Generalized equation of state for dark energy
Barboza, E. M. Jr.; Alcaniz, J. S.; Zhu, Z.-H.; Silva, R.
2009-08-15
A generalized parametrization w{sub {beta}}(z) for the dark energy equation of state is proposed and some of its cosmological consequences are investigated. We show that in the limit of the characteristic dimensionless parameter {beta}{yields}+1, 0 and -1 some well-known equation of state parametrizations are fully recovered whereas for other values of {beta} the proposed parametrization admits a wider and new range of cosmological solutions. We also discuss possible constraints on the w{sub {beta}}(z) parameters from current observational data.
Scaling cosmology with variable dark-energy equation of state
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.
Nonparametric reconstruction of the dark energy equation of state
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.
NASA Astrophysics Data System (ADS)
Kumar, Suresh; Xu, Lixin
2014-10-01
In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann-Robertson-Walker space-time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier-Polarski-Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch.
Observational constraints on dark energy with generalized equations of state
Capozziello, S.; Cardone, V.F.; Elizalde, E.; Odintsov, S.D.; Nojiri, S.
2006-02-15
We investigate the effects of viscosity terms depending on the Hubble parameter and its derivatives in the dark energy equation of state. Such terms are possible if dark energy is a fictitious fluid originating from corrections to the Einstein general relativity as is the case for some braneworld inspired models or fourth order gravity. We consider two classes of models whose singularities in the early and late time universe have been studied by testing the models against the dimensionless coordinate distance to Type Ia Supernovae and radio galaxies also including priors on the shift and the acoustic peak parameters. It turns out that both models are able to explain the observed cosmic speed up without the need of phantom (w<-1) dark energy.
The Unified Equation of State for Dark Matter and Dark Energy
NASA Astrophysics Data System (ADS)
Wang, Wei; Gui, Yuanxing; Zhang, Suhong; Guo, Guanghai; Shao, Ying
We assume that dark matter and dark energy satisfy the unified equation of state: p = B(z)?, with p = pdE, ? = ?dm+?dE, where the pressure of dark matter pdm = 0 has been taken into account. A special function B=-(A)/((1+z)? ) is presented, which can well describe the evolution of the universe. In this model, the universe will end up with a Big Rip. By further simple analysis, we know other choices of the function B can also describe the universe but lead to a different doomsday.
Equation of state of dark energy in f (R ) gravity
NASA Astrophysics Data System (ADS)
Takahashi, Kazufumi; Yokoyama, Jun'ichi
2015-04-01
f (R ) gravity is one of the simplest generalizations of general relativity, which may explain the accelerated cosmic expansion without introducing a cosmological constant. Transformed into the Einstein frame, a new scalar degree of freedom appears and it couples with matter fields. In order for f (R ) theories to pass the local tests of general relativity, it has been known that the chameleon mechanism with a so-called thin-shell solution must operate. If the thin-shell constraint is applied to a cosmological situation, it has been claimed that the equation-of-state parameter of dark energy w must be extremely close to -1 . We argue this is due to the incorrect use of the Poisson equation, which is valid only in the static case. By solving the correct Klein-Gordon equation perturbatively, we show that a thin-shell solution exists even if w deviates appreciably from -1 .
Nonparametric reconstruction of the dark energy equation of state
Holsclaw, Tracy; Sanso, Bruno; Lee, Herbert; Alam, Ujjaini; Heitmann, Katrin; Habib, Salman; Higdon, David
2010-11-15
A basic aim of ongoing and upcoming cosmological surveys is to unravel the mystery of dark energy. In the absence of a compelling theory to test, a natural approach is to better characterize the properties of dark energy in search of clues that can lead to a more fundamental understanding. One way to view this characterization is the improved determination of the redshift-dependence of the dark energy equation of state parameter, w(z). To do this requires a robust and bias-free method for reconstructing w(z) from data that does not rely on restrictive expansion schemes or assumed functional forms for w(z). We present a new nonparametric reconstruction method that solves for w(z) as a statistical inverse problem, based on a Gaussian process representation. This method reliably captures nontrivial behavior of w(z) and provides controlled error bounds. We demonstrate the power of the method on different sets of simulated supernova data; the approach can be easily extended to include diverse cosmological probes.
