy and Omegam~0.3 for relativistic matter are achieved at proper values of the decay rate. The resulting expansion of the Universe is in the de Sitter acceleration.

  19. Can we avoid dark energy?

    PubMed

    Zibin, James P; Moss, Adam; Scott, Douglas

    2008-12-19

    The idea that we live near the center of a large, nonlinear void has attracted attention recently as an alternative to dark energy or modified gravity. We show that an appropriate void profile can fit both the latest cosmic microwave background and supernova data. However, this requires either a fine-tuned primordial spectrum or a Hubble rate so low as to rule these models out. We also show that measurements of the radial baryon acoustic scale can provide very strong constraints. Our results present a serious challenge to void models of acceleration.

  20. Dark Energy: fiction or reality?

    NASA Astrophysics Data System (ADS)

    Triay, Roland

    2010-06-01

    Is Dark Energy justified as an alternative to the cosmological constant Λ in order to explain the acceleration of the cosmic expansion? It turns out that a straightforward dimensional analysis of Einstein equation provides us with clear evidences that the geometrical nature of Λ is the only viable source to this phenomenon, in addition of the application of Ockham's razor principle. This contribution is primarily a review of the main stream in the interpretation of Λ because it is at the origin of such a research program.

  1. Space Based Dark Energy Surveys

    NASA Astrophysics Data System (ADS)

    Dore, Olivier

    2016-03-01

    Dark energy, the name given to the cause of the accelerating expansion of the Universe, is one of the most tantalizing mystery in modern physics. Current cosmological models hold that dark energy is currently the dominant component of the Universe, but the exact nature of DE remains poorly understood. There are ambitious ground-based surveys underway that seek to understand DE and NASA is participating in the development of significantly more ambitious space-based surveys planned for the next decade. NASA has provided mission enabling technology to the European Space Agency's (ESA) Euclid mission in exchange for US scientists to participate in the Euclid mission. NASA is also developing the Wide Field Infrared Survey Telescope-Astrophysics Focused Telescope Asset (WFIRST) mission for possible launch in 2024. WFIRST was the highest ranked space mission in the Astro2010 Decadal Survey and the current design uses a 2.4m space telescope to go beyond what was then envisioned. Understanding DE is one of the primary science goals of WFIRST-AFTA. This talk will review the state of DE, the relevant activities of the Cosmic Structure Interest Group (CoSSIG) of the PhyPAG, and detail the status and complementarity between Euclid, WFIRST and ot ambitious ground-based efforts.

  2. Sourcing dark matter and dark energy from α-attractors

    NASA Astrophysics Data System (ADS)

    Mishra, Swagat S.; Sahni, Varun; Shtanov, Yuri

    2017-06-01

    In [1], Kallosh and Linde drew attention to a new family of superconformal inflationary potentials, subsequently called α-attractors [2]. The α-attractor family can interpolate between a large class of inflationary models. It also has an important theoretical underpinning within the framework of supergravity. We demonstrate that the α-attractors have an even wider appeal since they may describe dark matter and perhaps even dark energy. The dark matter associated with the α-attractors, which we call α-dark matter (αDM), shares many of the attractive features of fuzzy dark matter, with V(varphi) = ½m2varphi2, while having none of its drawbacks. Like fuzzy dark matter, αDM can have a large Jeans length which could resolve the cusp-core and substructure problems faced by standard cold dark matter. αDM also has an appealing tracker property which enables it to converge to the late-time dark matter asymptote, langlewrangle simeq 0, from a wide range of initial conditions. It thus avoids the enormous fine-tuning problems faced by the m2varphi2 potential in describing dark matter.

  3. Bianchi Type-I Anisotropic Dark Energy Model with Constant Deceleration Parameter

    NASA Astrophysics Data System (ADS)

    Pradhan, Anirudh; Amirhashchi, H.; Saha, Bijan

    2011-09-01

    A new dark energy model in anisotropic Bianchi type-I (B-I) space-time with time dependent equation of state (EoS) parameter and constant deceleration parameter has been investigated in the present paper. The Einstein's field equations have been solved by applying a variation law for generalized Hubble's parameter (Berman in Il Nuovo Cimento B 74:182, 1983) which generates two types of solutions, one is of power-law type and other is of the exponential form. The existing range of the dark energy EoS parameter ω for derived model is found to be in good agreement with the three recent observations (i) SNe Ia data (Knop et al. in Astrophys. J. 598:102, 2003), (ii) SNe Ia data collaborated with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004) and (iii) a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift type Ia supernovae and galaxy clustering (Hinshaw et al. in Astrophys. J. Suppl. Ser. 180:225, 2009 and Komatsu et al. in Astrophys. J. Suppl. Ser. 180:330, 2009). The cosmological constant Λ is found to be a decreasing function of time and it approaches a small positive value at the present epoch which is corroborated by results from recent supernovae Ia observations. It has also been suggested that the dark energy that explains the observed accelerating universe may arise due to the contribution to the vacuum energy of the EoS in a time dependent background. Geometric and kinematic properties of the model and the behaviour of the anisotropy of the dark energy have been carried out.

  4. Physical evidence for dark energy

    SciTech Connect

    Scranton, Ryan; Connolly, Andrew J.; Nichol, Robert C.; Stebbins, Albert; Szapudi, Istvan; Eisenstein, Daniel J.; Afshordi, Niayesh; Budavari, Tamas; Csabai, Istvan; Frieman, Joshua A.; Gunn, James E.; Johnston, David; Loh, Yeong-Shang; Lupton, Robert H.; Miller, Christopher J.; Sheldon, Erin Scott; Sheth, Ravi K.; Szalay, Alexander S.; Tegmark, Max; Xu, Yongzhong; Anderson, Scott F.; /Pittsburgh U. /Carnegie Mellon U. /Fermilab /Inst. Astron., Honolulu /Arizona U., Astron. Dept. - Steward Observ. /Princeton U. Observ. /Johns Hopkins U. /Eotvos U. /Chicago U., Astron. Astrophys. Ctr. /KICP, Chicago /Pennsylvania U. /Washington U., Seattle, Astron. Dept. /Apache Point Observ. /Illinois U., Urbana, Astron. Dept. /Tokyo U., ICRR /LLNL, Livermore /Sussex U., Astron. Ctr. /Baltimore, Space Telescope Sci. /Michigan U. /Naval Observ., Flagstaff /Penn State U., Astron. Astrophys.

    2003-07-01

    The authors present measurements of the angular cross-correlation between luminous red galaxies from the Sloan Digital Sky Survey and the cosmic microwave background temperature maps from the Wilkinson Microwave Anisotropy Probe. They find a statistically significant achromatic positive correlation between these two data sets, which is consistent with the expected signal from the late Integrated Sachs-Wolfe (ISW) effect. they do not detect any anti-correlation on small angular scales as would be produced from a large Sunyaev-Zel'dovich (SZ) effect, although they do see evidence for some SZ effect for their highest redshift samples. Assuming a flat universe, their preliminary detection of the ISW effect provides independent physical evidence for the existence of dark energy.

  5. The vacuum's dark particles behave like dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Haller, John

    2015-04-01

    Building on the governing hypothesis that self-information is equal to action, I solve for the time step of the vacuum. The resulting equations (both quantum diffusion and Friedmann's equations) argue that a dark particle, or special black hole, exists at hbar or twice the reduced Planck mass where the Hawking temperature breaks down. It is hypothesized that if neutral hydrogen is nearby the dark particles are able to couple with the background field and thus have a density that looks like dark matter. If hydrogen is not around, the dark particles become frozen leading to a constant density of black body radiation similar to dark energy. If the Universe's dark particles (away from neutral hydrogen) became frozen during the re-ionization of the Universe's history, its BBR density is well within confidence ranges for the cosmological constant. This hypothesis can also explain the recent observations that dark matter decays into dark energy.

  6. Dark energy and dark matter perturbations in singular universes

    SciTech Connect

    Denkiewicz, Tomasz

    2015-03-01

    We discuss the evolution of density perturbations of dark matter and dark energy in cosmological models which admit future singularities in a finite time. Up to now geometrical tests of the evolution of the universe do not differentiate between singular universes and ΛCDM scenario. We solve perturbation equations using the gauge invariant formalism. The analysis shows that the detailed reconstruction of the evolution of perturbations within singular cosmologies, in the dark sector, can exhibit important differences between the singular universes models and the ΛCDM cosmology. This is encouraging for further examination and gives hope for discriminating between those models with future galaxy weak lensing experiments like the Dark Energy Survey (DES) and Euclid or CMB observations like PRISM and CoRE.

  7. A two measure model of dark energy and dark matter

    SciTech Connect

    Guendelman, Eduardo; Singleton, Douglas; Yongram, N. E-mail: dougs@csufresno.edu

    2012-11-01

    In this work we construct a unified model of dark energy and dark matter. This is done with the following three elements: a gravitating scalar field, φ with a non-conventional kinetic term, as in the string theory tachyon; an arbitrary potential, V(φ); two measures — a metric measure ((−g){sup 1/2}) and a non-metric measure (Φ). The model has two interesting features: (i) For potentials which are unstable and would give rise to tachyonic scalar field, this model can stabilize the scalar field. (ii) The form of the dark energy and dark matter that results from this model is fairly insensitive to the exact form of the scalar field potential.

  8. Dark matter and dark energy from quark bag model

    SciTech Connect

    Brilenkov, Maxim; Eingorn, Maxim; Jenkovszky, Laszlo; Zhuk, Alexander E-mail: maxim.eingorn@gmail.com E-mail: ai.zhuk2@gmail.com

    2013-08-01

    We calculate the present expansion of our Universe endowed with relict colored objects — quarks and gluons — that survived hadronization either as isolated islands of quark-gluon ''nuggets'' or spread uniformly in the Universe. In the first scenario, the QNs can play the role of dark matter. In the second scenario, we demonstrate that uniform colored objects can play the role of dark energy providing the late-time accelerating expansion of the Universe.

  9. Similarity dark energy models in Bianchi type-I space-time

    NASA Astrophysics Data System (ADS)

    Ali, Ahmad T.; Kumar Yadav, Anil; Alzahrani, Abdulah K.

    2016-11-01

    We investigate some new similarity inhomogeneous solutions of anisotropic dark energy and perfect fluid in Bianchi type-I space-time. Three different equation-of-state (EoS) parameters along the spatial directions are introduced to quantify the deviation of pressure from isotropy. We consider the case when the dark energy is minimally coupled to the perfect fluid as well as the direct interaction with it. The Lie symmetry generators that leave the equation invariant are identified and we generate an optimal system of one-dimensional sub-algebras. Each element of the optimal system is used to reduce the partial differential equation to an ordinary differential equation which is further analyzed. We solve the Einstein field equations, described by a system of non-linear partial differential equations (NLPDEs), by using the Lie point symmetry analysis method. The geometrical and kinematic features of the models and the behavior of the anisotropy of dark energy are examined in detail.

  10. How clustering dark energy affects matter perturbations

    NASA Astrophysics Data System (ADS)

    Mehrabi, A.; Basilakos, S.; Pace, F.

    2015-09-01

    The rate of structure formation in the Universe is different in homogeneous and clustered dark energy models. The degree of dark energy clustering depends on the magnitude of its effective sound speed c2_eff and for c2_eff=0 dark energy clusters in a similar fashion to dark matter while for c2_eff=1 it stays (approximately) homogeneous. In this paper we consider two distinct equations of state for the dark energy component, wd = const and w_d=w_0+w_1(z/1+z) with c2_eff as a free parameter and we try to constrain the dark energy effective sound speed using current available data including Type Ia supernovae, baryon acoustic oscillation, cosmic microwave background shift parameter (Planck and WMAP), Hubble parameter, big bang nucleosynthesis and the growth rate of structures fσ8(z). At first we derive the most general form of the equations governing dark matter and dark energy clustering under the assumption that c2_eff=const. Finally, performing an overall likelihood analysis we find that the likelihood function peaks at c2_eff=0; however, the dark energy sound speed is degenerate with respect to the cosmological parameters, namely Ωm and wd.

  11. Cosmological constraints on superconducting dark energy models

    NASA Astrophysics Data System (ADS)

    Keresztes, Zoltán; Gergely, László Á.; Harko, Tiberiu; Liang, Shi-Dong

    2015-12-01

    We consider cosmological tests of a scalar-vector-tensor gravitational model, in which the dark energy is included in the total action through a gauge-invariant, electromagnetic type contribution. The ground state of dark energy, corresponding to a constant potential V , is a Bose-Einstein type condensate with spontaneously broken U(1) symmetry. In other words, dark energy appears as a massive vector field emerging from a superposition of a massless vector and a scalar field, the latter corresponding to the Goldstone boson. Two particular cosmological models, corresponding to pure electric and pure magnetic type potentials, respectively, are confronted with type IA supernovae and Hubble parameter data. In the electric case, a good fit is obtained along a narrow inclined stripe in the Ωm-ΩV parameter plane, which includes the Λ cold dark matter limit as the best fit. The other points on this admissible region represent superconducting dark energy as a sum of a cosmological constant and a time-evolving contribution. In the magnetic case the cosmological test selects either (i) parameter ranges of the superconducting dark energy allowing for the standard baryonic sector plus dark matter or (ii) a unified superconducting dark matter and dark energy model, additionally including only the baryonic sector.

  12. Interacting Dark Energy Models and Observations

    NASA Astrophysics Data System (ADS)

    Shojaei, Hamed; Urioste, Jazmin

    2017-01-01

    Dark energy is one of the mysteries of the twenty first century. Although there are candidates resembling some features of dark energy, there is no single model describing all the properties of dark energy. Dark energy is believed to be the most dominant component of the cosmic inventory, but a lot of models do not consider any interaction between dark energy and other constituents of the cosmic inventory. Introducing an interaction will change the equation governing the behavior of dark energy and matter and creates new ways to explain cosmic coincidence problem. In this work we studied how the Hubble parameter and density parameters evolve with time in the presence of certain types of interaction. The interaction serves as a way to convert dark energy into matter to avoid a dark energy-dominated universe by creating new equilibrium points for the differential equations. Then we will use numerical analysis to predict the values of distance moduli at different redshifts and compare them to the values for the distance moduli obtained by WMAP (Wilkinson Microwave Anisotropy Probe). Undergraduate Student

  13. Cosmological implications of DGP braneworld via well-known holographic dark energy models

    NASA Astrophysics Data System (ADS)

    Rani, Shamaila; Jawad, Abdul

    The cosmological analysis is being studied in the present work in Dvali-Gabadadze-Porrati (DGP) braneworld scenario by taking various interacting modified holographic dark energy (HDE) models. We discuss the various cosmological parameters such as deceleration parameter, equation-of-state (EoS) parameter and squared speed of sound. It is found that the trajectories of deceleration parameter exhibit in accelerated phase of the universe for all models. The EoS parameter corresponds to various phases of cosmic acceleration like quintessence, vacuum, phantom and also exhibits consistency with observational data. The squared speed of sound also gives stability of models in the current scenario. The ωϑ - ωϑ‧ also gives consistent results with various observational schemes. The statefinders plane also exhibits the cosmic acceleration. It is interesting to remark here that some of our results shows consistency with observational data like WMAP+CMB+BAO+H0+SNe.

  14. Description of dark energy and dark matter by vector fields

    NASA Astrophysics Data System (ADS)

    Meierovich, Boris E.

    A simple Lagrangian (with squared covariant divergence of a vector field as a kinetic term) turned out an adequate tool for oscopic description of dark sector. The zero-mass field acts as the dark energy. Its energy-momentum tensor is a simple additive to the cosmological constant. Space-like and time-like massive vector fields describe two different forms of dark matter. The space-like field is attractive. It is responsible for the observed plateau in galaxy rotation curves. The time-like massive field displays repulsive elasticity. In balance with dark energy and ordinary matter it provides a four-parametric diversity of regular solutions of the Einstein equations describing different possible cosmological and oscillating non-singular scenarios of evolution of the Universe. In particular, the singular "big bang" turns into a regular inflation-like transition from contraction to expansion with accelerated expansion at late times. The fine-tuned Friedman-Robertson-Walker singular solution is a particular limiting case at the boundary of existence of regular oscillating solutions (in the absence of vector fields). The simplicity of the general covariant expression for the energy-momentum tensor allows analyzing the main properties of the dark sector analytically, avoiding unnecessary model assumptions.

  15. Bouncing Cosmologies with Dark Matter and Dark Energy

    NASA Astrophysics Data System (ADS)

    Cai, Yi-Fu; Marcianò, Antonino; Wang, Dong-Gang; Wilson-Ewing, Edward

    2017-01-01

    We review matter bounce scenarios where the matter content is dark matter and dark energy. These cosmologies predict a nearly scale-invariant power spectrum with a slightly red tilt for scalar perturbations and a small tensor-to-scalar ratio. Importantly, these models predict a positive running of the scalar index, contrary to the predictions of the simplest inflationary and ekpyrotic models, and hence could potentially be falsified by future observations. We also review how bouncing cosmological space-times can arise in theories where either the Einstein equations are modified or where matter fields that violate the null energy condition are included.

  16. Renewable Energy Requirement Guidance for EPACT 2005 and EO 13423

    SciTech Connect

    2009-01-18

    Describes what counts toward the federal goals, the definition of "new" for renewable power/renewable energy certificate (REC) purchases, and what types of on-site projects will get double credit (Section 203 (C)).

  17. [Dark matter and dark energy of the universe].

    PubMed

    Aguilar Peris, José

    2005-01-01

    At the turn of the 20th Century, the Universe was thought to consist of our solar system, the Sun, planets, satellites and comets, floating under the Milky Way. The astronomers were ignorant of the existence of galaxies, clusters, quasars and black holes. Over the last ten years the Cosmology has made remarkable progress in our understanding of the composition of the Universe: 23 per cent is in an unknown form called dark matter; 73 per cent in another form called dark energy; 3 per cent is made of free hydrogen and helium atoms; 0.5 per cent makes up all the light we see in the night including the stars, clusters and superclusters; 0.3 per cent is in free neutrino particles; and finally, 0.03 per cent is in the heavier nuclei of which the Sun, the Earth and ourselves are made. In this work we study specially the dark matter and the dark energy. The first one appears to be attached to galaxies, and astronomers agree that it is cold, meaning that the particles that make up that matter are not moving fast. Very recently astronomers discovered that a tremendous amount of the so-cahled dark energy exists and that it is pushing and accelerating the expansion of the Universe. Should this expansion continue for another 14,000 million years, the sky will darken with only a handful of galaxies remaining visible.

  18. Possible dark energy imprints in the gravitational wave spectrum of mixed neutron-dark-energy stars

    SciTech Connect

    Yazadjiev, Stoytcho S.; Doneva, Daniela D. E-mail: daniela.doneva@uni-tuebingen.de

    2012-03-01

    In the present paper we study the oscillation spectrum of neutron stars containing both ordinary matter and dark energy in different proportions. Within the model we consider, the equilibrium configurations are numerically constructed and the results show that the properties of the mixed neuron-dark-energy star can differ significantly when the amount of dark energy in the stars is varied. The oscillations of the mixed neuron-dark-energy stars are studied in the Cowling approximation. As a result we find that the frequencies of the fundamental mode and the higher overtones are strongly affected by the dark energy content. This can be used in the future to detect the presence of dark energy in the neutron stars and to constrain the dark-energy models.

  19. Dark energy, inflation, and extra dimensions

    SciTech Connect

    Steinhardt, Paul J.; Wesley, Daniel

    2009-05-15

    We consider how accelerated expansion, whether due to inflation or dark energy, imposes strong constraints on fundamental theories obtained by compactification from higher dimensions. For theories that obey the null energy condition (NEC), we find that inflationary cosmology is impossible for a wide range of compactifications; and a dark energy phase consistent with observations is only possible if both Newton's gravitational constant and the dark energy equation of state vary with time. If the theory violates the NEC, inflation and dark energy are only possible if the NEC-violating elements are inhomogeneously distributed in the compact dimensions and vary with time in precise synchrony with the matter and energy density in the noncompact dimensions. Although our proofs are derived assuming general relativity applies in both four and higher dimensions and certain forms of metrics, we argue that similar constraints must apply for more general compactifications.

  20. A Modified Dark Energy Model and Quintessence

    NASA Astrophysics Data System (ADS)

    Zare Dehnavi, Naser; Fathi, Mohsen; Tavakoli, Farhad

    2013-11-01

    The observational data indicate that about 70 % of the total energy density of the current state universe has been occupied by Dark Energy. This is said to be the cause of the accelerated expansion of universe. In this letter we shall use a curvature constant as a scalar field in the quintessence Dark Energy model, for an isotropic universe. Connected to the so-called model, we will specify a definite dynamical field equation from the initial action of the theory.

  1. Status of the Dark Energy Survey

    NASA Astrophysics Data System (ADS)

    Buckley-Geer, Elizabeth J.; Dark Energy Science Collaboration

    2016-01-01

    The Dark Energy Survey is probing the origin of cosmic acceleration and the nature of dark energy by carrying out two interleaved, multi-band imaging surveys using the 570-megapixel Dark Energy Camera built by the collaboration for the NOAO Blanco 4-meter telescope at CTIO. The survey began in August 2013 and has completed two of its five 105-night observing seasons, including grizY imaging of several thousand square degrees and time-domain griz imaging of 30 sq. deg. with a 6-night cadence. I will describe the status of the survey and highlight some of the science results.

  2. Dark matter from dark energy in q-theory

    NASA Astrophysics Data System (ADS)

    Klinkhamer, F. R.; Volovik, G. E.

    2017-01-01

    A constant (spacetime-independent) q-field may play a crucial role for the cancellation of Planck-scale contributions to the gravitating vacuum energy density. We now show that a small spacetime-dependent perturbation of the equilibrium q-field behaves gravitationally as a pressureless perfect fluid. This makes the fluctuating part of the q-field a candidate for the inferred dark-matter component of the present universe. For a Planck-scale oscillation frequency of the q-field perturbation, the implication would be that direct searches for dark-matter particles would remain unsuccessful in the foreseeable future.

  3. Dark Matter and Dark Energy - Fact or Fantasy?

    NASA Astrophysics Data System (ADS)

    Mannheim, Philip

    We show that the origin of the dark matter and dark energy problems originates in the assumption of standard Einstein gravity that Newton's constant is fundamental. We discuss an alternate, conformal invariant, metric theory of gravity in which Newton's constant is induced dynamically, with the global induced one which is effective for cosmology being altogether weaker than the local induced one needed for the solar system. We find that in the theory dark matter is no longer needed, and that the accelerating universe data can be fitted without fine-tuning using a cosmological constant as large as particle physics suggests. In the conformal theory then it is not the cosmological constant which is quenched but rather the amount of gravity that it produces.

  4. Embrace the Dark Side: Advancing the Dark Energy Survey

    NASA Astrophysics Data System (ADS)

    Suchyta, Eric

    The Dark Energy Survey (DES) is an ongoing cosmological survey intended to study the properties of the accelerated expansion of the Universe. In this dissertation, I present work of mine that has advanced the progress of DES. First is an introduction, which explores the physics of the cosmos, as well as how DES intends to probe it. Attention is given to developing the theoretical framework cosmologists use to describe the Universe, and to explaining observational evidence which has furnished our current conception of the cosmos. Emphasis is placed on the dark sector - dark matter and dark energy - the content of the Universe not explained by the Standard Model of particle physics. As its name suggests, the Dark Energy Survey has been specially designed to measure the properties of dark energy. DES will use a combination of galaxy cluster, weak gravitational lensing, angular clustering, and supernovae measurements to derive its state of the art constraints, each of which is discussed in the text. The work described in this dissertation includes science measurements directly related to the first three of these probes. The dissertation presents my contributions to the readout and control system of the Dark Energy Camera (DECam); the name of this software is SISPI. SISPI uses client-server and publish-subscribe communication patterns to coordinate and command actions among the many hardware components of DECam - the survey instrument for DES, a 570 megapixel CCD camera, mounted at prime focus of the Blanco 4-m Telescope. The SISPI work I discuss includes coding applications for DECam's filter changer mechanism and hexapod, as well as developing the Scripts Editor, a GUI application for DECam users to edit and export observing sequence SISPI can load and execute. Next, the dissertation describes the processing of early DES data, which I contributed. This furnished the data products used in the first-completed DES science analysis, and contributed to improving the

  5. Effective equation of state for running vacuum: `mirage' quintessence and phantom dark energy

    NASA Astrophysics Data System (ADS)

    Basilakos, Spyros; Solà, Joan

    2014-02-01

    Past analyses of the equation of state (EoS) of the Dark Energy (DE) were not incompatible with a phantom phase near our time. This has been the case in the years of Wilkinson Microwave Anisotropy Probe observations, in combination with the remaining cosmological observables. Such situations did not completely disappear from the data collected from the Planck satellite mission. In it the EoS analysis may still be interpreted as suggesting ωD ≲ -1, and so a mildly evolving DE cannot be discarded. In our opinion, the usual ansatzs made on the structure of the EoS for dynamical DE models (e.g. quintessence and the like) is too simplified. In this work, we examine in detail some of these issues and suggest that a general class of models with a dynamical vacuum energy density could explain the persistent phantom anomaly, despite this there is no trace of real phantom behaviour in them. The spurious or `mirage' effect is caused by an attempt to describe them as if the DE would be caused by fundamental phantom scalar fields. Remarkably, the effective DE behaviour can also appear as quintessence in transit to phantom, or vice versa.

  6. Varying ghost dark energy and particle creation

    NASA Astrophysics Data System (ADS)

    Khurshudyan, M.

    2016-02-01

    One of the models of dark energy is the ghost dark energy, which has a geometrical origin. Recently, a certain type of phenomenological modification of ghost dark energy has been suggested which motivated us for this work. The goal of this paper is twofold. First, we would like to study the cosmological scenario involving interacting varying ghost dark energy. A cosmographic analysis of a non-interacting model is also performed. Then, we study the particle creation following the straight analogy between quantization in Minkowski background and canonical quantization of a scalar field in curved dynamical backgrounds. Particular attention will be paid to massless-particle production from a radiation-dominated universe (according to our toy model) which evolves to our large-scale universe. Constraints on the parameters of the models obtained during the cosmographic analysis did allow to demonstrate the possibility of a massless-particle creation in a radiation-dominated universe.

  7. Effective theory of interacting dark energy

    SciTech Connect

    Gleyzes, Jérôme; Mancarella, Michele; Vernizzi, Filippo; Langlois, David E-mail: langlois@apc.univ-paris7.fr E-mail: filippo.vernizzi@cea.fr

    2015-08-01

    We present a unifying treatment of dark energy and modified gravity that allows distinct conformal-disformal couplings of matter species to the gravitational sector. In this very general approach, we derive the conditions to avoid ghost and gradient instabilities. We compute the equations of motion for background quantities and linear perturbations. We illustrate our formalism with two simple scenarios, where either cold dark matter or a relativistic fluid is nonminimally coupled. This extends previous studies of coupled dark energy to a much broader spectrum of gravitational theories.

  8. Examining the viability of phantom dark energy

    NASA Astrophysics Data System (ADS)

    Ludwick, Kevin J.

    2015-09-01

    In the standard cosmological framework of the 0th-order Friedmann-Lemaître-Robertson-Walker (FLRW) metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter w <-1 (known as phantom dark energy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the accepted values for present-day w from Planck and WMAP9 include a significant range of values less than -1 . We find that it is not as obvious as one might think that phantom dark energy has negative kinetic energy categorically. Analogously, we find that field models of quintessence dark energy (wϕ>-1 ) do not necessarily have positive kinetic energy categorically. Staying within the confines of observational constraints and general relativity, for which there is good experimental validation, we consider a few reasonable departures from the standard 0th-order framework in an attempt to see if negative kinetic energy can be avoided in these settings despite an apparent w <-1 . We consider a more accurate description of the universe through the perturbing of the isotropic and homogeneous FLRW metric and the components of the stress-energy tensor, and we consider dynamic w and primordial isocurvature and adiabatic perturbations. We find that phantom dark energy does not necessarily have negative kinetic energy for all relevant length scales at all times, and we also find that, by the same token, quintessence dark energy does not necessarily have positive kinetic energy for all relevant length scales at all times.

  9. Dark Energy Research: A Space Odyssey

    NASA Astrophysics Data System (ADS)

    Dore, Olivier

    2015-04-01

    Dark energy, the name given to the cause of the accelerating expansion of the Universe, is one of the most tantalizing mystery in modern physics. Current cosmological models hold that dark energy is currently the dominant component of the Universe, but the exact nature of dark energy remains poorly understood. There are ambitious ground-based surveys underway that seek to understand dark energy and NASA is participating in the development of significantly more ambitious space-based surveys planned for the next decade. NASA has provided mission enabling technology to the European Space Agency's (ESA) Euclid mission in exchange for US scientists to participate in the Euclid mission. NASA is also developing the Wide Field Infrared Survey Telescope-Astrophysics Focused Telescope Asset (WFIRST-AFTA) mission for possible launch in ?2023. WFIRST was the highest ranked space mission in the Astro2010 Decadal Survey. Understanding dark energy is one of the primary science goals of WFIRST-AFTA. This talk will review the state of Dark Energy science, the relevant activities of the Physics of the Cosmos Program Analysis Group (PhysPAG), and detail the status and complementarity of Euclid and WFIRST.

  10. The accelerating universe and dark energy

    NASA Astrophysics Data System (ADS)

    Baltay, Charles

    2014-05-01

    The recent discovery by Riess et al.1 and Perlmutter et al.2 that the expansion of the universe is accelerating is one of the most significant discoveries in cosmology in the last few decades. To explain this acceleration a mysterious new component of the universe, dark energy, was hypothesized. Using general relativity (GR), the measured rate of acceleration translates to the present understanding that the baryonic matter, of which the familiar world is made of, is a mere 4% of the total mass-energy of the universe, with nonbaryonic dark matter making up 24% and dark energy making up the majority 72%. Dark matter, by definition, has attractive gravity, and even though we presently do not know what it is, it could be made of the next heavy particles discovered by particle physicists. Dark energy, however, is much more mysterious, in that even though we do not know what it is, it must have some kind of repulsive gravity and negative pressure, very unusual properties that are not part of the present understanding of physics. Investigating the nature of dark energy is therefore one of the most important areas of cosmology. In this review, the cosmology of an expanding universe, based on GR, is discussed. The methods of studying the acceleration of the universe, and the nature of dark energy, are presented. A large amount of experimentation on this topic has taken place in the decade since the discovery of the acceleration. These are discussed and the present state of knowledge of the cosmological parameters is summarized in Table 7 below. A vigorous program to further these studies is under way. These are presented and the expected results are summarized in Table 10 below. The hope is that at the end of this program, it would be possible to tell whether dark energy is due to Einstein's cosmological constant or is some other new constituent of the universe, or alternately the apparent acceleration is due to some modification of GR.

  11. Ghost Dark Energy in f(R) Model of Gravity

    NASA Astrophysics Data System (ADS)

    Saaidi, Kh.; Aghamohammadi, A.; Sabet, B.; Farooq, O.

    We study a correspondence between f(R) model of gravity in the Jordan frame and a phenomenological kind of dark energy (DE), which is known as QCD ghost DE. Since this kind of DE is not stable in the context of Einsteinian theory of gravity and Brans-Dicke model of gravity, we consider two kinds of correspondence between modified gravity and DE. By studding the dynamical evolution of model and finding relevant quantities such as, equation of state parameter, deceleration parameter, dimensionless density parameter, we show that the model can describe the present Universe and also the EoS parameter can cross the phantom divide line without needs to any kinetic energy with negative sign. Furthermore, by obtaining the adiabatic squared sound speed of the model for different cases of interaction, we show that this model is stable. Finally, we fit this model with supernova observational data in a noninteraction case and we find the best values of parameter at 1σ confidence interval as; f0 = 0.958+0.07-0.25, β = -0, 256+0.2-0.1 and {Ω }m0 = 0.23+0.3-0.15. These best-fit values show that DE equation of state parameter, ωd0, can cross the phantom divide line at the present time.

  12. Roles of dark energy perturbations in dynamical dark energy models: can we ignore them?

    PubMed

    Park, Chan-Gyung; Hwang, Jai-chan; Lee, Jae-heon; Noh, Hyerim

    2009-10-09

    We show the importance of properly including the perturbations of the dark energy component in the dynamical dark energy models based on a scalar field and modified gravity theories in order to meet with present and future observational precisions. Based on a simple scaling scalar field dark energy model, we show that observationally distinguishable substantial differences appear by ignoring the dark energy perturbation. By ignoring it the perturbed system of equations becomes inconsistent and deviations in (gauge-invariant) power spectra depend on the gauge choice.

  13. Report of the Dark Energy Task Force

    DOE R&D Accomplishments Database

    Albrecht, Andreas; Bernstein, Gary; Cahn, Robert; Freedman, Wendy L.; Hewitt, Jacqueline; Hu, Wayne; Huth, John; Kamionkowski, Marc; Kolb, Edward W.; Knox, Lloyd; Mather, John C.

    2006-01-01

    Dark energy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed phenomenon that most directly demonstrates that our theories of fundamental particles and gravity are either incorrect or incomplete. Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among the very most compelling of all outstanding problems in physical science. These circumstances demand an ambitious observational program to determine the dark energy properties as well as possible.

  14. Dark matter, dark energy, and alternate models: A review

    NASA Astrophysics Data System (ADS)

    Arun, Kenath; Gudennavar, S. B.; Sivaram, C.

    2017-07-01

    The nature of dark matter (DM) and dark energy (DE) which is supposed to constitute about 95% of the energy density of the universe is still a mystery. There is no shortage of ideas regarding the nature of both. While some candidates for DM are clearly ruled out, there is still a plethora of viable particles that fit the bill. In the context of DE, while current observations favour a cosmological constant picture, there are other competing models that are equally likely. This paper reviews the different possible candidates for DM including exotic candidates and their possible detection. This review also covers the different models for DE and the possibility of unified models for DM and DE. Keeping in mind the negative results in some of the ongoing DM detection experiments, here we also review the possible alternatives to both DM and DE (such as MOND and modifications of general relativity) and possible means of observationally distinguishing between the alternatives.

  15. Gravity resonance spectroscopy constrains dark energy and dark matter scenarios.

    PubMed

    Jenke, T; Cronenberg, G; Burgdörfer, J; Chizhova, L A; Geltenbort, P; Ivanov, A N; Lauer, T; Lins, T; Rotter, S; Saul, H; Schmidt, U; Abele, H

    2014-04-18

    We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton's inverse square law of gravity is understood at micron distances on an energy scale of 10-14  eV. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant β>5.8×108 at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength gsgp>3.7×10-16 (5.3×10-16) at a Yukawa length of λ=20  μm (95% C.L.).

  16. Dark Energy, Dark Matter and Science with Constellation-X

    NASA Technical Reports Server (NTRS)

    Cardiff, Ann Hornschemeier

    2005-01-01

    Constellation-X, with more than 100 times the collecting area of any previous spectroscopic mission operating in the 0.25-40 keV bandpass, will enable highthroughput, high spectral resolution studies of sources ranging from the most luminous accreting supermassive black holes in the Universe to the disks around young stars where planets form. This talk will review the updated Constellation-X science case, released in booklet form during summer 2005. The science areas where Constellation-X will have major impact include the exploration of the space-time geometry of black holes spanning nine orders of magnitude in mass and the nature of the dark energy and dark matter which govern the expansion and ultimate fate of the Universe. Constellation-X will also explore processes referred to as "cosmic feedback" whereby mechanical energy, radiation, and chemical elements from star formation and black holes are returned to interstellar and intergalactic medium, profoundly affecting the development of structure in the Universe, and will also probe all the important life cycles of matter, from stellar and planetary birth to stellar death via supernova to stellar endpoints in the form of accreting binaries and supernova remnants. This talk will touch upon all these areas, with particular emphasis on Constellation-X's role in the study of Dark Energy.

  17. Dark Energy, Dark Matter and Science with Constellation-X

    NASA Technical Reports Server (NTRS)

    Cardiff, Ann Hornschemeier

    2005-01-01

    Constellation-X, with more than 100 times the collecting area of any previous spectroscopic mission operating in the 0.25-40 keV bandpass, will enable highthroughput, high spectral resolution studies of sources ranging from the most luminous accreting supermassive black holes in the Universe to the disks around young stars where planets form. This talk will review the updated Constellation-X science case, released in booklet form during summer 2005. The science areas where Constellation-X will have major impact include the exploration of the space-time geometry of black holes spanning nine orders of magnitude in mass and the nature of the dark energy and dark matter which govern the expansion and ultimate fate of the Universe. Constellation-X will also explore processes referred to as "cosmic feedback" whereby mechanical energy, radiation, and chemical elements from star formation and black holes are returned to interstellar and intergalactic medium, profoundly affecting the development of structure in the Universe, and will also probe all the important life cycles of matter, from stellar and planetary birth to stellar death via supernova to stellar endpoints in the form of accreting binaries and supernova remnants. This talk will touch upon all these areas, with particular emphasis on Constellation-X's role in the study of Dark Energy.

  18. Cosmic Acceleration, Dark Energy, and Fundamental Physics

    NASA Astrophysics Data System (ADS)

    Turner, Michael S.; Huterer, Dragan

    2007-11-01

    A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic acceleration is a highly elastic ( p˜-ρ), very smooth form of energy called “dark energy” accounting for about 75% of the Universe. The “simplest” explanation for dark energy is the zero-point energy density associated with the quantum vacuum; however, all estimates for its value are many orders-of-magnitude too large. Other ideas for dark energy include a very light scalar field or a tangled network of topological defects. An alternate explanation invokes gravitational physics beyond general relativity. Observations and experiments underway and more precise cosmological measurements and laboratory experiments planned for the next decade will test whether or not dark energy is the quantum energy of the vacuum or something more exotic, and whether or not general relativity can self consistently explain cosmic acceleration. Dark energy is the most conspicuous example of physics beyond the standard model and perhaps the most profound mystery in all of science.

  19. Probing gravitation, dark energy, and acceleration

    SciTech Connect

    Linder, Eric V.

    2004-02-20

    The acceleration of the expansion of the universe arises from unknown physical processes involving either new fields in high energy physics or modifications of gravitation theory. It is crucial for our understanding to characterize the properties of the dark energy or gravity through cosmological observations and compare and distinguish between them. In fact, close consistencies exist between a dark energy equation of state function w(z) and changes to the framework of the Friedmann cosmological equations as well as direct spacetime geometry quantities involving the acceleration, such as ''geometric dark energy'' from the Ricci scalar. We investigate these interrelationships, including for the case of super acceleration or phantom energy where the fate of the universe may be more gentle than the Big Rip.

  20. "Dark energy" in the Local Void

    NASA Astrophysics Data System (ADS)

    Villata, M.

    2012-05-01

    The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "dark energy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that the Local Void could host an amount of antimatter (˜5×1015 M ⊙) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity field produced by this "dark repulsor" can explain the anomalous motion of the Local Sheet away from the Local Void, as well as several other properties of nearby galaxies that seem to require void evacuation and structure formation much faster than expected from the standard model. At the global cosmological level, gravitational repulsion from antimatter hidden in voids can provide more than enough potential energy to drive both the cosmic expansion and its acceleration, with no need for an initial "explosion" and dark energy. Moreover, the discrete distribution of these dark repulsors, in contrast to the uniformly permeating dark energy, can also explain dark flows and other recently observed excessive inhomogeneities and anisotropies of the Universe.

  1. Falsification of dark energy by fluid mechanics

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.

    2011-11-01

    The 2011 Nobel Prize in Physics has been awarded for the discovery from observations of increased supernovae dimness interpreted as distance, so that the Universe expansion rate has changed from a rate decreasing since the big bang to one that is now increasing, driven by anti-gravity forces of a mysterious dark energy material comprising 70% of the Universe mass-energy. Fluid mechanical considerations falsify both the accelerating expansion and dark energy concepts. Kinematic viscosity is neglected in current stan- dard models of self-gravitational structure formation, which rely on cold dark matter CDM condensations and clusterings that are also falsified by fluid mechanics. Weakly collisional CDM particles do not condense but diffuse away. Photon viscosity predicts su- perclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the plasma fragments into Earth-mass gas planets in trillion planet clumps (proto-globular-star-cluster PGCs). The hydrogen planets freeze to form the dark matter of galaxies and merge to form their stars. Dark energy is a systematic dimming error for Supernovae Ia caused by dark matter planets near hot white dwarf stars at the Chandrasekhar carbon limit. Evaporated planet atmospheres may or may not scatter light from the events depending on the line of sight.

  2. The symmetry energy at suprasaturation density and the ASY-EOS experiment at GSI

    NASA Astrophysics Data System (ADS)

    De Filippo, E.; Russotto, P.; Acosta, L.; Adamczyk, M.; Al-Ajlan, A.; Al-Garawi, M.; Al-Homaidhi, S.; Amorini, F.; Auditore, L.; Aumann, T.; Ayyad, Y.; Basrak, Z.; Benlliure, J.; Boisjoli, M.; Boretzky, K.; Brzychczyk, J.; Budzanowski, A.; Caesar, C.; Cardella, G.; Cammarata, P.; Chajecki, Z.; Chartier, M.; Chbihi, A.; Colonna, M.; Cozma, M. D.; Czech, B.; Di Toro, M.; Famiano, M.; Gannon, S.; Gašparić, I.; Grassi, L.; Guazzoni, C.; Guazzoni, P.; Heil, M.; Heilborn, L.; Introzzi, R.; Isobe, T.; Kezzar, K.; Kiš, M.; Krasznahorkay, A.; Kupny, S.; Kurz, N.; La Guidara, E.; Lanzalone, G.; Lasko, P.; Le Fèvre, A.; Leifels, Y.; Lemmon, R. C.; Li, Q. F.; Lombardo, I.; Łukasik, J.; Lynch, W. G.; Marini, P.; Matthews, Z.; May, L.; Minniti, T.; Mostazo, M.; Pagano, A.; Pagano, E. V.; Papa, M.; Pawłowski, P.; Pirrone, S.; Politi, G.; Porto, F.; Reviol, W.; Riccio, F.; Rizzo, F.; Rosato, E.; Rossi, D.; Santoro, S.; Sarantites, D. G.; Simon, H.; Skwirczynska, I.; Sosin, Z.; Stuhl, L.; Trautmann, W.; Trifirò, A.; Trimarchi, M.; Tsang, M. B.; Verde, G.; Veselsky, M.; Vigilante, M.; Wang, Yongjia; Wieloch, A.; Wigg, P.; Winkelbauer, J.; Wolter, H. H.; Wu, P.; Yennello, S.; Zambon, P.; Zetta, L.; Zoric, M.

    2017-03-01

    The ASY-EOS experiment at GSI laboratory measured the direct and elliptic flow of neutrons and light charged particles in the reaction 197Au+197 Au at 400 A MeV incident energy. The ratio of elliptic flow of neutrons with respect to that of the light charged particles was used as main experimental observable to probe the density dependence of the symmetry energy term of the nuclear equation of state. Results, obtained by comparison of the experimental data with the UrQMD model predictions, strongly support a moderately soft to linear density dependence of the symmetry energy at suprasaturation densities below 2ρ0.

  3. Examining the Viability of Phantom Dark Energy

    NASA Astrophysics Data System (ADS)

    Ludwick, Kevin

    2016-03-01

    In the standard cosmological framework of the 0th-order FLRW metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter w < - 1 (known as phantom dark energy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the accepted values for present-day w from Planck and WMAP9 include a significant range of values less than - 1 . Staying within the confines of observational constraints and general relativity, for which there is good experimental validation, we consider a few reasonable departures from the standard 0th-order framework in an attempt to see if negative kinetic energy can be avoided in these settings despite an apparent w < - 1 . We consider a more accurate description of the universe through the perturbing of the isotropic and homogeneous FLRW metric and the components of the stress-energy tensor, and we consider dynamic w and primordial isocurvature and adiabatic perturbations. We find that phantom dark energy does not necessarily have negative kinetic energy for all relevant length scales at all times and, by the same token, that quintessence dark energy does not necessarily have positive kinetic energy for all relevant length scales at all times.

  4. Dark Matter and Dark Energy from Gravitational Symmetry Breaking

    SciTech Connect

    Fuezfa, A.; Alimi, J.-M.

    2010-06-23

    We build a mechanism of gravitational symmetry breaking (GSB) of a global U(1) symmetry based on the relaxation of the equivalence principle due to the mass variation of pseudo Nambu-Goldstone dark matter (DM) particles. This GSB process is described by the modified cosmological convergence mechanism of the Abnormally Weighting Energy (AWE) Hypothesis previously introduced by the authors. Several remarkable constraints from the Hubble diagram of faraway supernovae are derived, notably on the explicit and gravitational symmetry breaking energy scales of the model. We then briefly present some consequences on neutrino masses when this mechanism is applied to the particular case of the breaking of lepton number symmetry.

  5. Dark energy and collapsing axial system

    NASA Astrophysics Data System (ADS)

    Sharif, M.; Manzoor, Rubab

    This paper investigates the effects of dark source term on the dissipative axially symmetric collapse by taking self-interacting Brans-Dicke (SBD) gravity as a dark energy (DE) candidate. We discuss physically feasible energy source of the model and formulate all the dynamical variables as well as structure scalars. It is found that the dark source term is one of the source of anisotropy and dissipation in the system. Further, we obtain structure scalars in this background. In order to discuss factors describing dissipative collapse, we develop equations related to the evolution of dynamical variables, heat transport equation as well as super-Poynting vector. We conclude that the thermodynamics of the collapse, evolution of kinematical terms (like expansion scalar, shear and vorticity) and inhomogeneity are affected by dark source term. Finally, we study the existence of radiation having repulsive gravitational nature in this collapse scenario.

  6. Yang Mills condensate dark energy coupled with matter and radiation

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Xia, T. Y.; Zhao, W.

    2007-07-01

    The coincidence problem is studied for the dark energy model of effective Yang Mills condensate (YMC) in a flat expanding universe during the matter-dominated stage. The YMC energy ρy(t) is taken to represent the dark energy, which is coupled either with the matter ρm(t), or with both the matter and the radiation components ρr(t). The effective YM Lagrangian is completely determined by the quantum field theory up to 1-loop order with an energy scale ~10-3 eV as a model parameter, and for each coupling, there is an extra model parameter. We have studied extensively the coupling models: the YMC decaying into the matter and the radiation; or vice versa the matter and radiation decaying into the YMC. It is found that, starting from the equality of radiation-matter ρmi = ρri, for a wide range of initial conditions of ρyi = (10-10, 10-2)ρmi, the models have a scaling solution during the early stages, and the YMC levels off and becomes dominant at late time, and the present state with Ωy sime 0.7, Ωm sime 0.3 and Ωr sime 10-5 is always achieved. If the YMC decays into a component, then this component also levels off later and approaches a constant value asymptotically, and the equation of state (EoS) of the YMC wy = ρy/py crosses over -1 and takes the value wy sime -1.1 at z = 0. If the matter and radiation decay into the YMC, then ρm(t) ~ a(t)-3 and ρr(t) ~ a(t)-4 approximately for all the time, and wy approaches -1 but does not cross over -1. We have also demonstrated that, at t → ∞, the coupled dynamics for (ρy(t), ρm(t), ρr(t)) is a stable attractor. Therefore, under generic circumstances, the existence of the scaling solution during the early stages and the subsequential exit from the scaling regime around z sime (0.3 0.5) are inevitable. Thus the coincidence problem can be naturally solved in the YMC dark energy models.

  7. Dark Energy and the Hubble Law

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Dolgachev, V. P.; Domozhilova, L. M.

    The Big Bang predicted by Friedmann could not be empirically discovered in the 1920th, since global cosmological distances (more than 300-1000 Mpc) were not available for observations at that time. Lemaitre and Hubble studied receding motions of galaxies at local distances of less than 20-30 Mpc and found that the motions followed the (nearly) linear velocity-distance relation, known now as Hubble's law. For decades, the real nature of this phenomenon has remained a mystery, in Sandage's words. After the discovery of dark energy, it was suggested that the dynamics of local expansion flows is dominated by omnipresent dark energy, and it is the dark energy antigravity that is able to introduce the linear velocity-distance relation to the flows. It implies that Hubble's law observed at local distances was in fact the first observational manifestation of dark energy. If this is the case, the commonly accepted criteria of scientific discovery lead to the conclusion: In 1927, Lemaitre discovered dark energy and Hubble confirmed this in 1929.