Dark energy as a modification of the Friedmann equation
Dvali, Gia; Turner, Michael S.; /Chicago U., Astron. Astrophys. Ctr. /KICP, Chicago /Chicago U., EFI /Fermilab
2003-01-01
Dark energy could actually be the manifestation of a modification to the Friendmann equation arising from new physics (e.g., extra dimensions). Writing the correction as (1 - {Omega}{sub M})H{sup {alpha}}/H{sub 0}{sup {alpha}-2}, they explore the phenomenology and detectability of such. They show that: (1) {alpha} must be {approx}< 1; (2) such a correction behaves like dark energy with equation-of-state w{sub eff} = -1 + {alpha}/2 in the recent past (10{sup 4} > z >> 1) and w = -1 in the distant future and can mimic w < -1 without violating the weak-energy condition; (3) w{sub eff} changes, dz/dw|{sub z {approx} 0.5} {approx} {Omicron}(0.2), which is likely detectable; and (4) a future supernova experiment like SNAP that can determine w with precision {sigma}{sub w}, could determine {alpha} to precision {sigma}{sub {alpha}} {approx} 2{sigma}{sub w}.
Reconstructing the dark energy equation of state with varying couplings
Avelino, P. P.; Martins, C. J. A. P.; Nunes, N. J.; Olive, K. A.
2006-10-15
We revisit the idea of using varying couplings to probe the nature of dark energy, in particular, by reconstructing its equation of state. We show that for the class of models studied this method can be far superior to the standard methods (using type Ia supernovae or weak lensing). We also show that the simultaneous use of measurements of the fine-structure constant {alpha} and the electron-to-proton mass ratio {mu} allows a direct probe of grand unification scenarios. We present forecasts for the sensitivity of this method, both for the near future and for the next generation of spectrographs--for the latter we focus on the planned CODEX instrument for ESO's Extremely Large Telescope (formerly known as OWL). A high-accuracy reconstruction of the equation of state may be possible all the way up to redshift z{approx}4.
Reconstruction of the dark energy equation of state
NASA Astrophysics Data System (ADS)
Vázquez, J. Alberto; Bridges, M.; Hobson, M. P.; Lasenby, A. N.
2012-09-01
One of the main challenges of modern cosmology is to investigate the nature of dark energy in our Universe. The properties of such a component are normally summarised as a perfect fluid with a (potentially) time-dependent equation-of-state parameter w(z). We investigate the evolution of this parameter with redshift by performing a Bayesian analysis of current cosmological observations. We model the temporal evolution as piecewise linear in redshift between 'nodes', whose w-values and redshifts are allowed to vary. The optimal number of nodes is chosen by the Bayesian evidence. In this way, we can both determine the complexity supported by current data and locate any features present in w(z). We compare this node-based reconstruction with some previously well-studied parameterisations: the Chevallier-Polarski-Linder (CPL), the Jassal-Bagla-Padmanabhan (JBP) and the Felice-Nesseris-Tsujikawa (FNT). By comparing the Bayesian evidence for all of these models we find an indication towards possible time-dependence in the dark energy equation-of-state. It is also worth noting that the CPL and JBP models are strongly disfavoured, whilst the FNT is just significantly disfavoured, when compared to a simple cosmological constant w = -1. We find that our node-based reconstruction model is slightly disfavoured with respect to the ΛCDM model.
Perceiving the equation of state of Dark Energy while living in a Cold Spot
Valkenburg, Wessel
2012-01-01
The Cold Spot could be an adiabatic perturbation on the surface of last scattering, in which case it is an over-density with comoving radius of the order of 1 Gpc. We assess the effect that living in a similar structure, without knowing it, has on our perception of the equation of state of Dark Energy. We find that structures of dimensions such that they could cause the Cold Spot on the CMB, affect the perceived equation of state of Dark Energy possibly up to ten percent.
Observational constraints on dark energy with a fast varying equation of state
NASA Astrophysics Data System (ADS)
De Felice, Antonio; Nesseris, Savvas; Tsujikawa, Shinji
2012-05-01
We place observational constraints on models with the late-time cosmic acceleration based on a number of parametrizations allowing fast transitions for the equation of state of dark energy. In addition to the model of Linder and Huterer where the dark energy equation of state w monotonically grows or decreases in time, we propose two new parametrizations in which w has an extremum. We carry out the likelihood analysis with the three parametrizations by using the observational data of supernovae type Ia, cosmic microwave background, and baryon acoustic oscillations. Although the transient cosmic acceleration models with fast transitions can give rise to the total chi square smaller than that in the Λ-Cold-Dark-Matter (ΛCDM) model, these models are not favored over ΛCDM when one uses the Akaike information criterion which penalizes the extra degrees of freedom present in the parametrizations.
Fables of reconstruction: controlling bias in the dark energy equation of state
Crittenden, Robert G.; Zhao, Gong-Bo; Samushia, Lado; Pogosian, Levon; Zhang, Xinmin E-mail: gong-bo.zhao@port.ac.uk E-mail: lado.samushia@port.ac.uk
2012-02-01
We develop an efficient, non-parametric Bayesian method for reconstructing the time evolution of the dark energy equation of state w(z) from observational data. Of particular importance is the choice of prior, which must be chosen carefully to minimise variance and bias in the reconstruction. Using a principal component analysis, we show how a correlated prior can be used to create a smooth reconstruction and also avoid bias in the mean behaviour of w(z). We test our method using Wiener reconstructions based on Fisher matrix projections, and also against more realistic MCMC analyses of simulated data sets for Planck and a future space-based dark energy mission. While the accuracy of our reconstruction depends on the smoothness of the assumed w(z), the relative error for typical dark energy models is ∼<10% out to redshift z = 1.5.
Dynamical mutation of dark energy
Abramo, L. R.; Batista, R. C.; Liberato, L.; Rosenfeld, R.
2008-03-15
We discuss the intriguing possibility that dark energy may change its equation of state in situations where large dark energy fluctuations are present. We show indications of this dynamical mutation in some generic models of dark energy.
Observational constraints on scalar field models of dark energy with barotropic equation of state
Sergijenko, Olga; Novosyadlyj, Bohdan; Durrer, Ruth E-mail: ruth.durrer@unige.ch
2011-08-01
We constrain the parameters of dynamical dark energy in the form of a classical or tachyonic scalar field with barotropic equation of state jointly with other cosmological parameters using the following datasets: the CMB power spectra from WMAP7, the baryon acoustic oscillations in the space distribution of galaxies from SDSS DR7, the power spectrum of luminous red galaxies from SDSS DR7 and the light curves of SN Ia from 2 different compilations: Union2 (SALT2 light curve fitting) and SDSS (SALT2 and MLCS2k2 light curve fittings). It has been found that the initial value of dark energy equation of state parameter is constrained very weakly by most of the data while the other cosmological parameters are well constrained: their likelihoods and posteriors are similar, their forms are close to Gaussian (or half-Gaussian) and the confidence ranges are narrow. The most reliable determinations of the best-fit value and 1σ confidence range for the initial value of the dark energy equation of state parameter are obtained from the combined datasets including SN Ia data from the full SDSS compilation with MLCS2k2 light curve fitting. In all such cases the best-fit value of this parameter is lower than the value of corresponding parameter for current epoch. Such dark energy loses its repulsive properties and in future the expansion of the Universe changes into contraction. We also perform a forecast for the Planck mock data and show that they narrow significantly the confidence ranges of cosmological parameters values, moreover, their combination with SN SDSS compilation with MLCS2k2 light curve fitting may exclude the fields with initial equation of state parameter > −0.1 at 2σ confidence level.
NASA Astrophysics Data System (ADS)
Ruiz-Lapuente, Pilar
2014-02-01
Preface; Part I. Theory: 1. Dark energy, gravitation and the Copernican principle J.-P. Uzan; 2. Dark energy and modified gravity R. Maartens and R. Durrer; 3. Some views on dark energy D. Polarski; 4. Emergent gravity and dark energy T. Padmanabhan; Part II. Observations: 5. Foundations of supernova cosmology R. P. Kirshner; 6. Dark energy and supernovae P. Ruiz-Lapuente; 7. The future of supernova cosmology M. Wood-Vasey; 8. The space advantage A. Kim; 9. Baryon acoustic oscillations B. Bassett and R. Hlozek; 10. Weak gravitational lensing A. Heavens; Index.