  8. Redshift drift constraints on holographic dark energy

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    The Sandage-Loeb (SL) test is a promising method for probing dark energy because it measures the redshift drift in the spectra of Lyman- α forest of distant quasars, covering the "redshift desert" of 2 ≲ z ≲ 5, which is not covered by existing cosmological observations. Therefore, it could provide an important supplement to current cosmological observations. In this paper, we explore the impact of SL test on the precision of cosmological constraints for two typical holographic dark energy models, i.e., the original holographic dark energy (HDE) model and the Ricci holographic dark energy (RDE) model. To avoid data inconsistency, we use the best-fit models based on current combined observational data as the fiducial models to simulate 30 mock SL test data. The results show that SL test can effectively break the existing strong degeneracy between the present-day matter density Ωm0 and the Hubble constant H 0 in other cosmological observations. For the considered two typical dark energy models, not only can a 30-year observation of SL test improve the constraint precision of Ωm0 and h dramatically, but can also enhance the constraint precision of the model parameters c and α significantly.

  9. Interacting dark energy: The role of microscopic feedback in the dark sector

    NASA Astrophysics Data System (ADS)

    Avelino, P. P.

    2015-04-01

    We investigate the impact on the classical dynamics of dark matter particles and dark energy of a nonminimal coupling in the dark sector, assuming that the mass of the dark matter particles is coupled to a dark energy scalar field. We show that standard results can be recovered only if the space-time variation of the dark energy scalar field is sufficiently smooth on the characteristic length scale of the dark matter particles, and we determine the associated constraint dependent on both the mass and radius of the dark matter particles and the coupling to the dark energy scalar field. We further show, using field theory numerical simulations, that a violation of such constraint results in a microscopic feedback effect strongly affecting the dynamics of dark matter particles, with a potential impact on structure formation and on the space-time evolution of the dark energy equation of state.

  10. Polytropic dark matter flows illuminate dark energy and accelerated expansion

    NASA Astrophysics Data System (ADS)

    Kleidis, K.; Spyrou, N. K.

    2015-04-01

    Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. In fact, polytropic processes in a DM fluid have been most successfully used in modeling dark galactic haloes, thus significantly improving the velocity dispersion profiles of galaxies. Motivated by such results, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluidlike properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, together with all the other physical characteristics, we also take the energy of this fluid's internal motions into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy, needed to compromise spatial flatness, namely, to justify that, today, the total energy density parameter is exactly unity. The polytropic cosmological model, depends on only one free parameter, the corresponding (polytropic) exponent, Γ. We find this model particularly interesting, because for Γ ≤ 0.541, without the need for either any exotic DE or the cosmological constant, the conventional pressure becomes negative enough so that the Universe accelerates its expansion at cosmological redshifts below a transition value. In fact, several physical reasons, e.g., the cosmological requirement for cold DM (CDM) and a positive velocity-of-sound square, impose further constraints on the value of Γ, which is eventually settled down to the range -0.089 < Γ ≤ 0. This cosmological model does not suffer either from the age problem or from the

  11. Constraining Dark Matter and Dark Energy Models using Astrophysical Surveys

    NASA Astrophysics Data System (ADS)

    Cieplak, Agnieszka M.

    This thesis addresses astrophysical probes to constrain dark matter (DM) and dark energy models. Primordial black holes (PBHs) remain one of the few DM candidates within the Standard Model of Particle Physics. This thesis presents a new probe of this PBH DM, using the microlensing of the source stars monitored by the already existing Kepler satellite. With its photometric precision and the large projected cross section of the nearby stars, it is found that previous constraints on PBH DM could theoretically be extended by two orders of magnitude. Correcting a well-known microlensing formula, a limb-darkening analysis is included, and a new approximation is calculated for future star selection. A preliminary prediction is calculated for the planned Wide-Field Infrared Survey Telescope. A preliminary study of the first two years of publicly available Kepler data is presented. The investigation yields many new sources of background error not predicted in the theoretical calculations, such as stellar flares and comets in the field of view. Since no PBH candidates are detected, an efficiency of detection is therefore calculated by running a Monte Carlo with fake limb-darkened finite-source microlensing events. It is found that with just the first 8 quarters of data, a full order of magnitude of the PBH mass range can be already constrained. Finally, one of the astrophysical probes of dark energy is also addressed - specifically, the baryon acoustic oscillations (BAO) measurement in the gas distribution, as detected in quasar absorption lines. This unique measurement of dark energy at intermediate redshifts is being measured by current telescope surveys. The last part of this thesis therefore focuses on understanding the systematic effects in such a detection. Since the bias between the underlying dark matter distribution and the measured gas flux distribution is based on gas physics, hydrodynamic simulations are used to understand the evolution of neutral hydrogen over

  12. Comparing symmetry energy predictions and recent constraints from the ASY-EOS experiment at GSI

    NASA Astrophysics Data System (ADS)

    Sammarruca, Francesca

    2017-04-01

    Predictions for the interaction part of the symmetry energy obtained from microscopic approaches based upon different foundations are reviewed and discussed in the light of recent updated constraints obtained from reaction observables in the ASY-EOS experiment at GSI. The discussion is then extended to the neutron skin thickness in 208Pb and its relation to the density derivatives of the symmetry energy at and below saturation density. With regard to the latter, the main point is to demonstrate the importance of proper consideration of the theoretical uncertainties of microscopic predictions in order to guide phenomenological analyses.

  13. Constraints on dark energy from new observations including Pan-STARRS

    SciTech Connect

    Zheng, Wei; Li, Si-Yu; Li, Hong; Xia, Jun-Qing; Li, Mingzhe; Lu, Tan E-mail: lisy@ihep.ac.cn E-mail: xiajq@ihep.ac.cn E-mail: t.lu@pmo.ac.cn

    2014-08-01

    In this paper, we set the new limits on the equation of state parameter (EoS) of dark energy with the observations of cosmic microwave background radiation (CMB) from Planck satellite, the type Ia supernovae from Pan-STARRS and the baryon acoustic oscillation (BAO). We consider two parametrization forms of EoS: a constant w and time evolving w(a)=w{sub 0}+w{sub a}(1-a). The results show that with a constant EoS, w=-1.141±0.075 68% C.L.), which is consistent with ΛCDM at about 2σ confidence level. For a time evolving w(a) model, we get w{sub 0}=-1.09{sup +0.16}{sub -0.18} 1σ C.L.), w{sub a}=-0.34{sup +0.87}{sub -0.51} 1σ C.L.), and in this case ΛCDM can be comparable with our observational data at 1σ confidence level. In order to do the parametrization independent analysis, additionally we adopt the so called principal component analysis (PCA) method, in which we divide redshift range into several bins and assume w as a constant in each redshift bin (bin-w). In such bin-w scenario, we find that for most of the bins cosmological constant can be comparable with the data, however, there exists few bins which give w deviating from ΛCDM at more than 2σ confidence level, which shows a weak hint for the time evolving behavior of dark energy. To further confirm this hint, we need more data with higher precision.

  14. Non-linear dark energy clustering

    SciTech Connect

    Anselmi, Stefano; Ballesteros, Guillermo; Pietroni, Massimo E-mail: ballesteros@pd.infn.it

    2011-11-01

    We consider a dark energy fluid with arbitrary sound speed and equation of state and discuss the effect of its clustering on the cold dark matter distribution at the non-linear level. We write the continuity, Euler and Poisson equations for the system in the Newtonian approximation. Then, using the time renormalization group method to resum perturbative corrections at all orders, we compute the total clustering power spectrum and matter power spectrum. At the linear level, a sound speed of dark energy different from that of light modifies the power spectrum on observationally interesting scales, such as those relevant for baryonic acoustic oscillations. We show that the effect of varying the sound speed of dark energy on the non-linear corrections to the matter power spectrum is below the per cent level, and therefore these corrections can be well modelled by their counterpart in cosmological scenarios with smooth dark energy. We also show that the non-linear effects on the matter growth index can be as large as 10–15 per cent for small scales.

  15. Dark energy and dark matter from an additional adiabatic fluid

    NASA Astrophysics Data System (ADS)

    Dunsby, Peter K. S.; Luongo, Orlando; Reverberi, Lorenzo

    2016-10-01

    The dark sector is described by an additional barotropic fluid which evolves adiabatically during the Universe's history and whose adiabatic exponent γ is derived from the standard definitions of specific heats. Although in general γ is a function of the redshift, the Hubble parameter and its derivatives, we find that our assumptions lead necessarily to solutions with γ =constant in a Friedmann-Lemaître-Robertson-Walker universe. The adiabatic fluid acts effectively as the sum of two distinct components, one evolving like nonrelativistic matter and the other depending on the value of the adiabatic index. This makes the model particularly interesting as a way of simultaneously explaining the nature of both dark energy and dark matter, at least at the level of the background cosmology. The Λ CDM model is included in this family of theories when γ =0 . We fit our model to supernovae Ia, H (z ) and baryonic acoustic oscillation data, discussing the model selection criteria. The implications for the early Universe and the growth of small perturbations in this model are also discussed.

  16. Clustering of galaxies with dynamical dark energy

    NASA Astrophysics Data System (ADS)

    Pourhassan, Behnam; Upadhyay, Sudhaker; Hameeda, Mir; Faizal, Mir

    2017-07-01

    In this paper, we study thermodynamics of the cluster of galaxies under the effect of dynamical dark energy. We evaluate the configurational integral for interacting system of galaxies in an expanding Universe by including the effects produced by the varying Λ. The gravitational partition function is obtained using this configuration integral. We obtain thermodynamics quantities in canonical ensemble which depend on time and investigate the second law of thermodynamics. We also calculate the distribution function in grand canonical ensemble. The time evolution of the clustering parameter of galaxies is investigated for the time-dependent (dynamical) dark energy. We conclude that the second law of thermodynamics is valid for the total system of cluster of galaxies and dynamical dark energy. We calculate the correlation function and show that our model is very close to Peebles's power law, in agreement with the N-body simulation. It is observed that thermodynamics quantities depend on the modified clustering parameter for this system of galaxies.

  17. Dark energy: recent observations and future prospects.

    PubMed

    Perlmutter, Saul

    2003-11-15

    Dark energy presents us with a challenging puzzle: understanding the new physics seen in the acceleration of the expansion of the Universe. Measurements using type-Ia supernovae (SNe) first detected this acceleration, and this approach remains the most direct route to studying the details of the Universe's expansion history that can teach us more about the nature of the dark energy. Such measurements are, however, extremely demanding in both precision and accuracy, since the different dark-energy models predict very small differences in the expansion history. While several cosmological probes may reach the required statistical uncertainties, the key measurement limit will be the systematic uncertainty. The supernova-measurement approach has the advantage of well-studied systematic uncertainties, allowing a next-generation experiment to be pursued. We briefly review the progress to date and examine the promise of future surveys with large numbers of SNe and well-bounded systematics.

  18. HETDEX: Measuring Dark Energy at High Redshift

    NASA Astrophysics Data System (ADS)

    Gebhardt, Karl; Hill, G.; Komatsu, E.; Drory, N.; DePoy, D.; Ciardullo, R.; Gronwall, C.; Fabricius, M.; Wisotzki, L.; HETDEX Collaboration

    2012-01-01

    The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is a blind spectroscopic survey to map the evolution of dark energy using Lyman-alpha emitting galaxies as tracers. The survey instrument, VIRUS, consists of 75 IFUs distributed across the 22-arcmin field of the upgraded 9.2-m HET. Each 50x50 sq. arcsec IFU is made up of 448 1.5-arcsec fibers, and feeds a pair of spectrographs with a fixed bandpass of 350-550 nm and resolving power R 700. Each exposure gathers 33,600 spectra. The baseline survey will deliver spectra of 0.8M LAEs in a 9 cubic Gpc volume with 1.9 < z < 3.5, and 1M [OII] emitters with z < 0.48. We expect to measure both the Hubble parameter and angular diameter distance to better than 1%. HETDEX will provide a unique window on the evolution of dark energy.

  19. A novel teleparallel dark energy model

    NASA Astrophysics Data System (ADS)

    Otalora, Giovanni

    2016-12-01

    Although equivalent to general relativity, teleparallel gravity (TG) is conceptually speaking a completely different theory. In this theory, the gravitational field is described by torsion, not by curvature. By working in this context, a new model is proposed in which the four-derivative of a canonical scalar field representing dark energy is nonminimally coupled to the “vector torsion”. This type of coupling is motivated by the fact that a scalar field couples to torsion through its four-derivative, which is consistent with local spacetime kinematics regulated by the de Sitter group SO(1, 4). It is found that the current state of accelerated expansion of the universe corresponds to a late-time attractor that can be (i) a dark energy-dominated de Sitter solution (ωϕ = -1), (ii) a quintessence-type solution with ωϕ ≥-1, or (iii) a phantom-type ωϕ < -1 dark energy.

  20. Dark energy and dark matter as due to zero point energy

    NASA Astrophysics Data System (ADS)

    Lehnert, Bo; Lehnert

    2013-06-01

    An attempt is made to explain dark energy and dark matter of the expanding universe in terms of the zero point vacuum energy. This analysis is mainly limited to later stages of an observable nearly flat universe. It is based on a revised formulation of the spectral distribution of the zero point energy, for an ensemble in a defined statistical equilibrium having finite total energy density. The steady and dynamic states are studied for a spherical cloud of zero point energy photons. The `antigravitational' force due to its pressure gradient then represents dark energy, and its gravitational force due to the energy density represents dark matter. Four fundamental results come out of the theory. First, the lack of emitted radiation becomes reconcilable with the concepts of dark energy and dark matter. Second, the crucial coincidence problem of equal orders of magnitude of mass density and vacuum energy density cannot be explained by the cosmological constant, but is resolved by the present variable concepts, which originate from the same photon gas balance. Third, the present approach becomes reconcilable with cosmical dimensions and with the radius of the observable universe. Fourth, the deduced acceleration of the expansion agrees with the observed one. In addition, mass polarity of a generalized gravitation law for matter and antimatter is proposed as a source of dark flow.

  1. Dark goo: bulk viscosity as an alternative to dark energy

    SciTech Connect

    Gagnon, Jean-Sebastien; Lesgourgues, Julien E-mail: julien.lesgourgues@cern.ch

    2011-09-01

    We present a simple (microscopic) model in which bulk viscosity plays a role in explaining the present acceleration of the universe. The effect of bulk viscosity on the Friedmann equations is to turn the pressure into an 'effective' pressure containing the bulk viscosity. For a sufficiently large bulk viscosity, the effective pressure becomes negative and could mimic a dark energy equation of state. Our microscopic model includes self-interacting spin-zero particles (for which the bulk viscosity is known) that are added to the usual energy content of the universe. We study both background equations and linear perturbations in this model. We show that a dark energy behavior is obtained for reasonable values of the two parameters of the model (i.e. the mass and coupling of the spin-zero particles) and that linear perturbations are well-behaved. There is no apparent fine tuning involved. We also discuss the conditions under which hydrodynamics holds, in particular that the spin-zero particles must be in local equilibrium today for viscous effects to be important.

  2. Challenges in Cosmology from the Big Bang to Dark Energy, Dark Matter and Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Silk, Joseph

    I review the current status of Big Bang Cosmology, with emphasis on current issues in dark matter, dark energy, and galaxy formation. These topics motivate many of the current goals of experimental cosmology which range from targeting the nature of dark energy and dark matter to probing the epoch of the first stars and galaxies.

  3. Dark Energy: A Crisis for Fundamental Physics

    ScienceCinema

    Stubbs, Christopher [Harvard University, Cambridge, Massachusetts, USA

    2016-07-12

    Astrophysical observations provide robust evidence that our current picture of fundamental physics is incomplete. The discovery in 1998 that the expansion of the Universe is accelerating (apparently due to gravitational repulsion between regions of empty space!) presents us with a profound challenge, at the interface between gravity and quantum mechanics. This "Dark Energy" problem is arguably the most pressing open question in modern fundamental physics. The first talk will describe why the Dark Energy problem constitutes a crisis, with wide-reaching ramifications. One consequence is that we should probe our understanding of gravity at all accessible scales, and the second talk will present experiments and observations that are exploring this issue.

  4. Dark Energy in Weyl- f ( R) Gravity

    NASA Astrophysics Data System (ADS)

    Karami-Fard, M.; Tanhayi, M. R.; Takook, M. V.

    2016-02-01

    We use the dark energy density of holographic methods to reconstruct f( R) in Weyl- f( R) gravity. We analyse f( R) by assuming that the combination of f( R) together with the Weyl gravity might actually be an effective description of dark energy models. The reconstructed model in the spatially flat FRW universe is considered for three version of scale factors: phantom, quintessence and de Sitter scale factors. For the de Sitter scale factor we also obtain the equation-of-state parameter.

  5. DESTINY, The Dark Energy Space Telescope

    NASA Technical Reports Server (NTRS)

    Pasquale, Bert A.; Woodruff, Robert A.; Benford, Dominic J.; Lauer, Tod

    2007-01-01

    We have proposed the development of a low-cost space telescope, Destiny, as a concept for the NASA/DOE Joint Dark Energy Mission. Destiny is a 1.65m space telescope, featuring a near-infrared (0.85-1.7m) survey camera/spectrometer with a moderate flat-field field of view (FOV). Destiny will probe the properties of dark energy by obtaining a Hubble diagram based on Type Ia supernovae and a large-scale mass power spectrum derived from weak lensing distortions of field galaxies as a function of redshift.

  6. Atomic interferometry test of dark energy

    NASA Astrophysics Data System (ADS)

    Brax, Philippe; Davis, Anne-Christine

    2016-11-01

    Atomic interferometry can be used to probe dark energy models coupled to matter. We consider the constraints coming from recent experimental results on models generalizing the inverse power law chameleons such as f (R ) gravity in the large curvature regime, the environmentally dependent dilaton and symmetrons. Using the tomographic description of these models, we find that only symmetrons with masses smaller than the dark energy scale can be efficiently tested. In this regime, the resulting constraints complement the bounds from the Eötwash experiment and exclude small values of the symmetron self-coupling.

  7. DESTINY, The Dark Energy Space Telescope

    NASA Technical Reports Server (NTRS)

    Pasquale, Bert A.; Woodruff, Robert A.; Benford, Dominic J.; Lauer, Tod

    2007-01-01

    We have proposed the development of a low-cost space telescope, Destiny, as a concept for the NASA/DOE Joint Dark Energy Mission. Destiny is a 1.65m space telescope, featuring a near-infrared (0.85-1.7m) survey camera/spectrometer with a moderate flat-field field of view (FOV). Destiny will probe the properties of dark energy by obtaining a Hubble diagram based on Type Ia supernovae and a large-scale mass power spectrum derived from weak lensing distortions of field galaxies as a function of redshift.

  8. Advanced Dark Energy Physics Telescope (ADEPT)

    SciTech Connect

    Charles L. Bennett

    2009-03-26

    In 2006, we proposed to NASA a detailed concept study of ADEPT (the Advanced Dark Energy Physics Telescope), a potential space mission to reliably measure the time-evolution of dark energy by conducting the largest effective volume survey of the universe ever done. A peer-review panel of scientific, management, and technical experts reported back the highest possible 'excellent' rating for ADEPT. We have since made substantial advances in the scientific and technical maturity of the mission design. With this Department of Energy (DOE) award we were granted supplemental funding to support specific extended research items that were not included in the NASA proposal, many of which were intended to broadly advance future dark energy research, as laid out by the Dark Energy Task Force (DETF). The proposed work had three targets: (1) the adaptation of large-format infrared arrays to a 2 micron cut-off; (2) analytical research to improve the understanding of the dark energy figure-of- merit; and (3) extended studies of baryon acoustic oscillation systematic uncertainties. Since the actual award was only for {approx}10% of the proposed amount item (1) was dropped and item (2) work was severely restricted, consistent with the referee reviews of the proposal, although there was considerable contradictions between reviewer comments and several comments that displayed a lack of familiarity with the research. None the less, item (3) was the focus of the work. To characterize the nature of the dark energy, ADEPT is designed to observe baryon acoustic oscillations (BAO) in a large galaxy redshift survey and to obtain substantial numbers of high-redshift Type Ia supernovae (SNe Ia). The 2003 Wilkinson Microwave Anisotropy Probe (WMAP) made a precise determination of the BAO 'standard ruler' scale, as it was imprinted on the cosmic microwave background (CMB) at z {approx} 1090. The standard ruler was also imprinted on the pattern of galaxies, and was first detected in 2005 in Sloan

  9. Dark energy in systems of galaxies

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.

    2013-11-01

    The precise observational data of the Hubble Space Telescope have been used to study nearby galaxy systems. The main result is the detection of dark energy in groups, clusters, and flows of galaxies on a spatial scale of about 1-10 Mpc. The local density of dark energy in these systems, which is determined by various methods, is close to the global value or even coincides with it. A theoretical model of the nearby Universe has been constructed, which describes the Local Group of galaxies with the flow of dwarf galaxies receding from this system. The key physical parameter of the group-flow system is zero gravity radius, which is the distance at which the gravity of dark matter is compensated by dark-energy antigravity. The model predicts the existence of local regions of space where Einstein antigravity is stronger than Newton gravity. Six such regions have been revealed in the data of the Hubble space telescope. The nearest of these regions is at a distance of 1-3 Mpc from the center of the Milky Way. Antigravity in this region is several times stronger than gravity. Quasiregular flows of receding galaxies, which are accelerated by the dark-energy antigravity, exist in these regions. The model of the nearby Universe at the scale of groups of galaxies (˜1 Mpc) can be extended to the scale of clusters (˜10 Mpc). The systems of galaxies with accelerated receding flows constitute a new and probably widespread class of metagalactic populations. Strong dynamic effects of local dark energy constitute the main characteristic feature of these systems.

  10. 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.

  11. Cosmic Visions Dark Energy: Technology

    SciTech Connect

    Dodelson, Scott; Heitmann, Katrin; Hirata, Chris; Honscheid, Klaus; Roodman, Aaron; Seljak, Uroš; Slosar, Anže; Trodden, Mark

    2016-04-26

    A strong instrumentation and detector R&D program has enabled the current generation of cosmic frontier surveys. A small investment in R&D will continue to pay dividends and enable new probes to investigate the accelerated expansion of the universe. Instrumentation and detector R&D provide critical training opportunities for future generations of experimentalists, skills that are important across the entire Department of Energy High Energy Physics program.

  12. Viscous extended holographic Ricci dark energy in the framework of standard Eckart theory

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, Surajit

    2016-11-01

    In this paper, we report a study on the viscous extended holographic Ricci dark energy (EHRDE) model under the assumption of existence of bulk viscosity in the linear barotropic fluid and the EHRDE in the framework of standard Eckart theory of relativistic irreversible thermodynamics and it has been observed that the non-equilibrium bulk viscous pressure is significantly smaller than the local equilibrium pressure. We have studied the equation of state (EoS) parameter and observed that the EoS behaves like “quintom” and is consistent with the constraints set by observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements in [S. Kumar and L. Xu, Phys. Lett. B 737, 244 (2014)]. Analysis of statefinder parameters has shown the possibility of attainment of Lambda cold dark matter (ΛCDM) phase under current model and at the same time it has been pointed out that the redshift z = 0, i.e. the current universe, the statefinder pair is different from that of ΛCDM and the ΛCDM can be attained in a later stage of the universe. An analysis of stability has shown that although the viscous EHRDE along with viscous barotropic is classically unstable in the present epoch, it can lead to a stable universe in very late stage. Considering an universe enveloped by event horizon, we have observed validity of generalized second law (GSL) of thermodynamics.

  13. New probes of dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Kim, Young-Rae

    We use N -body simulations of a LCDM universe to study dark matter and dark energy. First, we examine the possibility of detecting the gravitational effect on the total redshift observed for galaxies. For clusters of mass M ~ 10 15 [Special characters omitted.] , the difference in gravitational redshift between the brightest galaxy and the rest of the cluster members is ~ 10 kms - 1 . The most efficient way to detect gravitational redshifts using information from galaxies only involves using the full gravitational redshift profile of clusters. Test on our simulated clusters show that we need at least ~ 2500 clusters/groups with M > 5 x 10 13 [Special characters omitted.] for a detection of gravitational redshifts at the 2s level. Secondly, we investigate the possibility of probing dark energy by measuring the isotropy of the galaxy cluster autocorrelation function (an Alcock-Paczynski test). We assume that the redshift distortion due to peculiar velocities can be removed by measuring kSZ effect. We use the hydrodynamic simulation results of Nagai et al. (2003) to simulate various kSZ surveys. We find by model fitting that a measurement of the correlation function distortion can be used to recover the cosmological parameters that have been used to generate the simulation. With the simulated SPT and ACT surveys, O L could be measured to within 0.1 and 0.2 respectively at one sigma, but only upper limits on the equation of state parameter w will be possible. Finally, using cosmological hydrodynamic simulations we measure the mean transmitted flux in the Lya forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel- quasar separation distance can be fitted using a simple power law form including the usual correlation function parameters r 0 and g so that ([left angle bracket] F ( r )[right angle bracket] = SUMexp(-t eff (1 + [Special characters omitted.] ))). From the simulations we find the relation between r 0

  14. Zero point energy as origin of dark energy and dark matter

    NASA Astrophysics Data System (ADS)

    Lehnert, Bo

    2012-04-01

    An attempt is made to explain dark energy and dark matter of the expanding universe in terms of the zero point vacuum energy. This analysis is mainly limited to later stages of an observable nearly flat universe. It is based on a revised formulation of the spectral distribution of the zero point energy, for an ensemble in a defined statistical equilibrium having finite total energy density. The steady and dynamic states are studied for a spherical cloud of zero point energy photons. The "antigravitational" force due to its pressure gradient then represents dark energy, and its gravitational force due to the energy density represents dark matter. Four fundamental results come out of the theory. First, the lack of emitted radiation becomes reconcilable with the concepts of dark energy and dark matter. Second, the crucial coincidence problem of equal orders of magnitude of mass density and vacuum energy density cannot be explained by the cosmological constant, but is resolved by the present variable concepts which originate from the same photon gas balance. Third, the present approach becomes reconcilable with cosmical dimensions and with the radius of the observable universe. Fourth, the deduced acceleration of the expansion agrees with the observed one.

  15. Spherical collapse model in agegraphic dark energy cosmologies

    NASA Astrophysics Data System (ADS)

    Rezaei, Mehdi; Malekjani, Mohammad

    2017-09-01

    Under the commonly used spherical collapse model, we study how dark energy affects the growth of large scale structures of the Universe in the context of agegraphic dark energy models. The dynamics of the spherical collapse of dark matter halos in nonlinear regimes is determined by the properties of the dark energy model. We show that the main parameters of the spherical collapse model are directly affected by the evolution of dark energy in the agegraphic dark energy models. We compute the spherical collapse quantities for different values of agegraphic model parameter α in two different scenarios: first, when dark energy does not exhibit fluctuations on cluster scales, and second, when dark energy inside the overdense region collapses similar to dark matter. Using the Sheth-Tormen and Reed mass functions, we investigate the abundance of dark matter halos in the framework of agegraphic dark energy cosmologies. The model parameter α is a crucial parameter in order to count the abundance of dark matter halos. Specifically, the present analysis suggests that the agegraphic dark energy model with a bigger (smaller) value of α predicts less (more) virialized halos with respect to that of Λ CDM cosmology. We also show that in agegraphic dark energy models, the number of halos strongly depends on clustered or uniformed distributions of dark energy.

  16. Quasilinear observables in dark energy cosmologies

    NASA Astrophysics Data System (ADS)

    Rampf, Cornelius; Villa, Eleonora; Amendola, Luca

    2017-06-01

    What are the fundamental limitations of reconstructing the properties of dark energy, given cosmological observations in the quasilinear regime in a range of redshifts, to be as precise as required? The aim of this paper is to address this question by constructing model-independent observables, while completely ignoring practical problems of real-world observations. Non-Gaussianities already present in the initial conditions are not directly accessible from observations because of a perfect degeneracy with the non-Gaussianities arising from the (weakly) nonlinear matter evolution in generalized dark energy models. By imposing a specific set of evolution equations that should cover a range of dark energy cosmologies, we find, however, a constraint equation for the linear structure growth rate f1 expressed in terms of model-independent observables. Entire classes of dark energy models which do not satisfy this constraint equation could be ruled out, and for models satisfying it, we could reconstruct e.g. the nonlocal bias parameters b1 and b2.

  17. An introduction to the dark energy problem

    NASA Astrophysics Data System (ADS)

    Dobado, Antonio; Maroto, Antonio L.

    2009-04-01

    In this work we review briefly the origin and history of the cosmological constant and its recent reincarnation in the form of the dark energy component of the universe. We also comment on the fundamental problems associated to its existence and magnitude which require an urgent solution for the sake of the internal consistency of theoretical physics.

  18. Falsification of Dark Energy by Fluid Mechanics

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.

    2012-03-01

    The 2011 Nobel Prize in Physics was awarded for the discovery of accelerating super- novae dimness, suggesting a remarkable reversal in the expansion rate of the Universe from a decrease to an increase, driven by anti-gravity forces of a mysterious dark energy material comprising 70% of the Universe mass-energy. Fluid mechanics and Herschel- Planck-Spitzer-Hubble etc. space telescope observations falsify both the accelerating ex- pansion rate and dark energy concepts. Kinematic viscosity is neglected in models of self-gravitational structure formation. Large plasma photon viscosity predicts protosu- perclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the gas protogalaxies fragment into Earth-mass rogue plan- ets in highly persistent, trillion-planet clumps (proto-globular-star-cluster PGCs). PGC planets freeze to form the dark matter of galaxies and merge to form their stars, giving the hydrogen triple-point (14 K) infrared emissions observed. Dark energy is a system- atic dimming error for Supernovae Ia caused by partially evaporated planets feeding hot white dwarf stars at the Chandrasekhar carbon limit. Planet atmospheres may or may not dim light from SNe-Ia events depending on the line of sight.

  19. The Dark Energy Spectroscopic Instrument (DESI)

    SciTech Connect

    Flaugher, Brenna

    1998-03-01

    The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar spectroscopic redshift survey. The DESI instrument consists of a new wide- eld (3.2 deg. linear eld of view) corrector plus a multi-object spectrometer with up to 5000 robotically positioned optical bers and will be installed at prime focus on the Mayall 4m telescope at Kitt Peak, Arizona. The bers feed 10 three-arm spectrographs producing spectra that cover a wavelength range from 360-980 nm and have resolution of 2000-5500 depending on the wavelength. The DESI instrument is designed for a 14,000 sq. deg. multi-year survey of targets that trace the evolution of dark energy out to redshift 3.5 using the redshifts of luminous red galaxies (LRGs), emission line galaxies (ELGs) and quasars. DESI is the successor to the successful Stage-III BOSS spectroscopic redshift survey and complements imaging surveys such as the Stage-III Dark Energy Survey (DES, currently operating) and the Stage-IV Large Synoptic Survey Telescope (LSST, planned start early in the next decade.

  20. Stringy Model of Cosmological Dark Energy

    SciTech Connect

    Aref'eva, Irina Ya.

    2007-11-20

    A string field theory (SFT) nonlocal model of the cosmological dark energy providing w<-1 is briefly surveyed. We summarize recent developments and open problems, as well as point out some theoretical issues related with others applications of the SFT nonlocal models in cosmology, in particular, in inflation and cosmological singularity.

  1. On the determination of dark energy

    SciTech Connect

    Clarkson, Chris

    2010-06-23

    I consider some of the issues we face in trying to understand dark energy. Huge fluctuations in the unknown dark energy equation of state can be hidden in distance data, so I argue that model-independent tests which signal if the cosmological constant is wrong are valuable. These can be constructed to remove degeneracies with the cosmological parameters. Gravitational effects can play an important role. Even small inhomogeneity clouds our ability to say something definite about dark energy. I discuss how the averaging problem confuses our potential understanding of dark energy by considering the backreaction from density perturbations to second-order in the concordance model: this effect leads to at least a 10% increase in the dynamical value of the deceleration parameter, and could be significantly higher. Large Hubble-scale inhomogeneity has not been investigated in detail, and could conceivably be the cause of apparent cosmic acceleration. I discuss void models which defy the Copernican principle in our Hubble patch, and describe how we can potentially rule out these models.This article is a summary of two talks given at the Invisible Universe Conference, Paris, 2009.

  2. Planck priors for dark energy surveys

    SciTech Connect

    Mukherjee, Pia; Parkinson, David; Kunz, Martin; Wang Yun

    2008-10-15

    Although cosmic microwave background anisotropy data alone cannot constrain simultaneously the spatial curvature and the equation of state of dark energy, CMB data provide a valuable addition to other experimental results. However computing a full CMB power spectrum with a Boltzmann code is quite slow; for instance if we want to work with many dark energy and/or modified gravity models, or would like to optimize experiments where many different configurations need to be tested, it is possible to adopt a quicker and more efficient approach. In this paper we consider the compression of the projected Planck cosmic microwave background data into four parameters, R (scaled distance to last scattering surface), l{sub a} (angular scale of sound horizon at last scattering), {omega}{sub b}h{sup 2} (baryon density fraction) and n{sub s} (powerlaw index of primordial matter power spectrum), all of which can be computed quickly. We show that, although this compression loses information compared to the full likelihood, such information loss becomes negligible when more data is added. We also demonstrate that the method can be used for canonical scalar-field dark energy independently of the parametrization of the equation of state, and discuss how this method should be used for other kinds of dark energy models.

  3. The Logotropic Dark Fluid as a unification of dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri

    2016-07-01

    We propose a heuristic unification of dark matter and dark energy in terms of a single ;dark fluid; with a logotropic equation of state P = Aln ⁡ (ρ /ρP), where ρ is the rest-mass density, ρP = 5.16 ×1099gm-3 is the Planck density, and A is the logotropic temperature. The energy density ɛ is the sum of a rest-mass energy term ρc2 ∝a-3 mimicking dark matter and an internal energy term u (ρ) = - P (ρ) - A = 3 Aln ⁡ a + C mimicking dark energy (a is the scale factor). The logotropic temperature is approximately given by A ≃ρΛc2 / ln ⁡ (ρP /ρΛ) ≃ρΛc2 / [ 123 ln ⁡ (10) ], where ρΛ = 6.72 ×10-24gm-3 is the cosmological density and 123 is the famous number appearing in the ratio ρP /ρΛ ∼10123 between the Planck density and the cosmological density. More precisely, we obtain A = 2.13 ×10-9gm-1s-2 that we interpret as a fundamental constant. At the cosmological scale, our model fulfills the same observational constraints as the ΛCDM model (they will differ in about 25 Gyrs when the logotropic universe becomes phantom). However, the logotropic dark fluid has a nonzero speed of sound and a nonzero Jeans length which, at the beginning of the matter era, is about λJ = 40.4pc, in agreement with the minimum size of the dark matter halos observed in the universe. The existence of a nonzero Jeans length may solve the missing satellite problem. At the galactic scale, the logotropic pressure balances the gravitational attraction, providing halo cores instead of cusps. This may solve the cusp problem. The logotropic equation of state generates a universal rotation curve that agrees with the empirical Burkert profile of dark matter halos up to the halo radius. In addition, it implies that all the dark matter halos have the same surface density Σ0 =ρ0rh = 141M⊙ /pc2 and that the mass of dwarf galaxies enclosed within a sphere of fixed radius ru = 300pc has the same value M300 = 1.93 ×107M⊙, in remarkable agreement with the observations

  4. Dark Energy Found Stifling Growth in Universe

    NASA Astrophysics Data System (ADS)

    2008-12-01

    WASHINGTON -- For the first time, astronomers have clearly seen the effects of "dark energy" on the most massive collapsed objects in the universe using NASA's Chandra X-ray Observatory. By tracking how dark energy has stifled the growth of galaxy clusters and combining this with previous studies, scientists have obtained the best clues yet about what dark energy is and what the destiny of the universe could be. This work, which took years to complete, is separate from other methods of dark energy research such as supernovas. These new X-ray results provide a crucial independent test of dark energy, long sought by scientists, which depends on how gravity competes with accelerated expansion in the growth of cosmic structures. Techniques based on distance measurements, such as supernova work, do not have this special sensitivity. Scientists think dark energy is a form of repulsive gravity that now dominates the universe, although they have no clear picture of what it actually is. Understanding the nature of dark energy is one of the biggest problems in science. Possibilities include the cosmological constant, which is equivalent to the energy of empty space. Other possibilities include a modification in general relativity on the largest scales, or a more general physical field. People Who Read This Also Read... Chandra Data Reveal Rapidly Whirling Black Holes Ghostly Glow Reveals a Hidden Class of Long-Wavelength Radio Emitters Powerful Nearby Supernova Caught By Web Cassiopeia A Comes Alive Across Time and Space To help decide between these options, a new way of looking at dark energy is required. It is accomplished by observing how cosmic acceleration affects the growth of galaxy clusters over time. "This result could be described as 'arrested development of the universe'," said Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., who led the research. "Whatever is forcing the expansion of the universe to speed up is also forcing its

  5. Dark energy and the BOOMERANG data.

    PubMed

    Amendola, L

    2001-01-08

    The recent high-quality BOOMERANG data allow the testing of many competing cosmological models. Here I present a seven-parameter likelihood analysis of dark energy models with exponential potential and explicit coupling to dark matter. The BOOMERANG data constrain the dimensionless coupling beta to be smaller than 0.1, an order of magnitude better than previous limits. In terms of the constant xi of nonminimally coupled theories, this amounts to xi<0.01. On the other hand, BOOMERANG does not have enough sensitivity to put constraints on the potential slope.

  6. Dark Energy and Dark Matter from the same Vacuum Condensate

    NASA Astrophysics Data System (ADS)

    Sarfatti, Jack

    2003-04-01

    The micro-quantum Dirac negative energy electron Fermi sphere with Planck scale cutoff is unstable to the formation of off-mass-shell Cooper pairs of virtual electrons and positrons from their static Coulomb attraction. The resulting virtual BEC complex macro-quantum coherent local order parameter (0|e+e-|0) gives rise to both spin 2 gravity guv and spin 0 quintessence / from the Goldstone and Higgs oscillations respectively, Susskind's "world hologram" conjecture replaces the Planck scale Lp with Lp^2/3L^1/3 at scale L. Hagen Kleinert's strain tensor for the "world crystal" is Einstein's geometrodynamic field: guv = nuv + Lp^4/3L^2/3Du,Dvarg(0|e+e-|0)/2 nuv = Minkowski metric, = anti-commutator Du = ,u + TaAu^a is the spin 1 gauge covariant derivative for Lie group P with Lie algebra [Ta,Tb] = Cab^cTc / = Lp-4/3L-2/3[1 - Lp^2L|(0|e+e-|0)|^2] When L = size of visible universe 10^28 cm, Lp^2/3L^1/3 1 fermi / > 0 is anti-gravitating zero point vacuum dark energy, i.e. Kip Thorne's "exotic matter" for traversable wormhole time machines. / < 0 is gravitating zero point vacuum dark matter The non-perturbative BCS energy gap equation for a basic vacuum polarization closed loop with one virtual photon Feynman diagram is: z^2 = ge^-(1/gz) z = (Lp/L)^1/3 and the dimensionless coupling vertex is g^1/2 http://stardrive.org/Jack/nambu.pdf http://stardrive.org/Jack/Lambda1.pdf

  7. Supersymmetric cosmological FRW model and dark energy

    SciTech Connect

    Rosales, J. J.; Tkach, V. I.

    2010-11-15

    In this work we consider a flat cosmological model with a set of fluids in the framework of supersymmetric cosmology. The obtained supersymmetric algebra allowed us to take quantum solutions. It is shown that only in the case of a cosmological constant do we have a condition between the density of dark energy {rho}{sub {Lambda}} and density energy of matter {rho}{sub M}, {rho}{sub {Lambda}>}2{rho}{sub M}.

  8. Effects of the interaction between dark energy and dark matter on cosmological parameters

    SciTech Connect

    He, Jian-Hua; Wang, Bin E-mail: wangb@fudan.edu.cn

    2008-06-15

    We examine the effects of possible phenomenological interactions between dark energy and dark matter on cosmological parameters and their efficiency in solving the coincidence problem. We work with two simple parameterizations of the dynamical dark energy equation of state and the constant dark energy equation of state. Using observational data coming from the new 182 Gold type Ia supernova samples, the shift parameter of the Cosmic Microwave Background given by the three-year Wilkinson Microwave Anisotropy Probe observations and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, we perform a statistical joint analysis of different forms of phenomenological interaction between dark energy and dark matter.

  9. Novel Probes of Gravity and Dark Energy

    SciTech Connect

    Jain, Bhuvnesh; et al.

    2013-09-20

    The discovery of cosmic acceleration has stimulated theorists to consider dark energy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth dark energy -- modified gravity and interactions of dark energy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and spectroscopy and radio observations. In the coming decade, searches for these effects have the potential for discovering fundamental new physics. We discuss how the searches can be carried out using experiments that are already under way or with modest adaptations of existing telescopes or planned experiments. The accompanying paper on the Growth of Cosmic Structure describes complementary tests of gravity with observations of large-scale structure.

  10. Dark Energy and The Dark Matter Relic Abundance

    SciTech Connect

    Rosati, Francesca

    2004-11-17

    Two mechanisms by which the quintessence scalar could enhance the relic abundance of dark matter particles are discussed. These effects can have an impact on supersymmetric candidates for dark matter.

  11. Symmetron dark energy in laboratory experiments.

    PubMed

    Upadhye, Amol

    2013-01-18

    The symmetron scalar field is a matter-coupled dark energy candidate which effectively decouples from matter in high-density regions through a symmetry restoration. We consider a previously unexplored regime, in which the vacuum mass μ~2.4×10(-3) eV of the symmetron is near the dark energy scale, and the matter coupling parameter M~1 TeV is just beyond standard model energies. Such a field will give rise to a fifth force at submillimeter distances which can be probed by short-range gravity experiments. We show that a torsion pendulum experiment such as Eöt-Wash can exclude symmetrons in this regime for all self-couplings λ is < or approximately equal to 7.5.

  12. Report from the Dark Energy Task Force

    NASA Astrophysics Data System (ADS)

    Albrecht, Andreas

    2006-04-01

    Understanding the observed cosmic acceleration is widely ranked among the very most compelling of all outstanding problems in physical science. Many believe that nothing short of a revolution will be required in order to integrate the cosmic acceleration (often attributed to ``dark energy'') with our understanding of fundamental physics. The DETF was formed at the request of DOE, NASA and NSF as a joint subcommittee of the Astronomy and Astrophysics Advisory Committee (AAAC) and the High Energy Physics Advisory Panel (HEPAP) to give advice on optimizing our program of dark energy studies. To this end we have assessed a wide variety of possible techniques and strategies. I will present our main conclusions and discuss their implications.

  13. Interacting dark energy: Dynamical system analysis

    NASA Astrophysics Data System (ADS)

    Golchin, Hanif; Jamali, Sara; Ebrahimi, Esmaeil

    We investigate the impacts of interaction between dark matter (DM) and dark energy (DE) in the context of two DE models, holographic (HDE) and ghost dark energy (GDE). In fact, using the dynamical system analysis, we obtain the cosmological consequence of several interactions, considering all relevant component of universe, i.e. matter (dark and luminous), radiation and DE. Studying the phase space for all interactions in detail, we show the existence of unstable matter-dominated and stable DE-dominated phases. We also show that linear interactions suffer from the absence of standard radiation-dominated epoch. Interestingly, this failure resolved by adding the nonlinear interactions to the models. We find an upper bound for the value of the coupling constant of the interaction between DM and DE as b < 0.57in the case of holographic model, and b < 0.61 in the case of GDE model, to result in a cosmological viable matter-dominated epoch. More specifically, this bound is vital to satisfy instability and deceleration of matter-dominated epoch.

  14. Deformed matter bounce with dark energy epoch

    NASA Astrophysics Data System (ADS)

    Odintsov, S. D.; Oikonomou, V. K.

    2016-09-01

    We extend the loop quantum cosmology matter bounce scenario in order to include a dark energy era, which ends abruptly at a rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario," the Universe is contracting from an initial noncausal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, and thus the model is described by a dark energy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the dark energy era is quintessential as what follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the dark energy era, a rip singularity exists, where the scale factor and Hubble rate diverge; however, the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, first that the ordinary loop quantum cosmology matter bounce evolution stops, thus ending the infinite repetition of the ordinary matter bounce scenario. Second, the fact that both the pressure and the density become complex probably indicates that the description of the cosmic evolution within the theoretical context of loop quantum cosmology ceases to describe the physics of the system and possibly a more fundamental theory of quantum gravity is needed near the would be rip singularity. We describe the qualitative features of the model, and we also investigate how this cosmology could be realized by a viscous fluid in the context of loop quantum cosmology. In addition to this, we show how this deformed model can be realized by a canonical scalar field filled Universe, in the context of loop quantum cosmology. Finally, we demonstrate how the model can be generated by a vacuum F (R ) gravity.

  15. Dark energy simulacrum in nonlinear electrodynamics

    SciTech Connect

    Labun, Lance; Rafelski, Johann

    2010-03-15

    Quasiconstant external fields in nonlinear electromagnetism generate a global contribution proportional to g{sup {mu}{nu}}in the energy-momentum tensor, thus a simulacrum of dark energy. To provide a thorough understanding of the origin and strength of its effects, we undertake a complete theoretical and numerical study of the energy-momentum tensor T{sup {mu}{nu}}for nonlinear electromagnetism. The Euler-Heisenberg nonlinearity due to quantum fluctuations of spinor and scalar matter fields is considered and contrasted with the properties of classical nonlinear Born-Infeld electromagnetism. We address modifications of charged particle kinematics by strong background fields.

  16. A quintessential introduction to dark energy.

    PubMed

    Steinhardt, Paul J

    2003-11-15

    Most of the energy in the Universe consists of some form of dark energy that is gravitationally self-repulsive and that is causing the expansion of the Universe to accelerate. The possible candidates are a vacuum energy density (or, equivalently, a cosmological constant) and quintessence, a time-evolving, spatially inhomogeneous component with negative pressure. In this review, we focus on quintessence and ideas on how it might solve the cosmic coincidence problem, how it might be distinguished observationally from a cosmological constant, and how it may affect the overall cosmic history of the Universe.

  17. New Light on Dark Energy

    NASA Astrophysics Data System (ADS)

    2008-01-01

    observations show that the temperature changes with radius are much steeper than predicted by the currently favoured models, indicating that most of the near-infrared emission emerges from hot material located very close to the star, that is, within one or two times the Earth-Sun distance (1-2 AU). This also implies that dust cannot exist so close to the star, since the strong energy radiated by the star heats and ultimately destroys the dust grains. ESO PR Photo 03/08 ESO PR Photo 03b/08 The Region Around MWC 147 "We have performed detailed numerical simulations to understand these observations and reached the conclusion that we observe not only the outer dust disc, but also measure strong emission from a hot inner gaseous disc. This suggests that the disc is not a passive one, simply reprocessing the light from the star," explained Kraus. "Instead, the disc is active, and we see the material, which is just transported from the outer disc parts towards the forming star." ESO PR Photo 03/08 ESO PR Photo 03c/08 Close-up on MWC 147 The best-fit model is that of a disc extending out to 100 AU, with the star increasing in mass at a rate of seven millionths of a solar mass per year. "Our study demonstrates the power of ESO's VLTI to probe the inner structure of discs around young stars and to reveal how stars reach their final mass," said Stefan Kraus. More Information The authors report their results in a paper in the Astrophysical Journal ("Detection of an inner gaseous component in a Herbig Be star accretion disk: Near- and mid-infrared spectro-interferometry and radiative transfer modeling of MWC 147", by Stefan Kraus, Thomas Preibisch, Keichii Ohnaka").

  18. Simple implementation of general dark energy models

    SciTech Connect

    Bloomfield, Jolyon K.; Pearson, Jonathan A. E-mail: jonathan.pearson@durham.ac.uk

    2014-03-01

    We present a formalism for the numerical implementation of general theories of dark energy, combining the computational simplicity of the equation of state for perturbations approach with the generality of the effective field theory approach. An effective fluid description is employed, based on a general action describing single-scalar field models. The formalism is developed from first principles, and constructed keeping the goal of a simple implementation into CAMB in mind. Benefits of this approach include its straightforward implementation, the generality of the underlying theory, the fact that the evolved variables are physical quantities, and that model-independent phenomenological descriptions may be straightforwardly investigated. We hope this formulation will provide a powerful tool for the comparison of theoretical models of dark energy with observational data.

  19. Strong gravitational lensing and dark energy complementarity

    SciTech Connect

    Linder, Eric V.

    2004-01-21

    In the search for the nature of dark energy most cosmological probes measure simple functions of the expansion rate. While powerful, these all involve roughly the same dependence on the dark energy equation of state parameters, with anticorrelation between its present value w{sub 0} and time variation w{sub a}. Quantities that have instead positive correlation and so a sensitivity direction largely orthogonal to, e.g., distance probes offer the hope of achieving tight constraints through complementarity. Such quantities are found in strong gravitational lensing observations of image separations and time delays. While degeneracy between cosmological parameters prevents full complementarity, strong lensing measurements to 1 percent accuracy can improve equation of state characterization by 15-50 percent. Next generation surveys should provide data on roughly 105 lens systems, though systematic errors will remain challenging.

  20. Scale Dependence of Dark Energy Antigravity

    NASA Astrophysics Data System (ADS)

    Perivolaropoulos, L.

    2002-09-01

    We investigate the effects of negative pressure induced by dark energy (cosmological constant or quintessence) on the dynamics at various astrophysical scales. Negative pressure induces a repulsive term (antigravity) in Newton's law which dominates on large scales. Assuming a value of the cosmological constant consistent with the recent SnIa data we determine the critical scale $r_c$ beyond which antigravity dominates the dynamics ($r_c \\sim 1Mpc $) and discuss some of the dynamical effects implied. We show that dynamically induced mass estimates on the scale of the Local Group and beyond are significantly modified due to negative pressure. We also briefly discuss possible dynamical tests (eg effects on local Hubble flow) that can be applied on relatively small scales (a few $Mpc$) to determine the density and equation of state of dark energy.

  1. A dark energy view of inflation

    SciTech Connect

    Ilic, Stephane; Kunz, Martin; Liddle, Andrew R.; Frieman, Joshua A.; /Fermilab /Chicago U.

    2010-02-01

    Traditionally, inflationary models are analyzed in terms of parameters such as the scalar spectral index n{sub s} and the tensor to scalar ratio r, while dark energy models are studied in terms of the equation of state parameter w. Motivated by the fact that both deal with periods of accelerated expansion, we study the evolution of w during inflation, in order to derive observational constraints on its value during an earlier epoch likely dominated by a dynamic form of dark energy. We find that the cosmic microwave background and large-scale structure data is consistent with w{sub inflation} = -1 and provides an upper limit of 1 + w {le} 0.02. Nonetheless, an exact de Sitter expansion with a constant w = -1 is disfavored since this would result in n{sub s} = 1.

  2. Dark energy from the string axiverse.

    PubMed

    Kamionkowski, Marc; Pradler, Josef; Walker, Devin G E

    2014-12-19

    String theories suggest the existence of a plethora of axionlike fields with masses spread over a huge number of decades. Here, we show that these ideas lend themselves to a model of quintessence with no super-Planckian field excursions and in which all dimensionless numbers are order unity. The scenario addresses the "Why now?" problem-i.e., Why has accelerated expansion begun only recently?-by suggesting that the onset of dark-energy domination occurs randomly with a slowly decreasing probability per unit logarithmic interval in cosmic time. The standard axion potential requires us to postulate a rapid decay of most of the axion fields that do not become dark energy. The need for these decays is averted, though, with the introduction of a slightly modified axion potential. In either case, a universe like ours arises in roughly 1 in 100 universes. The scenario may have a host of observable consequences.

  3. Observational consequences of dark energy decay

    NASA Astrophysics Data System (ADS)

    Pen, Ue-Li; Zhang, Pengjie

    2014-03-01

    We consider the generic scenario of dark energy that arises through the latent heat of a hidden sector first-order cosmological phase transition. This field could account for the extra radiation degree of freedom suggested by the CMB. We present the bubble nucleation solution for the viscous limit. The decay rate of the field is constrained by published kSZ data. This model may provide an explanation of current excess ISW correlations. Cross correlation of current and future surveys can further constrain or test the parameter space. The decay model is plausibly in the observable range and avoids anthropic problems. This class of models is not well constrained by the popular dark energy figure of merit.

  4. The Discovery of Dark Energy: Historical Reflections

    NASA Astrophysics Data System (ADS)

    Crease, Robert P.

    2009-09-01

    The discovery of dark energy by supernovae-culminating in Riess et al. Astron. J. 116, 1998, 1009, and Perlmutter et al. Astrophys. J. 511 1999 565-is likely to become a classic discovery story in the history of science. It exhibits at lease five features that attract the interest of historians: 1) the role of evolving techniques in making a discovery possible; 2) the existence of ambiguities in the discovery process; 3) the existence of ambiguities in discovery announcements; 4) different forms of competition and cooperation; and 5) the way discoveries can open new chapters in science. The dark-energy discovery provides dramatic examples of such features, even apart from the differing memories and judgments that may exist about the events. This article engages in a thought-experiment: what in this discovery story is likely to attract the interest of a science historian looking back on this discovery a hundred years from now?

  5. Interacting dark sector with variable vacuum energy

    NASA Astrophysics Data System (ADS)

    Chimento, Luis P.; Richarte, Martín G.; García, Iván E. Sánchez

    2013-10-01

    We examine a cosmological scenario where dark matter is coupled to a variable vacuum energy while baryons and photons are two decoupled components for a spatially flat Friedmann-Robertson-Walker spacetime. We apply the χ2 method to the updated observational Hubble data for constraining the cosmological parameters and analyze the amount of dark energy in the radiation era. We show that our model fulfills the severe bound of Ωx(z≃1100)<0.009 at the 2σ level, so it is consistent with the recent analysis that includes cosmic microwave background anisotropy measurements from the Planck survey, the Atacama Cosmology Telescope, and the South Pole Telescope along with the future constraints achievable by the Euclid and CMBPol experiments, and fulfills the stringent bound Ωx(z≃1010)<0.04 at the 2σ level in the big-bang nucleosynthesis epoch.

  6. Dark energy domination in the Virgocentric flow

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Karachentsev, I. D.; Nasonova, O. G.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.

    2010-09-01

    Context. The standard ΛCDM cosmological model implies that all celestial bodies are embedded in a perfectly uniform dark energy background, represented by Einstein's cosmological constant, and experience its repulsive antigravity action. Aims: Can dark energy have strong dynamical effects on small cosmic scales as well as globally? Continuing our efforts to clarify this question, we now focus on the Virgo Cluster and the flow of expansion around it. Methods: We interpret the Hubble diagram from a new database of velocities and distances of galaxies in the cluster and its environment, using a nonlinear analytical model, which incorporates the antigravity force in terms of Newtonian mechanics. The key parameter is the zero-gravity radius, the distance at which gravity and antigravity are in balance. Results: 1. The interplay between the gravity of the cluster and the antigravity of the dark energy background determines the kinematical structure of the system and controls its evolution. 2. The gravity dominates the quasi-stationary bound cluster, while the antigravity controls the Virgocentric flow, bringing order and regularity to the flow, which reaches linearity and the global Hubble rate at distances ⪆15 Mpc. 3. The cluster and the flow form a system similar to the Local Group and its outflow. In the velocity-distance diagram, the cluster-flow structure reproduces the group-flow structure with a scaling factor of about 10; the zero-gravity radius for the cluster system is also 10 times larger. Conclusions: The phase and dynamical similarity of the systems on the scales of 1-30 Mpc suggests that a two-component pattern may be universal for groups and clusters: a quasi-stationary bound central component and an expanding outflow around it, caused by the nonlinear gravity-antigravity interplay with the dark energy dominating in the flow component.

  7. Dynamical dark energy: Current constraints and forecasts

    NASA Astrophysics Data System (ADS)

    Upadhye, Amol; Ishak, Mustapha; Steinhardt, Paul J.

    2005-09-01

    We consider how well the dark energy equation of state w as a function of redshift z will be measured using current and anticipated experiments. We use a procedure which takes fair account of the uncertainties in the functional dependence of w on z, as well as the parameter degeneracies, and avoids the use of strong prior constraints. We apply the procedure to current data from the Wilkinson Microwave Anisotropy Probe, Sloan Digital Sky Survey, and the supernova searches, and obtain results that are consistent with other analyses using different combinations of data sets. The effects of systematic experimental errors and variations in the analysis technique are discussed. Next, we use the same procedure to forecast the dark energy constraints achievable by the end of the decade, assuming 8 years of Wilkinson Microwave Anisotropy Probe data and realistic projections for ground-based measurements of supernovae and weak lensing. We find the 2σ constraints on the current value of w to be Δw0(2σ)=0.20, and on dw/dz (between z=0 and z=1) to be Δw1(2σ)=0.37. Finally, we compare these limits to other projections in the literature. Most show only a modest improvement; others show a more substantial improvement, but there are serious concerns about systematics. The remaining uncertainty still allows a significant span of competing dark energy models. Most likely, new kinds of measurements, or experiments more sophisticated than those currently planned, are needed to reveal the true nature of dark energy.

  8. Working Group Report: Dark Energy and CMB

    SciTech Connect

    Dodelson, S.; Honscheid, K.; Abazajian, K.; Carlstrom, J.; Huterer, D.; Jain, B.; Kim, A.; Kirkby, D.; Lee, A.; Padmanabhan, N.; Rhodes, J.; Weinberg, D.

    2013-09-20

    The American Physical Society's Division of Particles and Fields initiated a long-term planning exercise over 2012-13, with the goal of developing the community's long term aspirations. The sub-group "Dark Energy and CMB" prepared a series of papers explaining and highlighting the physics that will be studied with large galaxy surveys and cosmic microwave background experiments. This paper summarizes the findings of the other papers, all of which have been submitted jointly to the arXiv.

  9. Holographic dark energy model with Hubble horizon as an IR cut-off

    SciTech Connect

    Xu, Lixin

    2009-09-01

    The main task of this paper is to realize a cosmic observational compatible universe in the framework of holographic dark energy model when the Hubble horizon H is taken as the role of an IR cut-off. When the model parameter c of a time variable cosmological constant (CC) Λ(t) = 3c{sup 2}H{sup 2}(t) becomes time or scale dependent, an extra term enters in the effective equation of sate (EoS) of the vacuum energy w{sup eff}{sub Λ} = −c{sup 2}−dln c{sup 2}/3dln a. This extra term can make the effective EoS of time variable CC cross the cosmological boundary and be phantom-like at present. For the lack of a first principle and fundamental physics theory to obtain the form c{sup 2}, we give a simple parameterized form of c{sup 2} as an example. Then the model is confronted by the cosmic observations including SN Ia, BAO and CMB shift parameter R. The result shows that the model is consistent with cosmic observations.

  10. Using atom interferometry to detect dark energy

    NASA Astrophysics Data System (ADS)

    Burrage, Clare; Copeland, Edmund J.

    2016-04-01

    We review the tantalising prospect that the first evidence for the dark energy driving the observed acceleration of the universe on giga-parsec scales may be found through metre scale laboratory-based atom interferometry experiments. To do that, we first introduce the idea that scalar fields could be responsible for dark energy and show that in order to be compatible with fifth force constraints, these fields must have a screening mechanism which hides their effects from us within the solar system. Particular emphasis is placed on one such screening mechanism known as the chameleon effect where the field's mass becomes dependent on the environment. The way the field behaves in the presence of a spherical source is determined and we then go on to show how in the presence of the kind of high vacuum associated with atom interferometry experiments, and when the test particle is an atom, it is possible to use the associated interference pattern to place constraints on the acceleration due to the fifth force of the chameleon field - this has already been used to rule out large regions of the chameleon parameter space and maybe one day will be able to detect the force due to the dark energy field in the laboratory.

  11. 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.

  12. Evolving dark energy with w not = -1.

    PubMed

    Hall, Lawrence J; Nomura, Yasunori; Oliver, Steven J

    2005-09-30

    Theories of evolving quintessence are constructed that generically lead to deviations from the w = -1 prediction of nonevolving dark energy. The small mass scale that governs evolution, m(phi) approximately = 10(-33) eV, is radiatively stable, and the "Why now?" problem is solved. These results rest on seesaw cosmology: Fundamental physics and cosmology can be broadly understood from only two mass scales, the weak scale nu and the Planck scale M. Requiring a scale of dark energy rho(DE)(1/4) governed by nu2/M and a radiatively stable evolution rate m(phi) given by nu4/M3 leads to a distinctive form for the equation of state w(z). Dark energy resides in the potential of a hidden axion field that is generated by a new QCD-like force that gets strong at the scale lambda approximately = nu2/M approximately = rho(DE)(1/4). The evolution rate is given by a second seesaw that leads to the axion mass m(phi) approximately = lambda2/f, with f approximately = M.

  13. Evolving Dark Energy with w =/ -1

    SciTech Connect

    Hall, Lawrence J.; Nomura, Yasunori; Oliver, Steven J.

    2005-03-31

    Theories of evolving quintessence are constructed that generically lead to deviations from the w = -1 prediction of non-evolving dark energy. The small mass scale that governs evolution, m_\\phi \\approx 10^-33 eV, is radiatively stable, and the"Why Now?'' problem is solved. These results rest crucially on seesaw cosmology: in broad outline, fundamental physics and cosmology can be understood from only two mass scales, the weak scale, v, and the Planck scale, M. Requiring a scale of dark energy \\rho_DE^1/4 governed by v^2/M, and a radiatively stable evolution rate m_\\phi given by v^4/M^3, leads to a distinctive form for the equation of state w(z) that follows from a cosine quintessence potential. An explicit hidden axion model is constructed. Dark energy resides in the potential of the axion field which is generated by a new QCD-like force that gets strong at the scale \\Lambda \\approx v^2/M \\approx \\rho_DE^1/4. The evolution rate is given by a second seesaw that leads to the axion mass, m_\\phi \\approx \\Lambda^2/f, with f \\approx M.

  14. Holographic dark energy with cosmological constant

    SciTech Connect

    Hu, Yazhou; Li, Nan; Zhang, Zhenhui; Li, Miao E-mail: mli@itp.ac.cn E-mail: zhangzhh@mail.ustc.edu.cn

    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 using 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<Ω{sub Λ0}<0.68 and correspondingly 0.04<Ω{sub hde0}<0.79, implying at present there is considerable degeneracy between the holographic dark energy and cosmological constant components in the ΛHDE model.

  15. Initial conditions for the Galileon dark energy

    NASA Astrophysics Data System (ADS)

    Germani, Cristiano

    2017-03-01

    Galileon models are among the most appealing candidates for Dark Energy. The reason is twofold: classically, they provide a tracking solution leading to an almost DeSitter space starting from very generic initial conditions in the deep radiation era. The second reason is the standard lore that Galileons are quantum mechanically stable. The latter property is certainly true in flat space-time, thanks to the non-renormalisation theorems of Galilean coupling constants. However, in a cosmological background, we show that quantum effects might dominate the classical trajectory. Assuming the radiation era to last at least up to the electroweak phase transition, the trajectory with initial conditions sitting on the tracker is ruled out. On the other hand, it is always possible to find a sub-space of initial conditions such that the dark energy solution approaches stably the tracker at late times. Fixing the value of initial conditions that best fit current data, and assuming that the Galileon effective theory is valid up to the beginning of the radiation epoch, we found that the reheating temperature of the universe cannot be larger than 108 GeV. Reversing the argument, if dark energy will turn out to be in form of Galileons, the bounds by EUCLID on the initial conditions for these models will also be a bound on the reheating temperature of our Universe.

  16. Redshift drift exploration for interacting dark energy

    NASA Astrophysics Data System (ADS)

    Geng, Jia-Jia; Li, Yun-He; Zhang, Jing-Fei; Zhang, Xin

    2015-08-01

    By detecting redshift drift in the spectra of the Lyman- forest of distant quasars, the Sandage-Loeb (SL) test directly measures the expansion of the universe, covering the "redshift desert" of . Thus this method is definitely an important supplement to the other geometric measurements and will play a crucial role in cosmological constraints. In this paper, we quantify the ability of the SL test signal by a CODEX-like spectrograph for constraining interacting dark energy. Four typical interacting dark energy models are considered: (i) , (ii) , (iii) , and (iv) . The results show that for all the considered interacting dark energy models, relative to the current joint SN BAO CMB observations, the constraints on and would be improved by about 60 and 30-40 %, while the constraints on w and would be slightly improved, with a 30-year observation of the SL test. We also explore the impact of the SL test on future joint geometric observations. In this analysis, we take the model with as an example, and we simulate future SN and BAO data based on the space-based project WFIRST. We find that with the future geometric constraints, the redshift drift observations would help break the geometric degeneracies in a meaningful way, thus the measurement precisions of , , w, and could be substantially improved using future probes.

  17. Dark Energy from Violation of Energy Conservation.

    PubMed

    Josset, Thibaut; Perez, Alejandro; Sudarsky, Daniel

    2017-01-13

    In this Letter, we consider the possibility of reconciling metric theories of gravitation with a violation of the conservation of energy-momentum. Under some circumstances, this can be achieved in the context of unimodular gravity, and it leads to the emergence of an effective cosmological constant in Einstein's equation. We specifically investigate two potential sources of energy nonconservation-nonunitary modifications of quantum mechanics and phenomenological models motivated by quantum gravity theories with spacetime discreteness at the Planck scale-and show that such locally negligible phenomena can nevertheless become relevant at the cosmological scale.

  18. Dark Energy from Violation of Energy Conservation

    NASA Astrophysics Data System (ADS)

    Josset, Thibaut; Perez, Alejandro; Sudarsky, Daniel

    2017-01-01

    In this Letter, we consider the possibility of reconciling metric theories of gravitation with a violation of the conservation of energy-momentum. Under some circumstances, this can be achieved in the context of unimodular gravity, and it leads to the emergence of an effective cosmological constant in Einstein's equation. We specifically investigate two potential sources of energy nonconservation—nonunitary modifications of quantum mechanics and phenomenological models motivated by quantum gravity theories with spacetime discreteness at the Planck scale—and show that such locally negligible phenomena can nevertheless become relevant at the cosmological scale.

  19. Dark Matter and Energy as Antimatter

    NASA Astrophysics Data System (ADS)

    Lundberg, Wayne

    2005-04-01

    A new interpretation of dark matter observations via gravitational lensing through galaxy clusters is proposed. Gravitational lensing studies of SDSS J1004+4112 by Williams and Saha (astro-ph/0412445) indicate that any dark matter contribution to lensing is smoothly distributed in space. All particle theories (i.e WIMPs) which propose to explain dark matter inevitably yield gravitational clumping. Note that string theory requires that matter at radii, R, less than the Planck scale, α', is equivalent to matter at distance D=α'/R. The proposed interpretation involves antimatter existing within anti-deSitter spaces to explain the unexpected smoothness. This proposal asserts that a (non-Hawking) black hole exists with an AdS space at its singularity. Antimatter interactions also explain Galactic Annihilation Fountain(s) and similar observed phenomena. Non-temporal matter is thereby defined as matter which exists in 4-space, either advanced or retarded wrt the present. A `radical' form of cosmology is then developed in which the curvature tensor of Einstein's general relativity is treated as complex. FRW cosmology plus dark matter and energy results. Theories regarding the black hole ``end state'' and Seiberg's chronology protection lend support to this approach. Previous work (http://www-astro-theory.fnal.gov/Conferences/cosmo02/poster/lundberg.pdfhttp://www-astro-theory.fnal.gov/Conferences/cosmo02/poster/lundberg.pdf) to establish the architecture of a comprehensive theory is thus modified.

  20. Constraints on the coupling between dark energy and dark matter from CMB data

    SciTech Connect

    Murgia, R.; Gariazzo, S.; Fornengo, N. E-mail: gariazzo@to.infn.it

    2016-04-01

    We investigate a phenomenological non-gravitational coupling between dark energy and dark matter, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to dark energy or the opposite. The models are constrained by a whole host of updated cosmological data: cosmic microwave background temperature anisotropies and polarization, high-redshift supernovae, baryon acoustic oscillations, redshift space distortions and gravitational lensing. Both models are found to be compatible with all cosmological observables, but in the case where dark matter decays into dark energy, the tension with the independent determinations of H{sub 0} and σ{sub 8}, already present for standard cosmology, increases: this model in fact predicts lower H{sub 0} and higher σ{sub 8}, mostly as a consequence of the higher amount of dark matter at early times, leading to a stronger clustering during the evolution. Instead, when dark matter is fed by dark energy, the reconstructed values of H{sub 0} and σ{sub 8} nicely agree with their local determinations, with a full reconciliation between high- and low-redshift observations. A non-zero coupling between dark energy and dark matter, with an energy flow from the former to the latter, appears therefore to be in better agreement with cosmological data.

  1. Study of some cosmological parameters for interacting new holographic dark energy model in f(T) gravity

    NASA Astrophysics Data System (ADS)

    Ranjit, Chayan; Rudra, Prabir

    2016-10-01

    The present work is based on the idea of an interacting framework of new holographic dark energy (HDE) with cold dark matter in the background of f(T) gravity. Here, we have considered the flat modified Friedmann universe for f(T) gravity which is filled with new HDE and dark matter. We have derived some cosmological parameters like deceleration parameter, equation of state (EoS) parameter, state-finder parameters, cosmographic parameters, Om parameter and graphically investigated the nature of these parameters for the above mentioned interacting scenario. The results are found to be consistent with the accelerating universe. Also, we have graphically investigated the trajectories in ω-ω‧ plane for different values of the interacting parameter and explored the freezing region and thawing region in ω-ω‧ plane. Finally, we have analyzed the stability of this model.

  2. The ASY-EOS experiment at GSI: investigating symmetry energy at supra-saturation densities

    NASA Astrophysics Data System (ADS)

    Russotto, P.; Chartier, M.; Cozma, M. D.; De Filippo, E.; Le Fèvre, A.; Gannon, S.; Gašparić, I.; Kiš, M.; Kupny, S.; Leifels, Y.; Lemmon, R. C.; Li, Q.; Łukasik, J.; Marini, P.; Pawłowski, P.; Santoro, S.; Trautmann, W.; Veselsky, M.; Acosta, L.; Adamczyk, M.; Al-Ajlan, A.; Al-Garawi, M.; Al-Homaidhi, S.; Amorini, F.; Auditore, L.; Aumann, T.; Ayyad, Y.; Baran, V.; Basrak, Z.; Bassini, R.; Benlliure, J.; Boiano, C.; Boisjoli, M.; Boretzky, K.; Brzychczyk, J.; Budzanowski, A.; Cardella, G.; Cammarata, P.; Chajecki, Z.; Chbihi, A.; Colonna, M.; Czech, B.; Di Toro, M.; Famiano, M.; Greco, V.; Grassi, L.; Guazzoni, C.; Guazzoni, P.; Heil, M.; Heilborn, L.; Introzzi, R.; Isobe, T.; Kezzar, K.; Krasznahorkay, A.; Kurz, N.; La Guidara, E.; Lanzalone, G.; Lasko, P.; Lombardo, I.; Lynch, W. G.; Matthews, Z.; May, L.; Minniti, T.; Mostazo, M.; Pagano, A.; Papa, M.; Pirrone, S.; Pleskac, R.; Politi, G.; Porto, F.; Reifarth, R.; Reisdorf, W.; Riccio, F.; Rizzo, F.; Rosato, E.; Rossi, D.; Simon, H.; Skwirczynska, I.; Sosin, Z.; Stuhl, L.; Trifirò, A.; Trimarchi, M.; Tsang, M. B.; Verde, G.; Vigilante, M.; Wieloch, A.; Wigg, P.; Wolter, H. H.; Wu, P.; Yennello, S.; Zambon, P.; Zetta, L.; Zoric, M.

    2014-03-01

    The elliptic-flow ratio of neutrons with respect to protons or light complex particles in reactions of heavy-ions at pre-relativistic energies has been proposed as an observable sensitive to the strength of the symmetry term of the nuclear equation of state at supra-saturation densities. The results obtained from the existing FOPI/LAND data for 197Au+197Au collisions at 400 MeV/nucleon in comparison with the UrQMD model simulations favoured a moderately soft symmetry term, but suffer from a considerable statistical uncertainty. These results have been confirmed by an independent analysis based on the Tübingen QMD simulations. In order to obtain an improved data set for Au+Au collisions and to extend the study to other systems, a new experiment was carried out at the GSI laboratory by the ASY-EOS collaboration. The present status of the data analysis is reported

  3. Covariant generalized holographic dark energy and accelerating universe

    NASA Astrophysics Data System (ADS)

    Nojiri, Shin'ichi; Odintsov, S. D.

    2017-08-01

    We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F( R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy.

  4. Dark energy and the hierarchy problem

    NASA Astrophysics Data System (ADS)

    Chen, Pisin

    2009-03-01

    The well-known hierarchy between the Planck scale (˜10GeV) and the TeV scale, namely a ratio of ˜10 between the two, is coincidentally repeated in a inverted order between the TeV scale and the dark energy scale at ˜10eV implied by the observations. We argue that this is not a numerical coincidence. The same brane-world setups to address the first hierarchy problem may also in principle address this second hierarchy issue. Specifically, we consider supersymmetry in the bulk and its breaking on the brane and resort to the Casimir energy induced by the bulk graviton-gravitino mass-shift on the brane as the dark energy. For the ADD model we found that our notion is sensible only if the number of extra dimension n=2. We extend our study to the Randall-Sundrum model. Invoking the chirality-flip on the boundaries for SUSY-breaking, the zero-mode gravitino contribution to the Casimir energy does give rise to the double hierarchy. Unfortunately since the higher Kaluza-Klein modes acquire relative mass-shifts at the TeV level, the zero-mode contribution to Casimir energy is overshadowed.

  5. Dark Energy and the Hierarchy Problem

    SciTech Connect

    Chen, Pisin

    2006-12-06

    The well-known hierarchy between the Planck scale (>> 1019GeV) and the TeV scale, namely a ratio of {approx} 10{sup 16} between the two, is coincidentally repeated in a inverted order between the TeV scale and the dark energy scale at {approx} 10{sup -3} eV implied by the observations. We argue that this is not a numerical coincidence. The same brane-world setups to address the first hierarchy problem may also in principle address this second hierarchy issue. Specifically, we consider supersymmetry in the bulk and its breaking on the brane and resort to the Casimir energy induced by the bulk graviton-gravitino mass-shift on the brane as the dark energy. For the ADD model we found that our notion is sensible only if the number of extra dimension n = 2. We extend our study to the Randall-Sundrum model. Invoking the chirality-flip on the boundaries for SUSY-breaking, the zero-mode gravitino contribution to the Casimir energy does give rise to the double hierarchy. Unfortunately since the higher Kaluza-Klein modes acquire relative mass-shifts at the TeV level, the zero-mode contribution to Casimir energy is overshadowed.

  6. Atom-Interferometry Constraints on Dark Energy

    NASA Astrophysics Data System (ADS)

    Mueller, Holger

    2016-03-01

    If dark energy is a light scalar field, it might interact with normal matter. The interactions, however, are suppressed in some leading models, which are thus compatible with current cosmological observations as well as solar-system and laboratory studies. Such suppression typically relies on the scalar's interaction with macroscopic amounts of ordinary matter, but can be bypassed by studying the interaction with individual particles. Using an atom interferometer, we have placed tight constraints on so-called chameleon models, ruling out interaction parameters βM > 4 ×104 . This limit is improved by 2.5 orders of magnitude relative to previous experiments. We have already increased the sensitivity of our interferometer hundredfold and are expecting a new constraint soon. Purpose-built experiments in the lab or on the international space station will completely close the gap and rule out out chameleons and other theories, such as axions, dark photons, symmetrons or f (R) gravity.

  7. Interacting vacuum energy in the dark sector

    SciTech Connect

    Chimento, L. P.; Carneiro, S.

    2015-03-26

    We analyse three cosmological scenarios with interaction in the dark sector, which are particular cases of a general expression for the energy flux from vacuum to matter. In the first case the interaction leads to a transition from an unstable de Sitter phase to a radiation dominated universe, avoiding in this way the initial singularity. In the second case the interaction gives rise to a slow-roll power-law inflation. Finally, the third scenario is a concordance model for the late-time universe, with the vacuum term decaying into cold dark matter. We identify the physics behind these forms of interaction and show that they can be described as particular types of the modified Chaplygin gas.

  8. Interacting vacuum energy in the dark sector

    NASA Astrophysics Data System (ADS)

    Chimento, L. P.; Carneiro, S.

    2015-03-01

    We analyse three cosmological scenarios with interaction in the dark sector, which are particular cases of a general expression for the energy flux from vacuum to matter. In the first case the interaction leads to a transition from an unstable de Sitter phase to a radiation dominated universe, avoiding in this way the initial singularity. In the second case the interaction gives rise to a slow-roll power-law inflation. Finally, the third scenario is a concordance model for the late-time universe, with the vacuum term decaying into cold dark matter. We identify the physics behind these forms of interaction and show that they can be described as particular types of the modified Chaplygin gas.

  9. Sub-horizon evolution of cold dark matter perturbations through dark matter-dark energy equivalence epoch

    SciTech Connect

    Piattella, O.F.; Martins, D.L.A.; Casarini, L. E-mail: denilsonluizm@gmail.com

    2014-10-01

    We consider a cosmological model of the late universe constituted by standard cold dark matter plus a dark energy component with constant equation of state w and constant effective speed of sound. By neglecting fluctuations in the dark energy component, we obtain an equation describing the evolution of sub-horizon cold dark matter perturbations through the epoch of dark matter-dark energy equality. We explore its analytic solutions and calculate an exact w-dependent correction for the dark matter growth function, logarithmic growth function and growth index parameter through the epoch considered. We test our analytic approximation with the numerical solution and find that the discrepancy is less than 1% for 0k = during the cosmic evolution up to a = 100.

  10. Evidence for interacting dark energy from BOSS

    NASA Astrophysics Data System (ADS)

    Ferreira, Elisa G. M.; Quintin, Jerome; Costa, André A.; Abdalla, E.; Wang, Bin

    2017-02-01

    The result presented by the BOSS-SDSS Collaboration measuring the baryon acoustic oscillations of the Lyman-alpha forest from high-redshift quasars indicates a 2.5 σ departure from the standard Λ -cold-dark-matter model. This is the first time that the evolution of dark energy at high redshifts has been measured, and the current results cannot be explained by simple generalizations of the cosmological constant. We show here that a simple phenomenological interaction in the dark sector provides a good explanation for this deviation, naturally accommodating the Hubble parameter obtained by BOSS, H (z =2.34 )=222 ±7 km s-1 Mpc-1 . By performing a global fit of the parameters with the inclusion of this new data set together with the Planck data for the interacting model, we are able to show that some interacting models have constraints for H (2.34 ) and DA(2.34 ) that are compatible with the ones obtained by the BOSS Collaboration, showing a better concordance than Λ CDM . We also show that the interacting models that have a small positive coupling constant, which helps alleviate the coincidence problem, are compatible with the cosmological observations. Adding the likelihood of these new baryon acoustic oscillations data shows an improvement in the global fit, although it is not statistically significant. The coupling constant could not be fully constrained by the data sets used, but the dark energy equation of state shows a slight preference for a value different from a cosmological constant.

  11. Present and future evidence for evolving dark energy

    SciTech Connect

    Liddle, Andrew R.; Mukherjee, Pia; Parkinson, David; Wang Yun

    2006-12-15

    We compute the Bayesian evidences for one- and two-parameter models of evolving dark energy, and compare them to the evidence for a cosmological constant, using current data from Type Ia supernova, baryon acoustic oscillations, and the cosmic microwave background. We use only distance information, ignoring dark energy perturbations. We find that, under various priors on the dark energy parameters, {lambda}CDM is currently favored as compared to the dark energy models. We consider the parameter constraints that arise under Bayesian model averaging, and discuss the implication of our results for future dark energy projects seeking to detect dark energy evolution. The model selection approach complements and extends the figure-of-merit approach of the Dark Energy Task Force in assessing future experiments, and suggests a significantly-modified interpretation of that statistic.

  12. Stability analysis of a holographic dark energy model

    NASA Astrophysics Data System (ADS)

    Banerjee, Narayan; Roy, Nandan

    2015-08-01

    The stability of interacting holographic dark energy model is discussed. It is found that for some class of the rate of interaction between dark matter and dark energy, the system has a natural solution where the universe had been decelerating in the beginning but finally settles down to an accelerated phase of expansion.

  13. Relation Between the Dark Energy Density and Temperature

    NASA Astrophysics Data System (ADS)

    Saadat, H.

    2011-01-01

    In this article we investigate the relation between the temperature and density of the dark energy. We find that the temperature of the dark universe is proportional to the inverse of dark energy density. Also we discuss some values of the important parameters of the theory.

  14. Decaying Higgs Fields and Cosmological Dark Energy

    NASA Astrophysics Data System (ADS)

    Patla, B.; Nemiroff, R. J.

    2005-05-01

    The observed dark energy in the universe might give particles inertial mass. We investigate one realization of this idea, that the dark energy field might be a decayed scalar component of a scalar field in the early universe that creates inertial mass through spontaneous symmetry breaking, e.g. a Higgs field. To investigate this possibility, the cosmological Friedmann equation of energy balance is augmented in a standard way to incorporate a minimally coupled cosmological Higgs. For epochs where the expansion of the universe is driven by matter and radiation and not the scalar field, the observed hidden nature of the Higgs field can be codified into a single differential equation that we call the ``hidden higgs" condition. The resulting differential equation is solved for the time dependant scalar field and a simple and interesting solution is found analytically. Such a Higgs field decays from Planck scale energies rapidly and approximately exponentially from onset, leaving only the initially negligible constant term of the potential as a final cosmological constant. Such evolution replaces the hierarchy problem with the problem of explaining why such evolution is physically justified, leaving the coincidence problem still unresolved.

  15. Cosmological explorations: From primordial non-Gaussianity to dynamical dark energy

    NASA Astrophysics Data System (ADS)

    Sarkar, Devdeep

    Future-generation astronomical observations are expected to significantly improve our understanding of the nature of the constituents of the universe and the inherent mechanisms that led the universe to its current state. In this report I address the heart of some of these projects. I discuss the effect of gravitational lensing on the measurement of the CMB bispectrum, which is a well-known probe of the non-Gaussianity of primordial perturbations. In the context detecting gravity waves, which can open up a unique window to study the physics driving inflation, I discuss the possibility of such a detection through its effect on the cosmic shear. I then focus on the measurements of the Dark Energy Equation of State (EOS) from a combination of future-generation surveys. To this end, I first try to motivate a model-independent approach to constrain the EOS and emphasize the importance of a high-precision measurement of the Hubble constant in this context. I also discuss the consequences of the fact that the estimates of the EOS are intrinsically skewed toward the negative. Finally, I concentrate on two potential sources of uncertainties in the EOS: systematics incorporated due to the lensing of supernova (SN), and systematics based on the the existence of two different SN populations.

  16. A divergence-free parametrization of deceleration parameter for scalar field dark energy

    NASA Astrophysics Data System (ADS)

    Al Mamon, Abdulla; Das, Sudipta

    2016-01-01

    In this paper, we have considered a spatially flat FRW universe filled with pressureless matter and dark energy (DE). We have considered a phenomenological parametrization of the deceleration parameter q(z) and from this, we have reconstructed the equation-of-state (EoS) for DE ωϕ(z). This divergence-free parametrization of the deceleration parameter is inspired from one of the most popular parametrization of the DE EoS given by Barboza and Alcaniz [see E. M. Barboza and J. S. Alcaniz, Phys. Lett. B 666 (2008) 415]. Using the combination of datasets (Type Ia Supernova (SN Ia) + Hubble + baryonic acoustic oscillations/cosmic microwave background (BAO/CMB)), we have constrained the transition redshift zt (at which the universe switches from a decelerating to an accelerating phase) and have found the best fit value of zt. We have also compared the reconstructed results of q(z) and ωϕ(z) and have found that the results are compatible with a ΛCDM universe if we consider SN Ia + Hubble data, but inclusion of BAO/CMB data makes q(z) and ωϕ(z) incompatible with ΛCDM model. The potential term for the present toy model is found to be functionally similar to a Higgs potential.

  17. Eos Chasma

    NASA Image and Video Library

    2010-06-08

    At eastern end of Valles Marineris is Eos Chasma. In Eos, the canyon system transitions into a region of chaos and then into major outflow channels. This image from NASA 2001 Mars Odyssey shows the transition into chaos.

  18. Dark Energy and Key Physical Parameters of Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Bisnovatyi-Kogan, G. S.

    We discuss the physics of clusters of galaxies embedded in the cosmic dark energy background and show that 1) the halo cut-off radius of a cluster like the Virgo cluster is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the dark energy antigravity; 2) the halo averaged density is equal to two densities of dark energy; 3) the halo edge (cut-off) density is the dark energy density with a numerical factor of the unity order slightly depending on the halo profile.

  19. Matter sourced anisotropic stress for dark energy

    NASA Astrophysics Data System (ADS)

    Chang, Baorong; Lu, Jianbo; Xu, Lixin

    2014-11-01

    Usually a dark energy as a perfect fluid is characterized by the ratio of pressure to energy density (w =p /ρ ) and the ratio of their perturbations in its rest frame (cs2=δ p /δ ρ ). However, a dark energy would have other characteristics beyond its equation of state and the effective speed of sound. Here the extra property is the anisotropic stress sourced by matter as a simple extension to the perfect fluid model. At the background level, this anisotropic stress is zero with respect to the cosmological principle, but not at the first-order perturbation. We tested the viability of the existence of this kind of anisotropic stress by using the currently available cosmic observations through the geometrical and dynamical measurements. Using the Markov-chain Monte Carlo method, we found that the upper bounds on the anisotropic stress which enters into the summation of the Newtonian potentials should be of the order O (1 0-3)Δm . We did not find any strong evidence for the existence of this matter-sourced anisotropic stress, even in the 1 σ region.

  20. Imperfect dark energy from kinetic gravity braiding

    SciTech Connect

    Deffayet, Cédric; Pujolàs, Oriol; Sawicki, Ignacy; Vikman, Alexander E-mail: oriol.pujolas@cern.ch E-mail: alexander.vikman@nyu.edu

    2010-10-01

    We introduce a large class of scalar-tensor models with interactions containing the second derivatives of the scalar field but not leading to additional degrees of freedom. These models exhibit peculiar features, such as an essential mixing of scalar and tensor kinetic terms, which we have named kinetic braiding. This braiding causes the scalar stress tensor to deviate from the perfect-fluid form. Cosmology in these models possesses a rich phenomenology, even in the limit where the scalar is an exact Goldstone boson. Generically, there are attractor solutions where the scalar monitors the behaviour of external matter. Because of the kinetic braiding, the position of the attractor depends both on the form of the Lagrangian and on the external energy density. The late-time asymptotic of these cosmologies is a de Sitter state. The scalar can exhibit phantom behaviour and is able to cross the phantom divide with neither ghosts nor gradient instabilities. These features provide a new class of models for Dark Energy. As an example, we study in detail a simple one-parameter model. The possible observational signatures of this model include a sizeable Early Dark Energy and a specific equation of state evolving into the final de-Sitter state from a healthy phantom regime.

  1. The Dark Energy Survey CCD imager design

    SciTech Connect

    Cease, H.; DePoy, D.; Diehl, H.T.; Estrada, J.; Flaugher, B.; Guarino, V.; Kuk, K.; Kuhlmann, S.; Schultz, K.; Schmitt, R.L.; Stefanik, A.; /Fermilab /Ohio State U. /Argonne

    2008-06-01

    The Dark Energy Survey is planning to use a 3 sq. deg. camera that houses a {approx} 0.5m diameter focal plane of 62 2kx4k CCDs. The camera vessel including the optical window cell, focal plate, focal plate mounts, cooling system and thermal controls is described. As part of the development of the mechanical and cooling design, a full scale prototype camera vessel has been constructed and is now being used for multi-CCD readout tests. Results from this prototype camera are described.

  2. Probing dark energy with atom interferometry

    SciTech Connect

    Burrage, Clare; Copeland, Edmund J.; Hinds, E.A. E-mail: Edmund.Copeland@nottingham.ac.uk

    2015-03-01

    Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry.

  3. Geometrical Constraints on Dark Energy Models

    NASA Astrophysics Data System (ADS)

    Lazkoz, Ruth

    2007-11-01

    This contribution intends to give a pedagogical introduction to the topic of dark energy (the mysterious agent supposed to drive the observed late time acceleration of the Universe) and to various observational tests which require only assumptions on the geometry of the Universe. Those tests are the supernovae luminosity, the CMB shift, the direct Hubble data, and the baryon acoustic oscillations test. An historical overview of Cosmology is followed by some generalities on FRW spacetimes (the best large-scale description of the Universe), and then the test themselves are discussed. A convenient section on statistical inference is included as well.

  4. Probing dark energy with atom interferometry

    NASA Astrophysics Data System (ADS)

    Burrage, Clare; Copeland, Edmund J.; Hinds, E. A.

    2015-03-01

    Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry.

  5. Holographic Ricci dark energy as running vacuum

    NASA Astrophysics Data System (ADS)

    George, Paxy; Mathew, Titus K.

    2016-04-01

    Holographic Ricci dark energy (DE) that has been proposed ago has faced problems of future singularity. In the present work, we consider the Ricci DE with an additive constant in its density as running vacuum energy. We have analytically solved the Friedmann equations and also the role played by the general conservation law followed by the cosmic components together. We have shown that the running vacuum energy status of the Ricci DE helps to remove the possible future singularity in the model. The additive constant in the density of the running vacuum played an important role, such that, without that, the model predicts either eternal deceleration or eternal acceleration. But along with the additive constant, equivalent to a cosmological constant, the model predicts a late time acceleration in the expansion of the universe, and in the far future of the evolution it tends to de Sitter universe.

  6. Dark energy from primordial inflationary quantum fluctuations.

    PubMed

    Ringeval, Christophe; Suyama, Teruaki; Takahashi, Tomo; Yamaguchi, Masahide; Yokoyama, Shuichiro

    2010-09-17

    We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the Universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale.

  7. Dark energy and key physical parameters of clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Bisnovatyi-Kogan, G. S.; Chernin, A. D.

    2012-04-01

    We study physics of clusters of galaxies embedded in the cosmic dark energy background. Under the assumption that dark energy is described by the cosmological constant, we show that the dynamical effects of dark energy are strong in clusters like the Virgo cluster. Specifically, the key physical parameters of the dark mater halos in clusters are determined by dark energy: (1) the halo cut-off radius is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the dark energy antigravity; (2) the halo averaged density is equal to two densities of dark energy; (3) the halo edge (cut-off) density is the dark energy density with a numerical factor of the unity order slightly depending on the halo profile. The cluster gravitational potential well in which the particles of the dark halo (as well as galaxies and intracluster plasma) move is strongly affected by dark energy: the maximum of the potential is located at the zero-gravity radius of the cluster.

  8. Non-adiabatic perturbations in Ricci dark energy model

    SciTech Connect

    Karwan, Khamphee; Thitapura, Thiti E-mail: nanodsci2523@hotmail.com

    2012-01-01

    We show that the non-adiabatic perturbations between Ricci dark energy and matter can grow both on superhorizon and subhorizon scales, and these non-adiabatic perturbations on subhorizon scales can lead to instability in this dark energy model. The rapidly growing non-adiabatic modes on subhorizon scales always occur when the equation of state parameter of dark energy starts to drop towards -1 near the end of matter era, except that the parameter α of Ricci dark energy equals to 1/2. In the case where α = 1/2, the rapidly growing non-adiabatic modes disappear when the perturbations in dark energy and matter are adiabatic initially. However, an adiabaticity between dark energy and matter perturbations at early time implies a non-adiabaticity between matter and radiation, this can influence the ordinary Sachs-Wolfe (OSW) effect. Since the amount of Ricci dark energy is not small during matter domination, the integrated Sachs-Wolfe (ISW) effect is greatly modified by density perturbations of dark energy, leading to a wrong shape of CMB power spectrum. The instability in Ricci dark energy is difficult to be alleviated if the effects of coupling between baryon and photon on dark energy perturbations are included.

  9. Results of the ASY-EOS experiment at GSI: The symmetry energy at suprasaturation density

    NASA Astrophysics Data System (ADS)

    Russotto, P.; Gannon, S.; Kupny, S.; Lasko, P.; Acosta, L.; Adamczyk, M.; Al-Ajlan, A.; Al-Garawi, M.; Al-Homaidhi, S.; Amorini, F.; Auditore, L.; Aumann, T.; Ayyad, Y.; Basrak, Z.; Benlliure, J.; Boisjoli, M.; Boretzky, K.; Brzychczyk, J.; Budzanowski, A.; Caesar, C.; Cardella, G.; Cammarata, P.; Chajecki, Z.; Chartier, M.; Chbihi, A.; Colonna, M.; Cozma, M. D.; Czech, B.; De Filippo, E.; Di Toro, M.; Famiano, M.; Gašparić, I.; Grassi, L.; Guazzoni, C.; Guazzoni, P.; Heil, M.; Heilborn, L.; Introzzi, R.; Isobe, T.; Kezzar, K.; Kiš, M.; Krasznahorkay, A.; Kurz, N.; La Guidara, E.; Lanzalone, G.; Le Fèvre, A.; Leifels, Y.; Lemmon, R. C.; Li, Q. F.; Lombardo, I.; Łukasik, J.; Lynch, W. G.; Marini, P.; Matthews, Z.; May, L.; Minniti, T.; Mostazo, M.; Pagano, A.; Pagano, E. V.; Papa, M.; Pawłowski, P.; Pirrone, S.; Politi, G.; Porto, F.; Reviol, W.; Riccio, F.; Rizzo, F.; Rosato, E.; Rossi, D.; Santoro, S.; Sarantites, D. G.; Simon, H.; Skwirczynska, I.; Sosin, Z.; Stuhl, L.; Trautmann, W.; Trifirò, A.; Trimarchi, M.; Tsang, M. B.; Verde, G.; Veselsky, M.; Vigilante, M.; Wang, Yongjia; Wieloch, A.; Wigg, P.; Winkelbauer, J.; Wolter, H. H.; Wu, P.; Yennello, S.; Zambon, P.; Zetta, L.; Zoric, M.

    2016-09-01

    Directed and elliptic flows of neutrons and light-charged particles were measured for the reaction 197Au+197Au at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI laboratory. The detection system consisted of the Large Area Neutron Detector (LAND), combined with parts of the CHIMERA multidetector, the ALADIN Time-of-flight Wall, and the Washington University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA was used for complementary measurements of the isotopic composition and flows of light-charged particles. From the comparison of the elliptic-flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value γ =0.72 ±0.19 is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of suprasaturation density and confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence deduced from the earlier FOPI-LAND data. The densities probed are shown to reach beyond twice saturation.

  10. Probing Dark Energy with Constellation-X

    SciTech Connect

    Rapetti, David; Allen, Steven W.; /KIPAC, Menlo Park

    2006-09-08

    Constellation-X (Con-X) will carry out two powerful and independent sets of tests of dark energy based on X-ray observations of galaxy clusters, providing comparable accuracy to other leading dark energy probes. The first group of tests will measure the absolute distances to clusters, primarily using measurements of the X-ray gas mass fraction in the largest, dynamically relaxed clusters, but with additional constraining power provided by follow-up observations of the Sunyaev-Zel'dovich (SZ) effect. As with supernovae studies, such data determine the transformation between redshift and true distance, d(z), allowing cosmic acceleration to be measured directly. The second, independent group of tests will use the exquisite spectroscopic capabilities of Con-X to determine scaling relations between X-ray observables and mass. Together with forthcoming X-ray and SZ cluster surveys, these data will help to constrain the growth of structure, which is also a strong function of cosmological parameters.

  11. 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.

  12. A unifying description of dark energy

    NASA Astrophysics Data System (ADS)

    Gleyzes, Jérôme; Langlois, David; Vernizzi, Filippo

    2014-01-01

    We review and extend a novel approach that we recently introduced, to describe general dark energy or scalar-tensor models. Our approach relies on an Arnowitt-Deser-Misner (ADM) formulation based on the hypersurfaces where the underlying scalar field is uniform. The advantage of this approach is that it can describe in the same language and in a minimal way a vast number of existing models, such as quintessence, F(R) theories, scalar tensor theories, their Horndeski extensions and beyond. It also naturally includes Horava-Lifshitz theories. As summarized in this review, our approach provides a unified treatment of the linear cosmological perturbations about a Friedmann-Lemaître-Robertson-Walker (FLRW) universe, obtained by a systematic expansion of our general action up to quadratic order. This shows that the behavior of these linear perturbations is generically characterized by five time-dependent functions. We derive the full equations of motion in the Newtonian gauge. In the Horndeski case, we obtain the equation of state for dark energy perturbations in terms of these functions. Our unifying description thus provides the simplest and most systematic way to confront theoretical models with current and future cosmological observations.