Constraining the Dark Energy Equation of State using Alternative High-z Cosmic Tracers
NASA Astrophysics Data System (ADS)
Plionis, M.; Terlevich, R.; Basilakos, S.; Bresolin, F.; Terlevich, E.; Melnick, J.; Chavez, R.
2010-06-01
We propose to use alternative cosmic tracers to measure the dark energy equation of state and the matter content of the Universe [w(z)Ωm]. Our proposed method consists of two components: (a) tracing the Hubble relation using HII galaxies which can be detected up to very large redshifts, z~4, as an alternative to supernovae type Ia, and (b) measuring the clustering pattern of X-ray selected AGN at a median redshift of ~1. Each component of the method can in itself provide interesting constraints on the cosmological parameters, especially under our anticipation that we will reduce the corresponding random and systematic errors significantly. However, by joining their likelihood functions we will be able to put stringent cosmological constraints and break the known degeneracies between the dark energy equation of state (whether it is constant or variable) and the matter content of the universe and provide a powerful and alternative route to measure the contribution to the global dynamics and the equation of state of dark energy. A preliminary joint analysis of X-ray selected AGN (based on the largest to-date XMM survey; the 2XMM) and the currently largest SNIa sample (Hicken et al.), using as priors a flat universe and the WMAP5 normalization of the power-spectrum, provides: Ωm = 0.27+/-0.02 and w = -0.96+/-0.07.
Future Type Ia Supernova Data as Tests of Dark Energy from Modified Friedmann Equations
NASA Astrophysics Data System (ADS)
Wang, Yun; Freese, Katherine; Gondolo, Paolo; Lewis, Matthew
2003-09-01
In the Cardassian model, dark energy density arises from modifications to the Friedmann equation, which becomes H2=g(ρM), where g(ρM) is a new function of the energy density. The universe is flat, matter dominated, and accelerating. The distance-redshift relation predictions of generalized Cardassian models can be very different from generic quintessence models, and can be differentiated with data from upcoming pencil beam surveys of Type Ia supernovae such as Supernova/Acceleration Probe (SNAP). We have found the interesting result that, once Ωm is known to 10% accuracy, SNAP will be able to determine the sign of the time dependence of the dark energy density. Knowledge of this sign (which is related to the weak energy condition) will provide a first discrimination between various cosmological models that fit the current observational data (cosmological constant, quintessence, Cardassian expansion). Further, we have performed Monte Carlo simulations to illustrate how well one can reproduce the form of the dark energy density with SNAP. To be concrete we study a class of two-parameter (n, q) generalized Cardassian models that includes the original Cardassian model (parameterized by n only) as a special case. Examples are given of modified polytropic (MP) Cardassian models that fit current supernova and cosmic microwave background data, and prospects for differentiating between MP Cardassian and other models in future data are discussed. We also note that some Cardassian models can satisfy the weak energy condition w>-1 even with a dark energy component that has an effective equation of state wX<-1.
The dark energy cosmic clock: a new way to parametrise the equation of state
Tarrant, Ewan R.M.; Copeland, Edmund J.; Padilla, Antonio; Skordis, Constantinos E-mail: ed.copeland@nottingham.ac.uk E-mail: skordis@nottingham.ac.uk
2013-12-01
We propose a new parametrisation of the dark energy equation of state, which uses the dark energy density, Ω{sub e} as a cosmic clock. We expand the equation of state in a series of orthogonal polynomials, with Ω{sub e} as the expansion parameter and determine the expansion coefficients by fitting to SNIa and H(z) data. Assuming that Ω{sub e} is a monotonic function of time, we show that our parametrisation performs better than the popular Chevallier-Polarski-Linder (CPL) and Gerke and Efstathiou (GE) parametrisations, and we demonstrate that it is robust to the choice of prior. Expanding in orthogonal polynomials allows us to relate models of dark energy directly to our parametrisation, which we illustrate by placing constraints on the expansion coefficients extracted from two popular quintessence models. Finally, we comment on how this parametrisation could be modified to accommodate high redshift data, where any non-monotonicity of Ω{sub e} would need to be accounted for.
High-redshift investigation on the dark energy equation of state
NASA Astrophysics Data System (ADS)
Piedipalumbo, E.; Della Moglie, E.; De Laurentis, M.; Scudellaro, P.
2014-07-01
The understanding of the accelerated expansion of the Universe poses one of the most fundamental questions in physics and cosmology today. Whether or not the acceleration is driven by some form of dark energy, and in the absence of a well-based theory to interpret the observations, many models have been proposed to solve this problem, both in the context of General Relativity and alternative theories of gravity. Actually, a further possibility to investigate the nature of dark energy lies in measuring the dark energy equation of state (EOS), w, and its time (or redshift) dependence at high accuracy. However, since w(z) is not directly accessible to measurement, reconstruction methods are needed to extract it reliably from observations. Here, we investigate different models of dark energy, described through several parametrizations of the EOS. Our high-redshift analysis is based on the Union2 Type Ia supernovae data set (Suzuki et al.), the Hubble diagram constructed from some gamma-ray bursts luminosity-distance indicators, and Gaussian priors on the distance from the baryon acoustic oscillations, and the Hubble constant h (these priors have been included in order to help to break the degeneracies among model parameters). To perform our statistical analysis and to explore the probability distributions of the EOS parameters, we use the Markov Chain Monte Carlo Method. It turns out that, if exact flatness is assumed, the dark energy EOS is evolving for all the parametrizations that we considered. We finally compare our results with the ones obtained by previous cosmographic analyses performed on the same astronomical data sets, showing that the latter ones are sufficient to test and compare the new parametrizations.
Dark energy as a fixed point of the Einstein Yang-Mills Higgs equations
NASA Astrophysics Data System (ADS)
Rinaldi, Massimiliano
2015-10-01
We study the Einstein Yang-Mills Higgs equations in the SO(3) representation on a isotropic and homogeneous flat Universe, in the presence of radiation and matter fluids. We map the equations of motion into an autonomous dynamical system of first-order differential equations and we find the equilibrium points. We show that there is only one stable fixed point that corresponds to an accelerated expanding Universe in the future. In the past, instead, there is an unstable fixed point that implies a stiff-matter domination. In between, we find three other unstable fixed points, corresponding, in chronological order, to radiation domination, to matter domination, and, finally, to a transition from decelerated expansion to accelerated expansion. We solve the system numerically and we confirm that there are smooth trajectories that correctly describe the evolution of the Universe, from a remote past dominated by radiation to a remote future dominated by dark energy, passing through a matter-dominated phase.
NASA Astrophysics Data System (ADS)
Turner, Michael S.
2001-04-01
The discovery that the Universe is speeding up and not slowing down was greeted with open arms by theorists. First, because the dark energy powering the acceleration provided the "missing stuff" needed to make the Universe flat, in accord with a key prediction of inflation. Second, because theorists now have a new puzzle to solve, the nature of the mysterious dark energy. I have no doubt that the dark energy problem will be just as fundamental and just as interesting as the dark matter problem. Determining its nature will require the work of both astronomers and particle physics and will shed light on both fundamental physics and the fate of the Universe.
Bayesian model selection without evidences: application to the dark energy equation-of-state
NASA Astrophysics Data System (ADS)
Hee, S.; Handley, W. J.; Hobson, M. P.; Lasenby, A. N.
2016-01-01
A method is presented for Bayesian model selection without explicitly computing evidences, by using a combined likelihood and introducing an integer model selection parameter n so that Bayes factors, or more generally posterior odds ratios, may be read off directly from the posterior of n. If the total number of models under consideration is specified a priori, the full joint parameter space (θ, n) of the models is of fixed dimensionality and can be explored using standard Markov chain Monte Carlo (MCMC) or nested sampling methods, without the need for reversible jump MCMC techniques. The posterior on n is then obtained by straightforward marginalization. We demonstrate the efficacy of our approach by application to several toy models. We then apply it to constraining the dark energy equation of state using a free-form reconstruction technique. We show that Λ cold dark matter is significantly favoured over all extensions, including the simple w(z) = constant model.