  13. The effective field theory of dark energy

    SciTech Connect

    Gubitosi, Giulia; Vernizzi, Filippo; Piazza, Federico E-mail: fpiazza@apc.univ-paris7.fr

    2013-02-01

    We propose a universal description of dark energy and modified gravity that includes all single-field models. By extending a formalism previously applied to inflation, we consider the metric universally coupled to matter fields and we write in terms of it the most general unitary gauge action consistent with the residual unbroken symmetries of spatial diffeomorphisms. Our action is particularly suited for cosmological perturbation theory: the background evolution depends on only three operators. All other operators start at least at quadratic order in the perturbations and their effects can be studied independently and systematically. In particular, we focus on the properties of a few operators which appear in non-minimally coupled scalar-tensor gravity and galileon theories. In this context, we study the mixing between gravity and the scalar degree of freedom. We assess the quantum and classical stability, derive the speed of sound of fluctuations and the renormalization of the Newton constant. The scalar can always be de-mixed from gravity at quadratic order in the perturbations, but not necessarily through a conformal rescaling of the metric. We show how to express covariant field-operators in our formalism and give several explicit examples of dark energy and modified gravity models in our language. Finally, we discuss the relation with the covariant EFT methods recently appeared in the literature.

  14. HUBBLE PARAMETER MEASUREMENT CONSTRAINTS ON DARK ENERGY

    SciTech Connect

    Farooq, Omer; Mania, Data; Ratra, Bharat E-mail: mania@phys.ksu.edu

    2013-02-20

    We use 21 Hubble parameter versus redshift data points from Simon et al., Gaztanaga et al., Stern et al., and Moresco et al. to place constraints on model parameters of constant and time-evolving dark energy cosmologies. The inclusion of the eight new measurements results in H(z) constraints more restrictive than those derived by Chen and Ratra. These constraints are now almost as restrictive as those that follow from current Type Ia supernova (SNIa) apparent magnitude versus redshift data, which now more carefully account for systematic uncertainties. This is a remarkable result. We emphasize, however, that SNIa data have been studied for a longer time than the H(z) data, possibly resulting in a better estimate of potential systematic errors in the SNIa case. A joint analysis of the H(z), baryon acoustic oscillation peak length scale, and SNIa data favors a spatially flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude slowly evolving dark energy.

  15. The Dark Energy Survey instrument design

    SciTech Connect

    Flaugher, B.; /Fermilab

    2006-05-01

    We describe a new project, the Dark Energy Survey (DES), aimed at measuring the dark energy equation of state parameter, w, to a statistical precision of {approx}5%, with four complementary techniques. The survey will use a new 3 sq. deg. mosaic camera (DECam) mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a large mosaic camera, a five element optical corrector, four filters (g,r,i,z), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of 62 2K x 4K CCD modules (0.27''/pixel) arranged in a hexagon inscribed within the 2.2 deg. diameter field of view. We plan to use the 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). At Fermilab, we will establish a packaging factory to produce four-side buttable modules for the LBNL devices, as well as to test and grade the CCDs. R&D is underway and delivery of DECam to CTIO is scheduled for 2009.

  16. Structure formation in inhomogeneous Early Dark Energy models

    SciTech Connect

    Batista, R.C.; Pace, F. E-mail: francesco.pace@port.ac.uk

    2013-06-01

    We study the impact of Early Dark Energy fluctuations in the linear and non-linear regimes of structure formation. In these models the energy density of dark energy is non-negligible at high redshifts and the fluctuations in the dark energy component can have the same order of magnitude of dark matter fluctuations. Since two basic approximations usually taken in the standard scenario of quintessence models, that both dark energy density during the matter dominated period and dark energy fluctuations on small scales are negligible, are not valid in such models, we first study approximate analytical solutions for dark matter and dark energy perturbations in the linear regime. This study is helpful to find consistent initial conditions for the system of equations and to analytically understand the effects of Early Dark Energy and its fluctuations, which are also verified numerically. In the linear regime we compute the matter growth and variation of the gravitational potential associated with the Integrated Sachs-Wolf effect, showing that these observables present important modifications due to Early Dark Energy fluctuations, though making them more similar to the ΛCDM model. We also make use of the Spherical Collapse model to study the influence of Early Dark Energy fluctuations in the nonlinear regime of structure formation, especially on δ{sub c} parameter, and their contribution to the halo mass, which we show can be of the order of 10%. We finally compute how the number density of halos is modified in comparison to the ΛCDM model and address the problem of how to correct the mass function in order to take into account the contribution of clustered dark energy. We conclude that the inhomogeneous Early Dark Energy models are more similar to the ΛCDM model than its homogeneous counterparts.

  17. DARK FLUID: A UNIFIED FRAMEWORK FOR MODIFIED NEWTONIAN DYNAMICS, DARK MATTER, AND DARK ENERGY

    SciTech Connect

    Zhao Hongsheng; Li Baojiu E-mail: b.li@damtp.cam.ac.u

    2010-03-20

    Empirical theories of dark matter (DM) like modified Newtonian dynamics (MOND) gravity and of dark energy (DE) like f(R) gravity were motivated by astronomical data. But could these theories be branches rooted from a more general and hence generic framework? Here we propose a very generic Lagrangian of such a framework based on simple dimensional analysis and covariant symmetry requirements, and explore various outcomes in a top-down fashion. The desired effects of quintessence plus cold DM particle fields or MOND-like scalar field(s) are shown to be largely achievable by one vector field only. Our framework preserves the covariant formulation of general relativity, but allows the expanding physical metric to be bent by a single new species of dark fluid flowing in spacetime. Its non-uniform stress tensor and current vector are simple functions of a vector field with variable norm, not coupled with the baryonic fluid and the four-vector potential of the photon fluid. The dark fluid framework generically branches into a continuous spectrum of theories with DE and DM effects, including the f(R) gravity, tensor-vector-scalar-like theories, Einstein-Aether, and nuLAMBDA theories as limiting cases. When the vector field degenerates into a pure scalar field, we obtain the physics for quintessence. Choices of parameters can be made to pass Big Bang nucleosynthesis, parameterized post-Newtonian, and causality constraints. In this broad setting we emphasize the non-constant dynamical field behind the cosmological constant effect, and highlight plausible corrections beyond the classical MOND predictions.

  18. Dark Fluid: A Unified Framework for Modified Newtonian Dynamics, Dark Matter, and Dark Energy

    NASA Astrophysics Data System (ADS)

    Zhao, HongSheng; Li, Baojiu

    2010-03-01

    Empirical theories of dark matter (DM) like modified Newtonian dynamics (MOND) gravity and of dark energy (DE) like f(R) gravity were motivated by astronomical data. But could these theories be branches rooted from a more general and hence generic framework? Here we propose a very generic Lagrangian of such a framework based on simple dimensional analysis and covariant symmetry requirements, and explore various outcomes in a top-down fashion. The desired effects of quintessence plus cold DM particle fields or MOND-like scalar field(s) are shown to be largely achievable by one vector field only. Our framework preserves the covariant formulation of general relativity, but allows the expanding physical metric to be bent by a single new species of dark fluid flowing in spacetime. Its non-uniform stress tensor and current vector are simple functions of a vector field with variable norm, not coupled with the baryonic fluid and the four-vector potential of the photon fluid. The dark fluid framework generically branches into a continuous spectrum of theories with DE and DM effects, including the f(R) gravity, tensor-vector-scalar-like theories, Einstein-Aether, and νΛ theories as limiting cases. When the vector field degenerates into a pure scalar field, we obtain the physics for quintessence. Choices of parameters can be made to pass Big Bang nucleosynthesis, parameterized post-Newtonian, and causality constraints. In this broad setting we emphasize the non-constant dynamical field behind the cosmological constant effect, and highlight plausible corrections beyond the classical MOND predictions.

  19. Probing Dark Energy with High Redshift Supernovae

    NASA Astrophysics Data System (ADS)

    Perlmutter, S.

    2003-05-01

    The Hubble diagram of Type Ia Supernovae provides the most direct current measurement of the expansion history of the universe, including the present acceleration and the transition to matter-dominated deceleration. Recent measurements already yield statistical uncertainties small enough that we are close to being limited by systematics. I will review the anticipated improvement in systematics attainable by the next generations of experiments from ground and space that promise a systematics-controlled prize: a detailed expansion history of the universe that can teach us about the nature of the mysterious "dark energy" that accelerates the universe. This work is supported by the U.S. Dept. of Energy, Office of Science, under contract DE-AC03-76SF00098.

  20. Nonparametric dark energy reconstruction from supernova data.

    PubMed

    Holsclaw, Tracy; Alam, Ujjaini; Sansó, Bruno; Lee, Herbert; Heitmann, Katrin; Habib, Salman; Higdon, David

    2010-12-10

    Understanding the origin of the accelerated expansion of the Universe poses one of the greatest challenges in physics today. Lacking a compelling fundamental theory to test, observational efforts are targeted at a better characterization of the underlying cause. If a new form of mass-energy, dark energy, is driving the acceleration, the redshift evolution of the equation of state parameter w(z) will hold essential clues as to its origin. To best exploit data from observations it is necessary to develop a robust and accurate reconstruction approach, with controlled errors, for w(z). We introduce a new, nonparametric method for solving the associated statistical inverse problem based on Gaussian process modeling and Markov chain Monte Carlo sampling. Applying this method to recent supernova measurements, we reconstruct the continuous history of w out to redshift z=1.5.

  1. Cosmic Gauge-Field Dark Energy

    NASA Astrophysics Data System (ADS)

    Devulder, Christopher; Caldwell, Robert

    2017-01-01

    We present a cosmological model in which dark energy consists of a cosmic gauge field. At early times it behaves like radiation; at late times it drives cosmic acceleration. By varying the number of fields, their coupling strength and handedness, a wide range of behavior is shown to emerge. Joint constraints on the model from SNe, BAO and CMB data are presented. We discuss the possibility that the gauge field may seed a spectrum of primordial gravitational waves with a distinct imprint on the power spectrum, as well as act like a dissipative medium for high frequency gravitational waves. We show that this model could have an impact on the B-mode polarization pattern in the CMB, as well as future probes that use standard sirens to constrain the energy budget of the Universe.

  2. Variable deceleration parameter and dark energy models

    NASA Astrophysics Data System (ADS)

    Bishi, Binaya K.

    2016-03-01

    This paper deals with the Bianchi type-III dark energy model and equation of state parameter in a first class of f(R,T) gravity. Here, R and T represents the Ricci scalar and trace of the energy momentum tensor, respectively. The exact solutions of the modified field equations are obtained by using (i) linear relation between expansion scalar and shear scalar, (ii) linear relation between state parameter and skewness parameter and (iii) variable deceleration parameter. To obtain the physically plausible cosmological models, the variable deceleration parameter with the suitable substitution leads to the scale factor of the form a(t) = [sinh(αt)] 1 n, where α and n > 0 are arbitrary constants. It is observed that our models are accelerating for 0 < n < 1 and for n > 1, transition phase from deceleration to acceleration. Further, we have discussed physical properties of the models.

  3. Dynamical system analysis for DBI dark energy interacting with dark matter

    NASA Astrophysics Data System (ADS)

    Mahata, Nilanjana; Chakraborty, Subenoy

    2015-01-01

    A dynamical system analysis related to Dirac-Born-Infeld (DBI) cosmological model has been investigated in this present work. For spatially flat FRW spacetime, the Einstein field equation for DBI scenario has been used to study the dynamics of DBI dark energy interacting with dark matter. The DBI dark energy model is considered as a scalar field with a nonstandard kinetic energy term. An interaction between the DBI dark energy and dark matter is considered through a phenomenological interaction between DBI scalar field and the dark matter fluid. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables. The potential of the DBI scalar field is assumed to be exponential. Finally, critical points are determined, their nature have been analyzed and corresponding cosmological scenario has been discussed.

  4. Constraining a dark matter and dark energy interaction scenario with a dynamical equation of state

    NASA Astrophysics Data System (ADS)

    Yang, Weiqiang; Banerjee, Narayan; Pan, Supriya

    2017-06-01

    In this work we have used the recent cosmic chronometer data along with the latest estimation of the local Hubble parameter value, H0 at 2.4% precision as well as the standard dark energy probes, such as the Supernovae Type Ia, baryon acoustic oscillation distance measurements, and cosmic microwave background measurements (PlanckTT+ lowP ) to constrain a dark energy model where the dark energy is allowed to interact with the dark matter. A general equation of state of dark energy parametrized by a dimensionless parameter "β " is utilized. From our analysis, we find that the interaction is compatible with zero within the 1 σ confidence limit. We also show that the same evolution history can be reproduced by a small pressure of the dark matter.

  5. Phase-space analysis of teleparallel dark energy

    SciTech Connect

    Xu, Chen; Saridakis, Emmanuel N.; Leon, Genly E-mail: Emmanuel_Saridakis@baylor.edu

    2012-07-01

    We perform a detailed dynamical analysis of the teleparallel dark energy scenario, which is based on the teleparallel equivalent of General Relativity, in which one adds a canonical scalar field, allowing also for a nonminimal coupling with gravity. We find that the universe can result in the quintessence-like, dark-energy-dominated solution, or to the stiff dark-energy late-time attractor, similarly to standard quintessence. However, teleparallel dark energy possesses an additional late-time solution, in which dark energy behaves like a cosmological constant, independently of the specific values of the model parameters. Finally, during the evolution the dark energy equation-of-state parameter can be either above or below -1, offering a good description for its observed dynamical behavior and its stabilization close to the cosmological-constant value.

  6. Can the Existence of Dark Energy be Directly Detected?

    SciTech Connect

    Perl, Martin L.; /SLAC /KIPAC, Menlo Park

    2011-11-23

    The majority of astronomers and physicists accept the reality of dark energy and also believe that it can only be studied indirectly through observation of the motions of stars and galaxies. In this paper I open the experimental question of whether it is possible to directly detect dark energy through the presence of dark energy density. Two thirds of this paper outlines the major aspects of dark energy density as now comprehended by the astronomical and physics community. The final third summarizes various proposals for direct detection of dark energy density or its possible effects. At this time I do not have a fruitful answer to the question: Can the Existence of Dark Energy Be Directly Detected?

  7. Observational constraints on holographic tachyonic dark energy in interaction with dark matter

    SciTech Connect

    Micheletti, Sandro M. R.

    2010-05-01

    We discuss an interacting tachyonic dark energy model in the context of the holographic principle. The potential of the holographic tachyon field in interaction with dark matter is constructed. The model results are compared with CMB shift parameter, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. The coupling constant of the model is compatible with zero, but dark energy is not given by a cosmological constant.

  8. PHYSICS OF OUR DAYS: Dark energy: myths and reality

    NASA Astrophysics Data System (ADS)

    Lukash, V. N.; Rubakov, V. A.

    2008-03-01

    We discuss the questions related to dark energy in the Universe. We note that in spite of the effect of dark energy, large-scale structure is still being generated in the Universe and this will continue for about ten billion years. We also comment on some statements in the paper "Dark energy and universal antigravitation" by A D Chernin, Physics Uspekhi 51 (3) (2008).

  9. The growth of structure in interacting dark energy models

    SciTech Connect

    Caldera-Cabral, Gabriela; Maartens, Roy; Schaefer, Bjoern Malte E-mail: roy.maartens@port.ac.uk

    2009-07-01

    If dark energy interacts with dark matter, there is a change in the background evolution of the universe, since the dark matter density no longer evolves as a{sup −3}. In addition, the non-gravitational interaction affects the growth of structure. In principle, these changes allow us to detect and constrain an interaction in the dark sector. Here we investigate the growth factor and the weak lensing signal for a new class of interacting dark energy models. In these models, the interaction generalises the simple cases where one dark fluid decays into the other. In order to calculate the effect on structure formation, we perform a careful analysis of the perturbed interaction and its effect on peculiar velocities. Assuming a normalization to today's values of dark matter density and overdensity, the signal of the interaction is an enhancement (suppression) of both the growth factor and the lensing power, when the energy transfer in the background is from dark matter to dark energy (dark energy to dark matter)

  10. Chameleon dark energy models with characteristic signatures

    SciTech Connect

    Gannouji, Radouane; Moraes, Bruno; Polarski, David; Mota, David F.; Winther, Hans A.; Tsujikawa, Shinji

    2010-12-15

    In chameleon dark energy models, local gravity constraints tend to rule out parameters in which observable cosmological signatures can be found. We study viable chameleon potentials consistent with a number of recent observational and experimental bounds. A novel chameleon field potential, motivated by f(R) gravity, is constructed where observable cosmological signatures are present both at the background evolution and in the growth rate of the perturbations. We study the evolution of matter density perturbations on low redshifts for this potential and show that the growth index today {gamma}{sub 0} can have significant dispersion on scales relevant for large scale structures. The values of {gamma}{sub 0} can be even smaller than 0.2 with large variations of {gamma} on very low redshifts for the model parameters constrained by local gravity tests. This gives a possibility to clearly distinguish these chameleon models from the {Lambda}-cold-dark-matter ({Lambda}CDM) model in future high-precision observations.

  11. Mass functions in coupled dark energy models

    SciTech Connect

    Mainini, Roberto; Bonometto, Silvio

    2006-08-15

    We evaluate the mass function of virialized halos, by using Press and Schechter (PS) and/or Steth and Tormen (ST) expressions, for cosmologies where dark energy (DE) is due to a scalar self-interacting field, coupled with dark matter (DM). We keep to coupled DE (cDE) models known to fit linear observables. To implement the PS-ST approach, we start from reviewing and extending the results of a previous work on the growth of a spherical top-hat fluctuation in cDE models, confirming their most intriguing astrophysical feature, i.e. a significant baryon-DM segregation, occurring well before the onset of any hydrodynamical effect. Accordingly, the predicted mass function depends on how halo masses are measured. For any option, however, the coupling causes a distortion of the mass function, still at z=0. Furthermore, the z-dependence of cDE mass functions is mostly displaced, in respect to {lambda}CDM, in the opposite way of uncoupled dynamical DE. This is an aspect of the basic underlying result, that even a little DM-DE coupling induces relevant modifications in the nonlinear evolution. Therefore, without causing great shifts in linear astrophysical observables, the DM-baryon segregation induced by the coupling can have an impact on a number of cosmological problems, e.g., galaxy satellite abundance, spiral disk formation, apparent baryon shortage, entropy input in clusters, etc.

  12. Dissipative or conservative cosmology with dark energy?

    NASA Astrophysics Data System (ADS)

    Szydlowski, M.; Hrycyna, O.

    2007-12-01

    All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analyzed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property -- acceleration -- is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in a 1-dimensional potential which is parameterized by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We also confront viscous models with SNIa observations. The best fitted models are obtained by minimizing the $\\chi^{2}$ function which is illustrated by residuals and $\\chi^{2}$ levels in the space of model independent parameters. The general conclusion is that SNIa data supports the viscous model without the cosmological constant. The obtained values of $\\chi^{2}$ statistic are comparable for both the viscous model and LCDM model. The Bayesian information criteria are used to compare the models with different power law parameterization of viscous effects. Our result of this analysis shows that SNIa data supports viscous cosmology more than the LCDM model if the coefficient in viscosity parameterization is fixed. The Bayes factor is also used to obtain the posterior probability of the model.

  13. BOOK REVIEW Dark Energy: Theory and Observations Dark Energy: Theory and Observations

    NASA Astrophysics Data System (ADS)

    Faraoni, Valerio

    2011-02-01

    The 1998 discovery of what seems an acceleration of the cosmic expansion was made using type Ia supernovae and was later confirmed by other cosmological observations. It has made a huge impact on cosmology, prompting theoreticians to explain the observations and introducing the concept of dark energy into modern physics. A vast literature on dark energy and its alternatives has appeared since then, and this is the first comprehensive book devoted to the subject. This book is addressed to an advanced audience comprising graduate students and researchers in cosmology. Although it contains forty four fully solved problems and the first three chapters are rather introductory, they do not constitute a self-consistent course in cosmology and this book assumes graduate level knowledge of cosmology and general relativity. The fourth chapter focuses on observations, while the rest of this book addresses various classes of models proposed, including the cosmological constant, quintessence, k-essence, phantom energy, coupled dark energy, etc. The title of this book should not induce the reader into believing that only dark energy models are addressed—the authors devote two chapters to discussing conceptually very different approaches alternative to dark energy, including ƒ(R) and Gauss-Bonnet gravity, braneworld and void models, and the backreaction of inhomogeneities on the cosmic dynamics. Two chapters contain a general discussion of non-linear cosmological perturbations and statistical methods widely applicable in cosmology. The final chapter outlines future perspectives and the most likely lines of observational research on dark energy in the future. Overall, this book is carefully drafted, well presented, and does a good job of organizing the information available in the vast literature. The reader is pointed to the essential references and guided in a balanced way through the various proposals aimied at explaining the cosmological observations. Not all classes of

  14. Statefinder Diagnostic for the Yang-Mills Dark Energy Model

    NASA Astrophysics Data System (ADS)

    Zhao, Wen

    We study the statefinder parameters in the Yang-Mills condensate dark energy models, and find that the evolving trajectories of these models are different from those of other dark energy models. We also define two eigenfunctions of the Yang-Mills condensate dark energy models. The values of these eigenfunctions are quite close to zero if the equation of state of the Yang-Mills condensate is not far from -1, which can be used to simply differentiate between the Yang-Mills condensate models and other dark energy models.

  15. The Hubble constant and dark energy from cosmological distance measures

    SciTech Connect

    Ichikawa, Kazuhide; Takahashi, Tomo E-mail: tomot@cc.saga-u.ac.jp

    2008-04-15

    We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and dark energy are investigated using the cosmological observations of cosmic microwave background, baryon acoustic oscillations and type Ia supernovae. When one investigates dark energy, the Hubble constant is often a nuisance parameter; thus it is usually marginalized over. On the other hand, when one focuses on the Hubble constant, simple dark energy models such as a cosmological constant and a constant equation of state are usually assumed. Since we do not know the nature of dark energy yet, it is interesting to investigate the Hubble constant assuming some types of dark energy and see to what extent the constraint on the Hubble constant is affected by the assumption concerning dark energy. We show that the constraint on the Hubble constant is not affected much by the assumption for dark energy. We furthermore show that this holds true even if we remove the assumption that the universe is flat. We also discuss how the prior on the Hubble constant affects the constraints on dark energy and/or the curvature of the universe.

  16. Interacting diffusive unified dark energy and dark matter from scalar fields

    NASA Astrophysics Data System (ADS)

    Benisty, David; Guendelman, E. I.

    2017-06-01

    Here we generalize ideas of unified dark matter-dark energy in the context of two measure theories and of dynamical space time theories. In two measure theories one uses metric independent volume elements and this allows one to construct unified dark matter-dark energy, where the cosmological constant appears as an integration constant associated with the equation of motion of the measure fields. The dynamical space-time theories generalize the two measure theories by introducing a vector field whose equation of motion guarantees the conservation of a certain Energy Momentum tensor, which may be related, but in general is not the same as the gravitational Energy Momentum tensor. We propose two formulations of this idea: (I) by demanding that this vector field be the gradient of a scalar, (II) by considering the dynamical space field appearing in another part of the action. Then the dynamical space time theory becomes a theory of Diffusive Unified dark energy and dark matter. These generalizations produce non-conserved energy momentum tensors instead of conserved energy momentum tensors which leads at the end to a formulation of interacting DE-DM dust models in the form of a diffusive type interacting Unified dark energy and dark matter scenario. We solved analytically the theories for perturbative solution and asymptotic solution, and we show that the Λ CDM is a fixed point of these theories at large times. Also a preliminary argument as regards the good behavior of the theory at the quantum level is proposed for both theories.

  17. Calibration Monitor for Dark Energy Experiments

    SciTech Connect

    Kaiser, M. E.

    2009-11-23

    The goal of this program was to design, build, test, and characterize a flight qualified calibration source and monitor for a Dark Energy related experiment: ACCESS - 'Absolute Color Calibration Experiment for Standard Stars'. This calibration source, the On-board Calibration Monitor (OCM), is a key component of our ACCESS spectrophotometric calibration program. The OCM will be flown as part of the ACCESS sub-orbital rocket payload in addition to monitoring instrument sensitivity on the ground. The objective of the OCM is to minimize systematic errors associated with any potential changes in the ACCESS instrument sensitivity. Importantly, the OCM will be used to monitor instrument sensitivity immediately after astronomical observations while the instrument payload is parachuting to the ground. Through monitoring, we can detect, track, characterize, and thus correct for any changes in instrument senstivity over the proposed 5-year duration of the assembled and calibrated instrument.

  18. Supernovae and Dark Energy -- What's Next?

    NASA Astrophysics Data System (ADS)

    Perlmutter, Saul

    2003-04-01

    The existing supernova measurements of the universe's (accelerating) expansion history have pointed the way to the next generation of experiments. This next generation of supernova measurements must be made with a dramatic step forward in constraints on systematic uncertainties, since the previous measurements already have statistical uncertainties that are close to the current systematics limits. I will show how some recent results set the stage for these advances, and describe a series of ground- and space-based projects and a new satellite experiment (the SuperNova / Acceleration Probe, "SNAP") that promise a systematics-controlled prize: a detailed expansion history of the universe that can teach us about the nature of the mysterious "dark energy" that accelerates the universe.

  19. Does Cometary Panspermia Falsify Dark Energy?

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.

    2011-10-01

    The 2011 Nobel Prize for physics has been awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae", judged to be the "most important discovery or invention within the field of physics" (Excerpt from the will of Alfred Nobel). Are we forced by this claimed discovery to believe the universe is dominated by anti- gravitational dark energy? Can the discovery be falsified? Because life as we observe it on Earth is virtually impossible by the standard ΛCDMHC model, extraterrestrial life and cometary panspermia may provide the first definitive falsification of a Nobel Prize in Physics since its first award in 1901 to Wilhelm Röntgen for his discovery of X-rays.

  20. On cosmic acceleration without dark energy

    SciTech Connect

    Kolb, E.W.; Matarrese, S.; Riotto, A.; /INFN, Padua

    2005-06-01

    We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion. This invalidates the no-go theorem that there can be no acceleration in our local Hubble patch if the Universe only contains irrotational dust. We then study perturbatively the time behavior of general-relativistic cosmological perturbations, applying, where possible, the renormalization group to regularize the dynamics. We show that an instability occurs in the perturbative expansion involving sub-Hubble modes, which indicates that acceleration in our Hubble patch may originate from the backreaction of cosmological perturbations on observable scales.

  1. Neutrino dark energy in grand unified theories

    SciTech Connect

    Bhatt, Jitesh R.; Sarkar, Utpal; Singh, Santosh K.; Gu, P.-H.

    2009-10-01

    We studied a left-right symmetric model that can accommodate the neutrino dark energy ({nu}DE) proposal. The type-III seesaw mechanism is implemented to give masses to the neutrinos. After explaining the model, we study the consistency of the model by minimizing the scalar potential and obtaining the conditions for the required vacuum expectation values of the different scalar fields. This model is then embedded in an SO(10) grand unified theory and the allowed symmetry breaking scales are determined by the condition of the gauge coupling unification. Although SU(2){sub R} breaking is required to be high, its Abelian subgroup U(1){sub R} is broken in the TeV range, which can then give the required neutrino masses and predicts new gauge bosons that could be detected at LHC. The neutrino masses are studied in detail in this model, which shows that at least 3 singlet fermions are required.

  2. Frustrated expectations: Defect networks and dark energy

    SciTech Connect

    Avelino, P.P.; Oliveira, J.C.R.E.; Martins, C.J.A.P.; Menezes, J.; Menezes, R.

    2006-06-15

    We discuss necessary conditions for a network of cosmic domain walls to have a chance of providing the dark energy that might explain the recent acceleration of the Universe. We derive a strong bound on the curvature of the walls, which shows that viable candidate networks must be fine-tuned and nonstandard. We also discuss various requirements that any stable lattice of frustrated walls must obey. We conjecture that, even though one can build (by hand) lattices that would be stable, no such lattices will ever come out of realistic domain wall forming cosmological phase transitions. We provide some simple numerical simulations that illustrate our results and correct some misconceptions in the published literature, but a detailed numerical analysis is left for a companion paper.

  3. Neutrino dark energy in grand unified theories

    NASA Astrophysics Data System (ADS)

    Bhatt, Jitesh R.; Gu, Pei-Hong; Sarkar, Utpal; Singh, Santosh K.

    2009-10-01

    We studied a left-right symmetric model that can accommodate the neutrino dark energy (νDE) proposal. The type-III seesaw mechanism is implemented to give masses to the neutrinos. After explaining the model, we study the consistency of the model by minimizing the scalar potential and obtaining the conditions for the required vacuum expectation values of the different scalar fields. This model is then embedded in an SO(10) grand unified theory and the allowed symmetry breaking scales are determined by the condition of the gauge coupling unification. Although SU(2)R breaking is required to be high, its Abelian subgroup U(1)R is broken in the TeV range, which can then give the required neutrino masses and predicts new gauge bosons that could be detected at LHC. The neutrino masses are studied in detail in this model, which shows that at least 3 singlet fermions are required.

  4. Generalized dark energy interactions with multiple fluids

    NASA Astrophysics Data System (ADS)

    van de Bruck, Carsten; Mifsud, Jurgen; Mimoso, José P.; Nunes, Nelson J.

    2016-11-01

    In the search for an explanation for the current acceleration of the Universe, scalar fields are the most simple and useful tools to build models of dark energy. This field, however, must in principle couple with the rest of the world and not necessarily in the same way to different particles or fluids. We provide the most complete dynamical system analysis to date, consisting of a canonical scalar field conformally and disformally coupled to both dust and radiation. We perform a detailed study of the existence and stability conditions of the systems and comment on constraints imposed on the disformal coupling from Big-Bang Nucleosynthesis and given current limits on the variation of the fine-structure constant.

  5. Observational effects of the early episodically dominating dark energy

    NASA Astrophysics Data System (ADS)

    Park, Chan-Gyung; Lee, Jae-heon; Hwang, Jai-chan; Noh, Hyerim

    2014-10-01

    We investigate the observational consequences of the early episodically dominating dark energy on the evolution of cosmological structures. For this aim, we introduce the minimally coupled scalar-field dark energy model with the Albrecht-Skordis potential, which allows a sudden ephemeral domination of a dark energy component during the radiation or early matter era. The conventional cosmological parameters in the presence of such an early dark energy are constrained with WMAP and Planck cosmic microwave background radiation data including other external data sets. It is shown that in the presence of such an early dark energy, the estimated cosmological parameters can deviate substantially from the currently known Λ cold dark matter (Λ CDM )-based parameters, with best-fit values differing by several percent for WMAP and by a percent level for Planck data. For the latter case, only a limited amount of dark energy with episodic nature is allowed since the Planck data strongly favor the Λ CDM model. Compared with the conventional dark energy model, the early dark energy dominating near the radiation-matter equality or at the early matter era results in the shorter cosmic age or the presence of tensor-type perturbation, respectively. Our analysis demonstrates that the alternative cosmological parameter estimation is allowed based on the same observations even in Einstein's gravity.

  6. Triple unification of inflation, dark matter, and dark energy using a single field

    SciTech Connect

    Liddle, Andrew R.; Pahud, Cedric; Urena-Lopez, L. Arturo

    2008-06-15

    We construct an explicit scenario whereby the same material driving inflation in the early universe can comprise dark matter in the present universe, using a simple quadratic potential. Following inflation and preheating, the density of inflaton/dark matter particles is reduced to the observed level by a period of thermal inflation, of a duration already invoked in the literature for other reasons. Within the context of the string landscape, one can further argue for a nonzero vacuum energy of this field, thus unifying inflation, dark matter, and dark energy into a single fundamental field.

  7. New interaction between dark energy and dark matter changes sign during cosmological evolution

    NASA Astrophysics Data System (ADS)

    Sun, Cheng-Yi; Yue, Rui-Hong

    2012-02-01

    It is found by Cai and Su that the interaction between dark energy and cold dark matter is likely to change the sign during the cosmological evolution. Motivated by this, we suggest a new form of interaction between dark energy and dark matter, which changes from negative to positive as the expansion of or universe changes from decelerated to accelerated. We find that the interacting model is consistent with the second law of thermodynamics and the observational constraints. And, we also discuss the unified adiabatic-squared sound speed of the model.

  8. Interacting agegraphic dark energy models in phase space

    SciTech Connect

    Lemets, O.A.; Yerokhin, D.A.; Zazunov, L.G. E-mail: denyerokhin@gmail.com

    2011-01-01

    Agegraphic dark energy, has been recently proposed, based on the so-called Karolyhazy uncertainty relation, which arises from quantum mechanics together with general relativity. In the first part of the article we study the original agegraphic dark energy model by including the interaction between agegraphic dark energy and pressureless (dark) matter. The phase space analysis was made and the critical points were found, one of which is the attractor corresponding to an accelerated expanding Universe. Recent observations of near supernova show that the acceleration of Universe decreases. This phenomenon is called the transient acceleration. In the second part of Article we consider the 3-component Universe composed of a scalar field, interacting with the dark matter on the agegraphic dark energy background. We show that the transient acceleration appears in frame of such a model. The obtained results agree with the observations.

  9. Fingerprinting dark energy. II. Weak lensing and galaxy clustering tests

    SciTech Connect

    Sapone, Domenico; Amendola, Luca

    2010-11-15

    The characterization of dark energy is a central task of cosmology. To go beyond a cosmological constant, we need to introduce at least an equation of state and a sound speed and consider observational tests that involve perturbations. If dark energy is not completely homogeneous on observable scales, then the Poisson equation is modified and dark matter clustering is directly affected. One can then search for observational effects of dark energy clustering using dark matter as a probe. In this paper we exploit an analytical approximate solution of the perturbation equations in a general dark energy cosmology to analyze the performance of next-decade large-scale surveys in constraining equation of state and sound speed. We find that tomographic weak lensing and galaxy redshift surveys can constrain the sound speed of the dark energy only if the latter is small, of the order of c{sub s} < or approx. 0.01 (in units of c). For larger sound speeds the error grows to 100% and more. We conclude that large-scale structure observations contain very little information about the perturbations in canonical scalar field models with a sound speed of unity. Nevertheless, they are able to detect the presence of cold dark energy, i.e. a dark energy with nonrelativistic speed of sound.

  10. The traces of anisotropic dark energy in light of Planck

    SciTech Connect

    Cardona, Wilmar; Kunz, Martin; Hollenstein, Lukas E-mail: lukas.hollenstein@zhaw.ch

    2014-07-01

    We study a dark energy model with non-zero anisotropic stress, either linked to the dark energy density or to the dark matter density. We compute approximate solutions that allow to characterise the behaviour of the dark energy model and to assess the stability of the perturbations. We also determine the current limits on such an anisotropic stress from the cosmic microwave background data by the Planck satellite, and derive the corresponding constraints on the modified growth parameters like the growth index, the effective Newton's constant and the gravitational slip.

  11. New perspective on the relation between dark energy perturbations and the late-time integrated Sachs-Wolfe effect

    SciTech Connect

    Dent, James B.; Dutta, Sourish; Weiler, Thomas J.

    2009-01-15

    The effect of quintessence perturbations on the integrated Sachs-Wolfe (ISW) effect is studied for a mixed dynamical scalar field dark energy (DDE) and pressureless perfect fluid dark matter. A new and general methodology is developed to track the growth of the perturbations, which uses only the equation of state (EoS) parameter w{sub DDE}(z){identical_to}p{sub DDE}/{rho}{sub DDE} of the scalar field DDE, and the initial values of the relative entropy perturbation (between the matter and DDE) and the intrinsic entropy perturbation of the scalar field DDE as inputs. We also derive a relation between the rest-frame sound speed c-circumflex{sub s,DDE}{sup 2} of an arbitrary scalar field DDE component and its EoS w{sub DDE}(z). We show that the ISW signal differs from that expected in a {lambda}CDM cosmology by as much as +20% to -80% for parametrizations of w{sub DDE} consistent with SNIa data, and about {+-}20% for parametrizations of w{sub DDE} consistent with SNIa+CMB+BAO data, at 95% confidence. Our results indicate that, at least in principle, the ISW effect can be used to phenomenologically distinguish a cosmological constant from DDE.

  12. Dark energy and doubly coupled bigravity

    NASA Astrophysics Data System (ADS)

    Brax, Philippe; Davis, Anne-Christine; Noller, Johannes

    2017-05-01

    We analyse the late time cosmology and the gravitational properties of doubly coupled bigravity in the constrained vielbein formalism (equivalent to the metric formalism) when the mass of the massive graviton is of the order of the present Hubble rate. We focus on one of the two branches of background cosmology where the ratio between the scale factors of the two metrics is algebraically determined. We find that the late time physics depends on the mass of the graviton, which dictates the future asymptotic cosmological constant. The Universe evolves from a matter dominated epoch to a dark energy dominated era where the equation of state of dark energy can always be made close to  -1 now by appropriately tuning the graviton mass. We also analyse the perturbative spectrum of the theory in the quasi-static approximation, well below the strong coupling scale where no instability is present, and we show that there are five scalar degrees of freedom, two vectors and two gravitons. In Minkowski space, where the four Newtonian potentials vanish, the theory manifestly reduces to one massive and one massless graviton. In a cosmological FRW background for both metrics, four of the five scalars are Newtonian potentials which lead to a modification of gravity on large scales. The fifth one gives rise to a ghost which decouples from pressure-less matter in the quasi-static approximation. In this scalar sector, gravity is modified with effects on both the growth of structure and the lensing potential. In particular, we find that the Σ parameter governing the Poisson equation of the weak lensing potential can differ from one in the recent past of the Universe. Overall, the nature of the modification of gravity at low energy, which reveals itself in the growth of structure and the lensing potential, is intrinsically dependent on the couplings to matter and the potential term of the vielbeins. We also find that the time variation of Newton’s constant in the Jordan frame can

  13. Age problem in the holographic dark energy model

    SciTech Connect

    Wei Hao; Zhang Shuangnan

    2007-09-15

    In this paper, we test the original holographic dark energy model with some old high redshift objects. The main idea is very simple: the universe cannot be younger than its constituents. We find that the original holographic dark energy model can be ruled out, unless a lower Hubble constant is taken.

  14. Constraints on holographic dark energy from type Ia supernova observations

    SciTech Connect

    Zhang Xin; Wu Fengquan

    2005-08-15

    In this paper, we use the type Ia supernovae data to constrain the holographic dark energy model proposed by Li. We also apply a cosmic age test to this analysis. We consider in this paper a spatially flat Friedmann-Robertson-Walker universe with a matter component and a holographic dark energy component. The fit result shows that the case c<1 (c=0.21) is favored, which implies that the holographic dark energy behaves as a quintom-type dark energy. Furthermore, we also perform a joint analysis of SNe+CMB+LSS to this model; the result is well improved and still upholds the quintom dark energy conclusion. The best fit results in our analysis are c=0.81, {omega}{sub m}{sup 0}=0.28, and h=0.65, which lead to the present equation of state of dark energy w{sub 0}=-1.03 and the deceleration/acceleration transition redshift z{sub T}=0.63. Finally, an expected supernova/acceleration probe simulation using {lambda}CDM as a fiducial model is performed on this model, and the result shows that the holographic dark energy model takes on c<1 (c=0.92) even though the dark energy is indeed a cosmological constant.

  15. Hubble Expansion Parameter in a New Model of Dark Energy

    NASA Astrophysics Data System (ADS)

    Saadat, Hassan

    2012-01-01

    In this study, we consider new model of dark energy based on Taylor expansion of its density and calculate the Hubble expansion parameter for various parameterizations of equation of state. This model is useful to probe a possible evolving of dark energy component in comparison with current observational data.

  16. Cosmological anisotropy from non-comoving dark matter and dark energy

    SciTech Connect

    Harko, Tiberiu; Lobo, Francisco S. N. E-mail: flobo@cii.fc.ul.pt

    2013-07-01

    We consider a cosmological model in which the two major fluid components of the Universe, dark energy and dark matter, flow with distinct four-velocities. This cosmological configuration is equivalent to a single anisotropic fluid, expanding with a four-velocity that is an appropriate combination of the two fluid four-velocities. The energy density of the single cosmological fluid is larger than the sum of the energy densities of the two perfect fluids, i.e., dark energy and dark matter, respectively, and contains a correction term due to the anisotropy generated by the differences in the four-velocities. Furthermore, the gravitational field equations of the two-fluid anisotropic cosmological model are obtained for a Bianchi type I geometry. By assuming that the non-comoving motion of the dark energy and dark matter induces small perturbations in the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker type cosmological background, and that the anisotropy parameter is small, the equations of the cosmological perturbations due to the non-comoving nature of the two major components are obtained. The time evolution of the metric perturbations is explicitly obtained for the cases of the exponential and power law background cosmological expansion. The imprints of a non-comoving dark energy - dark matter on the Cosmic Microwave Background and on the luminosity distance are briefly discussed, and the temperature anisotropies and the quadrupole are explicitly obtained in terms of the metric perturbations of the flat background metric. Therefore, if there is a slight difference between the four-velocities of the dark energy and dark matter, the Universe would acquire some anisotropic characteristics, and its geometry will deviate from the standard FLRW one. In fact, the recent Planck results show that the presence of an intrinsic large scale anisotropy in the Universe cannot be excluded a priori, so that the model presented in this work can be considered as a

  17. Planck constraints on holographic dark energy

    SciTech Connect

    Li, Miao; Zhang, Zhenhui; Li, Xiao-Dong; Ma, Yin-Zhe; Zhang, Xin E-mail: xiaodongli@kias.re.kr E-mail: zhangxin@mail.neu.edu.cn

    2013-09-01

    We perform a detailed investigation on the cosmological constraints on the holographic dark energy (HDE) model by using the Plank data. We find that HDE can provide a good fit to the Plank high-l (l ∼> 40) temperature power spectrum, while the discrepancy at l ≅ 20-40 found in the ΛCDM model remains unsolved in the HDE model. The Plank data alone can lead to strong and reliable constraint on the HDE parameter c. At the 68% confidence level (CL), we obtain c = 0.508 ± 0.207 with Plank+WP+lensing, favoring the present phantom behavior of HDE at the more than 2σ CL. By combining Plank+WP with the external astrophysical data sets, i.e. the BAO measurements from 6dFGS+SDSS DR7(R)+BOSS DR9, the direct Hubble constant measurement result (H{sub 0} = 73.8 ± 2.4 kms{sup −1}Mpc{sup −1}) from the HST, the SNLS3 supernovae data set, and Union2.1 supernovae data set, we get the 68% CL constraint results c = 0.484 ± 0.070, 0.474 ± 0.049, 0.594 ± 0.051, and 0.642 ± 0.066, respectively. The constraints can be improved by 2%-15% if we further add the Plank lensing data into the analysis. Compared with the WMAP-9 results, the Plank results reduce the error by 30%-60%, and prefer a phantom-like HDE at higher significant level. We also investigate the tension between different data sets. We find no evident tension when we combine Plank data with BAO and HST. Especially, we find that the strong correlation between Ω{sub m}h{sup 3} and dark energy parameters is helpful in relieving the tension between the Plank and HST measurements. The residual value of χ{sup 2}{sub Plank+WP+HST}−χ{sup 2}{sub Plank+WP} is 7.8 in the ΛCDM model, and is reduced to 1.0 or 0.3 if we switch the dark energy to w model or the holographic model. When we introduce supernovae data sets into the analysis, some tension appears. We find that the SNLS3 data set is in tension with all other data sets; for example, for the Plank+WP, WMAP-9 and BAO+HST, the corresponding Δχ{sup 2} is equal to 6

  18. Planck constraints on holographic dark energy

    NASA Astrophysics Data System (ADS)

    Li, Miao; Li, Xiao-Dong; Ma, Yin-Zhe; Zhang, Xin; Zhang, Zhenhui

    2013-09-01

    We perform a detailed investigation on the cosmological constraints on the holographic dark energy (HDE) model by using the Plank data. We find that HDE can provide a good fit to the Plank high-l (l gtrsim 40) temperature power spectrum, while the discrepancy at l simeq 20-40 found in the ΛCDM model remains unsolved in the HDE model. The Plank data alone can lead to strong and reliable constraint on the HDE parameter c. At the 68% confidence level (CL), we obtain c = 0.508 ± 0.207 with Plank+WP+lensing, favoring the present phantom behavior of HDE at the more than 2σ CL. By combining Plank+WP with the external astrophysical data sets, i.e. the BAO measurements from 6dFGS+SDSS DR7(R)+BOSS DR9, the direct Hubble constant measurement result (H0 = 73.8 ± 2.4 kms-1Mpc-1) from the HST, the SNLS3 supernovae data set, and Union2.1 supernovae data set, we get the 68% CL constraint results c = 0.484 ± 0.070, 0.474 ± 0.049, 0.594 ± 0.051, and 0.642 ± 0.066, respectively. The constraints can be improved by 2%-15% if we further add the Plank lensing data into the analysis. Compared with the WMAP-9 results, the Plank results reduce the error by 30%-60%, and prefer a phantom-like HDE at higher significant level. We also investigate the tension between different data sets. We find no evident tension when we combine Plank data with BAO and HST. Especially, we find that the strong correlation between Ωmh3 and dark energy parameters is helpful in relieving the tension between the Plank and HST measurements. The residual value of χ2Plank+WP+HST-χ2Plank+WP is 7.8 in the ΛCDM model, and is reduced to 1.0 or 0.3 if we switch the dark energy to w model or the holographic model. When we introduce supernovae data sets into the analysis, some tension appears. We find that the SNLS3 data set is in tension with all other data sets; for example, for the Plank+WP, WMAP-9 and BAO+HST, the corresponding Δχ2 is equal to 6.4, 3.5 and 4.1, respectively. As a comparison, the Union2

  19. The CHASE laboratory search for chameleon dark energy

    SciTech Connect

    Steffen, Jason H.; /Fermilab

    2010-11-01

    A scalar field is a favorite candidate for the particle responsible for dark energy. However, few theoretical means exist that can simultaneously explain the observed acceleration of the Universe and evade tests of gravity. The chameleon mechanism, whereby the properties of a particle depend upon the local environment, is one possible avenue. We present the results of the Chameleon Afterglow Search (CHASE) experiment, a laboratory probe for chameleon dark energy. CHASE marks a significant improvement other searches for chameleons both in terms of its sensitivity to the photon/chameleon coupling as well as its sensitivity to the classes of chameleon dark energy models and standard power-law models. Since chameleon dark energy is virtually indistinguishable from a cosmological constant, CHASE tests dark energy models in a manner not accessible to astronomical surveys.

  20. Baryon Acoustic Oscillation Intensity Mapping of Dark Energy

    NASA Astrophysics Data System (ADS)

    Chang, Tzu-Ching; Pen, Ue-Li; Peterson, Jeffrey B.; McDonald, Patrick

    2008-03-01

    The expansion of the Universe appears to be accelerating, and the mysterious antigravity agent of this acceleration has been called “dark energy.” To measure the dynamics of dark energy, baryon acoustic oscillations (BAO) can be used. Previous discussions of the BAO dark energy test have focused on direct measurements of redshifts of as many as 109 individual galaxies, by observing the 21 cm line or by detecting optical emission. Here we show how the study of acoustic oscillation in the 21 cm brightness can be accomplished by economical three-dimensional intensity mapping. If our estimates gain acceptance they may be the starting point for a new class of dark energy experiments dedicated to large angular scale mapping of the radio sky, shedding light on dark energy.

  1. Baryon acoustic oscillation intensity mapping of dark energy.

    PubMed

    Chang, Tzu-Ching; Pen, Ue-Li; Peterson, Jeffrey B; McDonald, Patrick

    2008-03-07

    The expansion of the Universe appears to be accelerating, and the mysterious antigravity agent of this acceleration has been called "dark energy." To measure the dynamics of dark energy, baryon acoustic oscillations (BAO) can be used. Previous discussions of the BAO dark energy test have focused on direct measurements of redshifts of as many as 10(9) individual galaxies, by observing the 21 cm line or by detecting optical emission. Here we show how the study of acoustic oscillation in the 21 cm brightness can be accomplished by economical three-dimensional intensity mapping. If our estimates gain acceptance they may be the starting point for a new class of dark energy experiments dedicated to large angular scale mapping of the radio sky, shedding light on dark energy.

  2. Dark matter and dark energy from the solution of the strong CP problem.

    PubMed

    Mainini, Roberto; Bonometto, Silvio A

    2004-09-17

    The Peccei-Quinn (PQ) solution of the strong CP problem requires the existence of axions, which are viable candidates for dark matter. If the Nambu-Goldstone potential of the PQ model is replaced by a potential V(|Phi|) admitting a tracker solution, the scalar field |Phi| can account for dark energy, while the phase of Phi yields axion dark matter. If V is a supergravity (SUGRA) potential, the model essentially depends on a single parameter, the energy scale Lambda. Once we set Lambda approximately equal to 10(10) GeV at the quark-hadron transition, |Phi| naturally passes through values suitable to solve the strong CP problem, later growing to values providing fair amounts of dark matter and dark energy.