The dark energy equation of state using alternative cosmic high-z tracers
NASA Astrophysics Data System (ADS)
Plionis, M.; Terlevich, R.; Basilakos, S.; Bresolin, F.; Terlevich, E.; Melnick, J.; Chavez, R.
2010-04-01
We propose to use alternative cosmic tracers to measure the dark energy equation of state and the matter content of the Universe [w(z) & Ωm]. Our proposed method consists of two components: (a) tracing the Hubble relation using HII galaxies which can be detected up to very large redshifts, z ~ 4, as an alternative to supernovae type Ia, and (b) measuring the clustering pattern of X-ray selected AGN at a median redshift of ~ 1. Each component of the method can in itself provide interesting constraints on the cosmological parameters, especially under our anticipation that we will reduce the corresponding random and systematic errors significantly. However, by joining their likelihood functions we will be able to put stringent cosmological constraints and break the known degeneracies between the dark energy equation of state (whether it is constant or variable) and the matter content of the universe and provide a powerful and alternative route to measure the contribution to the global dynamics and the equation of state of dark energy. A preliminary joint analysis of X-ray selected AGN clustering (based on the largest to-date XMM survey; the 2XMM) and the currently largest SNIa sample, the Constitution set (Hicken et al.), using as priors a flat universe and the WMAP5 normalization of the power-spectrum, provides: Ωm = 0.27 ± 0.02 and w= -0.96 ± 0.07. Equivalent and consistent results are provided by the joint analysis of X-ray selected AGN clustering and the latest Baryonic Acoustic Oscillation measures, providing: Ωm = 0.27±0.02 and w= -0.97±0.04.
The effects of parametrization of the dark energy equation of state
NASA Astrophysics Data System (ADS)
Shi, Ke; Huang, Yong-Feng; Lu, Tan
2011-12-01
We investigate in detail the influence of parametrizations of the dark energy equation of state on reconstructing dark energy geometrical parameters, such as the deceleration parameter q(z) and Om diagnostic. We use a type Ia supernova sample, baryon acoustic oscillation data, cosmic microwave background information along with twelve observational Hubble data points to constrain cosmological parameters. With the joint analysis of these current datasets, we find that the parametrizations of w(z) have little influence on the reconstruction result of q(z) and Om. The same is true for the transition (cosmic deceleration to acceleration) redshift zt, for which we find that for different parametrizations of w(z), the best fitted values of zt are very close to each other (about 0.65). All of our results are in good agreement with the ?CDM model. Furthermore, using the combination of datasets, we do not find any signal of decreasing cosmic acceleration as suggested in some recent papers. The results suggest that the influence of the prior w(z) is not as severe as one may anticipate, and thus we can, to some extent, safely use a reasonable parametrization of w(z) to reconstruct some other dark energy parameters (e.g. q(z), Om) with a combination of datasets.
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.
Detecting features in the dark energy equation of state: a wavelet approach
Hojjati, Alireza; Pogosian, Levon; Zhao, Gong-Bo E-mail: levon@sfu.ca
2010-04-01
We study the utility of wavelets for detecting the redshift evolution of the dark energy equation of state w(z) from the combination of supernovae (SNe), CMB and BAO data. We show that local features in w, such as bumps, can be detected efficiently using wavelets. To demonstrate, we first generate a mock supernovae data sample for a SNAP-like survey with a bump feature in w(z) hidden in, then successfully discover it by performing a blind wavelet analysis. We also apply our method to analyze the recently released ''Constitution'' SNe data, combined with WMAP and BAO from SDSS, and find weak hints of dark energy dynamics. Namely, we find that models with w(z) < −1 for 0.2 < z < 0.5, and w(z) > −1 for 0.5 < z < 1, are mildly favored at 95% confidence level. This is in good agreement with several recent studies using other methods, such as redshift binning with principal component analysis (PCA) (e.g. Zhao and Zhang, arXiv: 0908.1568)
Linden, Sebastian; Virey, Jean-Marc
2008-07-15
We test the robustness and flexibility of the Chevallier-Polarski-Linder (CPL) parametrization of the dark energy equation of state w(z)=w{sub 0}+w{sub a}(z/1+z) in recovering a four-parameter steplike fiducial model. We constrain the parameter space region of the underlying fiducial model where the CPL parametrization offers a reliable reconstruction. It turns out that non-negligible biases leak into the results for recent (z<2.5) rapid transitions, but that CPL yields a good reconstruction in all other cases. The presented analysis is performed with supernova Ia data as forecasted for a space mission like SNAP/JDEM, combined with future expectations for the cosmic microwave background shift parameter R and the baryonic acoustic oscillation parameter A.