  3. Effects of tidal gravitational fields in clustering dark energy models

    NASA Astrophysics Data System (ADS)

    Pace, Francesco; Reischke, Robert; Meyer, Sven; Schäfer, Björn Malte

    2017-04-01

    We extend a previous work by Reischke et al. by studying the effects of tidal shear on clustering dark energy models within the framework of the extended spherical collapse model and using the Zel'dovich approximation. As in previous works on clustering dark energy, we assumed a vanishing effective sound speed describing the perturbations in dark energy models. To be self-consistent, our treatment is valid only on linear scales since we do not intend to introduce any heuristic models. This approach makes the linear overdensity δc mass dependent and similarly to the case of smooth dark energy, its effects are predominant at small masses and redshifts. Tidal shear has effects of the order of per cent or less, regardless of the model and preserves a well-known feature of clustering dark energy: When dark energy perturbations are included, the models resemble better the Lambda cold dark matter evolution of perturbations. We also showed that effects on the comoving number density of haloes are small and qualitatively and quantitatively in agreement with what were previously found for smooth dark energy models.

  4. WMAP five-year data constraints on the unified model of dark energy and dark matter

    SciTech Connect

    Barreiro, T.; Bertolami, O.; Torres, P.

    2008-08-15

    We derive constraints on the parameter space of the unified model of dark energy and dark matter, the generalized Chaplygin gas, from the amplitudes and positions of the first few peaks and first trough of the cosmic microwave background radiation power spectrum, using the latest WMAP five-year data.

  5. Heavy ion reaction measurements with the EOS TPC (looking for central collisions with missing energy)

    SciTech Connect

    Wieman, H.H.; EOS Collaboration

    1994-05-01

    The EOS TPC was constructed for complete event measurement of heavy ion collisions at the Bevalac. We report here on the TPC design and some preliminary measurements of conserved event quantities such as total invariant mass, total momentum, total A and Z.

  6. Spherical collapse of dark energy with an arbitrary sound speed

    SciTech Connect

    Basse, Tobias; Bjælde, Ole Eggers; Wong, Yvonne Y.Y. E-mail: oeb@phys.au.dk

    2011-10-01

    We consider a generic type of dark energy fluid, characterised by a constant equation of state parameter w and sound speed c{sub s}, and investigate the impact of dark energy clustering on cosmic structure formation using the spherical collapse model. Along the way, we also discuss in detail the evolution of dark energy perturbations in the linear regime. We find that the introduction of a finite sound speed into the picture necessarily induces a scale-dependence in the dark energy clustering, which in turn affects the dynamics of the spherical collapse in a scale-dependent way. As with other, more conventional fluids, we can define a Jeans scale for the dark energy clustering, and hence a Jeans mass M{sub J} for the dark matter which feels the effect of dark energy clustering via gravitational interactions. For bound objects (halos) with masses M >> M{sub J}, the effect of dark energy clustering is maximal. For those with M << M{sub J}, the dark energy component is effectively homogeneous, and its role in the formation of these structures is reduced to its effects on the Hubble expansion rate. To compute quantitatively the virial density and the linearly extrapolated threshold density, we use a quasi-linear approach which is expected to be valid up to around the Jeans mass. We find an interesting dependence of these quantities on the halo mass M, given some w and c{sub s}. The dependence is the strongest for masses lying in the vicinity of M ∼ M{sub J}. Observing this M-dependence will be a tell-tale sign that dark energy is dynamic, and a great leap towards pinning down its clustering properties.

  7. Fingerprinting dark energy. III. Distinctive marks of viscosity

    NASA Astrophysics Data System (ADS)

    Sapone, Domenico; Majerotto, Elisabetta

    2012-06-01

    The characterization of dark energy is one of the primary goals in cosmology especially now that many new experiments are being planned with the aim of reaching a high sensitivity on cosmological parameters. It is known that if we move away from the simple cosmological constant model then we need to consider perturbations in the dark energy fluid. This means that dark energy has two extra degrees of freedom: the sound speed cs2 and the anisotropic stress σ. If dark energy is inhomogenous at the scales of interest then the gravitational potentials are modified and the evolution of the dark matter perturbations is also directly affected. In this paper we add an anisotropic component to the dark energy perturbations. Following the idea introduced in D. Sapone and M. Kunz, Phys. Rev. DPRVDAQ1550-7998 80, 083519 (2009)10.1103/PhysRevD.80.083519, we solve analytically the equations of perturbations in the dark sector, finding simple and accurate approximated solutions. We also find that the evolution of the density perturbations is governed by an effective sound speed that depends on both the sound speed and the anisotropic stress parameter. We then use these solutions to look at the impact of the dark energy perturbations on the matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background.

  8. New holographic dark energy model with non-linear interaction

    NASA Astrophysics Data System (ADS)

    Oliveros, A.; Acero, Mario A.

    2015-05-01

    In this paper the cosmological evolution of a holographic dark energy model with a non-linear interaction between the dark energy and dark matter components in a FRW type flat universe is analysed. In this context, the deceleration parameter q and the equation state w Λ are obtained. We found that, as the square of the speed of sound remains positive, the model is stable under perturbations since early times; it also shows that the evolution of the matter and dark energy densities are of the same order for a long period of time, avoiding the so-called coincidence problem. We have also made the correspondence of the model with the dark energy densities and pressures for the quintessence and tachyon fields. From this correspondence we have reconstructed the potential of scalar fields and their dynamics.

  9. Quantum Yang-Mills Dark Energy

    NASA Astrophysics Data System (ADS)

    Pasechnik, Roman

    2016-02-01

    In this short review, I discuss basic qualitative characteristics of quantum non-Abelian gauge dynamics in the non-stationary background of the expanding Universe in the framework of the standard Einstein--Yang--Mills formulation. A brief outlook of existing studies of cosmological Yang--Mills fields and their properties will be given. Quantum effects have a profound impact on the gauge field-driven cosmological evolution. In particular, a dynamical formation of the spatially-homogeneous and isotropic gauge field condensate may be responsible for both early and late-time acceleration, as well as for dynamical compensation of non-perturbative quantum vacua contributions to the ground state of the Universe. The main properties of such a condensate in the effective QCD theory at the flat Friedmann--Lema\\'itre--Robertson--Walker (FLRW) background will be discussed within and beyond perturbation theory. Finally, a phenomenologically consistent dark energy can be induced dynamically as a remnant of the QCD vacua compensation arising from leading-order graviton-mediated corrections to the QCD ground state.

  10. Essential building blocks of dark energy

    NASA Astrophysics Data System (ADS)

    Gleyzes, Jerome; Langlois, David; Piazza, Federico; Vernizzi, Filippo

    2013-08-01

    We propose a minimal description of single field dark energy/modified gravity within the effective field theory formalism for cosmological perturbations, which encompasses most existing models. We start from a generic Lagrangian given as an arbitrary function of the lapse and of the extrinsic and intrinsic curvature tensors of the time hypersurfaces in unitary gauge, i.e. choosing as time slicing the uniform scalar field hypersurfaces. Focusing on linear perturbations, we identify seven Lagrangian operators that lead to equations of motion containing at most two (space or time) derivatives, the background evolution being determined by the time-dependent coefficients of only three of these operators. We then establish a dictionary that translates any existing or future model whose Lagrangian can be written in the above form into our parametrized framework. As an illustration, we study Horndeski's — or generalized Galileon — theories and show that they can be described, up to linear order, by only six of the seven operators mentioned above. This implies, remarkably, that the dynamics of linear perturbations can be more general than that of Horndeski while remaining second order. Finally, in order to make the link with observations, we provide the entire set of linear perturbation equations in Newtonian gauge, the effective Newton constant in the quasi-static approximation and the ratio of the two gravitational potentials, in terms of the time-dependent coefficients of our Lagrangian.

  11. Cooling the dark energy camera instrument

    SciTech Connect

    Schmitt, R.L.; Cease, H.; DePoy, D.; Diehl, H.T.; Estrada, J.; Flaugher, B.; Kuhlmann, S.; Onal, Birce; Stefanik, A.; /Fermilab

    2008-06-01

    DECam, camera for the Dark Energy Survey (DES), is undergoing general design and component testing. For an overview see DePoy, et al in these proceedings. For a description of the imager, see Cease, et al in these proceedings. The CCD instrument will be mounted at the prime focus of the CTIO Blanco 4m telescope. The instrument temperature will be 173K with a heat load of 113W. In similar applications, cooling CCD instruments at the prime focus has been accomplished by three general methods. Liquid nitrogen reservoirs have been constructed to operate in any orientation, pulse tube cryocoolers have been used when tilt angles are limited and Joule-Thompson or Stirling cryocoolers have been used with smaller heat loads. Gifford-MacMahon cooling has been used at the Cassegrain but not at the prime focus. For DES, the combined requirements of high heat load, temperature stability, low vibration, operation in any orientation, liquid nitrogen cost and limited space available led to the design of a pumped, closed loop, circulating nitrogen system. At zenith the instrument will be twelve meters above the pump/cryocooler station. This cooling system expected to have a 10,000 hour maintenance interval. This paper will describe the engineering basis including the thermal model, unbalanced forces, cooldown time, the single and two-phase flow model.

  12. Graviweak Unification, Invisible Universe and Dark Energy

    NASA Astrophysics Data System (ADS)

    Das, C. R.; Laperashvili, L. V.; Tureanu, A.

    2013-07-01

    We consider a graviweak unification model with the assumption of the existence of a hidden (invisible) sector of our Universe, parallel to the visible world. This Hidden World (HW) is assumed to be a Mirror World (MW) with broken mirror parity. We start with a diffeomorphism invariant theory of a gauge field valued in a Lie algebra g, which is broken spontaneously to the direct sum of the space-time Lorentz algebra and the Yang-Mills algebra: ˜ {g} = {{su}}(2) (grav)L ⊕ {{su}}(2)L — in the ordinary world, and ˜ {g}' = {{su}}(2){' (grav)}R ⊕ {{su}}(2)'R — in the hidden world. Using an extension of the Plebanski action for general relativity, we recover the actions for gravity, SU(2) Yang-Mills and Higgs fields in both (visible and invisible) sectors of the Universe, and also the total action. After symmetry breaking, all physical constants, including the Newton's constants, cosmological constants, Yang-Mills couplings, and other parameters, are determined by a single parameter g present in the initial action, and by the Higgs VEVs. The dark energy problem of this model predicts a too large supersymmetric breaking scale (MSUSY 1010GeV), which is not within the reach of the LHC experiments.

  13. Spectroscopic Needs for Imaging Dark Energy Experiments

    DOE PAGES

    Newman, Jeffrey A.; Slosar, Anze; Abate, Alexandra; ...

    2015-03-15

    Ongoing and near-future imaging-based dark energy experiments are critically dependent upon photometric redshifts (a.k.a. photo-z’s): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-z’s will result in smaller random errors on cosmological parameters; while systematic errors in photometric redshift estimates, if not constrained, may dominate all other uncertainties from these experiments. The desired optimization and calibration is dependent upon spectroscopic measurements for secure redshift information; this is the key application of galaxy spectroscopy for imaging-based dark energy experiments. Hence, to achieve their full potential, imaging-based experiments will require large setsmore » of objects with spectroscopically-determined redshifts, for two purposes: Training: Objects with known redshift are needed to map out the relationship between object color and z (or, equivalently, to determine empirically-calibrated templates describing the rest-frame spectra of the full range of galaxies, which may be used to predict the color-z relation). The ultimate goal of training is to minimize each moment of the distribution of differences between photometric redshift estimates and the true redshifts of objects, making the relationship between them as tight as possible. The larger and more complete our “training set” of spectroscopic redshifts is, the smaller the RMS photo-z errors should be, increasing the constraining power of imaging experiments; Requirements: Spectroscopic redshift measurements for ~30,000 objects over >~15 widely-separated regions, each at least ~20 arcmin in diameter, and reaching the faintest objects used in a given experiment, will likely be necessary if photometric redshifts are to be trained and calibrated with conventional techniques. Larger, more complete samples (i.e., with longer exposure times) can improve photo-z algorithms and reduce

  14. Spectroscopic Needs for Imaging Dark Energy Experiments

    SciTech Connect

    Newman, Jeffrey A.; Slosar, Anze; Abate, Alexandra; Abdalla, Filipe B.; Allam, Sahar; Allen, Steven W.; Ansari, Reza; Bailey, Stephen; Barkhouse, Wayne A.; Beers, Timothy C.; Blanton, Michael R.; Brodwin, Mark; Brownstein, Joel R.; Brunner, Robert J.; Carrasco-Kind, Matias; Cervantes-Cota, Jorge; Chisari, Nora Elisa; Colless, Matthew; Comparat, Johan; Coupon, Jean; Cheu, Elliott; Cunha, Carlos E.; de la Macorra, Alex; Dell’Antonio, Ian P.; Frye, Brenda L.; Gawiser, Eric J.; Gehrels, Neil; Grady, Kevin; Hagen, Alex; Hall, Patrick B.; Hearin, Andrew P.; Hildebrandt, Hendrik; Hirata, Christopher M.; Ho, Shirley; Honscheid, Klaus; Huterer, Dragan; Ivezic, Zeljko; Kneib, Jean -Paul; Kruk, Jeffrey W.; Lahav, Ofer; Mandelbaum, Rachel; Marshall, Jennifer L.; Matthews, Daniel J.; Menard, Brice; Miquel, Ramon; Moniez, Marc; Moos, H. W.; Moustakas, John; Papovich, Casey; Peacock, John A.; Park, Changbom; Rhodes, Jason; Sadeh, Iftach; Schmidt, Samuel J.; Stern, Daniel K.; Tyson, J. Anthony; von der Linden, Anja; Wechsler, Risa H.; Wood-Vasey, W. M.; Zentner, A.

    2015-03-15

    Ongoing and near-future imaging-based dark energy experiments are critically dependent upon photometric redshifts (a.k.a. photo-z’s): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-z’s will result in smaller random errors on cosmological parameters; while systematic errors in photometric redshift estimates, if not constrained, may dominate all other uncertainties from these experiments. The desired optimization and calibration is dependent upon spectroscopic measurements for secure redshift information; this is the key application of galaxy spectroscopy for imaging-based dark energy experiments. Hence, to achieve their full potential, imaging-based experiments will require large sets of objects with spectroscopically-determined redshifts, for two purposes: Training: Objects with known redshift are needed to map out the relationship between object color and z (or, equivalently, to determine empirically-calibrated templates describing the rest-frame spectra of the full range of galaxies, which may be used to predict the color-z relation). The ultimate goal of training is to minimize each moment of the distribution of differences between photometric redshift estimates and the true redshifts of objects, making the relationship between them as tight as possible. The larger and more complete our “training set” of spectroscopic redshifts is, the smaller the RMS photo-z errors should be, increasing the constraining power of imaging experiments; Requirements: Spectroscopic redshift measurements for ~30,000 objects over >~15 widely-separated regions, each at least ~20 arcmin in diameter, and reaching the faintest objects used in a given experiment, will likely be necessary if photometric redshifts are to be trained and calibrated with conventional techniques. Larger, more complete samples (i.e., with longer exposure times) can improve photo-z algorithms and reduce scatter

  15. Dark Energy Domination In The Virgocentric Flow

    NASA Astrophysics Data System (ADS)

    Byrd, Gene; Chernin, A. D.; Karachentsev, I. D.; Teerikorpi, P.; Valtonen, M.; Dolgachev, V. P.; Domozhilova, L. M.

    2011-04-01

    Dark energy (DE) was first observationally detected at large Gpc distances. If it is a vacuum energy formulated as Einstein's cosmological constant, Λ, DE should also have dynamical effects at much smaller scales. Previously, we found its effects on much smaller Mpc scales in our Local Group (LG) as well as in other nearby groups. We used new HST observations of member 3D distances from the group centers and Doppler shifts. We find each group's gravity dominates a bound central system of galaxies but DE antigravity results in a radial recession increasing with distance from the group center of the outer members. Here we focus on the much larger (but still cosmologically local) Virgo Cluster and systems around it using new observations of velocities and distances. We propose an analytic model whose key parameter is the zero-gravity radius (ZGR) from the cluster center where gravity and DE antigravity balance. DE brings regularity to the Virgocentric flow. Beyond Virgo's 10 Mpc ZGR, the flow curves to approach a linear global Hubble law at larger distances. The Virgo cluster and its outer flow are similar to the Local Group and its local outflow with a scaling factor of about 10; the ZGR for Virgo is 10 times larger than that of the LG. The similarity of the two systems on the scales of 1 to 30 Mpc suggests that a quasi-stationary bound central component and an expanding outflow applies to a wide range of groups and clusters due to small scale action of DE as well as gravity. Chernin, et al 2009 Astronomy and Astrophysics 507, 1271 http://arxiv.org/abs/1006.0066 http://arxiv.org/abs/1006.0555

  16. EOS standards

    SciTech Connect

    Greeff, Carl W

    2011-01-12

    An approach to creating accurate EOS for pressure standards is described. Applications to Cu, Au, and Ta are shown. Extension of the method to high compressions using DFT is illustrated. Comparisons with modern functionals show promise.

  17. Large-scale instability in interacting dark energy and dark matter fluids

    SciTech Connect

    Vaeliviita, Jussi; Majerotto, Elisabetta; Maartens, Roy E-mail: elisabetta.majerotto@port.ac.uk

    2008-07-15

    If dark energy interacts with dark matter, this gives a new approach to the coincidence problem. But interacting dark energy models can suffer from pathologies. We consider the case where the dark energy is modelled as a fluid with constant equation of state parameter w. Non-interacting constant-w models are well behaved in the background and in the perturbed universe. But the combination of constant w and a simple interaction with dark matter leads to an instability in the dark sector perturbations at early times: the curvature perturbation blows up on super-Hubble scales. Our results underline how important it is to carefully analyse the relativistic perturbations when considering models of coupled dark energy. The instability that we find has been missed in some previous work where the perturbations were not consistently treated. The unstable mode dominates even if adiabatic initial conditions are used. The instability also arises regardless of how weak the coupling is. This non-adiabatic instability is different from previously discovered adiabatic instabilities on small scales in the strong-coupling regime.

  18. Scalar perturbations in cosmological models with dark energy-dark matter interaction

    SciTech Connect

    Eingorn, Maxim; Kiefer, Claus E-mail: kiefer@thp.uni-koeln.de

    2015-07-01

    Scalar cosmological perturbations are investigated in the framework of a model with interacting dark energy and dark matter. In addition to these constituents, the inhomogeneous Universe is supposed to be filled with the standard noninteracting constituents corresponding to the conventional ΛCDM model. The interaction term is chosen in the form of a linear combination of dark sector energy densities with evolving coefficients. The methods of discrete cosmology are applied, and strong theoretical constraints on the parameters of the model are derived. A brief comparison with observational data is performed.

  19. Cosmological consequences of interacting modified holographic Ricci dark energy

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, Surajit

    2016-07-01

    In this present work, we have studied various aspects of modified holographic Ricci dark energy interacting with pressureless dark matter in a flat Friedman-Robertson-Walker universe. We have observed that reconstructed Hubble parameter H={dot{a}}/{a}, expressed as a function of redshift z=a^{-1}-1, exhibits an increasing pattern with evolution of the universe. The equation of state parameter has behaved like ``quintessence" for various combinations of α and β. Deceleration parameter has stayed in negative level and this has indicated accelerated expansion of the universe. Fractional densities expressed as function of z has indicated transition of the universe from a matter dominated to dark energy dominated phase. Finally we have created statefinder trajectories in {r-s} plane and we have observed that for modified holographic Ricci dark energy interacting with pressureless dark matter it is possible to attain ΛCDM phase of the universe.

  20. Time-Dependent Dark Energy Density and Holographic DE Model with Interaction

    NASA Astrophysics Data System (ADS)

    Saadat, H.; Saadat, A. M.

    2011-05-01

    In this article we consider holographic dark energy model with interaction and space curvature. We calculate cosmic scale factor by using the time-dependent dark energy density. Then we obtain phenomenological interaction between holographic dark energy and matter.

  1. Studies of dark energy with X-ray observatories.

    PubMed

    Vikhlinin, Alexey

    2010-04-20

    I review the contribution of Chandra X-ray Observatory to studies of dark energy. There are two broad classes of observable effects of dark energy: evolution of the expansion rate of the Universe, and slow down in the rate of growth of cosmic structures. Chandra has detected and measured both of these effects through observations of galaxy clusters. A combination of the Chandra results with other cosmological datasets leads to 5% constraints on the dark energy equation-of-state parameter, and limits possible deviations of gravity on large scales from general relativity.

  2. Scalar field descriptions of two dark energy models

    NASA Astrophysics Data System (ADS)

    Panotopoulos, Grigorios

    2017-07-01

    We give a scalar field description of two dark energy parametrizations, and we analyze in detail its cosmology both at the level of background evolution and at the level of linear perturbations. In particular, we compute the statefinder parameters and the growth index as functions of the redshift for both dark energy parametrizations, and the comparison with the Λ CDM model as well as with a few well-known geometrical dark energy models is shown. In addition, the combination parameter A =f σ8 of both models is compared against current data.

  3. Neutrino mass and dark energy from weak lensing.

    PubMed

    Abazajian, Kevork N; Dodelson, Scott

    2003-07-25

    Weak gravitational lensing of background galaxies by intervening matter directly probes the mass distribution in the Universe. This distribution is sensitive to both the dark energy and neutrino mass. We examine the potential of lensing experiments to measure features of both simultaneously. Focusing on the radial information contained in a future deep 4000 deg(2) survey, we find that the expected (1-sigma) error on a neutrino mass is 0.1 eV, if the dark-energy parameters are allowed to vary. The constraints on dark-energy parameters are similarly restrictive, with errors on w of 0.09.

  4. The distinguishability of interacting dark energy from modified gravity

    SciTech Connect

    Clemson, Timothy; Koyama, Kazuya E-mail: kazuya.koyama@port.ac.uk

    2013-01-01

    We study the observational viability of coupled quintessence models with their expansion and growth histories matched to modified gravity cosmologies. We find that for a Dvali-Gabadadze-Porrati model which has been fitted to observations, the matched interacting dark energy models are observationally disfavoured. We also study the distinguishability of interacting dark energy models matched to scalar-tensor theory cosmologies and show that it is not always possible to find a physical interacting dark energy model which shares their expansion and growth histories.

  5. Inflation via logarithmic entropy-corrected holographic dark energy model

    NASA Astrophysics Data System (ADS)

    Darabi, F.; Felegary, F.; Setare, M. R.

    2016-12-01

    We study the inflation in terms of the logarithmic entropy-corrected holographic dark energy (LECHDE) model with future event horizon, particle horizon, and Hubble horizon cut-offs, and we compare the results with those obtained in the study of inflation by the holographic dark energy HDE model. In comparison, the spectrum of primordial scalar power spectrum in the LECHDE model becomes redder than the spectrum in the HDE model. Moreover, the consistency with the observational data in the LECHDE model of inflation constrains the reheating temperature and Hubble parameter by one parameter of holographic dark energy and two new parameters of logarithmic corrections.

  6. Studies of dark energy with x-ray observatories

    PubMed Central

    Vikhlinin, Alexey

    2010-01-01

    I review the contribution of Chandra X-ray Observatory to studies of dark energy. There are two broad classes of observable effects of dark energy: evolution of the expansion rate of the Universe, and slow down in the rate of growth of cosmic structures. Chandra has detected and measured both of these effects through observations of galaxy clusters. A combination of the Chandra results with other cosmological datasets leads to 5% constraints on the dark energy equation-of-state parameter, and limits possible deviations of gravity on large scales from general relativity. PMID:20404207

  7. Dark energy and the quietness of the local Hubble flow

    NASA Astrophysics Data System (ADS)

    Axenides, M.; Perivolaropoulos, L.

    2002-06-01

    The linearity and quietness of the local (<10 Mpc) Hubble flow (LHF) in view of the very clumpy local universe is a long standing puzzle in standard and in open CDM (cold dark matter) cosmogony. The question addressed in this paper is whether the antigravity component of the recently discovered dark energy can cool the velocity flow enough to provide a solution to this puzzle. We calculate the growth of matter fluctuations in a flat universe containing a fraction ΩX(t0) of dark energy obeying the time independent equation of state pX=wρX. We find that dark energy can indeed cool the LHF. However the dark energy parameter values required to make the predicted velocity dispersion consistent with the observed value vrms~=40 km/s have been ruled out by other observational tests constraining the dark energy parameters w and ΩX. Therefore despite the claims of recent qualitative studies, dark energy with time independent equation of state cannot by itself explain the quietness and linearity of the local Hubble flow.

  8. The Dark Energy Survey Data Management System

    SciTech Connect

    Mohr, Joseph J.; Barkhouse, Wayne; Beldica, Cristina; Bertin, Emmanuel; Dora Cai, Y.; Nicolaci da Costa, Luiz A.; Darnell, J.Anthony; Daues, Gregory E.; Jarvis, Michael; Gower, Michelle; Lin, Huan; /Fermilab /Rio de Janeiro Observ.

    2008-07-01

    The Dark Energy Survey (DES) collaboration will study cosmic acceleration with a 5000 deg2 griZY survey in the southern sky over 525 nights from 2011-2016. The DES data management (DESDM) system will be used to process and archive these data and the resulting science ready data products. The DESDM system consists of an integrated archive, a processing framework, an ensemble of astronomy codes and a data access framework. We are developing the DESDM system for operation in the high performance computing (HPC) environments at the National Center for Supercomputing Applications (NCSA) and Fermilab. Operating the DESDM system in an HPC environment offers both speed and flexibility. We will employ it for our regular nightly processing needs, and for more compute-intensive tasks such as large scale image coaddition campaigns, extraction of weak lensing shear from the full survey dataset, and massive seasonal reprocessing of the DES data. Data products will be available to the Collaboration and later to the public through a virtual-observatory compatible web portal. Our approach leverages investments in publicly available HPC systems, greatly reducing hardware and maintenance costs to the project, which must deploy and maintain only the storage, database platforms and orchestration and web portal nodes that are specific to DESDM. In Fall 2007, we tested the current DESDM system on both simulated and real survey data. We used TeraGrid to process 10 simulated DES nights (3TB of raw data), ingesting and calibrating approximately 250 million objects into the DES Archive database. We also used DESDM to process and calibrate over 50 nights of survey data acquired with the Mosaic2 camera. Comparison to truth tables in the case of the simulated data and internal crosschecks in the case of the real data indicate that astrometric and photometric data quality is excellent.

  9. 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.

  10. Dark matter and dark energy accretion on to intermediate-mass black holes

    NASA Astrophysics Data System (ADS)

    Pepe, C.; Pellizza, L. J.; Romero, G. E.

    2012-03-01

    In this work we investigate the accretion of cosmological fluids on to an intermediate-mass black hole at the centre of a globular cluster, focusing on the influence of the parent stellar system on the accretion flow. We show that the accretion of cosmic background radiation and the so-called dark energy on to an intermediate-mass black hole is negligible. On the other hand, if cold dark matter has a non-vanishing pressure, the accretion of dark matter is large enough to increase the black hole mass well beyond the present observed upper limits. We conclude that either intermediate-mass black holes do not exist, or dark matter does not exist, or it is not strictly collisionless. In the latter case, we set a lower limit for the parameter of the cold dark matter equation of state.

  11. Can interacting dark energy solve the H0 tension?

    NASA Astrophysics Data System (ADS)

    Di Valentino, Eleonora; Melchiorri, Alessandro; Mena, Olga

    2017-08-01

    The answer is yes. We indeed find that interacting dark energy can alleviate the current tension on the value of the Hubble constant H0 between the cosmic microwave background anisotropies constraints obtained from the Planck satellite and the recent direct measurements reported by Riess et al. 2016. The combination of these two data sets points toward a nonzero dark matter-dark energy coupling ξ at more than two standard deviations, with ξ =-0.2 6-0.12+0.16 at 95% C.L., i.e. with a moderate evidence for interacting dark energy with an odds ratio of 6 ∶1 respect to a non interacting cosmological constant. However the H0 tension is better solved when the equation of state of the interacting dark energy component is allowed to freely vary, with a phantomlike equation of state w =-1.185 ±0.064 (at 68% C.L.), ruling out the pure cosmological constant case, w =-1 , again at more than two standard deviations. When Planck data are combined with external datasets, as BAO, JLA Supernovae Ia luminosity distances, cosmic shear or lensing data, we find perfect consistency with the cosmological constant scenario and no compelling evidence for a dark matter-dark energy coupling.

  12. Evolution of density and velocity profiles of dark matter and dark energy in spherical voids

    NASA Astrophysics Data System (ADS)

    Novosyadlyj, Bohdan; Tsizh, Maksym; Kulinich, Yurij

    2017-02-01

    We analyse the evolution of cosmological perturbations which leads to the formation of large isolated voids in the Universe. We assume that initial perturbations are spherical and all components of the Universe (radiation, matter and dark energy) are continuous media with ideal fluid energy-momentum tensors, which interact only gravitationally. Equations of the evolution of perturbations for every component in the comoving to cosmological background reference frame are obtained from equations of energy and momentum conservation and Einstein's ones and are integrated numerically. Initial conditions are set at the early stage of evolution in the radiation-dominated epoch, when the scale of perturbation is much larger than the particle horizon. Results show how the profiles of density and velocity of matter and dark energy are formed and how they depend on parameters of dark energy and initial conditions. In particular, it is shown that final matter density and velocity amplitudes change within range ˜4-7 per cent when the value of equation-of-state parameter of dark energy w vary in the range from -0.8 to -1.2, and change within ˜1 per cent only when the value of effective sound speed of dark energy vary over all allowable range of its values.

  13. Observational Constraints of Red-shift Parametrization Parameters of Dark Energy in Horava-Lifshitz Gravity

    NASA Astrophysics Data System (ADS)

    Biswas, Ritabrata; Debnath, Ujjal

    2015-02-01

    We have assumed that the FRW universe filled with baryonic matter, radiation and dark matter along with dark energy in the frame-work of Horava-Lifshitz gravity. Here three parameterizations like Linear, CPL and JBP for the dark energy have been assumed for the variations of EOS parameter w( z). The observational data analysis by χ 2 minimum test have been analyzed for our models. From Stern, Stern+BAO and Stern+BAO+CMB joint data analysis, we have obtained the bounds of the arbitrary parameters w 0 and w 1. The best fit values of the parameters w 0 and w 1 for these three models and the minimum values of χ 2 have been obtained by observational data analysis. Also the bounds of the parameters w 0 and w 1 are obtained by 66 %, 90 % and 99 % confidence levels for linear, CPL and JBP models. Next red shift-magnitude observational data points from type Ia supernovae have been considered and which contains 557 data points. From this observation, the distance modulus μ( z) against red shift z has been investigated for our predicted theoretical model (three DE models) for the best fit values of the parameters and the observed SNe Ia Union2 data sample. Finally, we have investigated that our predicted theoretical three models permitted the observational data sets.

  14. Searching for dark energy with matter wave interferometry

    NASA Astrophysics Data System (ADS)

    Hamilton, Paul

    2016-05-01

    The nature of dark energy, which makes up 70% of the mass-energy of the universe, remains completely unknown. Chameleons are a simple scalar model for dark energy that mediate a force which is screened by bulk matter. However we can now probe these scalar fields using atoms as nearly ideal test masses in the vacuum of our cavity-based matter wave interferometer. Our first measurements ruled out a range of chameleons that would reproduce the observed cosmic acceleration. Since then we have improved sensitivity by a factor of 100. With a similar future improvement, we will be sensitive to any possible chameleon field and other exotic models for dark energy and dark matter, such as symmetrons or f(R) gravity.

  15. Cosmological viability conditions for f(T) dark energy models

    SciTech Connect

    Setare, M.R.; Mohammadipour, N. E-mail: N.Mohammadipour@uok.ac.ir

    2012-11-01

    Recently f(T) modified teleparallel gravity where T is the torsion scalar has been proposed as the natural gravitational alternative for dark energy. We perform a detailed dynamical analysis of these models and find conditions for the cosmological viability of f(T) dark energy models as geometrical constraints on the derivatives of these models. We show that in the phase space exists two cosmologically viable trajectory which (i) The universe would start from an unstable radiation point, then pass a saddle standard matter point which is followed by accelerated expansion de sitter point. (ii) The universe starts from a saddle radiation epoch, then falls onto the stable matter era and the system can not evolve to the dark energy dominated epoch. Finally, for a number of f(T) dark energy models were proposed in the more literature, the viability conditions are investigated.

  16. Updating the axion cold dark matter energy density

    SciTech Connect

    Bae, Kyu Jung; Huh, Ji-Haeng; Kim, Jihn E E-mail: jhhuh@phya.snu.ac.kr

    2008-09-15

    We improve the estimate of the axion cold dark matter energy density by considering the new values of current quark masses, the quantum chromodynamics phase transition effect and a possible anharmonic effect.

  17. Dark Energy Drives Vibrating Atoms, Chain reactions, Etc.:

    NASA Astrophysics Data System (ADS)

    Sven, Charles

    2010-03-01

    The 14 billion year old atom - destroyed Hiroshima, vibrates at a 100 trillion times/sec, emanates photons at the speed of light, contains atom sized proton force field that attracts electrons, all driven by ``Dark Energy.'' This ageless atom's superpowerful requirements, must be supplied from a huge, external, super high-frequency, super-cooled, ``Dark Energy field,'' undetected by current technology, existing for 14+ billion years without degradation. Demonstrating this age-old atom's ``dark energy'' power source requires the synthesis of a number of elements, forces, observations and experiments, many of which are combined in novel but only in replicable venues. Solution includes ``Dark Energy'' participation in celestial observations. Expanded excerpt from my presentation at: the American Physical Society's April meeting in Denver 2009 Section T8: Cosmology

  18. Model selection as a science driver for dark energy surveys

    NASA Astrophysics Data System (ADS)

    Mukherjee, Pia; Parkinson, David; Corasaniti, Pier Stefano; Liddle, Andrew R.; Kunz, Martin

    2006-07-01

    A key science goal of upcoming dark energy surveys is to seek time-evolution of the dark energy. This problem is one of model selection, where the aim is to differentiate between cosmological models with different numbers of parameters. However, the power of these surveys is traditionally assessed by estimating their ability to constrain parameters, which is a different statistical problem. In this paper, we use Bayesian model selection techniques, specifically forecasting of the Bayes factors, to compare the abilities of different proposed surveys in discovering dark energy evolution. We consider six experiments - supernova luminosity measurements by the Supernova Legacy Survey, SNAP, JEDI and ALPACA, and baryon acoustic oscillation measurements by WFMOS and JEDI - and use Bayes factor plots to compare their statistical constraining power. The concept of Bayes factor forecasting has much broader applicability than dark energy surveys.

  19. New Light on Dark Energy (LBNL Science at the Theater)

    ScienceCinema

    Linder, Eric; Ho, Shirly; Aldering, Greg; Fraiknoi, Andrew

    2016-07-12

    A panel of Lab scientists — including Eric Linder, Shirly Ho, and Greg Aldering — along with Andrew Fraiknoi, the Bay Area's most popular astronomy explainer, gathered at the Berkeley Repertory Theatre on Monday, April 25, 2011, for a discussion about "New Light on Dark Energy." Topics will include hunting down Type 1a supernovae, measuring the universe using baryon oscillation, and whether dark energy is the true driver of the universe.

  20. Cosmology with massive neutrinos coupled to dark energy.

    PubMed

    Brookfield, A W; van de Bruck, C; Mota, D F; Tocchini-Valentini, D

    2006-02-17

    Cosmological consequences of a coupling between massive neutrinos and dark energy are investigated. In such models, the neutrino mass is a function of a scalar field, which plays the role of dark energy. The evolution of the background and cosmological perturbations are discussed. We find that mass-varying neutrinos can leave a significant imprint on the anisotropies in the cosmic microwave background and even lead to a reduction of power on large angular scales.

  1. What do we really know about dark energy?

    PubMed

    Durrer, Ruth

    2011-12-28

    In this paper, we discuss what we truly know about dark energy. I shall argue that, to date, our single indication for the existence of dark energy comes from distance measurements and their relation to redshift. Supernovae, cosmic microwave background anisotropies and observations of baryon acoustic oscillations simply tell us that the observed distance to a given redshift z is larger than the one expected from a Friedmann-Lemaître universe with matter only and the locally measured Hubble parameter.

  2. Cosmological degeneracy versus cosmography: A cosmographic dark energy model

    NASA Astrophysics Data System (ADS)

    Luongo, Orlando; Pisani, Giovanni Battista; Troisi, Antonio

    In this work, we use cosmography to alleviate the degeneracy among cosmological models, proposing a way to parametrize matter and dark energy in terms of cosmokinematics quantities. The recipe of using cosmography allows to expand observable quantities in Taylor series and to directly compare those expansions with data. The strategy involves the expansions of q and j, up to the second-order around a(t) = 1. This includes additional cosmographic parameters which are fixed by current values of q0 and j0. We therefore propose a fully self-consistent parametrization of the total energy density driving the late-time universe speed up. This stratagem does not remove all the degeneracy but enables one to pass from the model-dependent couple of coefficients, ω0 and Ωm,0, to model-independent quantities determined from cosmography. Afterwards, we describe a feasible cosmographic dark energy model, in which matter is fixed whereas dark energy evolves by means of the cosmographic series. Our technique provides robust constraints on cosmokinematic parameters, permitting one to separately bound matter from dark energy densities. Our cosmographic dark energy model turns out to be one parameter only, but differently from the lambda cold dark matter (ΛCDM) paradigm, it does not contain ansatz on the dark energy form. In addition, we even determine the free parameter of our model in suitable 1σ intervals through Monte Carlo analyses based on the Metropolis algorithm. We compare our results with the standard concordance model and we find that our treatment seems to indicate that dark energy slightly evolves in time, reducing to a pure cosmological constant only as z → 0.

  3. New Light on Dark Energy (LBNL Science at the Theater)

    SciTech Connect

    Linder, Eric; Ho, Shirly; Aldering, Greg; Fraiknoi, Andrew

    2011-04-25

    A panel of Lab scientists — including Eric Linder, Shirly Ho, and Greg Aldering — along with Andrew Fraiknoi, the Bay Area's most popular astronomy explainer, gathered at the Berkeley Repertory Theatre on Monday, April 25, 2011, for a discussion about "New Light on Dark Energy." Topics will include hunting down Type 1a supernovae, measuring the universe using baryon oscillation, and whether dark energy is the true driver of the universe.

  4. Interacting Dark matter and Holographic dark energy in Bianchi type-V universe

    NASA Astrophysics Data System (ADS)

    Adhav, K. S.; Munde, S. L.; Tayade, G. B.; Bokey, V. D.

    2015-09-01

    The spatially homogeneous and anisotropic Bianchi type-V universe filled with interacting Dark matter and Holographic dark energy has been studied. The exact solutions of Einstein's field equations are obtained by (i) applying the special law of variation of Hubble parameter that yields constant values of the deceleration parameter and (ii) using a special form of deceleration parameter. It has been observed that for suitable choice of interaction between dark matter and holographic dark energy there is no coincidence problem (unlike CDM). Also, in all the resulting models the anisotropy of expansion dies out very quickly and attains isotropy after some finite time. The physical and geometrical aspects of the models are also discussed.

  5. Dark matter and dark energy interactions: theoretical challenges, cosmological implications and observational signatures

    NASA Astrophysics Data System (ADS)

    Wang, B.; Abdalla, E.; Atrio-Barandela, F.; Pavón, D.

    2016-09-01

    Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.

  6. Dark matter and dark energy interactions: theoretical challenges, cosmological implications and observational signatures.

    PubMed

    Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D

    2016-09-01

    Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.

  7. Consequences of dark matter-dark energy interaction on cosmological parameters derived from type Ia supernova data

    SciTech Connect

    Amendola, Luca; Campos, Gabriela Camargo; Rosenfeld, Rogerio

    2007-04-15

    Models where the dark matter component of the Universe interacts with the dark energy field have been proposed as a solution to the cosmic coincidence problem, since in the attractor regime both dark energy and dark matter scale in the same way. In these models the mass of the cold dark matter particles is a function of the dark energy field responsible for the present acceleration of the Universe, and different scenarios can be parametrized by how the mass of the cold dark matter particles evolves with time. In this article we study the impact of a constant coupling {delta} between dark energy and dark matter on the determination of a redshift dependent dark energy equation of state w{sub DE}(z) and on the dark matter density today from SNIa data. We derive an analytical expression for the luminosity distance in this case. In particular, we show that the presence of such a coupling increases the tension between the cosmic microwave background data from the analysis of the shift parameter in models with constant w{sub DE} and SNIa data for realistic values of the present dark matter density fraction. Thus, an independent measurement of the present dark matter density can place constraints on models with interacting dark energy.

  8. EOS Directory

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This Earth Observing System (EOS) directory is divided into two main sections: white and yellow pages. The white pages list alphabetically the names and addresses -- including e-mail, phone, and fax when available -- of all individuals involved with EOS, from graduate students to panel members to program management and more. The yellow pages list the names, affiliation, and phone number of participants divided by project management, program management, individual project participants, interdisciplinary investigations (listed alphabetically by PI), the Science Executive Committee, various panels, platforms, working groups, fellowships, and contractors.

  9. GALAXY CLUSTERS AS A PROBE OF EARLY DARK ENERGY

    SciTech Connect

    Alam, Ujjaini; Lukic, Zarija; Bhattacharya, Suman E-mail: zarija@lanl.gov

    2011-02-01

    We study a class of early dark energy (EDE) models, in which, unlike in standard dark energy models, a substantial amount of dark energy exists in the matter-dominated era. We self-consistently include dark energy perturbations, and show that these models may be successfully constrained using future observations of galaxy clusters, in particular the redshift abundance, and the Sunyaev-Zel'dovich (SZ) power spectrum. We make predictions for EDE models, as well as {Lambda}CDM for incoming X-ray (eROSITA) and microwave (South Pole Telescope) observations. We show that galaxy clusters' mass function and the SZ power spectrum will put strong constraints both on the equation of state of dark energy today and the redshift at which EDE transits to present-day {Lambda}CDM-like behavior for these models, thus providing complementary information to the geometric probes of dark energy. Not including perturbations in EDE models leads to those models being practically indistinguishable from {Lambda}CDM. An MCMC analysis of future galaxy cluster surveys provides constraints for EDE parameters that are competitive with and complementary to background expansion observations such as supernovae.

  10. Comparison of dark energy models after Planck 2015

    NASA Astrophysics Data System (ADS)

    Xu, Yue-Yao; Zhang, Xin

    2016-11-01

    We make a comparison for ten typical, popular dark energy models according to their capabilities of fitting the current observational data. The observational data we use in this work include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the direct measurement of the Hubble constant. Since the models have different numbers of parameters, in order to make a fair comparison, we employ the Akaike and Bayesian information criteria to assess the worth of the models. The analysis results show that, according to the capability of explaining observations, the cosmological constant model is still the best one among all the dark energy models. The generalized Chaplygin gas model, the constant w model, and the α dark energy model are worse than the cosmological constant model, but still are good models compared to others. The holographic dark energy model, the new generalized Chaplygin gas model, and the Chevalliear-Polarski-Linder model can still fit the current observations well, but from an economically feasible perspective, they are not so good. The new agegraphic dark energy model, the Dvali-Gabadadze-Porrati model, and the Ricci dark energy model are excluded by the current observations.

  11. Reconstruction of dark energy and expansion dynamics using Gaussian processes

    SciTech Connect

    Seikel, Marina; Clarkson, Chris; Smith, Mathew E-mail: chris.clarkson@uct.ac.za

    2012-06-01

    An important issue in cosmology is reconstructing the effective dark energy equation of state directly from observations. With few physically motivated models, future dark energy studies cannot only be based on constraining a dark energy parameter space, as the errors found depend strongly on the parametrisation considered. We present a new non-parametric approach to reconstructing the history of the expansion rate and dark energy using Gaussian Processes, which is a fully Bayesian approach for smoothing data. We present a pedagogical introduction to Gaussian Processes, and discuss how it can be used to robustly differentiate data in a suitable way. Using this method we show that the Dark Energy Survey - Supernova Survey (DES) can accurately recover a slowly evolving equation of state to σ{sub w} = ±0.05 (95% CL) at z = 0 and ±0.25 at z = 0.7, with a minimum error of ±0.025 at the sweet-spot at z ∼ 0.16, provided the other parameters of the model are known. Errors on the expansion history are an order of magnitude smaller, yet make no assumptions about dark energy whatsoever. A code for calculating functions and their first three derivatives using Gaussian processes has been developed and is available for download.

  12. Direct probe of dark energy through gravitational lensing effect

    NASA Astrophysics Data System (ADS)

    He, Hong-Jian; Zhang, Zhen

    2017-08-01

    We show that gravitational lensing can provide a direct method to probe the nature of dark energy at astrophysical scales. For lensing system as an isolated astrophysical object, we derive the dark energy contribution to gravitational potential as a repulsive power-law term, containing a generic equation of state parameter w. We find that it generates w-dependent and position-dependent modification to the conventional light orbital equation of w=‑1. With post-Newtonian approximation, we compute its direct effect for an isolated lensing system at astrophysical scales and find that the dark energy force can deflect the path of incident light rays. We demonstrate that the dark-energy-induced deflection angle ΔαDEpropto M(1+1/3w) (with 1+1/3w > 0), which increases with the lensing mass M and consistently approaches zero in the limit M→ 0. This effect is distinctive because dark energy tends to diffuse the rays and generates concave lensing effect. This is in contrast to the conventional convex lensing effect caused by both visible and dark matter. Measuring such concave lensing effect can directly probe the existence and nature of dark energy. We estimate this effect and show that the current gravitational lensing experiments are sensitive to the direct probe of dark energy at astrophysical scales. For the special case w=‑1, our independent study favors the previous works that the cosmological constant can affect light bending, but our prediction qualitatively and quantitatively differ from the literature, including our consistent realization of ΔαDE → 0 (under 0M→ ) at the leading order.

  13. The abnormally weighting energy hypothesis: the missing link between dark matter and dark energy

    SciTech Connect

    Alimi, J-M; Fuezfa, A E-mail: andre.fuzfa@fundp.ac.be

    2008-09-15

    We generalize tensor-scalar theories of gravitation by the introduction of an 'abnormally weighting' type of energy. This theory of tensor-scalar anomalous gravity is based on a relaxation of the weak equivalence principle that is currently restricted to ordinary visible matter only. As a consequence, the mechanism of convergence toward general relativity is modified and produces cosmic acceleration naturally as an inescapable gravitational feedback induced by the mass variation of some invisible sector. The cosmological implications of this new theoretical framework are studied. From the Hubble diagram cosmological test alone, this theory provides estimates of the amount of baryons and dark matter in the Universe that are consistent with the independent cosmological tests of the cosmic microwave background and big bang nucleosynthesis. Cosmic coincidence is naturally achieved from an equally natural assumption on the amplitude of the scalar coupling strength. Finally, from the adequacy for supernovae data, we derive a new intriguing relation between the space-time dependences of the gravitational coupling and the dark matter mass, providing an example of a crucial constraint on microphysics from cosmology. This provides glimpses of an enticing new symmetry between the visible and invisible sectors, namely that the scalar charges of visible and invisible matter are exactly opposite.

  14. Integrating EO data for applying the Nexus of water, energy and agriculture to monitor SDG Indicators within transboundary river basins

    NASA Astrophysics Data System (ADS)

    Zalidis, G.; Kavvada, A.; Crisman, T.

    2016-12-01

    The NEXUS of water, energy and agriculture is widely recognized as an integrated approach for innovative management solutions and actions to protect natural resources. Soil Spectral Libraries (SSL) implement the NEXUS approach by combining Earth Observation (EO) and Geospatial Information (GI) data and tools to extract information on soil attributes rapidly, reliably and cost effectively. NEXUS approach for soil resources at large scales- across landscapes or regions- remains a challenge however, especially for stakeholders, and in regards to promoting the concept, disseminating the methodology, and discussing potential benefits at both local and transboundary river basin levels. The CEOS Data Cube is an excellent tool for collecting, processing and disseminating EO data, and providing `Analysis Ready Data' utilized both as a management tool for policy makers, and a tool boosting economic activity and supporting end-users. Thus, it helps supporting the tracking of, and reporting on, the Sustainable Development Goals (SDGs), and promoting targeted approaches to address specific SDG Indicators. Although several European projects in the Balkan transboundary river basin areas focus on existing/potential ties to specific SDG Indicators under the leadership of i-BEC, data are lacking for some regions, and there is an exigent need for country/region - specific case studies. A case study in Albania, the 3rd for CEOS and the 1st for Europe, will seek to build synergies between different sectors and activities (water, energy, food) and natural resources, while also accounting for ecosystem climate- regulating functions. This will contribute to the global expansion of the Data Cube initiative, while adding high quality datasets in GEOSS. Engagement of EO ecosystem stakeholders, together with National Statistical Offices, regionally and globally, should exploit the networking capacities of multipliers, maximizing the impact and reach of SSL. The H2020 project GEOCRADLE has

  15. Coupled dark matter-dark energy in light of near universe observations

    SciTech Connect

    Honorez, Laura Lopez; Mena, Olga E-mail: beth.ann.reid@gmail.com E-mail: liciaverde@gmail.com

    2010-09-01

    Cosmological analysis based on currently available observations are unable to rule out a sizeable coupling among the dark energy and dark matter fluids. We explore a variety of coupled dark matter-dark energy models, which satisfy cosmic microwave background constraints, in light of low redshift and near universe observations. We illustrate the phenomenology of different classes of dark coupling models, paying particular attention in distinguishing between effects that appear only on the expansion history and those that appear in the growth of structure. We find that while a broad class of dark coupling models are effectively models where general relativity (GR) is modified — and thus can be probed by a combination of tests for the expansion history and the growth of structure —, there is a class of dark coupling models where gravity is still GR, but the growth of perturbations is, in principle modified. While this effect is small in the specific models we have considered, one should bear in mind that an inconsistency between reconstructed expansion history and growth may not uniquely indicate deviations from GR. Our low redshift constraints arise from cosmic velocities, redshift space distortions and dark matter abundance in galaxy voids. We find that current data constrain the dimensionless coupling to be |ξ| < 0.2, but prospects from forthcoming data are for a significant improvement. Future, precise measurements of the Hubble constant, combined with high-precision constraints on the growth of structure, could provide the key to rule out dark coupling models which survive other tests. We shall exploit as well weak equivalence principle violation arguments, which have the potential to highly disfavour a broad family of coupled models.

  16. Scaling cosmology with variable dark-energy equation of state

    NASA Astrophysics Data System (ADS)

    Castro, David R.; Velten, Hermano; Zimdahl, Winfried

    2012-06-01

    Interactions between dark matter and dark energy which result in a power-law behavior (with respect to the cosmic scale factor) of the ratio between the energy densities of the dark components (thus generalizing the ΛCDM model) have been considered as an attempt to alleviate the cosmic coincidence problem phenomenologically. We generalize this approach by allowing for a variable equation of state for the dark energy within the CPL-parametrization. Based on analytic solutions for the Hubble rate and using the Constitution and Union2 SNIa sets, we present a statistical analysis and classify different interacting and non-interacting models according to the Akaike (AIC) and the Bayesian (BIC) information criteria. We do not find noticeable evidence for an alleviation of the coincidence problem with the mentioned type of interaction.

  17. Scaling cosmology with variable dark-energy equation of state

    SciTech Connect

    Castro, David R.; Velten, Hermano; Zimdahl, Winfried E-mail: velten@physik.uni-bielefeld.de

    2012-06-01

    Interactions between dark matter and dark energy which result in a power-law behavior (with respect to the cosmic scale factor) of the ratio between the energy densities of the dark components (thus generalizing the ΛCDM model) have been considered as an attempt to alleviate the cosmic coincidence problem phenomenologically. We generalize this approach by allowing for a variable equation of state for the dark energy within the CPL-parametrization. Based on analytic solutions for the Hubble rate and using the Constitution and Union2 SNIa sets, we present a statistical analysis and classify different interacting and non-interacting models according to the Akaike (AIC) and the Bayesian (BIC) information criteria. We do not find noticeable evidence for an alleviation of the coincidence problem with the mentioned type of interaction.

  18. Ghost Dark Energy with Non-Linear Interaction Term

    NASA Astrophysics Data System (ADS)

    Ebrahimi, E.

    2016-06-01

    Here we investigate ghost dark energy (GDE) in the presence of a non-linear interaction term between dark matter and dark energy. To this end we take into account a general form for the interaction term. Then we discuss about different features of three choices of the non-linear interacting GDE. In all cases we obtain equation of state parameter, w D = p/ ρ, the deceleration parameter and evolution equation of the dark energy density parameter (Ω D ). We find that in one case, w D cross the phantom line ( w D < -1). However in two other classes w D can not cross the phantom divide. The coincidence problem can be solved in these models completely and there exist good agreement between the models and observational values of w D , q. We study squared sound speed {vs2}, and find that for one case of non-linear interaction term {vs2} can achieves positive values at late time of evolution.

  19. Interacting quintom dark energy with Nonminimal Derivative Coupling

    NASA Astrophysics Data System (ADS)

    Behrouz, Noushin; Nozari, Kourosh; Rashidi, Narges

    2017-03-01

    Following our recent work on interacting dark energy models (Nozari and Behrouz, 2016), we study cosmological dynamics of an extended dark energy model in which gravity is non-minimally coupled to the derivatives of a quintessence and a phantom field in a quintom model. There is also a phenomenological interaction between the dark energy and dark matter components. By considering an exponential potential as a self-interaction potential for quintom model, we obtain a scaling solution to alleviate the coincidence problem. The existence and stability of the critical points are discussed in details and it has been shown that in this setup the universe experiences a phantom divide crossing. We compare the model with recent observational data and find some constraints on the model's parameters. We investigate also perturbations around the homogeneous and isotropic background in our Nonminimal Derivative Coupling (NMDC) quintom model.

  20. An effective description of dark matter and dark energy in the mildly non-linear regime

    DOE PAGES

    Lewandowski, Matthew; Maleknejad, Azadeh; Senatore, Leonardo

    2017-05-18

    In the next few years, we are going to probe the low-redshift universe with unprecedented accuracy. Among the various fruits that this will bear, it will greatly improve our knowledge of the dynamics of dark energy, though for this there is a strong theoretical preference for a cosmological constant. We assume that dark energy is described by the so-called Effective Field Theory of Dark Energy, which assumes that dark energy is the Goldstone boson of time translations. Such a formalism makes it easy to ensure that our signatures are consistent with well-established principles of physics. Since most of the informationmore » resides at high wavenumbers, it is important to be able to make predictions at the highest wavenumber that is possible. Furthermore, the Effective Field Theory of Large-Scale Structure (EFTofLSS) is a theoretical framework that has allowed us to make accurate predictions in the mildly non-linear regime. In this paper, we derive the non-linear equations that extend the EFTofLSS to include the effect of dark energy both on the matter fields and on the biased tracers. For the specific case of clustering quintessence, we then perturbatively solve to cubic order the resulting non-linear equations and construct the one-loop power spectrum of the total density contrast.« less

  1. Interacting ghost dark energy models with variable G and Λ

    SciTech Connect

    Sadeghi, J.; Farahani, H.; Khurshudyan, M.; Movsisyan, A. E-mail: martiros.khurshudyan@nano.cnr.it E-mail: h.farahani@umz.ac.ir

    2013-12-01

    In this paper we consider several phenomenological models of variable Λ. Model of a flat Universe with variable Λ and G is accepted. It is well known, that varying G and Λ gives rise to modified field equations and modified conservation laws, which gives rise to many different manipulations and assumptions in literature. We will consider two component fluid, which parameters will enter to Λ. Interaction between fluids with energy densities ρ{sub 1} and ρ{sub 2} assumed as Q = 3Hb(ρ{sub 1}+ρ{sub 2}). We have numerical analyze of important cosmological parameters like EoS parameter of the composed fluid and deceleration parameter q of the model.

  2. Agegraphic dark energy: growth index and cosmological implications

    NASA Astrophysics Data System (ADS)

    Malekjani, M.; Basilakos, S.; Mehrabi, A.; Davari, Z.; Rezaei, M.

    2017-01-01

    We study the main cosmological properties of the agegraphic dark energy model at the expansion and perturbation levels. Initially, using the latest cosmological data, we implement a joint likelihood analysis in order to constrain the cosmological parameters. Then, we test the performance of the agegraphic dark energy model at the perturbation level and we define its difference from the usual Lambda cold dark matter (ΛCDM) model. Within this context, we verify that the growth index of matter fluctuations depends on the choice of the considered agegraphic dark energy (homogeneous or clustered). In particular, assuming a homogeneous agegraphic dark energy, we find, for the first time, that the asymptotic value of the growth index is γ ≈ 5/9, which is close to that of the usual Λ cosmology, γ(Λ) ≈ 6/11. Finally, if the distribution of dark energy is clustered, then we obtain γ ≈ 1/2 which is ˜8 per cent smaller than that of the ΛCDM model.

  3. Interacting warm dark matter

    SciTech Connect

    Cruz, Norman; Palma, Guillermo; Zambrano, David; Avelino, Arturo E-mail: guillermo.palma@usach.cl E-mail: avelino@fisica.ugto.mx

    2013-05-01

    We explore a cosmological model composed by a dark matter fluid interacting with a dark energy fluid. The interaction term has the non-linear λρ{sub m}{sup α}ρ{sub e}{sup β} form, where ρ{sub m} and ρ{sub e} are the energy densities of the dark matter and dark energy, respectively. The parameters α and β are in principle not constrained to take any particular values, and were estimated from observations. We perform an analytical study of the evolution equations, finding the fixed points and their stability properties in order to characterize suitable physical regions in the phase space of the dark matter and dark energy densities. The constants (λ,α,β) as well as w{sub m} and w{sub e} of the EoS of dark matter and dark energy respectively, were estimated using the cosmological observations of the type Ia supernovae and the Hubble expansion rate H(z) data sets. We find that the best estimated values for the free parameters of the model correspond to a warm dark matter interacting with a phantom dark energy component, with a well goodness-of-fit to data. However, using the Bayesian Information Criterion (BIC) we find that this model is overcame by a warm dark matter – phantom dark energy model without interaction, as well as by the ΛCDM model. We find also a large dispersion on the best estimated values of the (λ,α,β) parameters, so even if we are not able to set strong constraints on their values, given the goodness-of-fit to data of the model, we find that a large variety of theirs values are well compatible with the observational data used.

  4. Testing the interaction between dark energy and dark matter with H(z) data

    NASA Astrophysics Data System (ADS)

    Yu, Pan; Li, Li; Shuo, Cao; Na-na, Pan; Yi, Zhang; Zi-xuan, Hu

    2016-04-01

    With the Markov Chain Monte Carlo (MCMC) method, we constrain an interactive dark energy model by combing the up-to-date observational data of Hubble parameter H(z) with the 7-year baryon acoustic oscillation (BAO) data, and the cosmic microwave background (CMB) data observed by the Planck satellite. Under the joint constraint of the three kinds of data, the best-fit values of the model parameters and their 1-σ errors are obtained as follows: the energy density Ωm =0.266-0.028+0.028 (1 σ) , the interaction factor γ =0.090-0.098+0.100 (1 σ) , the parameter of state equation of dark matter wX = -1.307-0.269+0.263 (1 σ) , and the Hubble Constant H0 =7420-4.56+4.66 (1 σ) , where the coupling parameter γ > 0 means that the energy is transferred from dark matter to dark energy, and the coincidence problem in the Lambda-Cold Dark Matter (ΛCDM) model is slightly alleviated in the 1σ range. For comparisons, we constrain the same model with the BAO+CMB observations and H(z) data separately. The results are as follows: (1) The H(z) data could put stricter constraint on the parameter γ than the BAO+CMB observations. (2) The ΛCDM model is best fitted, and the coupling parameter γ is correlated with parameters Ωm and H0. (3) The inconsistency of the constraint results of H0 between the local distance ladder measurements and the Planck observations can be alleviated after taking account of the interaction between dark energy and dark matter.

  5. Does the diffusion dark matter-dark energy interaction model solve cosmological puzzles?

    NASA Astrophysics Data System (ADS)

    Szydłowski, Marek; Stachowski, Aleksander

    2016-08-01

    We study dynamics of cosmological models with diffusion effects modeling dark matter and dark energy interactions. We show the simple model with diffusion between the cosmological constant sector and dark matter, where the canonical scaling law of dark matter (ρd m ,0a-3(t )) is modified by an additive ɛ (t )=γ t a-3(t ) to the form ρd m=ρd m ,0a-3(t )+ɛ (t ). We reduced this model to the autonomous dynamical system and investigate it using dynamical system methods. This system possesses a two-dimensional invariant submanifold on which the dark matter-dark energy (DM-DE) interaction can be analyzed on the phase plane. The state variables are density parameter for matter (dark and visible) and parameter δ characterizing the rate of growth of energy transfer between the dark sectors. A corresponding dynamical system belongs to a general class of jungle type of cosmologies represented by coupled cosmological models in a Lotka-Volterra framework. We demonstrate that the de Sitter solution is a global attractor for all trajectories in the phase space and there are two repellers: the Einstein-de Sitter universe and the de Sitter universe state dominating by the diffusion effects. We distinguish in the phase space trajectories, which become in good agreement with the data. They should intersect a rectangle with sides of Ωm ,0∈[0.2724 ,0.3624 ] , δ ∈[0.0000 ,0.0364 ] at the 95% CL. Our model could solve some of the puzzles of the Λ CDM model, such as the coincidence and fine-tuning problems. In the context of the coincidence problem, our model can explain the present ratio of ρm to ρd e, which is equal 0.457 6-0.0831+0.1109 at a 2 σ confidence level.

  6. Precessing supermassive black hole binaries and dark energy measurements with LISA

    SciTech Connect

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

    2009-09-15

    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 respect to the nonprecessing case depending on the total mass and the redshift.

  7. A Possible Connection Between Dark Energy And the Hierarchy

    SciTech Connect

    Chen, Pisin; Gu, Je-An; /NCTS, Hsinchu

    2007-11-16

    Recently it was suggested that the dark energy maybe related to the well-known hierarchy between the Planck scale ({approx} 10{sup 19} GeV) and the TeV scale. The same brane-world setup to address this hierarchy problem may also in principle address the smallness problem of dark energy. Specifically, the Planck-SM hierarchy ratio was viewed as a quantum gravity-related, dimensionless fine structure constant where various physical energy scales in the system are associated with the Planck mass through different powers of the 'gravity fine structure constant'. In this paper we provide a toy model based on the Randall-Sundrum geometry where SUSY-breaking is induced by the coupling between a SUSY-breaking Higgs field on the brane and the KK gravitinos. We show that the associated Casimir energy density indeed conforms with the dark energy scale.

  8. PHYSICS OF OUR DAYS: Dark energy and universal antigravitation

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.

    2008-03-01

    Universal antigravitation, a new physical phenomenon discovered astronomically at distances of 5 to 8 billion light years, manifests itself as cosmic repulsion that acts between distant galaxies and overcomes their gravitational attraction, resulting in the accelerating expansion of the Universe. The source of the antigravitation is not galaxies or any other bodies of nature but a previously unknown form of mass/energy that has been termed dark energy. Dark energy accounts for 70 to 80% of the total mass and energy of the Universe and, in macroscopic terms, is a kind of continuous medium that fills the entire space of the Universe and is characterized by positive density and negative pressure. With its physical nature and microscopic structure unknown, dark energy is among the most critical challenges fundamental science faces in the twenty-first century.

  9. Model of dark matter and dark energy based on gravitational polarization

    SciTech Connect

    Blanchet, Luc; Le Tiec, Alexandre

    2008-07-15

    A model of dark matter and dark energy based on the concept of gravitational polarization is investigated. We propose an action in standard general relativity for describing, at some effective or phenomenological level, the dynamics of a dipolar medium, i.e. one endowed with a dipole moment vector, and polarizable in a gravitational field. Using first-order cosmological perturbations, we show that the dipolar fluid is undistinguishable from standard dark energy (a cosmological constant {lambda}) plus standard dark matter (a pressureless perfect fluid), and therefore benefits from the successes of the {lambda}-cold-dark-matter scenario at cosmological scales. Invoking an argument of 'weak clusterization' of the mass distribution of dipole moments, we find that the dipolar dark matter reproduces the phenomenology of the modified Newtonian dynamics at galactic scales. The dipolar medium action naturally contains a cosmological constant, and we show that if the model is to come from some fundamental underlying physics, the cosmological constant {lambda} should be of the order of a{sub 0}{sup 2}/c{sup 4}, where a{sub 0} denotes the modified Newtonian dynamics constant acceleration scale, in good agreement with observations.

  10. Differentiating dark energy and modified gravity with galaxy redshift surveys

    NASA Astrophysics Data System (ADS)

    Wang, Yun

    2008-05-01

    The observed cosmic acceleration today could be due to an unknown energy component (dark energy), or a modification to general relativity (modified gravity). If dark energy models and modified gravity models are required to predict the same cosmic expansion history H(z), they will predict different growth rates for cosmic large scale structure, fg(z). If gravity is not modified, the measured H(z) leads to a unique prediction for fg(z), fgH(z), if dark energy and dark matter are separate. Comparing fgH(z) with the measured fg(z) provides a transparent and straightforward test of gravity. We show that a simple χ2 test provides a general figure of merit for our ability to distinguish between dark energy and modified gravity given the measured H(z) and fg(z). We find that a magnitude-limited NIR galaxy redshift survey covering >10 000 (deg)2 and a redshift range of 0.5dark energy model that predict the same H(z), a survey area of 11 931 (deg)2 is required to rule out the DGP gravity model at the 99.99% confidence level. It is feasible for such a galaxy redshift survey to be carried out by the next generation space missions from NASA and ESA, and it will revolutionize our understanding of the universe by differentiating between dark energy and modified gravity.

  11. Inflation, Bifurcations of Nonlinear Curvature Lagrangians and Dark Energy

    NASA Astrophysics Data System (ADS)

    Mielke, Eckehard W.; Kusmartsev, Fjodor V.; Schunck, Franz E.

    2008-09-01

    A possible equivalence of scalar dark matter, the inflaton, and modified gravity is analyzed. After a conformal mapping, the dependence of the effective Lagrangian on the curvature is not only singular but also bifurcates into several almost Einsteinian spaces, distinguished only by a different effective gravitational strength and cosmological constant. A swallow tail catastrophe in the bifurcation set indicates the possibility for the coexistence of different Einsteinian domains in our Universe. This 'triple unification' may shed new light on the nature and large scale distribution not only of dark matter but also on 'dark energy', regarded as an effective cosmological constant, and inflation.

  12. Testing coupled dark energy models with their cosmological background evolution

    NASA Astrophysics Data System (ADS)

    van de Bruck, Carsten; Mifsud, Jurgen; Morrice, Jack

    2017-02-01

    We consider a cosmology in which dark matter and a quintessence scalar field responsible for the acceleration of the Universe are allowed to interact. Allowing for both conformal and disformal couplings, we perform a global analysis of the constraints on our model using Hubble parameter measurements, baryon acoustic oscillation distance measurements, and a Supernovae Type Ia data set. We find that the additional disformal coupling relaxes the conformal coupling constraints. Moreover, we show that, at the background level, a disformal interaction within the dark sector is preferred to both Λ CDM and uncoupled quintessence, hence favoring interacting dark energy.

  13. Exacerbating the Cosmological Constant Problem with Interacting Dark Energy Models

    NASA Astrophysics Data System (ADS)

    Marsh, M. C. David

    2017-01-01

    Future cosmological surveys will probe the expansion history of the Universe and constrain phenomenological models of dark energy. Such models do not address the fine-tuning problem of the vacuum energy, i.e., the cosmological constant problem (CCP), but can make it spectacularly worse. We show that this is the case for "interacting dark energy" models in which the masses of the dark matter states depend on the dark energy sector. If realized in nature, these models have far-reaching implications for proposed solutions to the CCP that require the number of vacua to exceed the fine-tuning of the vacuum energy density. We show that current estimates of the number of flux vacua in string theory, Nvac˜O (1 0272 000) , are far too small to realize certain simple models of interacting dark energy and solve the cosmological constant problem anthropically. These models admit distinctive observational signatures that can be targeted by future gamma-ray observatories, hence making it possible to observationally rule out the anthropic solution to the cosmological constant problem in theories with a finite number of vacua.

  14. Phenomenology of hybrid scenarios of neutrino dark energy

    SciTech Connect

    Antusch, Stefan; Dutta, Koushik; Das, Subinoy E-mail: subinoy@nyu.edu

    2008-10-15

    We study the phenomenology of hybrid scenarios of neutrino dark energy, where in addition to a so-called mass-varying neutrino (MaVaN) sector a cosmological constant (from a false vacuum) is driving the accelerated expansion of the universe today. For general power law potentials we calculate the effective equation of state parameter w{sub eff}(z) in terms of the neutrino mass scale. Due to the interaction of the dark energy field ('acceleron') with the neutrino sector, w{sub eff}(z) is predicted to become smaller than -1 for z>0, which could be tested in future cosmological observations. For the scenarios considered, the neutrino mass scale additionally determines which fraction of the dark energy is dynamical, and which originates from the 'cosmological-constant-like' vacuum energy of the false vacuum. On the other hand, the field value of the 'acceleron' field today as well as the masses of the right-handed neutrinos, which appear in the seesaw-type mechanism for small neutrino masses, are not fixed. This, in principle, allows us to realize hybrid scenarios of neutrino dark energy with a 'high-scale' seesaw where the right-handed neutrino masses are close to the GUT scale. We also comment on how MaVaN hybrid scenarios with 'high-scale' seesaw might help to resolve stability problems of dark energy models with non-relativistic neutrinos.

  15. Exacerbating the Cosmological Constant Problem with Interacting Dark Energy Models.

    PubMed

    Marsh, M C David

    2017-01-06

    Future cosmological surveys will probe the expansion history of the Universe and constrain phenomenological models of dark energy. Such models do not address the fine-tuning problem of the vacuum energy, i.e., the cosmological constant problem (CCP), but can make it spectacularly worse. We show that this is the case for "interacting dark energy" models in which the masses of the dark matter states depend on the dark energy sector. If realized in nature, these models have far-reaching implications for proposed solutions to the CCP that require the number of vacua to exceed the fine-tuning of the vacuum energy density. We show that current estimates of the number of flux vacua in string theory, N_{vac}∼O(10^{272 000}), are far too small to realize certain simple models of interacting dark energy and solve the cosmological constant problem anthropically. These models admit distinctive observational signatures that can be targeted by future gamma-ray observatories, hence making it possible to observationally rule out the anthropic solution to the cosmological constant problem in theories with a finite number of vacua.

  16. Unified dark energy and dark matter from a scalar field different from quintessence

    SciTech Connect

    Gao Changjun; Kunz, Martin; Liddle, Andrew R.; Parkinson, David

    2010-02-15

    We explore unification of dark matter and dark energy in a theory containing a scalar field of non-Lagrangian type, obtained by direct insertion of a kinetic term into the energy-momentum tensor. This scalar is different from quintessence, having an equation of state between -1 and 0 and a zero sound speed in its rest frame. We solve the equations of motion for an exponential potential via a rewriting as an autonomous system, and demonstrate the observational viability of the scenario, for sufficiently small exponential potential parameter {lambda}, by comparison to a compilation of kinematical cosmological data.

  17. Chandra Opens New Line of Investigation on Dark Energy

    NASA Astrophysics Data System (ADS)

    2004-05-01

    Astronomers have detected and probed dark energy by applying a powerful, new method that uses images of galaxy clusters made by NASA's Chandra X-ray Observatory. The results trace the transition of the expansion of the Universe from a decelerating to an accelerating phase several billion years ago, and give intriguing clues about the nature of dark energy and the fate of the Universe. "Dark energy is perhaps the biggest mystery in physics," said Steve Allen of the Institute of Astronomy (IoA) at the University of Cambridge in England, and leader of the study. "As such, it is extremely important to make an independent test of its existence and properties." Abell 2029 Chandra X-ray Image of Abell 2029 Allen and his colleagues used Chandra to study 26 clusters of galaxies at distances corresponding to light travel times of between one and eight billion years. These data span the time when the Universe slowed from its original expansion, before speeding up again because of the repulsive effect of dark energy. "We're directly seeing that the expansion of the Universe is accelerating by measuring the distances to these galaxy clusters," said Andy Fabian also of the IoA, a co-author on the study. The new Chandra results suggest that the dark energy density does not change quickly with time and may even be constant, consistent with the "cosmological constant" concept first introduced by Albert Einstein. If so, the Universe is expected to continue expanding forever, so that in many billions of years only a tiny fraction of the known galaxies will be observable. More Animations Animation of the "Big Rip" If the dark energy density is constant, more dramatic fates for the Universe would be avoided. These include the "Big Rip," where dark energy increases until galaxies, stars, planets and eventually atoms are eventually torn apart. The "Big Crunch," where the Universe eventually collapses on itself, would also be ruled out. Chandra's probe of dark energy relies on the unique

  18. Holographic Ricci dark energy: Current observational constraints, quintom feature, and the reconstruction of scalar-field dark energy

    SciTech Connect

    Zhang Xin

    2009-05-15

    In this work, we consider the cosmological constraints on the holographic Ricci dark energy proposed by Gao et al.[Phys. Rev. D 79, 043511 (2009)], by using the observational data currently available. The main characteristic of holographic Ricci dark energy is governed by a positive numerical parameter {alpha} in the model. When {alpha}<1/2, the holographic Ricci dark energy will exhibit a quintomlike behavior; i.e., its equation of state will evolve across the cosmological-constant boundary w=-1. The parameter {alpha} can be determined only by observations. Thus, in order to characterize the evolving feature of dark energy and to predict the fate of the Universe, it is of extraordinary importance to constrain the parameter {alpha} by using the observational data. In this paper, we derive constraints on the holographic Ricci dark energy model from the latest observational data including the Union sample of 307 type Ia supernovae, the shift parameter of the cosmic microwave background given by the five-year Wilkinson Microwave Anisotropy Probe observations, and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey. The joint analysis gives the best-fit results (with 1{sigma} uncertainty): {alpha}=0.359{sub -0.025}{sup +0.024} and {omega}{sub m0}=0.318{sub -0.024}{sup +0.026}. That is to say, according to the observations, the holographic Ricci dark energy takes on the quintom feature. Finally, in light of the results of the cosmological constraints, we discuss the issue of the scalar-field dark energy reconstruction, based on the scenario of the holographic Ricci vacuum energy.

  19. Dynamical dark energy in light of the latest observations

    NASA Astrophysics Data System (ADS)

    Zhao, Gong-Bo; Raveri, Marco; Pogosian, Levon; Wang, Yuting; Crittenden, Robert G.; Handley, Will J.; Percival, Will J.; Beutler, Florian; Brinkmann, Jonathan; Chuang, Chia-Hsun; Cuesta, Antonio J.; Eisenstein, Daniel J.; Kitaura, Francisco-Shu; Koyama, Kazuya; L'Huillier, Benjamin; Nichol, Robert C.; Pieri, Matthew M.; Rodriguez-Torres, Sergio; Ross, Ashley J.; Rossi, Graziano; Sánchez, Ariel G.; Shafieloo, Arman; Tinker, Jeremy L.; Tojeiro, Rita; Vazquez, Jose A.; Zhang, Hanyu

    2017-09-01

    A flat Friedmann-Robertson-Walker universe dominated by a cosmological constant (Λ) and cold dark matter (CDM) has been the working model preferred by cosmologists since the discovery of cosmic acceleration1,2. However, tensions of various degrees of significance are known to be present among existing datasets within the ΛCDM framework3-11. In particular, the Lyman-α forest measurement of the baryon acoustic oscillations (BAO) by the Baryon Oscillation Spectroscopic Survey3 prefers a smaller value of the matter density fraction ΩM than that preferred by cosmic microwave background (CMB). Also, the recently measured value of the Hubble constant, H0 = 73.24 ± 1.74 km s-1 Mpc-1 (ref. 12), is 3.4σ higher than the 66.93 ± 0.62 km s-1 Mpc-1 inferred from the Planck CMB data7. In this work, we investigate whether these tensions can be interpreted as evidence for a non-constant dynamical dark energy. Using the Kullback-Leibler divergence13 to quantify the tension between datasets, we find that the tensions are relieved by an evolving dark energy, with the dynamical dark energy model preferred at a 3.5σ significance level based on the improvement in the fit alone. While, at present, the Bayesian evidence for the dynamical dark energy is insufficient to favour it over ΛCDM, we show that, if the current best-fit dark energy happened to be the true model, it would be decisively detected by the upcoming Dark Energy Spectroscopic Instrument survey14.

  20. Explaining the dark energy, baryon and dark matter coincidence via domain-dependent random densities

    SciTech Connect

    McDonald, John

    2013-05-01

    The dark energy, dark matter and baryon densities in the Universe are observed to be similar, with a factor of no more than 20 between the largest and smallest densities. We show that this coincidence can be understood via superhorizon domains of randomly varying densities when the baryon density at initial collapse of galaxy-forming perturbations is determined by anthropic selection. The baryon and dark matter densities are assumed to be dependent on random variables θ{sub d} and θ{sub b} according to ρ{sub dm}∝θ{sub d}{sup α} and ρ{sub b}∝θ{sub b}{sup β}, while the effectively constant dark energy density is dependent upon a random variable φ{sub Q} according to ρ{sub Q}∝φ{sub Q}{sup n}. The ratio of the baryon density to the dark energy density at initial collapse, r{sub Q}, and the baryon-to-dark matter ratio, r, are then determined purely statistically, with no dependence on the anthropically-preferred baryon density. We compute the probability distribution for r{sub Q} and r and show that the observed values of r{sub Q} and r can be naturally understood within this framework. In particular, for the case α = 2, β = 1 and n = 4, which can be physically realized via a combination of axion dark matter, Affleck-Dine baryogenesis and frozen quintessence with a φ{sub Q}{sup 4} potential, the range of r{sub Q} and r which corresponds to the observed Universe is a quite natural, with a probability which is broadly similar to other ranges of r{sub Q} and r.

  1. Higgs seesaw mechanism as a source for dark energy.

    PubMed

    Krauss, Lawrence M; Dent, James B

    2013-08-09

    Motivated by the seesaw mechanism for neutrinos which naturally generates small neutrino masses, we explore how a small grand-unified-theory-scale mixing between the standard model Higgs boson and an otherwise massless hidden sector scalar can naturally generate a small mass and vacuum expectation value for the new scalar which produces a false vacuum energy density contribution comparable to that of the observed dark energy dominating the current expansion of the Universe. This provides a simple and natural mechanism for producing the correct scale for dark energy, even if it does not address the long-standing question of why much larger dark energy contributions are not produced from the visible sector. The new scalar produces no discernible signatures in existing terrestrial experiments so that one may have to rely on other cosmological tests of this idea.

  2. Fundamentalist physics: why Dark Energy is bad for astronomy

    NASA Astrophysics Data System (ADS)

    White, Simon D. M.

    2007-06-01

    Astronomers carry out observations to explore the diverse processes and objects which populate our Universe. High-energy physicists carry out experiments to approach the Fundamental Theory underlying space, time and matter. Dark Energy is a unique link between them, reflecting deep aspects of the Fundamental Theory, yet apparently accessible only through astronomical observation. Large sections of the two communities have therefore converged in support of astronomical projects to constrain Dark Energy. In this essay I argue that this convergence can be damaging for astronomy. The two communities have different methodologies and different scientific cultures. By uncritically adopting the values of an alien system, astronomers risk undermining the foundations of their own current success and endangering the future vitality of their field. Dark Energy is undeniably an interesting problem to tackle through astronomical observation, but it is one of many and not necessarily the one where significant progress is most likely to follow a major investment of resources.

  3. Inflation and dark energy arising from geometrical tachyons

    SciTech Connect

    Panda, Sudhakar; Sami, M.; Tsujikawa, Shinji

    2006-01-15

    We study the motion of a Bogomol'nyi-Prasad-Sommerfield D3-brane in the NS5-brane ring background. The radion field becomes tachyonic in this geometrical setup. We investigate the potential of this geometrical tachyon in the cosmological scenario for inflation as well as dark energy. We evaluate the spectra of scalar and tensor perturbations generated during tachyon inflation and show that this model is compatible with recent observations of cosmic microwave background due to an extra freedom of the number of NS5-branes. It is not possible to explain the origin of both inflation and dark energy by using a single tachyon field, since the energy density at the potential minimum is not negligibly small because of the amplitude of scalar perturbations set by cosmic microwave background anisotropies. However, the geometrical tachyon can account for dark energy when the number of NS5-branes is large, provided that inflation is realized by another scalar field.

  4. Higgs Seesaw Mechanism as a Source for Dark Energy

    NASA Astrophysics Data System (ADS)

    Krauss, Lawrence M.; Dent, James B.

    2013-08-01

    Motivated by the seesaw mechanism for neutrinos which naturally generates small neutrino masses, we explore how a small grand-unified-theory-scale mixing between the standard model Higgs boson and an otherwise massless hidden sector scalar can naturally generate a small mass and vacuum expectation value for the new scalar which produces a false vacuum energy density contribution comparable to that of the observed dark energy dominating the current expansion of the Universe. This provides a simple and natural mechanism for producing the correct scale for dark energy, even if it does not address the long-standing question of why much larger dark energy contributions are not produced from the visible sector. The new scalar produces no discernible signatures in existing terrestrial experiments so that one may have to rely on other cosmological tests of this idea.

  5. New limit on logotropic unified dark energy models

    NASA Astrophysics Data System (ADS)

    Ferreira, V. M. C.; Avelino, P. P.

    2017-07-01

    A unification of dark matter and dark energy in terms of a logotropic perfect dark fluid has recently been proposed, where deviations with respect to the standard ΛCDM model are dependent on a single parameter B. In this paper we show that the requirement that the linear growth of cosmic structures on comoving scales larger than 8h-1Mpc is not significantly affected with respect to the standard ΛCDM result provides the strongest limit to date on the model (B < 6 ×10-7), an improvement of more than three orders of magnitude over previous upper limits on the value of B. We further show that this limit rules out the logotropic Unified Dark Energy model as a possible solution to the small scale problems of the ΛCDM model, including the cusp problem of Dark Matter halos or the missing satellite problem, as well as the original version of the model where the Planck energy density was taken as one of the two parameters characterizing the logotropic dark fluid.

  6. A possible connection between massive fermions and dark energy

    SciTech Connect

    Goldman, Terrance; Stephenson, G J; Alsing, P M; Mckellar, B H J

    2009-01-01

    In a dense cloud of massive fermions interacting by exchange of a light scalar field, the effective mass of the fermion can become negligibly small. As the cloud expands, the effective mass and the total energy density eventually increase with decreasing density. In this regime, the pressure-density relation can approximate that required for dark energy. They apply this phenomenon to the expansion of the Universe with a very light scalar field and infer relations between the parameters available and cosmological observations. Majorana neutrinos at a mass that may have been recently determined, and fermions such as the Lightest Supersymmetric Particle (LSP) may both be consistent with current observations of dark energy.

  7. In Theory: Dark Energy as a Power Source

    NASA Astrophysics Data System (ADS)

    Nemiroff, Robert J.; Russell, David; Tangmatitham, Matipon

    2017-01-01

    In theory, it is possible to use the dark energy of the universe as a power source. In practice, the amount of energy that could be liberated in a local setting is many orders of magnitude too small to be useful or even detectable. Nevertheless, in the interests of education and amusement, simple machines that could, in theory, extract local power from the gravitationally repulsive cosmological constant are discussed. The gravitational neutral buoyancy distance -- the distance where local Newtonian gravity balances cosmological dark energy in a concordance cosmology -- is computed between two point objects of low mass.

  8. Coincidence problem in YM field dark energy model

    NASA Astrophysics Data System (ADS)

    Zhao, Wen; Zhang, Yang

    2006-09-01

    The coincidence problem is studied in the effective Yang Mills condensate dark energy model. As the effective YM Lagrangian is completely determined by quantum field theory, there is no adjustable parameter in this model except the energy scale, and the cosmic evolution only depends on the initial conditions. For generic initial conditions with the YM condensate subdominant to the radiation and matter, the model always has a tracking solution, the Universe transits from matter-dominated into the dark energy dominated stage only recently z˜0.3, and evolve to the present state with Ω˜0.73 and Ω˜0.27.

  9. Interacting Holographic Dark Energy, Future Singularity and Polytropic Gas Model of Dark Energy in Closed FRW Universe

    NASA Astrophysics Data System (ADS)

    Sarkar, Sanjay

    2016-01-01

    The present work deals with the accretion of two interacting fluids: dark matter and a hypothetical fluid as the holographic dark energy components onto wormhole in a non-flat FRW universe. First of all, following Cruz et al. (Phys. Lett. B 669, 271 2008), we obtained an exact solution of the Einstein's field equations. Solution describes effectively the actual acceleration and indicates a big rip type future singularity of the universe. After that we have studied the evolution of the mass of wormhole embedded in this FRW universe in order to reproduce a stable universe protected against future-time singularity. We found that the accretion of these dark components leads to a gradual increase of wormhole mass. It is also observed that contrary to the case as shown by Cruz et al. (Phys. Lett. B 669, 271 2008), the big rip singularity of the universe with a divergent Hubble parameter of this dark energy model may be avoided by a big trip. We have established a correspondence between the holographic dark energy with the polytropic gas dark energy model and obtained the potential as well as dynamics of the scalar field which describes the polytropic cosmology.

  10. Nonparametric reconstruction of the dark energy equation of state

    SciTech Connect

    Heitmann, Katrin; Holsclaw, Tracy; Alam, Ujjaini; Habib, Salman; Higdon, David; Sanso, Bruno; Lee, Herbie

    2009-01-01

    The major aim of ongoing and upcoming cosmological surveys is to unravel the nature of dark energy. In the absence of a compelling theory to test, a natural approach is to first attempt to characterize the nature of dark energy in detail, the hope being that this will lead to clues about the underlying fundamental theory. A major target in this characterization is the determination of the dynamical properties of the dark energy equation of state w. The discovery of a time variation in w(z) could then lead to insights about the dynamical origin of dark energy. This approach requires a robust and bias-free method for reconstructing w(z) from data, which does not rely on restrictive expansion schemes or assumed functional forms for w(z). We present a new non parametric reconstruction method for the dark energy equation of state based on Gaussian Process models. This method reliably captures nontrivial behavior of w(z) and provides controlled error bounds. We demollstrate the power of the method on different sets of simulated supernova data. The GP model approach is very easily extended to include diverse cosmological probes.

  11. Interacting Generalized Ghost Dark Energy in Non-isotropic Background

    NASA Astrophysics Data System (ADS)

    Barati, F.

    2016-04-01

    In this work, the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity is investigated. At first, the non-interacting generalized ghost dark energy in a Bianchi type I (BI) background is discussed. Then the equation of state parameter, ω D = p D / ρ D , the deceleration parameter, and the evolution equation of the generalized ghost dark energy are obtained. It was found that, in this case, ω D cannot cross the phantom line (ω D >-1) and eventually the universe approaches a de-Sitter phase of expansion (ω D →-1). Then, this investigation was extended to the interacting ghost dark energy in a non-isotropic universe. It was found that the equation of state parameter of the interacting generalized ghost dark energy can cross the phantom line (ω D <-1) provided the parameters of the model are chosen suitably. It was considered a specific model which permits the standard continuity equation in this theory. Besides ΩΛ and Ω m in standard Einstein cosmology, another density parameter, Ω σ , is expected by the anisotropy. The anisotropy of the universe decreases and the universe transits to an isotropic flat FRW universe accommodating the present acceleration.

  12. EOS workstation

    NASA Technical Reports Server (NTRS)

    Leberl, Franz; Karspeck, Milan; Millot, Michel; Maurice, Kelly; Jackson, Matt

    1992-01-01

    This final report summarizes the work done from mid-1989 until January 1992 to develop a prototype set of tools for the analysis of EOS-type images. Such images are characterized by great multiplicity and quantity. A single 'snapshot' of EOS-type imagery may contain several hundred component images so that on a particular pixel, one finds multiple gray values. A prototype EOS-sensor, AVIRIS, has 224 gray values at each pixel. The work focused on the ability to utilize very large images and continuously roam through those images, zoom and be able to hold more than one black and white or color image, for example for stereo viewing or for image comparisons. A second focus was the utilization of so-called 'image cubes', where multiple images need to be co-registered and then jointly analyzed, viewed, and manipulated. The target computer platform that was selected was a high-performance graphics superworkstation, Stardent 3000. This particular platform offered many particular graphics tools such as the Application Visualization System (AVS) or Dore, but it missed availability of commercial third-party software for relational data bases, image processing, etc. The project was able to cope with these limitations and a phase-3 activity is currently being negotiated to port the software and enhance it for use with a novel graphics superworkstation to be introduced into the market in the Spring of 1993.

  13. Thermodynamics of Interacting new Agegraphic Dark Energy and Dark Matter Due to Bianchi Type I Model

    NASA Astrophysics Data System (ADS)

    Hossienkhani, Hossien

    2016-11-01

    We study a thermodynamical description of the interaction between new agegraphic dark energy (NADE) and dark matter (DM) in an anisotropic universe. We find expressions for the entropy changes of these dark energy (DE) candidates. In addition, considering thermal fluctuations, thermodynamics of the DE component interacting with a DM sector is addressed. We also show that if one wants to solve the coincidence problem by using this mutual interaction, then the coupling constants of the interaction will be constrained. Finally, we obtain a physical expression for the interaction which is consistent with phenomenological descriptions and passes reasonably well the observational tests. Our study shows that, with the local equilibrium assumption, the generalized second law of thermodynamics is fulfilled in a region enclosed by the apparent horizon.

  14. Matter power spectra in dynamical dark energy cosmologies

    NASA Astrophysics Data System (ADS)

    Fedeli, C.; Dolag, K.; Moscardini, L.

    2012-01-01

    We used a suite of numerical cosmological simulations in order to investigate the effect of gas cooling and star formation on the large-scale matter distribution. The simulations follow the formation of cosmic structures in five different dark energy models: the fiducial Λcold dark matter (ΛCDM) cosmology and four models where the dark energy density is allowed to have a non-trivial redshift evolution. Each simulation includes a variety of gas physics, ranging from radiative cooling to UV heating and supernova feedback [although the active galactic nuclei (AGN) feedback is not incorporated]. Moreover, for each cosmology we have a control run with dark matter only, in order to allow a direct assessment of the effect of baryonic processes. We found that the power spectra of gas and stars, as well as the total matter power spectrum, are in qualitative agreement with the results of previous works not including the AGN effects in the framework of the fiducial model, although several quantitative differences exist. We used the physically motivated halo model in order to investigate the backreaction of gas and stars on the dark matter distribution, finding that it is very well reproduced by simply increasing the average dark matter halo concentration by 17 per cent, irrespective of the mass. This is in agreement with the cooling of gas dragging dark matter in the very centre of haloes, as well as adiabatic contraction steepening the relative potential wells. Moving to model universes dominated by dynamical dark energy, it turns out that they introduce a specific signature on the power spectra of the various matter components, which is qualitatively independent of the exact cosmology considered. This generic shape is well captured by the halo model if we blindly consider the cosmology dependences of the halo mass function, bias and concentration. However, the details of the dark matter power spectrum can be precisely captured only at the cost of a few slight

  15. Constraining the Runaway Dilaton and Quintessential Dark Energy

    NASA Astrophysics Data System (ADS)

    Neupane, Ishwaree P.; Trowland, Holly

    Dark energy is some of the weirdest and most mysterious stuff in the universe that tends to increase the rate of expansion of the universe. Two commonly known forms of dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli whose energy density can vary with time. We explore one particular model for dynamic dark energy: quintessence driven by a scalar dilaton field. We propose an ansatz for the form of the dilaton field, |ϕ(a)|mP ≡ α1 ln t + α2tn = α ln a + βa2ζ, where a is the scale factor and α and ζ are parameters of the model. This phenomenological ansatz for ϕ can be motivated by generic solutions of a scalar dilaton field in many effective string theory and string-inspired gravity models in four dimensions. Most of the earlier discussions in the literature correspond to the choice that ζ = 0 so that ϕ(t) ∝ ln t or ϕ(t) ∝ ln a(t). Using a compilation of current data including type Ia supernovae, we impose observational constraints on the slope parameters like α and ζ and then discuss the relation of our results to analytical constraints on various cosmological parameters, including the dark energy equation of state. Some useful constraints are imposed on model parameters like α and ζ as well as on the dark energy/dark matter couplings using results from structure formation. The constraints of this model are shown to encompass the cosmological constant limit within 1σ error bars.

  16. Precision Photometry to Study the Nature of Dark Energy

    SciTech Connect

    Lorenzon, Wolfgang; Schubnell, Michael

    2011-01-30

    Over the past decade scientists have collected convincing evidence that the expansion of the universe is accelerating, leading to the conclusion that the content of our universe is dominated by a mysterious 'dark energy'. The fact that present theory cannot account for the dark energy has made the determination of the nature of dark energy central to the field of high energy physics. It is expected that nothing short of a revolution in our understanding of the fundamental laws of physics is required to fully understand the accelerating universe. Discovering the nature of dark energy is a very difficult task, and requires experiments that employ a combination of different observational techniques, such as type-Ia supernovae, gravitational weak lensing surveys, galaxy and galaxy cluster surveys, and baryon acoustic oscillations. A critical component of any approach to understanding the nature of dark energy is precision photometry. This report addresses just that. Most dark energy missions will require photometric calibration over a wide range of intensities using standardized stars and internal reference sources. All of the techniques proposed for these missions rely on a complete understanding of the linearity of the detectors. The technical report focuses on the investigation and characterization of 'reciprocity failure', a newly discovered count-rate dependent nonlinearity in the NICMOS cameras on the Hubble Space Telescope. In order to quantify reciprocity failure for modern astronomical detectors, we built a dedicated reciprocity test setup that produced a known amount of light on a detector, and to measured its response as a function of light intensity and wavelength.

  17. New limits on coupled dark energy from Planck

    SciTech Connect

    Xia, Jun-Qing

    2013-11-01

    Recently, the Planck collaboration has released the first cosmological papers providing the high resolution, full sky, maps of the cosmic microwave background (CMB) temperature anisotropies. It is crucial to understand that whether the accelerating expansion of our universe at present is driven by an unknown energy component (Dark Energy) or a modification to general relativity (Modified Gravity). In this paper we study the coupled dark energy models, in which the quintessence scalar field nontrivially couples to the cold dark matter, with the strength parameter of interaction β. Using the Planck data alone, we obtain that the strength of interaction between dark sectors is constrained as β < 0.102 at 95% confidence level, which is tighter than that from the WMAP9 data alone. Combining the Planck data with other probes, like the Baryon Acoustic Oscillation (BAO), Type-Ia supernovae ''Union2.1 compilation'' and the CMB lensing data from Planck measurement, we find the tight constraint on the strength of interaction β < 0.052 (95% C.L.). Interestingly, we also find a non-zero coupling β = 0.078±0.022 (68% C.L.) when we use the Planck, the ''SNLS'' supernovae samples, and the prior on the Hubble constant from the Hubble Space Telescope (HST) together. This evidence for the coupled dark energy models mainly comes from a tension between constraints on the Hubble constant from the Planck measurement and the local direct H{sub 0} probes from HST.

  18. Reconstruction of interaction rate in holographic dark energy

    NASA Astrophysics Data System (ADS)

    Mukherjee, Ankan

    2016-11-01

    The present work is based on the holographic dark energy model with Hubble horizon as the infrared cut-off. The interaction rate between dark energy and dark matter has been reconstructed for three different parameterizations of the deceleration parameter. Observational constraints on the model parameters have been obtained by maximum likelihood analysis using the observational Hubble parameter data (OHD), type Ia supernovab data (SNe), baryon acoustic oscillation data (BAO) and the distance prior of cosmic microwave background (CMB) namely the CMB shift parameter data (CMBShift). The interaction rate obtained in the present work remains always positive and increases with expansion. It is very similar to the result obtained by Sen and Pavon [1] where the interaction rate has been reconstructed for a parametrization of the dark energy equation of state. Tighter constraints on the interaction rate have been obtained in the present work as it is based on larger data sets. The nature of the dark energy equation of state parameter has also been studied for the present models. Though the reconstruction is done from different parametrizations, the overall nature of the interaction rate is very similar in all the cases. Different information criteria and the Bayesian evidence, which have been invoked in the context of model selection, show that the these models are at close proximity of each other.

  19. LSST Dark Energy Science Final Report

    SciTech Connect

    Asztalos, S

    2007-02-15

    Three decadal surveys recommend a large-aperture synoptic survey telescope (LSST) to allow time-domain and cosmological studies of distant objects. LLNL designed the optical system and also is expected to play a significant role in the engineering associated with the camera. Precision cosmology from ground-based instruments is in a sense terra incognita. Numerous systematic effects occur that would be minimal or absent in their space-based counterparts. We proposed developing some basic tools and techniques for investigating ''dark sector'' cosmological science with such next-generation, large-aperture, real-time telescopes. The critical research involved determining whether systematic effects might dominate the extremely small distortions (''shears'') in images of faint background galaxies. To address these issues we carried out a comprehensive data campaign and developed detailed computer simulations.

  20. Interrelations between EOS parameters and cohesive energy of transition metals: Thermostatistical approach, ab initio calculations and analysis of ;universality; features

    NASA Astrophysics Data System (ADS)

    Bertoldi, Dalía S.; Ramos, Susana B.; Guillermet, Armando Fernández

    2017-08-01

    We present a theoretical analysis of the equation of state (EOS) of metals using a quasi-harmonic Einstein model with a dimensionless cohesive energy versus distance function (F(z)) involving the Wigner-Seitz radius and a material-dependent scaling length, as suggested in classical works by Rose, Ferrante, Smith and collaborators. Using this model, and ;universal; values for the function and its first and second derivatives at the equilibrium distance (z=0), three general interrelations between EOS parameters and the cohesive energy are obtained. The first correlation involves the bulk modulus, and the second, the thermal expansion coefficient. In order to test these results an extensive database is developed, which involves available experimental data, and results of current ab initio density-functional-theory calculations using the VASP code. In particular, the 0 K values for volume, bulk modulus, its pressure derivative, and the cohesive energy of 27 elements belonging to the first (Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn), second (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd) and third (Hf, Ta, W, Re, Os, Ir, Pt, Au) transition row of the Periodic Table are calculated ab initio and used to test the present results. The third correlation obtained, allows an evaluation of the third derivative of F(z) at z=0 for the current elements. With this new information, a discussion is presented of the possibility of finding a ;universal; F(z) versus z function able to account accurately for the pressure derivative of the bulk modulus of the transition elements.

  1. A divergence-free parametrization for dynamical dark energy

    SciTech Connect

    Akarsu, Özgür; Dereli, Tekin; Vazquez, J. Alberto E-mail: tdereli@ku.edu.tr

    2015-06-01

    We introduce a new parametrization for the dark energy, led by the same idea to the linear expansion of the equation of state in scale factor a and in redshift z, which diverges neither in the past nor future and contains the same number of degrees of freedom with the former two. We present constraints of the cosmological parameters using the most updated baryon acoustic oscillation (BAO) measurements along with cosmic microwave background (CMB) data and a recent reanalysis of Type Ia supernova (SN) data. This new parametrization allowed us to carry out successive observational analyses by decreasing its degrees of freedom systematically until ending up with a dynamical dark energy model that has the same number of parameters with ΛCDM . We found that the dark energy source with a dynamical equation of state parameter equal −2/3 at the early universe and −1 today fits the data slightly better than Λ.

  2. A geometric measure of dark energy with pairs of galaxies

    NASA Astrophysics Data System (ADS)

    Marinoni, Christian; Buzzi, Adeline

    2010-11-01

    Observations indicate that the expansion of the Universe is accelerating, which is attributed to a `dark energy' component that opposes gravity. There is a purely geometric test of the expansion of the Universe (the Alcock-Paczynski test), which would provide an independent way of investigating the abundance () and equation of state () of dark energy. It is based on an analysis of the geometrical distortions expected from comparing the real-space and redshift-space shape of distant cosmic structures, but it has proved difficult to implement. Here we report an analysis of the symmetry properties of distant pairs of galaxies from archival data. This allows us to determine that the Universe is flat. By alternately fixing its spatial geometry at and the dark energy equation-of-state parameter at , and using the results of baryon acoustic oscillations, we can establish at the 68.3% confidence level that and .

  3. Status of the Dark Energy Survey Camera (DECam) Project

    SciTech Connect

    Flaugher, Brenna L.; Abbott, Timothy M.C.; Angstadt, Robert; Annis, Jim; Antonik, Michelle, L.; Bailey, Jim; Ballester, Otger.; Bernstein, Joseph P.; Bernstein, Rebbeca; Bonati, Marco; Bremer, Gale; /Fermilab /Cerro-Tololo InterAmerican Obs. /ANL /Texas A-M /Michigan U. /Illinois U., Urbana /Ohio State U. /University Coll. London /LBNL /SLAC /IFAE

    2012-06-29

    The Dark Energy Survey Collaboration has completed construction of the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the remainder of the time, and after the survey, DECam will be available as a community instrument. All components of DECam have been shipped to Chile and post-shipping checkout finished in Jan. 2012. Installation is in progress. A summary of lessons learned and an update of the performance of DECam and the status of the DECam installation and commissioning will be presented.

  4. Evolution of spherical overdensities in new agegraphic dark energy model

    NASA Astrophysics Data System (ADS)

    Setare, M. R.; Felegary, F.; Darabi, F.

    We study the structure formation by investigating the spherical collapse model in the context of new agegraphic dark energy (NADE) model in flat FRW cosmology. We compute the perturbational quantities g(a), δc(zc), λ(zc), ξ(zc), Δvir(zc), log[νf(ν)] and log[n(k)] for the NADE model and compare the results with those of EdS and ΛCDM models. We find that there is a dark energy-dominated universe at low redshifts and a matter-dominated universe at high redshifts in agreement with the observations. Also, the size of structures, the overdense spherical region, and the halo size in the NADE model are found to be smaller, denser, and larger than those of EdS and ΛCDM models. We compare our results with the results of tachyon scalar field and holographic dark energy models.

  5. Voids as a precision probe of dark energy

    SciTech Connect

    Biswas, Rahul; Alizadeh, Esfandiar; Wandelt, Benjamin D.

    2010-07-15

    The shapes of cosmic voids, as measured in spectroscopic galaxy redshift surveys, constitute a promising new probe of dark energy (DE). We forecast constraints on the DE equation of state and its variation from current and future surveys and find that the promise of void shape measurements compares favorably to that of standard methods such as supernovae and cluster counts even for currently available data. Owing to the complementary nature of the constraints, void shape measurements improve the Dark Energy Task Force figure of merit by 2 orders of magnitude for a future large scale experiment such as EUCLID when combined with other probes of dark energy available on a similar time scale. Modeling several observational and theoretical systematics has only moderate effects on these forecasts. We discuss additional systematics which will require further study using simulations.

  6. What We Know About Dark Energy From Supernovae

    ScienceCinema

    Filippenko, Alex [University of California, Berkeley, California, United States

    2016-07-12

    The measured distances of type Ia (white dwarf) supernovae as a function of redshift (z) have shown that the expansion of the Universe is currently accelerating, probably due to the presence of dark energy (X) having a negative pressure. Combining all of the data with existing results from large-scale structure surveys, we find a best fit for Omega M and Omega X of 0.28 and 0.72 (respectively), in excellent agreement with the values derived independently from WMAP measurements of the cosmic microwave background radiation. Thus far, the best-fit value for the dark energy equation-of-state parameter is -1, and its first derivative is consistent with zero, suggesting that the dark energy may indeed be Einstein's cosmological constant.

  7. Quantum matter bounce with a dark energy expanding phase

    NASA Astrophysics Data System (ADS)

    Colin, Samuel; Pinto-Neto, Nelson

    2017-09-01

    Analyzing quantum cosmological scenarios containing one scalar field with exponential potential, we have obtained a universe model which realizes a classical dust contraction from very large scales, the initial repeller of the model, and moves to a stiff matter contraction near the singularity, which is avoided due to a quantum bounce. The universe is then launched in a stiff matter expanding phase, which then moves to a dark energy era, finally returning to the dust expanding phase, the final attractor of the model. Hence, one has obtained a nonsingular cosmological model where a single scalar field can describe both the matter contracting phase of a bouncing model, necessary to give an almost scale invariant spectrum of scalar cosmological perturbations, and a transient expanding dark energy phase. As the universe is necessarily dust dominated in the far past, usual adiabatic vacuum initial conditions can be easily imposed in this era, avoiding the usual issues appearing when dark energy is considered in bouncing models.

  8. Dark energy cosmology with the alternative cosmic microwave background data

    SciTech Connect

    Wei, Hao

    2011-04-01

    Recently, in a series of works by Liu and Li (L and L), they claimed that there exists a timing asynchrony of -25.6 ms between the spacecraft attitude and radiometer output timestamps in the original raw WMAP time-ordered data (TOD). L and L reprocessed the WMAP data while the aforementioned timing asynchrony has been corrected, and they obtained an alternative CMB map in which the quadrupole dropped to nearly zero. In the present work, we try to see the implications to dark energy cosmology if L and L are right. While L and L claimed that there is a bug in the WMAP pipeline which leads to significantly different cosmological parameters, an interesting question naturally arises, namely, how robust is the current dark energy cosmology with respect to systematic errors and bugs? So, in this work, we adopt the alternative CMB data of L and L as a strawman to study the robustness of dark energy predictions.

  9. Finding possibility of dynamical dark energy with Hubble parameters

    NASA Astrophysics Data System (ADS)

    Wang, Jiaxin; Meng, Xinhe

    2014-10-01

    The Hubble parameter is a critical measurement in cosmology, which contains the most direct information of the cosmic expansion history. Since discrepancy is found between low redshift and high redshift estimations of Hubble constant, we are interested in whether that tension indicates dynamical dark energy. In this paper, we emphasize that the observed Hubble parameters at various redshifts, along with observed Hubble constant, can help us in probing the evolutional behavior of the mysterious dark energy. Null hypothesis tests are carried out with two diagnostic approaches. We find out that, according to the present measurements of Hubble parameters, rejection of constant dark energy is captured at 1σ level from null tests with and without the observed value of Hubble constant.

  10. Energy weighted x-ray dark-field imaging.

    PubMed

    Pelzer, Georg; Zang, Andrea; Anton, Gisela; Bayer, Florian; Horn, Florian; Kraus, Manuel; Rieger, Jens; Ritter, Andre; Wandner, Johannes; Weber, Thomas; Fauler, Alex; Fiederle, Michael; Wong, Winnie S; Campbell, Michael; Meiser, Jan; Meyer, Pascal; Mohr, Jürgen; Michel, Thilo

    2014-10-06

    The dark-field image obtained in grating-based x-ray phase-contrast imaging can provide information about the objects' microstructures on a scale smaller than the pixel size even with low geometric magnification. In this publication we demonstrate that the dark-field image quality can be enhanced with an energy-resolving pixel detector. Energy-resolved x-ray dark-field images were acquired with a 16-energy-channel photon-counting pixel detector with a 1 mm thick CdTe sensor in a Talbot-Lau x-ray interferometer. A method for contrast-noise-ratio (CNR) enhancement is proposed and validated experimentally. In measurements, a CNR improvement by a factor of 1.14 was obtained. This is equivalent to a possible radiation dose reduction of 23%.

  11. Determination of Dark Matter Properties at High-Energy Collider

    SciTech Connect

    Baltz, Edward A.; Battaglia, Marco; Peskin, Michael E.; Wizansky, Tommer

    2006-02-24

    If the cosmic dark matter consists of weakly-interacting massive particles, these particles should be produced in reactions at the next generation of high-energy accelerators. Measurements at these accelerators can then be used to determine the microscopic properties of the dark matter. From this, we can predict the cosmic density, the annihilation cross sections, and the cross sections relevant to direct detection. In this paper, we present studies in supersymmetry models with neutralino dark matter that give quantitative estimates of the accuracy that can be expected. We show that these are well matched to the requirements of anticipated astrophysical observations of dark matter. The capabilities of the proposed International Linear Collider (ILC) are expected to play a particularly important role in this study.

  12. Determination of Dark Matter Properties at High-Energy Colliders

    SciTech Connect

    Baltz, Edward A.; Battaglia, Marco; Peskin, Michael E.; Wizansky, Tommer

    2006-11-05

    If the cosmic dark matter consists of weakly-interacting massive particles, these particles should be produced in reactions at the nextgeneration of high-energy accelerators. Measurements at these accelerators can then be used to determine the microscopic properties of the dark matter. From this, we can predict the cosmic density, the annihilation cross sections, and the cross sections relevant to direct detection. In this paper, we present studies in supersymmetry models with neutralino dark matter that give quantitative estimates of the accuracy that can be expected. We show that these are well matched to the requirements of anticipated astrophysical observations of dark matter. The capabilities of the proposed International Linear Collider (ILC) are expected to play a particularly important role in this study.

  13. Dark energy records in lensed cosmic microwave background

    NASA Astrophysics Data System (ADS)

    Acquaviva, Viviana; Baccigalupi, Carlo

    2006-11-01

    We consider the weak lensing effect induced by linear cosmological perturbations on the cosmic microwave background (CMB) polarization anisotropies. We find that the amplitude of the lensing peak in the BB mode power spectrum is a faithful tracer of the dark energy dynamics at the onset of cosmic acceleration. This is due to two reasons. First, the lensing power is nonzero only at intermediate redshifts between the observer and the source, keeping record of the linear perturbation growth rate at the corresponding epoch. Second, the BB lensing signal is expected to dominate over the other sources. The lensing distortion on the TT and EE spectra do exhibit a similar dependence on the dark energy dynamics, although those are dominated by primary anisotropies. We investigate and quantify the effect by means of exact tracking quintessence models, as well as parameterizing the dark energy equation of state in terms of the present value (w0) and its asymptotic value in the past (w∞); in the interval allowed by the present constraints on dark energy, the variation of w∞ induces a significant change in the BB mode lensing amplitude. A Fisher matrix analysis, under conservative assumptions concerning the increase of the sample variance due to the lensing non-Gaussian statistics, shows that a precision of order 10% on both w0 and w∞ is achievable by the future experiments probing a large sky area with angular resolution and sensitivity appropriate to detect the lensing effect on the CMB angular power spectrum; the forecast precision reaches a few percent for highly dynamic models whose dark energy abundance at the epoch when lensing is most effective is sensibly larger than the present one, i.e. for w∞≳-0.5. These results show that the CMB can probe the differential redshift behavior of the dark energy equation of state, beyond its average.

  14. Analytic study of the effect of dark energy-dark matter interaction on the growth of structures

    NASA Astrophysics Data System (ADS)

    Marcondes, Rafael J. F.; Landim, Ricardo C. G.; Costa, André A.; Wang, Bin; Abdalla, Elcio

    2016-12-01

    Large-scale structure has been shown as a promising cosmic probe for distinguishing and constraining dark energy models. Using the growth index parametrization, we obtain an analytic formula for the growth rate of structures in a coupled dark energy model in which the exchange of energy-momentum is proportional to the dark energy density. We find that the evolution of fσ8 can be determined analytically once we know the coupling, the dark energy equation of state, the present value of the dark energy density parameter and the current mean amplitude of dark matter fluctuations. After correcting the growth function for the correspondence with the velocity field through the continuity equation in the interacting model, we use our analytic result to compare the model's predictions with large-scale structure observations.

  15. Dark energy in thermal equilibrium with the cosmological horizon?

    NASA Astrophysics Data System (ADS)

    Poitras, Vincent

    2014-03-01

    According to a generalization of black hole thermodynamics to a cosmological framework, it is possible to define a temperature for the cosmological horizon. The hypothesis of thermal equilibrium between the dark energy and the horizon has been considered by many authors. We find the restrictions imposed by this hypothesis on the energy transfer rate (Qi) between the cosmological fluids, assuming that the temperature of the horizon has the form T =b/2πR, where R is the radius of the horizon. We more specifically consider two types of dark energy: Chaplygin gas (CG) and dark energy with a constant equation of state parameter (wDE). In each case, we show that for a given radius R, there is a unique term Qde that is consistent with thermal equilibrium. We also consider the situation where, in addition to dark energy, other fluids (cold matter, radiation) are in thermal equilibrium with the horizon. We find that the interaction terms required for this will generally violate energy conservation (∑iQi=0).

  16. 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.

  17. Holographic dark energy model from Ricci scalar curvature

    SciTech Connect

    Gao Changjun; Wu Fengquan; Chen Xuelei; Shen Yougen

    2009-02-15

    Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area of the event horizon of the Universe. However, such a model would have a causality problem. In this paper, we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We show that this model does not only avoid the causality problem and is phenomenologically viable, but also naturally solves the coincidence problem of dark energy. Our analysis of the evolution of density perturbations show that the matter power spectra and cosmic microwave background temperature anisotropy is only slightly affected by such modification.

  18. Dark Energy Studies with LSST Image Simulations, Final Report

    SciTech Connect

    Peterson, John Russell

    2016-07-26

    This grant funded the development and dissemination of the Photon Simulator (PhoSim) for the purpose of studying dark energy at high precision with the upcoming Large Synoptic Survey Telescope (LSST) astronomical survey. The work was in collaboration with the LSST Dark Energy Science Collaboration (DESC). Several detailed physics improvements were made in the optics, atmosphere, and sensor, a number of validation studies were performed, and a significant number of usability features were implemented. Future work in DESC will use PhoSim as the image simulation tool for data challenges used by the analysis groups.

  19. Quantisation of the holographic Ricci dark energy model

    SciTech Connect

    Albarran, Imanol; Bouhmadi-López, Mariam E-mail: mbl@ubi.pt

    2015-08-01

    While general relativity is an extremely robust theory to describe the gravitational interaction in our Universe, it is expected to fail close to singularities like the cosmological ones. On the other hand, it is well known that some dark energy models might induce future singularities; this can be the case for example within the setup of the Holographic Ricci Dark Energy model (HRDE). On this work, we perform a cosmological quantisation of the HRDE model and obtain under which conditions a cosmic doomsday can be avoided within the quantum realm. We show as well that this quantum model not only avoid future singularities but also the past Big Bang.

  20. Time arrow is influenced by the dark energy

    NASA Astrophysics Data System (ADS)

    Allahverdyan, A. E.; Gurzadyan, V. G.

    2016-05-01

    The arrow of time and the accelerated expansion are two fundamental empirical facts of the universe. We advance the viewpoint that the dark energy (positive cosmological constant) accelerating the expansion of the universe also supports the time asymmetry. It is related to the decay of metastable states under generic perturbations, as we show on example of a microcanonical ensemble. These states will not be metastable without dark energy. The latter also ensures a hyperbolic motion leading to dynamic entropy production with the rate determined by the cosmological constant.

  1. Time arrow is influenced by the dark energy.

    PubMed

    Allahverdyan, A E; Gurzadyan, V G

    2016-05-01

    The arrow of time and the accelerated expansion are two fundamental empirical facts of the universe. We advance the viewpoint that the dark energy (positive cosmological constant) accelerating the expansion of the universe also supports the time asymmetry. It is related to the decay of metastable states under generic perturbations, as we show on example of a microcanonical ensemble. These states will not be metastable without dark energy. The latter also ensures a hyperbolic motion leading to dynamic entropy production with the rate determined by the cosmological constant.

  2. Constraining dark energy with Sunyaev-Zel'dovich cluster surveys.

    PubMed

    Weller, Jochen; Battye, Richard A; Kneissl, Rüdiger

    2002-06-10

    We discuss the prospects of constraining the properties of a dark energy component, with particular reference to a time varying equation of state, using future cluster surveys selected by their Sunyaev-Zel'dovich effect. We compute the number of clusters expected for a given set of cosmological parameters and propogate the errors expected from a variety of surveys. In the short term they will constrain dark energy in conjunction with future observations of type Ia supernovae, but may in time do so in their own right.

  3. First SN Discoveries from the Dark Energy Survey

    NASA Astrophysics Data System (ADS)

    Abbott, T.; Abdalla, F.; Achitouv, I.; Ahn, E.; Aldering, G.; Allam, S.; Alonso, D.; Amara, A.; Annis, J.; Antonik, M.; Aragon-Salamanca, A.; Armstrong, R.; Ashall, C.; Asorey, J.; Bacon, D.; Balbinot, E.; Banerji, M.; Barbary, K.; Barkhouse, W.; Baruah, L.; Bauer, A.; Bechtol, K.; Becker, M.; Bender, R.; Benoist, C.; Benoit-Levy, A.; Bernardi, M.; Bernstein, G.; Bernstein, J. P.; Bernstein, R.; Bertin, E.; Beynon, E.; Bhattacharya, S.; Biesiadzinski, T.; Biswas, R.; Blake, C.; Bloom, J. S.; Bocquet, S.; Brandt, C.; Bridle, S.; Brooks, D.; Brown, P. J.; Brunner, R.; Buckley-Geer, E.; Burke, D.; Burkert, A.; Busha, M.; Campa, J.; Campbell, H.; Cane, R.; Capozzi, D.; Carlstrom, J.; Rosell, A. Carnero; Carollo, M.; Carrasco-Kind, M.; Carretero, J.; Carter, M.; Casas, R.; Castander, F. J.; Chen, Y.; Chiu, I.; Chue, C.; Clampitt, J.; Clerkin, L.; Cohn, J.; Colless, M.; Copeland, E.; Covarrubias, R. A.; Crittenden, R.; Crocce, M.; Cunha, C.; Costa, L. da; D, C.; #39; Andrea; Das, S.; Das, R.; Davis, T. M.; Deb, S.; DePoy, D.; Derylo, G.; Desai, S.; de Simoni, F.; Devlin, M.; Diehl, H. T.; Dietrich, J.; Dodelson, S.; Doel, P.; Dolag, K.; Efstathiou, G.; Eifler, T.; Erickson, B.; Eriksen, M.; Estrada, J.; Etherington, J.; Evrard, A.; Farrens, S.; Neto, A. Fausti; Fernandez, E.; Ferreira, P. C.; Finley, D.; Fischer, J. A.; Flaugher, B.; Fosalba, P.; Frieman, J.; Furlanetto, C.; Garcia-Bellido, J.; Gaztanaga, E.; Gelman, M.; Gerdes, D.; Giannantonio, T.; Gilhool, S.; Gill, M.; Gladders, M.; Gladney, L.; Glazebrook, K.; Gray, M.; Gruen, D.; Gruendl, R.; Gupta, R.; Gutierrez, G.; Habib, S.; Hall, E.; Hansen, S.; Hao, J.; Heitmann, K.; Helsby, J.; Henderson, R.; Hennig, C.; High, W.; Hirsch, M.; Hoffmann, K.; Holhjem, K.; Honscheid, K.; Host, O.; Hoyle, B.; Hu, W.; Huff, E.; Huterer, D.; Jain, B.; James, D.; Jarvis, M.; Jarvis, M. J.; Jeltema, T.; Johnson, M.; Jouvel, S.; Kacprzak, T.; Karliner, I.; Katsaros, J.; Kent, S.; Kessler, R.; Kim, A.; Kim-Vy, T.; King, L.; Kirk, D.; Kochanek, C.; Kopp, M.; Koppenhoefer, J.; Kovacs, E.; Krause, E.; Kravtsov, A.; Kron, R.; Kuehn, K.; Kuemmel, M.; Kuhlmann, S.; Kunder, A.; Kuropatkin, N.; Kwan, J.; Lahav, O.; Leistedt, B.; Levi, M.; Lewis, P.; Liddle, A.; Lidman, C.; Lilly, S.; Lin, H.; Liu, J.; Lopez-Arenillas, C.; Lorenzon, W.; LoVerde, M.; Ma, Z.; Maartens, R.; Maccrann, N.; Macri, L.; Maia, M.; Makler, M.; Manera, M.; Maraston, C.; March, M.; Markovic, K.; Marriner, J.; Marshall, J.; Marshall, S.; Martini, P.; Sanahuja, P. Marti; Mayers, J.; McKay, T.; McMahon, R.; Melchior, P.; Merritt, K. W.; Merson, A.; Miller, C.; Miquel, R.; Mohr, J.; Moore, T.; Mortonson, M.; Mosher, J.; Mould, J.; Mukherjee, P.; Neilsen, E.; Ngeow, C.; Nichol, R.; Nidever, D.; Nord, B.; Nugent, P.; Ogando, R.; Old, L.; Olsen, J.; Ostrovski, F.; Paech, K.; Papadopoulos, A.; Papovich, C.; Patton, K.; Peacock, J.; Pellegrini, P. S. S.; Peoples, J.; Percival, W.; Perlmutter, S.; Petravick, D.; Plazas, A.; Ponce, R.; Poole, G.; Pope, A.; Refregier, A.; Reyes, R.; Ricker, P.; Roe, N.; Romer, K.; Roodman, A.; Rooney, P.; Ross, A.; Rowe, B.; Rozo, E.; Rykoff, E.; Sabiu, C.; Saglia, R.; Sako, M.; Sanchez, A.; Sanchez, C.; Sanchez, E.; Sanchez, J.; Santiago, B.; Saro, A.; Scarpine, V.; Schindler, R.; Schmidt, B. P.; Schmitt, R. L.; Schubnell, M.; Seitz, S.; Senger, R.; Sevilla, I.; Sharp, R.; Sheldon, E.; Sheth, R.; Smith, R. C.; Smith, M.; Snigula, J.; Soares-Santos, M.; Sobreira, F.; Song, J.; Soumagnac, M.; Spinka, H.; Stebbins, A.; Stoughton, C.; Suchyta, E.; Suhada, R.; Sullivan, M.; Sun, F.; Suntzeff, N.; Sutherland, W.; Swanson, M. E. C.; Sypniewski, A. J.; Szepietowski, R.; Talaga, R.; Tarle, G.; Tarrant, E.; Balan, S. Thaithara; Thaler, J.; Thomas, D.; Thomas, R. C.; Tucker, D.; Uddin, S. A.; Ural, S.; Vikram, V.; Voigt, L.; Walker, A. R.; Walker, T.; Wechsler, R.; Weinberg, D.; Weller, J.; Wester, W.; Wetzstein, M.; White, M.; Wilcox, H.; Wilman, D.; Yanny, B.; Young, J.; Zablocki, A.; Zenteno, A.; Zhang, Y.; Zuntz, J.

    2012-12-01

    The Dark Energy Survey (DES) report the discovery of the first set of supernovae (SN) from the project. Images were observed as part of the DES Science Verification phase using the newly-installed 570-Megapixel Dark Energy Camera on the CTIO Blanco 4-m telescope by observers J. Annis, E. Buckley-Geer, and H. Lin. SN observations are planned throughout the observing campaign on a regular cadence of 4-6 days in each of the ten 3-deg2 fields in the DES griz filters.

  4. Dark energy properties from large future galaxy surveys

    SciTech Connect

    Basse, Tobias; Bjælde, Ole Eggers; Hannestad, Steen; Hamann, Jan; Wong, Yvonne Y.Y. E-mail: oeb@phys.au.dk E-mail: sth@phys.au.dk

    2014-05-01

    We perform a detailed forecast on how well a Euclid-like survey will be able to constrain dark energy and neutrino parameters from a combination of its cosmic shear power spectrum, galaxy power spectrum, and cluster mass function measurements. We find that the combination of these three probes vastly improves the survey's potential to measure the time evolution of dark energy. In terms of a dark energy figure-of-merit defined as (σ(w{sub p})σ(w{sub a})){sup −1}, we find a value of 690 for Euclid-like data combined with Planck-like measurements of the cosmic microwave background anisotropies in a 10-dimensional cosmological parameter space, assuming a ΛCDM fiducial cosmology. For the more commonly used 7-parameter model, we find a figure-of-merit of 1900 for the same data combination. We consider also the survey's potential to measure dark energy perturbations in models wherein the dark energy is parameterised as a fluid with a nonstandard non-adiabatic sound speed, and find that in an optimistic scenario in which w{sub 0} deviates from -1 by as much as is currently observationally allowed, models with c-circumflex {sub s}{sup 2} = 10{sup −6} and c-circumflex {sub s}{sup 2} = 1 can be distinguished from one another at more than 2σ significance. We emphasise that constraints on the dark energy sound speed from cluster measurements are strongly dependent on the modelling of the cluster mass function; significantly weaker sensitivities ensue if we modify our model to include fewer features of nonlinear dark energy clustering. Finally, we find that the sum of neutrino masses can be measured with a 1σ precision of 0.015 eV, even in complex cosmological models in which the dark energy equation of state varies with time. The 1σ sensitivity to the effective number of relativistic species N{sub eff}{sup ml} is approximately 0.03, meaning that the small deviation of 0.046 from 3 in the standard value of N{sub eff}{sup ml} due to non-instantaneous decoupling and

  5. Restoring New Agegraphic Dark Energy in RS II Braneworld

    NASA Astrophysics Data System (ADS)

    Jamil, Mubasher; Karami, K.; Sheykhi, A.

    2011-10-01

    Motivated by recent works (Saridakis in Phys. Lett. B 660:138, 2008; Sheykhi in Int. J. Mod. Phys. D 19(3):305, 2010), we investigate the new agegraphic model of dark energy in the framework of RS II braneworld. We also include the case of variable gravitational constant G in our model. Moreover, we reconstruct the potential and the dynamics of the quintessence, tachyon, K-essence and dilaton scalar field models according to the evolutionary behavior of the new agegraphic dark energy model in RS II braneworld cosmology including varying G.

  6. Dark energy cosmology with tachyon field in teleparallel gravity

    SciTech Connect

    Motavalli, H. Akbarieh, A. Rezaei; Nasiry, M.

    2016-07-15

    We construct a tachyon teleparallel dark energy model for a homogeneous and isotropic flat universe in which a tachyon as a non-canonical scalar field is non-minimally coupled to gravity in the framework of teleparallel gravity. The explicit form of potential and coupling functions are obtained under the assumption that the Lagrangian admits the Noether symmetry approach. The dynamical behavior of the basic cosmological observables is compared to recent observational data, which implies that the tachyon field may serve as a candidate for dark energy.

  7. Search for Kilonovae in Dark Energy Survey Supernova Fields

    NASA Astrophysics Data System (ADS)

    Doctor, Zoheyr; DES-GW Team; DES-SN Team

    2016-03-01

    The Dark Energy Camera on the Blanco 4-m Telescope is an ideal instrument for identifying rapid optical transients with its large field of view and four optical filters. We utilize two seasons of data from the Dark Energy Survey to search for kilonovae, an optical counterpart to gravitational waves from binary neutron star mergers. Kilonova lightcurves from Barnes and Kasen inform our analysis for removing background signals such as supernovae. We simulate DES observations of kilonovae with the SNANA software package to estimate our search efficiency and optimize cuts. Finally, we report rate limits for binary neutron star mergers and compare to existing rate estimates.

  8. Dark energy cosmology with tachyon field in teleparallel gravity

    NASA Astrophysics Data System (ADS)

    Motavalli, H.; Akbarieh, A. Rezaei; Nasiry, M.

    2016-07-01

    We construct a tachyon teleparallel dark energy model for a homogeneous and isotropic flat universe in which a tachyon as a non-canonical scalar field is non-minimally coupled to gravity in the framework of teleparallel gravity. The explicit form of potential and coupling functions are obtained under the assumption that the Lagrangian admits the Noether symmetry approach. The dynamical behavior of the basic cosmological observables is compared to recent observational data, which implies that the tachyon field may serve as a candidate for dark energy.

  9. Dark energy properties from large future galaxy surveys

    NASA Astrophysics Data System (ADS)

    Basse, Tobias; Eggers Bjælde, Ole; Hamann, Jan; Hannestad, Steen; Wong, Yvonne Y. Y.

    2014-05-01

    We perform a detailed forecast on how well a Euclid-like survey will be able to constrain dark energy and neutrino parameters from a combination of its cosmic shear power spectrum, galaxy power spectrum, and cluster mass function measurements. We find that the combination of these three probes vastly improves the survey's potential to measure the time evolution of dark energy. In terms of a dark energy figure-of-merit defined as (σ(wp)σ(wa))-1, we find a value of 690 for Euclid-like data combined with Planck-like measurements of the cosmic microwave background anisotropies in a 10-dimensional cosmological parameter space, assuming a ΛCDM fiducial cosmology. For the more commonly used 7-parameter model, we find a figure-of-merit of 1900 for the same data combination. We consider also the survey's potential to measure dark energy perturbations in models wherein the dark energy is parameterised as a fluid with a nonstandard non-adiabatic sound speed, and find that in an optimistic scenario in which w0 deviates from -1 by as much as is currently observationally allowed, models with hat cs2 = 10-6 and hat cs2 = 1 can be distinguished from one another at more than 2σ significance. We emphasise that constraints on the dark energy sound speed from cluster measurements are strongly dependent on the modelling of the cluster mass function; significantly weaker sensitivities ensue if we modify our model to include fewer features of nonlinear dark energy clustering. Finally, we find that the sum of neutrino masses can be measured with a 1σ precision of 0.015 eV, even in complex cosmological models in which the dark energy equation of state varies with time. The 1σ sensitivity to the effective number of relativistic species Neffml is approximately 0.03, meaning that the small deviation of 0.046 from 3 in the standard value of Neffml due to non-instantaneous decoupling and finite temperature effects can be probed with 1σ precision for the first time.

  10. Reducing Zero-point Systematics in Dark Energy Supernova Experiments

    SciTech Connect

    Faccioli, Lorenzo; Kim, Alex G; Miquel, Ramon; Bernstein, Gary; Bonissent, Alain; Brown, Matthew; Carithers, William; Christiansen, Jodi; Connolly, Natalia; Deustua, Susana; Gerdes, David; Gladney, Larry; Kushner, Gary; Linder, Eric; McKee, Shawn; Mostek, Nick; Shukla, Hemant; Stebbins, Albert; Stoughton, Chris; Tucker, David

    2011-04-01

    We study the effect of filter zero-point uncertainties on future supernova dark energy missions. Fitting for calibration parameters using simultaneous analysis of all Type Ia supernova standard candles achieves a significant improvement over more traditional fit methods. This conclusion is robust under diverse experimental configurations (number of observed supernovae, maximum survey redshift, inclusion of additional systematics). This approach to supernova fitting considerably eases otherwise stringent mission cali- bration requirements. As an example we simulate a space-based mission based on the proposed JDEM satellite; however the method and conclusions are general and valid for any future supernova dark energy mission, ground or space-based.

  11. Inelastic frontier: Discovering dark matter at high recoil energy

    DOE PAGES

    Bramante, Joseph; Fox, Patrick J.; Kribs, Graham D.; ...

    2016-12-27

    There exist well-motivated models of particle dark matter which predominantly scatter inelastically off nuclei in direct detection experiments. This inelastic transition causes the dark matter to upscatter in terrestrial experiments into an excited state up to 550 keV heavier than the dark matter itself. An inelastic transition of this size is highly suppressed by both kinematics and nuclear form factors. In this paper, we extend previous studies of inelastic dark matter to determine the present bounds on the scattering cross section and the prospects for improvements in sensitivity. Three scenarios provide illustrative examples: nearly pure Higgsino supersymmetric dark matter, magnetic inelasticmore » dark matter, and inelastic models with dark photon exchange. We determine the elastic scattering rate (through loop diagrams involving the heavy state) as well as verify that exothermic transitions are negligible (in the parameter space we consider). Presently, the strongest bounds on the cross section are from xenon at LUX-PandaX (when the mass splitting δ≲160 keV), iodine at PICO (when 160≲δ≲300 keV), and tungsten at CRESST (when δ≳300 keV). Amusingly, once δ≳200 keV, weak scale (and larger) dark matter–nucleon scattering cross sections are allowed. The relative competitiveness of these diverse experiments is governed by the upper bound on the recoil energies employed by each experiment, as well as strong sensitivity to the mass of the heaviest element in the detector. Several implications, including sizable recoil energy-dependent annual modulation and improvements for future experiments, are discussed. We show that the xenon experiments can improve on the PICO results, if they were to analyze their existing data over a larger range of recoil energies, i.e., 20–500 keV Intriguingly, CRESST has reported several events in the recoil energy range 45–100 keV that, if interpreted as dark matter scattering, is compatible with δ~200 keV and an

  12. Inelastic frontier: Discovering dark matter at high recoil energy

    NASA Astrophysics Data System (ADS)

    Bramante, Joseph; Fox, Patrick J.; Kribs, Graham D.; Martin, Adam

    2016-12-01

    There exist well-motivated models of particle dark matter which predominantly scatter inelastically off nuclei in direct detection experiments. This inelastic transition causes the dark matter to upscatter in terrestrial experiments into an excited state up to 550 keV heavier than the dark matter itself. An inelastic transition of this size is highly suppressed by both kinematics and nuclear form factors. In this paper, we extend previous studies of inelastic dark matter to determine the present bounds on the scattering cross section and the prospects for improvements in sensitivity. Three scenarios provide illustrative examples: nearly pure Higgsino supersymmetric dark matter, magnetic inelastic dark matter, and inelastic models with dark photon exchange. We determine the elastic scattering rate (through loop diagrams involving the heavy state) as well as verify that exothermic transitions are negligible (in the parameter space we consider). Presently, the strongest bounds on the cross section are from xenon at LUX-PandaX (when the mass splitting δ ≲160 keV ), iodine at PICO (when 160 ≲δ ≲300 keV ), and tungsten at CRESST (when δ ≳300 keV ). Amusingly, once δ ≳200 keV , weak scale (and larger) dark matter-nucleon scattering cross sections are allowed. The relative competitiveness of these diverse experiments is governed by the upper bound on the recoil energies employed by each experiment, as well as strong sensitivity to the mass of the heaviest element in the detector. Several implications, including sizable recoil energy-dependent annual modulation and improvements for future experiments, are discussed. We show that the xenon experiments can improve on the PICO results, if they were to analyze their existing data over a larger range of recoil energies, i.e., 20-500 keV Intriguingly, CRESST has reported several events in the recoil energy range 45-100 keV that, if interpreted as dark matter scattering, is compatible with δ ˜200 keV and an

  13. Inelastic frontier: Discovering dark matter at high recoil energy

    SciTech Connect

    Bramante, Joseph; Fox, Patrick J.; Kribs, Graham D.; Martin, Adam

    2016-12-27

    There exist well-motivated models of particle dark matter which predominantly scatter inelastically off nuclei in direct detection experiments. This inelastic transition causes the dark matter to upscatter in terrestrial experiments into an excited state up to 550 keV heavier than the dark matter itself. An inelastic transition of this size is highly suppressed by both kinematics and nuclear form factors. In this paper, we extend previous studies of inelastic dark matter to determine the present bounds on the scattering cross section and the prospects for improvements in sensitivity. Three scenarios provide illustrative examples: nearly pure Higgsino supersymmetric dark matter, magnetic inelastic dark matter, and inelastic models with dark photon exchange. We determine the elastic scattering rate (through loop diagrams involving the heavy state) as well as verify that exothermic transitions are negligible (in the parameter space we consider). Presently, the strongest bounds on the cross section are from xenon at LUX-PandaX (when the mass splitting δ≲160 keV), iodine at PICO (when 160≲δ≲300 keV), and tungsten at CRESST (when δ≳300 keV). Amusingly, once δ≳200 keV, weak scale (and larger) dark matter–nucleon scattering cross sections are allowed. The relative competitiveness of these diverse experiments is governed by the upper bound on the recoil energies employed by each experiment, as well as strong sensitivity to the mass of the heaviest element in the detector. Several implications, including sizable recoil energy-dependent annual modulation and improvements for future experiments, are discussed. We show that the xenon experiments can improve on the PICO results, if they were to analyze their existing data over a larger range of recoil energies, i.e., 20–500 keV Intriguingly, CRESST has reported several events in the recoil energy range 45–100 keV that, if interpreted as dark matter scattering, is compatible with δ~200 keV and an

  14. LSST as a precision probe of dark energy

    NASA Astrophysics Data System (ADS)

    Tyson, Tony; Wittman, David; Hennawi, Joe; Spergel, David

    2002-04-01

    The distortion of images of high-redshift background galaxies can be used to probe the intervening mass distribution. This weak gravitational lens effect can be used to detect clusters of dark matter, weigh them, image their mass distribution, and determine their 3-D location. The number of mass clusters detected and their redshift distribution are very sensitive to the density of matter Ωm and the equation of state of dark energy w. The degeneracy curve in the Ωm -- w plane is nearly orthogonal to that from the CMB measurements, so that a combination of CMB data with weak lensing by clusters can yield precision measurements of Ωm and w, independently of the supernova observations. The planned Large Synoptic Survey Telescope (LSST) will repeatedly survey 14,000 square degrees of the sky to unprecedented depths. LSST will create a 3-D mass tomographic assay of mass overdensities back to half the age of the universe by measuring the weak gravitational shear and color-redshift of billions of high redshift galaxies. LSST measurements of shear versus source redshift and lens redshift constrain the dark energy density and equation of state. By simultaneously measuring a range of properties of cosmic shear and cluster abundance, the LSST is able to provide a number of independent constraints on the dark energy density and the equation of state. LSST will determine the dark energy equation of state w to within one percent, sharply constraining the nature of dark energy. See the web site http://lssto.org for plots.

  15. Dark Energy and Dark Matter as w = -1 Virtual Particles and the World Hologram Model

    NASA Astrophysics Data System (ADS)

    Sarfatti, Jack

    2011-04-01

    The elementary physics battle-tested principles of Lorentz invariance, Einstein equivalence principle and the boson commutation and fermion anti-commutation rules of quantum field theory explain gravitationally repulsive dark energy as virtual bosons and gravitationally attractive dark matter as virtual fermion-antifermion pairs. The small dark energy density in our past light cone is the reciprocal entropy-area of our future light cone's 2D future event horizon in a Novikov consistent loop in time in our accelerating universe. Yakir Aharonov's "back-from-the-future" post-selected final boundary condition is set at our observer-dependent future horizon that also explains why the irreversible thermodynamic arrow of time of is aligned with the accelerating dark energy expansion of the bulk 3D space interior to our future 2D horizon surrounding it as the hologram screen. Seth Lloyd has argued that all 2D horizon surrounding surfaces are pixelated quantum computers projecting interior bulk 3D quanta of volume (Planck area)Sqrt(area of future horizon) as their hologram images in 1-1 correspondence.

  16. Testing the cosmic coincidence problem and the nature of dark energy.

    PubMed

    Dalal, N; Abazajian, K; Jenkins, E; Manohar, A V

    2001-10-01

    Dark energy models which alter the relative scaling behavior of dark energy and matter could provide a natural solution to the cosmic coincidence problem-why the densities of dark energy and dark matter are comparable today. A generalized class of dark energy models is introduced which allows noncanonical scaling of the ratio of dark matter and dark energy with the Robertson-Walker scale factor a(t). We show that determining whether there is a coincidence problem, and the extent of cosmic coincidence, can be addressed by several forthcoming experiments.

  17. Instability in interacting dark sector: an appropriate holographic Ricci dark energy model

    NASA Astrophysics Data System (ADS)

    Herrera, Ramón; Hipólito-Ricaldi, W. S.; Videla, Nelson

    2016-08-01

    In this paper we investigate the consequences of phantom crossing considering the perturbative dynamics in models with interaction in their dark sector. By mean of a general study of gauge-invariant variables in comoving gauge, we relate the sources of instabilities in the structure formation process with the phantom crossing. In order to illustrate these relations and its consequences in more detail, we consider a specific case of an holographic dark energy interacting with dark matter. We find that in spite of the model is in excellent agreement with observational data at background level, however it is plagued of instabilities in its perturbative dynamics. We reconstruct the model in order to avoid these undesirable instabilities, and we show that this implies a modification of the concordance model at background. Also we find drastic changes on the parameters space in our model when instabilities are avoided.

  18. Fatal error of the relativity and the research for dark matter-;dark energy -the physical "dark world"

    NASA Astrophysics Data System (ADS)

    Tong, Zhengrong

    2014-07-01

    1. The hard facts we given in text prove that, relativity theory is the fallacy from mathematical errors and experimental perjuries. 2. Conclusion of the study show that one called "fundamental gravitino" (the theoretical mass-energy value given at mw = 3.636 x 10-45 kg) is the Material composition of dark matter in the universe and also it's the material composition of all the elementary particles too. This is the root cause that the gravitation has universality. In-depth research, the results show that the fundamental gravitino" in all space is the material foundation of the electromagnetic interaction and propagation of light and other physical phenomena. Furthermore it shows that Stable elementary particles are the "droplets" under the strong gravitino pressure (strength calculated are consistent with the strong interaction) in the entire universe, similar to the droplets in the saturated gas. There are steady-state solutions in Mathematical models corresponding to the proton, the electron and the neutron.The theory for topics such as the dark matter, the dark energy, and the Higgs particle has the perfect explanation and reasonable conclusion... It seems, Chinese began to keep up with the world's physical trend, started a new physics era of fundamental gravitino the mass energy source of the universe.

  19. Non-virialized clusters for detection of dark energy-dark matter interaction

    NASA Astrophysics Data System (ADS)

    Le Delliou, M.; Marcondes, R. J. F.; Lima Neto, G. B.; Abdalla, E.

    2015-10-01

    The observation of galaxy and gas distributions, as well as cosmological simulations in a ΛCDM cold dark matter universe, suggests that clusters of galaxies are still accreting mass and are not expected to be in equilibrium. In this work, we investigate the possibility to evaluate the departure from virial equilibrium in order to detect, in that balance, effects from a dark matter-dark energy interaction. We continue, from previous works, using a simple model of interacting dark sector, the Layzer-Irvine equation for dynamical virial evolution, and employ optical observations in order to obtain the mass profiles through weak-lensing and X-ray observations giving the intracluster gas temperatures. Through a Monte Carlo method, we generate, for a set of clusters, measurements of observed virial ratios, interaction strength, rest virial ratio and departure from equilibrium factors. We found a compounded interaction strength of -1.99^{+2.56}_{-16.00}, compatible with no interaction, but also a compounded rest virial ratio of -0.79 ± 0.13, which would entail a 2σ detection. We confirm quantitatively that clusters of galaxies are out of equilibrium but further investigation is needed to constrain a possible interaction in the dark sector.

  20. Thermodynamics of Viscous Dark Energy in AN Rsii Braneworld

    NASA Astrophysics Data System (ADS)

    Setare, M. R.; Sheykhi, A.

    We show that for an RSII braneworld filled with interacting viscous dark energy and dark matter, one can always rewrite the Friedmann equation in the form of the first law of thermodynamics, dE = ThdSh + WdV, at the apparent horizon. In addition, the generalized second law of thermodynamics can be fulfilled in a region enclosed by the apparent horizon on the brane for both constant and time-variable five-dimensional Newton's constant G5. These results hold regardless of the specific form of the dark energy. Our study further supports the belief that in an accelerating universe with spatial curvature, the apparent horizon is a physical boundary from the thermodynamical point of view.

  1. Decoherent neutrino mixing, dark energy, and matter-antimatter asymmetry

    SciTech Connect

    Barenboim, Gabriela; Mavromatos, Nick E.

    2004-11-01

    A CPT violating decoherence scenario can easily account for all the experimental evidence in the neutrino sector including Liquid Scincillator Neutrino Detector. In this work it is argued that this framework can also accommodate the dark energy content of the Universe, as well as the observed matter-antimatter asymmetry.

  2. 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,…

  3. Swiss cheese model with the superstring dark energy

    NASA Astrophysics Data System (ADS)

    Stuchlík, Zdeněk; Kološ, Martin

    2005-12-01

    The Swiss cheese model of the Universe with the superstring dark energy is constructed. The junction conditions are shown to be fulfilled and time evolution of the matching hypersurface of the internal Schwarzschild spacetime and homogeneous external Friedman Universe is studied.

  4. Observational constraints on the interacting Ricci dark energy model

    SciTech Connect

    Suwa, Masashi; Nihei, Takeshi

    2010-01-15

    We consider an extension of the holographic Ricci dark energy model by introducing an interaction between dark energy and matter. In this model, the dark energy density is given by {rho}{sub {Lambda}=}-(1/2){alpha}M{sub p}{sup 2}R, where R is the Ricci scalar curvature, M{sub p} is the reduced Planck mass, and {alpha} is a dimensionless parameter. The interaction rate is given by Q={gamma}H{rho}{sub {Lambda},} where H is the Hubble expansion rate, and {gamma} is a dimensionless parameter. We investigate current observational constraints on this model by applying the type Ia supernovae, the baryon acoustic oscillation and the cosmic microwave background anisotropy data. It is shown that a nonvanishing interaction rate is favored by the observations. The best fit values are {alpha}=0.45{+-}0.03 and {gamma}=0.15{+-}0.03 for the present dark energy density parameter {Omega}{sub {Lambda}0}=0.73{+-}0.03.

  5. Stability of Dark Energy Models on the Brane Universes

    NASA Astrophysics Data System (ADS)

    Saadat, Hassan

    2013-08-01

    In this paper the equation of state formalism for the dark energy models on the brane considered and stability of theory investigated. We consider four different cases of the Little Rip, Asymptotic de Sitter, Asymptotic breakdown, and Big Freeze singularity models and find that the only stable model is Asymptotic de Sitter case. In other cases we get negative value of squared sound speed.

  6. The solutions and thermodynamic dark energy in the accelerating universe

    SciTech Connect

    Demirel, E. C. Günay

    2016-03-25

    Recently, Tachyonic matter expressed in terms of scalar field is suggested to be the reason of acceleration of the universe as dark energy [1]-[3]. In this study, dynamic solutions and thermodynamic properties of matters such as Tachyonic matters were investigated.

  7. Dark energy oscillations in mimetic F (R ) gravity

    NASA Astrophysics Data System (ADS)

    Odintsov, S. D.; Oikonomou, V. K.

    2016-08-01

    In this paper we address the problem of dark energy oscillations in the context of mimetic F (R ) gravity with potential. The issue of dark energy oscillations can be a problem in some models of ordinary F (R ) gravity, and a remedy that can make the oscillations milder is to introduce additional modifications in the functional form of the F (R ) gravity. As we demonstrate, the power-law modifications are not necessary in the mimetic F (R ) case, and by appropriately choosing the mimetic potential and the Lagrange multiplier, it is possible to make the oscillations almost vanish at the end of the matter domination era and during the late-time acceleration era. We examine the behavior of the dark energy equation of state parameter and of the total effective equation of state parameter as functions of the redshift, and we compare the resulting picture with the ordinary F (R ) gravity case. As we also show that the present day values of the dark energy equation of state parameter and of the total effective equation of state parameter are in better agreement with the observational data, in comparison to the ordinary F (R ) gravity case. Finally, we study the evolution of the growth factor as a function of the redshift for all the mimetic models we use.

  8. Evolution of dark energy perturbations in scalar-tensor cosmologies

    SciTech Connect

    Bueno Sanchez, J. C.; Perivolaropoulos, L.

    2010-05-15

    We solve analytically and numerically the generalized Einstein equations in scalar-tensor cosmologies to obtain the evolution of dark energy and matter linear perturbations. We compare our results with the corresponding results for minimally coupled quintessence perturbations. We find that scalar-tensor dark energy density perturbations are amplified by a factor of about 10{sup 4} compared to minimally coupled quintessence perturbations on scales less than about 1000 h{sup -1} Mpc (sub-Hubble scales). On these scales dark energy perturbations constitute a fraction of about 10% compared to matter density perturbations. Scalar-tensor dark energy density perturbations are anticorrelated with matter linear perturbations on sub-Hubble scales. This anticorrelation of matter with negative pressure perturbations induces a mild amplification of matter perturbations by about 10% on sub-Hubble scales. The evolution of scalar field perturbations on sub-Hubble scales is scale independent and therefore corresponds to a vanishing effective speed of sound (c{sub s{Phi}=}0). We briefly discuss the observational implications of our results, which may include predictions for galaxy and cluster halo profiles that are modified compared to {Lambda}CDM. The observed properties of these profiles are known to be in some tension with the predictions of {Lambda}CDM.

  9. Varying constants and dark energy with the E-ELT .

    NASA Astrophysics Data System (ADS)

    Vielzeuf, P. E.; Martins, C. J. A. P.

    The observational possibilities enabled by an ultra-stable CODEX-like spectrograph at the E-ELT will open new doors in the characterisation of the nature of Dark Energy. Indeed, it will provide measurements of a so far unexplored redshift-range (2

  10. Inflation, Dark Energy, and the Fate of the Universe

    SciTech Connect

    Linde, Andrei

    2003-11-12

    Inflationary theory, which describes an accelerated expansion of the early universe, gradually becomes a standard cosmological paradigm. It solves many complicated problems of the usual big bang theory, explains the origin of galaxies, and makes several predictions, which, so far, are in a good agreement with cosmological observations. Recently we learned that few billion years ago the universe entered the second stage of acceleration, driven by mysterious 'dark energy'. According to the simplest version of inflationary theory, the universe is an eternally existing self-reproducing fractal consisting of different balloons of exponentially large size. The universe as a whole can be immortal, but the fate of each of these balloons, including the one in which we live now, depends on the properties of dark energy. According to some of the theories of dark energy, our part of the universe will continue its accelerated expansion forever. Other theories predict that eventually our part of the universe will become ten-dimensional and stop accelerating. Still another possibility is that our part of the universe will collapse. I will describe recent developments in inflationary theory and the theory of dark energy, and discuss the possibility to find our fate by cosmological observations.

  11. 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,…

  12. Distance measurements from supernovae and dark energy constraints

    SciTech Connect

    Wang Yun

    2009-12-15

    Constraints on dark energy from current observational data are sensitive to how distances are measured from Type Ia supernova (SN Ia) data. We find that flux averaging of SNe Ia can be used to test the presence of unknown systematic uncertainties, and yield more robust distance measurements from SNe Ia. We have applied this approach to the nearby+SDSS+ESSENCE+SNLS+HST set of 288 SNe Ia, and the 'Constitution' set of 397 SNe Ia. Combining the SN Ia data with cosmic microwave background anisotropy data from Wilkinson Microwave Anisotropy Probe 5 yr observations, the Sloan Digital Sky Survey baryon acoustic oscillation measurements, the data of 69 gamma-ray bursts (GRBs) , and the Hubble constant measurement from the Hubble Space Telescope project SHOES, we measure the dark energy density function X(z){identical_to}{rho}{sub X}(z)/{rho}{sub X}(0) as a free function of redshift (assumed to be a constant at z>1 or z>1.5). Without the flux averaging of SNe Ia, the combined data using the Constitution set of SNe Ia seem to indicate a deviation from a cosmological constant at {approx}95% confidence level at 0 < or apporx. z < or approx. 0.8; they are consistent with a cosmological constant at {approx}68% confidence level when SNe Ia are flux averaged. The combined data using the nearby+SDSS+ESSENCE+SNLS+HST data set of SNe Ia are consistent with a cosmological constant at 68% confidence level with or without flux averaging of SNe Ia, and give dark energy constraints that are significantly more stringent than that using the Constitution set of SNe Ia. Assuming a flat Universe, dark energy is detected at >98% confidence level for z{<=}0.75 using the combined data with 288 SNe Ia from nearby+SDSS+ESSENCE+SNLS+HST, independent of the assumptions about X(z{>=}1). We quantify dark energy constraints without assuming a flat Universe using the dark energy figure of merit for both X(z) and a dark energy equation-of-state linear in the cosmic scale factor.

  13. Accretions of dark matter and dark energy onto (n+2)-dimensional Schwarzschild black hole and Morris-Thorne wormhole

    NASA Astrophysics Data System (ADS)

    Debnath, Ujjal

    2015-12-01

    In this work, we have studied accretion of the dark matter and dark energy onto of (n+2)-dimensional Schwarzschild black hole and Morris-Thorne wormhole. The mass and the rate of change of mass for (n+2)-dimensional Schwarzschild black hole and Morris-Thorne wormhole have been found. We have assumed some candidates of dark energy like holographic dark energy, new agegraphic dark energy, quintessence, tachyon, DBI-essence, etc. The black hole mass and the wormhole mass have been calculated in term of redshift when dark matter and above types of dark energies accrete onto them separately. We have shown that the black hole mass increases and wormhole mass decreases for holographic dark energy, new agegraphic dark energy, quintessence, tachyon accretion and the slope of increasing/decreasing of mass sensitively depends on the dimension. But for DBI-essence accretion, the black hole mass first increases and then decreases and the wormhole mass first decreases and then increases and the slope of increasing/decreasing of mass not sensitively depends on the dimension.

  14. Probing dark energy using convergence power spectrum and bi-spectrum

    NASA Astrophysics Data System (ADS)

    Dinda, Bikash R.

    2017-09-01

    Weak lensing convergence statistics is a powerful tool to probe dark energy. Dark energy plays an important role to the structure formation and the effects can be detected through the convergence power spectrum, bi-spectrum etc. One of the most promising and simplest dark energy model is the ΛCDM . However, it is worth investigating different dark energy models with evolving equation of state of the dark energy. In this work, detectability of different dark energy models from ΛCDM model has been explored through convergence power spectrum and bi-spectrum.

  15. Dynamical behavior of the extended holographic dark energy with the Hubble horizon

    SciTech Connect

    Liu Jie; Gong Yungui; Chen Ximing

    2010-04-15

    The extended holographic dark energy model with the Hubble horizon as the infrared cutoff avoids the problem of the circular reasoning of the holographic dark energy model. Unfortunately, it is hit with the no-go theorem. In this paper, we consider the extended holographic dark energy model with a potential, V({phi}), for the Brans-Dicke scalar field. With the addition of a potential for the Brans-Dicke scalar field, the extended holographic dark energy model using the Hubble horizon as the infrared cutoff is a viable dark energy model, and the model has the dark energy dominated attractor solution.

  16. Topology and dark energy: testing gravity in voids.

    PubMed

    Spolyar, Douglas; Sahlén, Martin; Silk, Joe

    2013-12-13

    Modified gravity has garnered interest as a backstop against dark matter and dark energy (DE). As one possible modification, the graviton can become massive, which introduces a new scalar field--here with a Galileon-type symmetry. The field can lead to a nontrivial equation of state of DE which is density and scale dependent. Tension between type Ia supernovae and Planck could be reduced. In voids, the scalar field dramatically alters the equation of state of DE, induces a soon-observable gravitational slip between the two metric potentials, and develops a topological defect (domain wall) due to a nontrivial vacuum structure for the field.

  17. Probing dark energy beyond z=2 with CODEX

    NASA Astrophysics Data System (ADS)

    Vielzeuf, P. E.; Martins, C. J. A. P.

    2012-04-01

    Precision measurements of nature’s fundamental couplings and a first measurement of the cosmological redshift drift are two of the key targets for future high-resolution ultrastable spectrographs such as CODEX. Being able to do both gives CODEX a unique advantage, allowing it to probe dynamical dark energy models (by measuring the behavior of their equation of state) deep in the matter era and thereby testing classes of models that would otherwise be difficult to distinguish from the standard lambda-cold dark matter paradigm. We illustrate this point with two simple case studies.

  18. Holographic dark energy reconstruction in gravity

    NASA Astrophysics Data System (ADS)

    Salako, Ines G.; Jawad, Abdul; Chattopadhyay, Surajit

    2015-07-01

    The present paper reports a holographic reconstruction scheme for gravity proposed in Harko et al. (J. Cosmol. Astropart. Phys. 12:021, 2014), where is the torsion scalar and is the trace of the energy-momentum tensor considering future event horizon as the enveloping horizon of the universe. We consider and for reconstruction. We also extract the equation of state parameter for these models. We also give the comparison of the results with observational data and found the consistency of our results.

  19. Resource Letter DEAU-1: Dark energy and the accelerating universe

    NASA Astrophysics Data System (ADS)

    Linder, Eric V.

    2008-03-01

    This Resource Letter provides a guide to the literature on dark energy and the accelerating universe. It is intended to be of use to researchers, teachers, and students at several levels. Journal articles, books, and websites are cited for the following topics: Einstein's cosmological constant, quintessence or dynamical scalar fields, modified cosmic gravity, relations to high-energy physics, cosmological probes and observations, terrestrial probes, calculational tools and parameter estimation, teaching strategies and educational resources, and the fate of the universe.

  20. Encircling the dark: constraining dark energy via cosmic density in spheres

    NASA Astrophysics Data System (ADS)

    Codis, S.; Pichon, C.; Bernardeau, F.; Uhlemann, C.; Prunet, S.

    2016-08-01

    The recently published analytic probability density function for the mildly non-linear cosmic density field within spherical cells is used to build a simple but accurate maximum likelihood estimate for the redshift evolution of the variance of the density, which, as expected, is shown to have smaller relative error than the sample variance. This estimator provides a competitive probe for the equation of state of dark energy, reaching a few per cent accuracy on wp and wa for a Euclid-like survey. The corresponding likelihood function can take into account the configuration of the cells via their relative separations. A code to compute one-cell-density probability density functions for arbitrary initial power spectrum, top-hat smoothing and various spherical-collapse dynamics is made available online, so as to provide straightforward means of testing the effect of alternative dark energy models and initial power spectra on the low-redshift matter distribution.

  1. Integrated Sachs-Wolfe effect in interacting dark energy models

    SciTech Connect

    Olivares, German; Pavon, Diego; Atrio-Barandela, Fernando

    2008-05-15

    Models with dark energy decaying into dark matter have been proposed in cosmology to solve the coincidence problem. We study the effect of such coupling on the cosmic microwave background temperature anisotropies. The interaction changes the rate of evolution of the metric potentials and the growth rate of matter density perturbations and modifies the integrated Sachs-Wolfe component of cosmic microwave background temperature anisotropies, enhancing the effect. Cross correlation of galaxy catalogs with cosmic microwave background maps provides a model-independent test to constrain the interaction. We particularize our analysis for a specific interacting model and show that galaxy catalogs with median redshifts z{sub m}=0.1-0.9 can rule out models with an interaction parameter strength of c{sup 2}{approx_equal}0.1 better than 99.95% confidence level. Values of c{sup 2}{<=}0.01 are compatible with the data and may account for the possible discrepancy between the fraction of dark energy derived from Wilkinson microwave anisotropy probe 3 yr data and the fraction obtained from the integrated Sachs-Wolfe effect. Measuring the fraction of dark energy by these two methods could provide evidence of an interaction.

  2. Dark energy from large-scale structure lensing information

    SciTech Connect

    Lu Tingting; Pen Ueli; Dore, Oliver

    2010-06-15

    Wide area large-scale structure (LSS) surveys are planning to map a substantial fraction of the visible Universe to quantify dark energy through baryon acoustic oscillations. At increasing redshift, for example, that probed by proposed 21-cm intensity mapping surveys, gravitational lensing potentially limits the fidelity (Hui et al., 2007) because it distorts the apparent matter distribution. In this paper we show that these distortions can be reconstructed, and actually used to map the distribution of intervening dark matter. The lensing information for sources at z=1-3 allows accurate reconstruction of the gravitational potential on large scales, l < or approx. 100, which is well matched for integrated Sachs-Wolfe effect measurements of dark energy and its sound speed, and a strong constraint for modified gravity models of dark energy. We built an optimal quadratic lensing estimator for non-Gaussian sources, which is necessary for LSS. The phenomenon of 'information saturation' (Rimes and Hamilton, 2005) saturates reconstruction at mildly nonlinear scales, where the linear source power spectrum {Delta}{sup 2{approx}}0.2-0.5, depending on power spectrum slope. Naive Gaussian estimators with nonlinear cutoff can be tuned to reproduce the optimal non-Gaussian errors within a factor of 2. We compute the effective number densities of independent lensing sources for LSS lensing, and find that they increase rapidly with redshifts. For LSS/21-cm sources at z{approx}2-4, the lensing reconstruction is limited by cosmic variance at l < or approx. 100.

  3. Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion

    DOE PAGES

    Huterer, Dragan; Kirkby, David; Bean, Rachel; ...

    2014-03-15

    The quantity and quality of cosmic structure observations have greatly accelerated in recent years, and further leaps forward will be facilitated by imminent projects. These will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to several pieces of fundamental physics: the primordial perturbations generated by GUT-scale physics; neutrino masses and interactions; the nature of dark matter and dark energy. We focus on the last of these here: the ways that combining probes of growth with those of the cosmic expansionmore » such as distance-redshift relations will pin down the mechanism driving the acceleration of the Universe.« less

  4. Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion

    SciTech Connect

    Huterer, Dragan; Kirkby, David; Bean, Rachel; Connolly, Andrew; Dawson, Kyle; Dodelson, Scott; Evrard, August; Jain, Bhuvnesh; Jarvis, Michael; Linder, Eric; Mandelbaum, Rachel; May, Morgan; Raccanelli, Alvise; Reid, Beth; Rozo, Eduardo; Schmidt, Fabian; Sehgal, Neelima; Slosar, Anze; Van Engelen, Alex; Wu, Hao-Yi; Zhao, Gongbo

    2014-03-15

    The quantity and quality of cosmic structure observations have greatly accelerated in recent years, and further leaps forward will be facilitated by imminent projects. These will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to several pieces of fundamental physics: the primordial perturbations generated by GUT-scale physics; neutrino masses and interactions; the nature of dark matter and dark energy. We focus on the last of these here: the ways that combining probes of growth with those of the cosmic expansion such as distance-redshift relations will pin down the mechanism driving the acceleration of the Universe.

  5. Growth of cosmic structure: Probing dark energy beyond expansion

    SciTech Connect

    Huterer, Dragan; Kirkby, David; Bean, Rachel; Connolly, Andrew; Dawson, Kyle; Dodelson, Scott; Evrard, August; Jain, Bhuvnesh; Jarvis, Michael; Linder, Eric; Mandelbaum, Rachel; May, Morgan; Raccanelli, Alvise; Reid, Beth; Rozo, Eduardo; Schmidt, Fabian; Sehgal, Neelima; Slosar, Anže; van Engelen, Alex; Wu, Hao-Yi; Zhao, Gongbo

    2015-03-01

    The quantity and quality of cosmic structure observations have greatly accelerated in recent years, and further leaps forward will be facilitated by imminent projects. These will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to several pieces of fundamental physics: the primordial perturbations generated by GUT-scale physics; neutrino masses and interactions; the nature of dark matter and dark energy. We focus on the last of these here: the ways that combining probes of growth with those of the cosmic expansion such as distance-redshift relations will pin down the mechanism driving the acceleration of the Universe.

  6. Constraining dark energy from the abundance of weak gravitational lenses

    NASA Astrophysics Data System (ADS)

    Weinberg, Nevin N.; Kamionkowski, Marc

    2003-05-01

    We examine the prospect of using the observed abundance of weak gravitational lenses to constrain the equation-of-state parameter w=p/ρ of dark energy. Dark energy modifies the distance-redshift relation, the amplitude of the matter power spectrum, and the rate of structure growth. As a result, it affects the efficiency with which dark-matter concentrations produce detectable weak-lensing signals. Here we solve the spherical-collapse model with dark energy, clarifying some ambiguities found in the literature. We also provide fitting formulae for the non-linear overdensity at virialization and the linear-theory overdensity at collapse. We then compute the variation in the predicted weak-lens abundance with w. We find that the predicted redshift distribution and number count of weak lenses are highly degenerate in w and the present matter density Ω0. If we fix Ω0 the number count of weak lenses for w=-2/3 is a factor of ~2 smaller than for the Λ cold dark matter (CDM) model w=-1. However, if we allow Ω0 to vary with w such that the amplitude of the matter power spectrum as measured by the Cosmic Background Explorer (COBE) matches that obtained from the X-ray cluster abundance, the decrease in the predicted lens abundance is less than 25 per cent for -1 <=w< -0.4. We show that a more promising method for constraining dark energy - one that is largely unaffected by the Ω0-w degeneracy as well as uncertainties in observational noise - is to compare the relative abundance of virialized X-ray lensing clusters with the abundance of non-virialized, X-ray underluminous, lensing haloes. For aperture sizes of ~15 arcmin, the predicted ratio of the non-virialized to virialized lenses is greater than 40 per cent and varies by ~20 per cent between w=-1 and -0.6. Overall, we find that, if all other weak-lensing parameters are fixed, a survey must cover at least ~40 deg2 in order for the weak-lens number count to differentiate a ΛCDM cosmology from a dark-energy model with w

  7. Consistency of nonlinear interacting ghost dark energy with recent observations

    NASA Astrophysics Data System (ADS)

    Ebrahimi, E.; Golchin, H.; Mehrabi, A.; Movahed, S. M. S.

    In this paper, we investigate ghost dark energy model in the presence of nonlinear interaction between dark energy and dark matter. We also extend the analysis to the so-called generalized ghost dark energy (GGDE) which ρD = αH + βH2. The model contains three free parameters as ΩD,ζ(= 8πGβ 3 ) and b2 (the coupling coefficient of interactions). We propose three kinds of nonlinear interaction terms and discuss the behavior of equation of state, deceleration and dark energy density parameters of the model. We also find the squared sound speed and search for signs of stability of the model. To compare the interacting GGDE model with observational data sets, we use more recent observational outcomes, namely SNIa from JLA catalog, Hubble parameter, baryonic acoustic oscillation and the most relevant CMB parameters including, the position of acoustic peaks, shift parameters and redshift to recombination. For GGDE with the first nonlinear interaction, the joint analysis indicates that ΩD = 0.7192 ± 0.0062, b2 = 0.146 ‑0.026+0.030 and ζ = 0.104 ± 0.047 at 1 optimal variance error. For the second interaction, the best fit values at 1σ confidence are ΩD = 0.72091 ± 0.0065, b2 = 0.0395 ± 0.0080 and ζ ≤ 0.0173. According to combination of all observational data sets considered in this paper, the best fit values for third nonlinearly interacting model are ΩD = 0.7287 ± 0.0062, b2 = 0.0109 ± 0.0023 and ζ ≤ 0.00764 at 1σ confidence interval. Finally, we found that the presence of interaction is compatible in mentioned models via current observational datasets.

  8. 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 .

  9. Wormhole supported by dark energy admitting conformal motion

    NASA Astrophysics Data System (ADS)

    Bhar, Piyali; Rahaman, Farook; Manna, Tuhina; Banerjee, Ayan

    2016-12-01

    In this article, we study the possibility of sustaining static and spherically symmetric traversable wormhole geometries admitting conformal motion in Einstein gravity, which presents a more systematic approach to search a relation between matter and geometry. In wormhole physics, the presence of exotic matter is a fundamental ingredient and we show that this exotic source can be dark energy type which support the existence of wormhole spacetimes. In this work we model a wormhole supported by dark energy which admits conformal motion. We also discuss the possibility of the detection of wormholes in the outer regions of galactic halos by means of gravitational lensing. Studies of the total gravitational energy for the exotic matter inside a static wormhole configuration are also performed.

  10. Higgs production as a probe of chameleon dark energy

    SciTech Connect

    Brax, Philippe; Burrage, Clare; Davis, Anne-Christine; Seery, David; Weltman, Amanda

    2010-05-15

    In this paper we study various particle physics effects of a light, scalar dark energy field with chameleonlike couplings to matter. We show that a chameleon model with only matter couplings will induce a coupling to photons. In doing so, we derive the first microphysical realization of a chameleonic dark energy model coupled to the electromagnetic field strength. This analysis provides additional motivation for current and near-future tests of axionlike and chameleon particles. We find a new bound on the coupling strength of chameleons in uniformly coupled models. We also study the effect of chameleon fields on Higgs production, which is relevant for hadron colliders. These are expected to manufacture Higgs particles through weak boson fusion, or associated production with a Z or W{sup {+-}.} We show that, like the Tevatron, the LHC will not be able to rule out or observe chameleons through this mechanism, because gauge invariance of the low energy Lagrangian suppresses the corrections that may arise.

  11. Do stochastic inhomogeneities affect dark-energy precision measurements?

    PubMed

    Ben-Dayan, I; Gasperini, M; Marozzi, G; Nugier, F; Veneziano, G

    2013-01-11

    The effect of a stochastic background of cosmological perturbations on the luminosity-redshift relation is computed to second order through a recently proposed covariant and gauge-invariant light-cone averaging procedure. The resulting expressions are free from both ultraviolet and infrared divergences, implying that such perturbations cannot mimic a sizable fraction of dark energy. Different averages are estimated and depend on the particular function of the luminosity distance being averaged. The energy flux being minimally affected by perturbations at large z is proposed as the best choice for precision estimates of dark-energy parameters. Nonetheless, its irreducible (stochastic) variance induces statistical errors on Ω(Λ)(z) typically lying in the few-percent range.

  12. Strategies for Learning the Nature of Dark Energy

    NASA Astrophysics Data System (ADS)

    Albrecht, Andreas

    2006-06-01

    Understanding the observed cosmic acceleration is widely ranked among the very most compelling of all outstanding problems in physical science. Many believe that nothing short of a revolution will be required in order to integrate the cosmic acceleration (often attributed to "dark energy") with our understanding of fundamental physics. The DETF was formed at the request of DOE, NASA and NSF as a joint subcommittee of the Astronomy and Astrophysics Advisory Committee (AAAC) and the High Energy Physics Advisory Panel (HEPAP) to give advice on optimizing our program of dark energy studies. To this end we have assessed a wide variety of possible techniques and strategies. I will present our main conclusions and discuss their implications.

  13. Testing the cosmological constant as a candidate for dark energy

    SciTech Connect

    Kratochvil, Jan; Linde, Andrei; Linder, Eric V.; Shmakova, Marina

    2003-12-03

    It may be difficult to single out the best model of dark energy on the basis of the existing and planned cosmological observations, because many different models can lead to similar observational consequences. However, each particular model can be studied and either found consistent with observations or ruled out. In this paper, we concentrate on the possibility to test and rule out the simplest and by far the most popular of the models of dark energy, the theory described by general relativity with positive vacuum energy (the cosmological constant). We evaluate the conditions under which this model could be ruled out by the future observations made by the Supernova/Acceleration Probe SNAP (both for supernovae and weak lensing) and by the Planck Surveyor cosmic microwave background satellite.

  14. Quintessence in a quandary: Prior dependence in dark energy models

    NASA Astrophysics Data System (ADS)

    Marsh, David J. E.; Bull, Philip; Ferreira, Pedro G.; Pontzen, Andrew

    2014-11-01

    The archetypal theory of dark energy is quintessence: a minimally coupled scalar field with a canonical kinetic energy and potential. By studying random potentials, we show that quintessence imposes a restricted set of priors on the equation of state of dark energy. Focusing on the commonly used parametrization, w (a )≈w0+wa(1 -a ) , we show that there is a natural scale and direction in the (w0,wa) plane that distinguishes quintessence as a general framework. We calculate the expected information gain for a given survey and show that, because of the nontrivial prior information, it is a function of more than just the figure of merit. This allows us to make a quantitative case for novel survey strategies. We show that the scale of the prior sets target observational requirements for gaining significant information. This corresponds to a figure of merit FOM ≳200 , a requirement that future galaxy redshift surveys will meet.

  15. Fine Structure of Dark Energy and New Physics

    DOE PAGES

    Jejjala, Vishnu; Kavic, Michael; Minic, Djordje

    2007-01-01

    Following our recent work on the cosmological constant problem, in this letter we make a specific proposal regarding the fine structure (i.e., the spectrum) of dark energy. The proposal is motivated by a deep analogy between the blackbody radiation problem, which led to the development of quantum theory, and the cosmological constant problem, for which we have recently argued calls for a conceptual extension of the quantum theory. We argue that the fine structure of dark energy is governed by a Wien distribution, indicating its dual quantum and classical nature. We discuss observational consequences of such a picture of darkmore » energy and constrain the distribution function.« less

  16. Testing the Cosmological constant as a Candidate for Dark Energy

    SciTech Connect

    Kratochvil, J

    2004-01-08

    It may be difficult to single out the best model of dark energy on the basis of the existing and planned cosmological observations, because many different models can lead to similar observational consequences. However, each particular model can be studied and either found consistent with observations or ruled out. In this paper, we concentrate on the possibility to test and rule out the simplest and by far the most popular of the models of dark energy, the theory described by general relativity with positive vacuum energy (the cosmological constant). We evaluate the conditions under which this model could be ruled out by the future observations made by the Supernova/Acceleration Probe SNAP (both for supernovae and weak lensing) and by the Planck Surveyor cosmic microwave background satellite.

  17. Dark matter haloes in modified gravity and dark energy: interaction rate, small- and large-scale alignment

    NASA Astrophysics Data System (ADS)

    L'Huillier, Benjamin; Winther, Hans A.; Mota, David F.; Park, Changbom; Kim, Juhan

    2017-07-01

    We study the properties of dark matter haloes in a wide range of modified gravity models, namely, f(R), DGP and interacting dark energy models. We study the effects of modified gravity and dark energy on the internal properties of haloes, such as the spin and the structural parameters. We find that f(R) gravity enhances the median value of the Bullock spin parameter, but could not detect such effects for DGP and coupled dark energy. f(R) also yields a lower median sphericity and oblateness, while coupled dark energy has the opposite effect. However, these effects are very small. We then study the interaction rate of haloes in different gravity and find that only strongly coupled dark energy models enhance the interaction rate. We then quantify the enhancement of the alignment of the spins of interacting halo pairs by modified gravity. Finally, we study the alignment of the major axes of haloes with the large-scale structures. The alignment of the spins of interacting pairs of haloes in DGP and coupled dark energy models show no discrepancy with GR, while f(R) shows a weaker alignment. Strongly coupled dark energy shows a stronger alignment of the halo shape with the large-scale structures.

  18. Disease and the brain's dark energy.

    PubMed

    Zhang, Dongyang; Raichle, Marcus E

    2010-01-01

    Brain function has traditionally been studied in terms of physiological responses to environmental demands. This approach, however, ignores the fact that much of the brain's energy is devoted to intrinsic neuronal signaling. Recent studies indicate that intrinsic neuronal activity manifests as spontaneous fluctuations in the blood oxygen level-dependent (BOLD) functional MRI (fMRI) signal. The study of such fluctuations could potentially provide insight into the brain's functional organization. In this article, we begin by presenting an overview of the strategies used to explore intrinsic neuronal activity. Considering the possibility that intrinsic signaling accounts for a large proportion of brain activity, we then examine whether the functional architecture of intrinsic activity is altered in neurological and psychiatric diseases. We also review a clinical application of brain mapping, in which intrinsic activity is employed for the preoperative localization of functional brain networks in patients undergoing neurosurgery. To end the article, we explore some of the basic science pursuits that have been undertaken to further understand the physiology behind intrinsic activity as imaged with BOLD fMRI.

  19. James Webb Space Telescope Studies of Dark Energy

    NASA Technical Reports Server (NTRS)

    Gardner, Jonathan P.; Stiavelli, Massimo; Mather, John C.

    2010-01-01

    The Hubble Space Telescope (HST) has contributed significantly to studies of dark energy. It was used to find the first evidence of deceleration at z=1.8 (Riess et al. 2001) through the serendipitous discovery of a type 1a supernova (SN1a) in the Hubble Deep Field. The discovery of deceleration at z greater than 1 was confirmation that the apparent acceleration at low redshift (Riess et al. 1998; Perlmutter et al. 1999) was due to dark energy rather than observational or astrophysical effects such as systematic errors, evolution in the SN1a population or intergalactic dust. The GOODS project and associated follow-up discovered 21 SN1a, expanding on this result (Riess et al. 2007). HST has also been used to constrain cosmological parameters and dark energy through weak lensing measurements in the COSMOS survey (Massey et al 2007; Schrabback et al 2009) and strong gravitational lensing with measured time delays (Suyu et al 2010). Constraints on dark energy are often parameterized as the equation of state, w = P/p. For the cosmological constant model, w = -1 at all times; other models predict a change with time, sometimes parameterized generally as w(a) or approximated as w(sub 0)+(1-a)w(sub a), where a = (1+z)(sup -1) is the scale factor of the universe relative to its current scale. Dark energy can be constrained through several measurements. Standard candles, such as SN1a, provide a direct measurement of the luminosity distance as a function of redshift, which can be converted to H(z), the change in the Hubble constant with redshift. An analysis of weak lensing in a galaxy field can be used to derive the angular-diameter distance from the weak-lensing equation and to measure the power spectrum of dark-matter halos, which constrains the growth of structure in the Universe. Baryonic acoustic oscillations (BAO), imprinted on the distribution of matter at recombination, provide a standard rod for measuring the cosmological geometry. Strong gravitational lensing of a

  20. Dark Energy is "Dying” and Other Student Ideas About Cosmology

    NASA Astrophysics Data System (ADS)

    Bailey, Janelle M.; Coble, K.; Cochran, G. L.; Sanchez, R.; Larrieu, D.; Hayes, V. L.; Nickerson, M.; Cominsky, L. R.; McLin, K. M.

    2011-05-01

    Determining the range and frequency of "alternative conceptions” is an important first step to improving instructional effectiveness. Modern topics in astronomy, such as cosmology, are of primary interest to many educators and students, but we are only beginning to understand students’ alternative conceptions in this area. Through analysis of pre-instructional open-ended surveys (N > 500), our research group is attempting to classify students’ ideas about concepts important to modern cosmology, including the structure, age, and evolution of the universe; dark matter and dark energy; and the Big Bang. Survey responses, analyzed through an iterative process of thematic coding, reveal a number of alternative conceptions. For example, students frequently conflate structure terms such as solar system, galaxy, and universe or do not understand the relationship between the terms; believe the universe to be infinitely old; and may not be aware of dark matter or dark energy. This work was supported by NASA ROSES E/PO Grant #NNXlOAC89G, as well as by the Illinois Space Grant Consortium and National Science Foundation CCLI Grant #0632563 at Chicago State University and the Fermi E/PO program at Sonoma State University.

  1. Testing coupled dark energy with large scale structure observation

    SciTech Connect

    Yang, Weiqiang; Xu, Lixin E-mail: lxxu@dlut.edu.cn

    2014-08-01

    The coupling between the dark components provides a new approach to mitigate the coincidence problem of cosmological standard model. In this paper, dark energy is treated as a fluid with a constant equation of state, whose coupling with dark matter is Q-bar =3Hξ{sub x}ρ-bar {sub x}. In the frame of dark energy, we derive the evolution equations for the density and velocity perturbations. According to the Markov Chain Monte Carlo method, we constrain the model by currently available cosmic observations which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and fσ{sub 8}(z) data points from redshift-space distortion. The results show the interaction rate in σ regions: ξ{sub x} = 0.00328{sub -0.00328-0.00328-0.00328}{sup +0.000736+0.00549+0.00816}, which means that the recently cosmic observations favor a small interaction rate which is up to the order of 10{sup -2}, meanwhile, the measurement of redshift-space distortion could rule out the large interaction rate in the σ region.

  2. Gravitational collapse of dark energy field configurations and supermassive black hole formation

    SciTech Connect

    Jhalani, V.; Kharkwal, H.; Singh, A.

    2016-11-15

    Dark energy is the dominant component of the total energy density of our Universe. The primary interaction of dark energy with the rest of the Universe is gravitational. It is therefore important to understand the gravitational dynamics of dark energy. Since dark energy is a low-energy phenomenon from the perspective of particle physics and field theory, a fundamental approach based on fields in curved space should be sufficient to understand the current dynamics of dark energy. Here, we take a field theory approach to dark energy. We discuss the evolution equations for a generic dark energy field in curved space-time and then discuss the gravitational collapse for dark energy field configurations. We describe the 3 + 1 BSSN formalism to study the gravitational collapse of fields for any general potential for the fields and apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting equations for the time evolution of field configurations and the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our Universe. We also demonstrate the black hole formation as a result of the gravitational collapse of the dark energy field configurations. The black holes produced by the collapse of dark energy fields are in the supermassive black hole category with the masses of these black holes being comparable to the masses of black holes at the centers of galaxies.

  3. On the internal consistency of holographic dark energy models

    SciTech Connect

    Horvat, R

    2008-10-15

    Holographic dark energy (HDE) models, underpinned by an effective quantum field theory (QFT) with a manifest UV/IR connection, have become convincing candidates for providing an explanation of the dark energy in the universe. On the other hand, the maximum number of quantum states that a conventional QFT for a box of size L is capable of describing relates to those boxes which are on the brink of experiencing a sudden collapse to a black hole. Another restriction on the underlying QFT is that the UV cut-off, which cannot be chosen independently of the IR cut-off and therefore becomes a function of time in a cosmological setting, should stay the largest energy scale even in the standard cosmological epochs preceding a dark energy dominated one. We show that, irrespective of whether one deals with the saturated form of HDE or takes a certain degree of non-saturation in the past, the above restrictions cannot be met in a radiation dominated universe, an epoch in the history of the universe which is expected to be perfectly describable within conventional QFT.

  4. Dark energy and the cosmic microwave background radiation.

    PubMed

    Dodelson, S; Knox, L

    2000-04-17

    We find that current cosmic microwave background anisotropy data strongly constrain the mean spatial curvature of the Universe to be near zero, or, equivalently, the total energy density to be near critical-as predicted by inflation. This result is robust to editing of data sets, and variation of other cosmological parameters (totaling seven, including a cosmological constant). Other lines of argument indicate that the energy density of nonrelativistic matter is much less than critical. Together, these results are evidence, independent of supernovae data, for dark energy in the Universe.

  5. No-go theorem for k-essence dark energy.

    PubMed

    Bonvin, Camille; Caprini, Chiara; Durrer, Ruth

    2006-08-25

    We demonstrate that if k-essence can solve the coincidence problem and play the role of dark energy in the Universe, the fluctuations of the field have to propagate superluminally at some stage. We argue that this implies that successful k-essence models violate causality. It is not possible to define a time ordered succession of events in a Lorentz invariant way. Therefore, k-essence cannot arise as a low energy effective field theory of a causal, consistent high energy theory.

  6. Dark energy and the cosmic microwave background radiation

    NASA Technical Reports Server (NTRS)

    Dodelson, S.; Knox, L.

    2000-01-01

    We find that current cosmic microwave background anisotropy data strongly constrain the mean spatial curvature of the Universe to be near zero, or, equivalently, the total energy density to be near critical-as predicted by inflation. This result is robust to editing of data sets, and variation of other cosmological parameters (totaling seven, including a cosmological constant). Other lines of argument indicate that the energy density of nonrelativistic matter is much less than critical. Together, these results are evidence, independent of supernovae data, for dark energy in the Universe.

  7. Dark energy and the cosmic microwave background radiation

    NASA Technical Reports Server (NTRS)

    Dodelson, S.; Knox, L.

    2000-01-01

    We find that current cosmic microwave background anisotropy data strongly constrain the mean spatial curvature of the Universe to be near zero, or, equivalently, the total energy density to be near critical-as predicted by inflation. This result is robust to editing of data sets, and variation of other cosmological parameters (totaling seven, including a cosmological constant). Other lines of argument indicate that the energy density of nonrelativistic matter is much less than critical. Together, these results are evidence, independent of supernovae data, for dark energy in the Universe.

  8. Clustering GCG: a viable option for unified dark matter-dark energy?

    SciTech Connect

    Kumar, Sumit; Sen, Anjan A E-mail: aasen@jmi.ac.in

    2014-10-01

    We study the clustering Generalized Chaplygin Gas (GCG) as a possible candidate for dark matter-dark energy unification. The vanishing speed of sound 0c{sub s}{sup 2} = ) for the GCG fluid can be obtained by incorporating higher derivative operator in the original K-essence Lagrangian. The evolution of the density fluctuations in the GCG+Baryon fluid is studied in the linear regime. The observational constraints on the model are obtained using latest data from SNIa, H(z), BAO and also for the fσ{sub 8} measurements. The matter power spectra for the allowed parameter values are well behaved without any unphysical features.

  9. Correspondence of F-Essence with Holographic and New Agegraphic Dark Energy Models

    NASA Astrophysics Data System (ADS)

    Maity, Sayani; Debnath, Ujjal

    2016-02-01

    In this work, we consider a non-flat universe filled with Fermionic field. First, we have considered the holographic dark energy and new agegraphic dark energy in the framework of F-essence cosmology and investigated the consequences for their co-existence. The correspondence of F-essence with the above types of dark energy models have been investigated. The natures of K and Y for these correspondence of F-essence with the above dark energies have been analyzed.

  10. A Note on Equivalence Among Various Scalar Field Models of Dark Energies

    NASA Astrophysics Data System (ADS)

    Mandal, Jyotirmay Das; Debnath, Ujjal

    2017-08-01

    In this work, we have tried to find out similarities between various available models of scalar field dark energies (e.g., quintessence, k-essence, tachyon, phantom, quintom, dilatonic dark energy, etc). We have defined an equivalence relation from elementary set theory between scalar field models of dark energies and used fundamental ideas from linear algebra to set up our model. Consequently, we have obtained mutually disjoint subsets of scalar field dark energies with similar properties and discussed our observation.

  11. Constraints on interacting dark energy models from Planck 2015 and redshift-space distortion data

    NASA Astrophysics Data System (ADS)

    Costa, André A.; Xu, Xiao-Dong; Wang, Bin; Abdalla, E.

    2017-01-01

    We investigate phenomenological interactions between dark matter and dark energy and constrain these models by employing the most recent cosmological data including the cosmic microwave background radiation anisotropies from Planck 2015, Type Ia supernovae, baryon acoustic oscillations, the Hubble constant and redshift-space distortions. We find that the interaction in the dark sector parameterized as an energy transfer from dark matter to dark energy is strongly suppressed by the whole updated cosmological data. On the other hand, an interaction between dark sectors with the energy flow from dark energy to dark matter is proved in better agreement with the available cosmological observations. This coupling between dark sectors is needed to alleviate the coincidence problem.

  12. Covariant extrinsic gravity and the geometric origin of dark energy

    NASA Astrophysics Data System (ADS)

    Jalalzadeh, S.; Rostami, T.

    2015-01-01

    In this paper, we construct the covariant or model independent induced Einstein-Yang-Mills field equations on a four-dimensional brane embedded isometrically in an D-dimensional bulk space, assuming the matter fields are confined to the brane. Applying this formalism to cosmology, we derive the generalized Friedmann equations. We derive the density parameter of dark energy in terms of width of the brane, normal curvature radii and the number of extra large dimensions. We show that dark energy could actually be the manifestation of the local extrinsic shape of the brane. It is shown that the predictions of this model are in good agreement with observation if we consider an 11-dimensional bulk space.

  13. ASTROPHYSICS. Atom-interferometry constraints on dark energy.

    PubMed

    Hamilton, P; Jaffe, M; Haslinger, P; Simmons, Q; Müller, H; Khoury, J

    2015-08-21

    If dark energy, which drives the accelerated expansion of the universe, consists of a light scalar field, it might be detectable as a "fifth force" between normal-matter objects, in potential conflict with precision tests of gravity. Chameleon fields and other theories with screening mechanisms, however, can evade these tests by suppressing the forces in regions of high density, such as the laboratory. Using a cesium matter-wave interferometer near a spherical mass in an ultrahigh-vacuum chamber, we reduced the screening mechanism by probing the field with individual atoms rather than with bulk matter. We thereby constrained a wide class of dark energy theories, including a range of chameleon and other theories that reproduce the observed cosmic acceleration. Copyright © 2015, American Association for the Advancement of Science.

  14. Dark energy from Gauss-Bonnet and nonminimal couplings

    NASA Astrophysics Data System (ADS)

    Granda, L. N.; Jimenez, D. F.

    2014-12-01

    We consider a scalar-tensor model of dark energy with Gauss-Bonnet and nonminimal couplings. Exact cosmological solutions were found in the absence of potential that give equations of state of dark energy consistent with current observational constraints, but with different asymptotic behaviors depending on the couplings of the model. A detailed reconstruction procedure is given for the scalar potential and the Gauss-Bonnet coupling for any given cosmological scenario. In particular we consider conditions for the existence of a variety of cosmological solutions with accelerated expansion, including quintessence, phantom, de Sitter, and Little Rip. For the case of quintessence and phantom we have found a scalar potential of the Albrecht-Skordis type, where the potential is an exponential with a polynomial factor.

  15. Dark energy reflections in the redshift-space quadrupole.

    PubMed

    Yamamoto, Kazuhiro; Bassett, Bruce A; Nishioka, Hiroaki

    2005-02-11

    We show that the redshift-space quadrupole will be a powerful tool for constraining dark energy even if the baryon oscillations are missing from the monopole power spectrum and bias is scale and time dependent. We calculate the accuracy with which next-generation galaxy surveys such as KAOS will measure the quadrupole power spectrum, which gives the leading anisotropies in the power spectrum in redshift space due to linear velocity, and the so-called "Finger of God" and Alcock-Paczynski effects. Combining the monopole and quadrupole power spectra, in the complete absence of baryon oscillations (Omegab=0), leads to a roughly 500% improvement in constraints on dark energy compared with those from the monopole spectrum alone.

  16. Dark energy and the return of the phoenix universe

    SciTech Connect

    Lehners, Jean-Luc; Steinhardt, Paul J.

    2009-03-15

    In cyclic universe models based on a single scalar field (e.g., the radion determining the distance between branes in M theory), virtually the entire Universe makes it through the ekpyrotic smoothing and flattening phase, bounces, and enters a new epoch of expansion and cooling. This stable evolution cannot occur, however, if scale-invariant curvature perturbations are produced by the entropic mechanism because it requires two scalar fields (e.g., the radion and the Calabi-Yau dilaton) evolving along an unstable classical trajectory. In fact, we show here that an overwhelming fraction of the Universe fails to make it through the ekpyrotic phase; nevertheless, a sufficient volume survives and cycling continues forever provided the dark energy phase of the cycle lasts long enough, of order a trillion years. Two consequences are a new role for dark energy and a global structure of the Universe radically different from that of eternal inflation.

  17. System Architecture of the Dark Energy Survey Camera Readout Electronics

    SciTech Connect

    Shaw, Theresa; Ballester, Otger; Cardiel-Sas, Laia; Castilla, Javier; Chappa, Steve; de Vicente, Juan; Holm, Scott; Huffman, Dave; Kozlovsky, Mark; Martinez, Gustavo; Moore, Todd; /Madrid, CIEMAT /Fermilab /Illinois U., Urbana /Fermilab

    2010-05-27

    The Dark Energy Survey makes use of a new camera, the Dark Energy Camera (DECam). DECam will be installed in the Blanco 4M telescope at Cerro Tololo Inter-American Observatory (CTIO). DECam is presently under construction and is expected to be ready for observations in the fall of 2011. The focal plane will make use of 62 2Kx4K and 12 2kx2k fully depleted Charge-Coupled Devices (CCDs) for guiding, alignment and focus. This paper will describe design considerations of the system; including, the entire signal path used to read out the CCDs, the development of a custom crate and backplane, the overall grounding scheme and early results of system tests.

  18. The evaluation of electrical energy per order (E(Eo)) for photooxidative decolorization of four textile dye solutions by the kinetic model.

    PubMed

    Daneshvar, N; Aleboyeh, A; Khataee, A R

    2005-05-01

    Photooxidative decolorization of four textile dyestuffs, C.I. Acid Orange 7 (AO7), C.I. Acid Orange 8 (AO8), C.I. Acid Orange 52 (AO52) and C.I. Acid Blue 74 (AB74), by UV/H2O2 was investigated in a laboratory scale photoreactor equipped with a 15 W low pressure mercury vapour lamp. The decolorization of the dyes was found to follow pseudo-first-order kinetics, and hence the figure-of-merit electrical energy per order (E(Eo)) is appropriate for estimating the electrical energy efficiency. The E(Eo) values were found to depend on the concentration of H2O2, concentration and basic structure of the dye. This study shows that these textile dyes can be treated easily and effectively with the UV/H2O2 process with E(Eo) values between 0.4 and 5 kW h m-3 order-1, depending on the initial concentrations of dyes and H2O2. The kinetic model, based on the initial rates of degradation, provided good prediction of the E(Eo) values for a variety of conditions.

  19. New Approaches To Off-Shore Wind Energy Management Exploiting Satellite EO Data

    NASA Astrophysics Data System (ADS)

    Morelli, Marco; Masini, Andrea; Venafra, Sara; Potenza, Marco Alberto Carlo

    2013-12-01

    Wind as an energy resource has been increasingly in focus over the past decades, starting with the global oil crisis in the 1970s. The possibility of expanding wind power production to off-shore locations is attractive, especially in sites where wind levels tend to be higher and more constant. Off-shore high-potential sites for wind energy plants are currently being looked up by means of wind atlases, which are essentially based on NWP (Numerical Weather Prediction) archive data and that supply information with low spatial resolution and very low accuracy. Moreover, real-time monitoring of active off- shore wind plants is being carried out using in-situ installed anemometers, that are not very reliable (especially on long time periods) and that should be periodically substituted when malfunctions or damages occur. These activities could be greatly supported exploiting archived and near real-time satellite imagery, that could provide accurate, global coverage and high spatial resolution information about both averaged and near real-time off-shore windiness. In this work we present new methodologies aimed to support both planning and near-real-time monitoring of off-shore wind energy plants using satellite SAR(Synthetic Aperture Radar) imagery. Such methodologies are currently being developed in the scope of SATENERG, a research project funded by ASI (Italian Space Agency). SAR wind data are derived from radar backscattering using empirical geophysical model functions, thus achieving greater accuracy and greater resolution with respect to other wind measurement methods. In detail, we calculate wind speed from X-band and C- band satellite SAR data, such as Cosmo-SkyMed (XMOD2) and ERS and ENVISAT (CMOD4) respectively. Then, using also detailed models of each part of the wind plant, we are able to calculate the AC power yield expected behavior, which can be used to support either the design of potential plants (using historical series of satellite images) or the

  20. Holographic Dark Energy Model with Interaction and Cosmological Constant in the Flat Space-Time

    NASA Astrophysics Data System (ADS)

    Saadat, Hassan

    2012-06-01

    In this paper we consider holographic dark energy model with interaction in the flat space-time with non-zero cosmological constant. We calculate cosmic scale factor and Hubble expansion parameter by using the time-dependent dark energy density. Then, we obtain phenomenological interaction between holographic dark energy and matter. We fixed our solution by using the observational data.