Cosmic chronometers: constraining the equation of state of dark energy. I: H(z) measurements
Stern, Daniel; Jimenez, Raul; Verde, Licia; Kamionkowski, Marc; Stanford, S. Adam E-mail: raul@icc.ub.edu E-mail: kamion@tapir.caltech.edu
2010-02-01
We present new determinations of the cosmic expansion history from red-envelope galaxies. We have obtained for this purpose high-quality spectra with the Keck-LRIS spectrograph of red-envelope galaxies in 24 galaxy clusters in the redshift range 0.2 < z < 1.0. We complement these Keck spectra with high-quality, publicly available archival spectra from the SPICES and VVDS surveys. We improve over our previous expansion history measurements in Simon et al. (2005) by providing two new determinations of the expansion history: H(z) = 97±62 km sec{sup −1} Mpc{sup −1} at z ≅ 0.5 and H(z) = 90±40 km sec{sup −1} Mpc{sup −1} at z ≅ 0.9. We discuss the uncertainty in the expansion history determination that arises from uncertainties in the synthetic stellar-population models. We then use these new measurements in concert with cosmic-microwave-background (CMB) measurements to constrain cosmological parameters, with a special emphasis on dark-energy parameters and constraints to the curvature. In particular, we demonstrate the usefulness of direct H(z) measurements by constraining the dark-energy equation of state parameterized by w{sub 0} and w{sub a} and allowing for arbitrary curvature. Further, we also constrain, using only CMB and H(z) data, the number of relativistic degrees of freedom to be 4±0.5 and their total mass to be < 0.2 eV, both at 1σ.
Dark-energy thermodynamic models
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.
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.
NASA Astrophysics Data System (ADS)
Liang, Shi-Dong; Harko, Tiberiu
2015-04-01
Based on the analogy with superconductor physics we consider a scalar-vector-tensor gravitational model, in which the dark energy action is described by a gauge invariant electromagnetic type functional. By assuming that the ground state of the dark energy is in a form of a condensate with the U(1) symmetry spontaneously broken, the gauge invariant electromagnetic dark energy can be described in terms of the combination of a vector and of a scalar field (corresponding to the Goldstone boson), respectively. The gravitational field equations are obtained by also assuming the possibility of a nonminimal coupling between the cosmological mass current and the superconducting dark energy. The cosmological implications of the dark energy model are investigated for a Friedmann-Robertson-Walker homogeneous and isotropic geometry for two particular choices of the electromagnetic type potential, corresponding to a pure electric type field, and to a pure magnetic field, respectively. The time evolutions of the scale factor, matter energy density and deceleration parameter are obtained for both cases, and it is shown that in the presence of the superconducting dark energy the Universe ends its evolution in an exponentially accelerating vacuum de Sitter state. By using the formalism of the irreversible thermodynamic processes for open systems we interpret the generalized conservation equations in the superconducting dark energy model as describing matter creation. The particle production rates, the creation pressure and the entropy evolution are explicitly obtained.
Oscillations in the dark energy equation of state: New MCMC lessons
NASA Astrophysics Data System (ADS)
Lazkoz, Ruth; Salzano, Vincenzo; Sendra, Irene
2010-11-01
We study the possibility of detecting oscillating patterns in the equation of state (EoS) of the dark energy using different cosmological datasets. We follow a phenomenological approach and study three different oscillating models for the EoS, one of them periodic and the other two damped (proposed here for the first time). All the models are characterized by the amplitude, the center and the frequency of oscillations. In contrast to previous works in the literature, we do not fix the frequency to a fiducial value related to the time extension of chosen datasets, but consider a discrete set of values, so to avoid arbitrariness and try to detect any possible time period in the EoS. We test the models using a recent collection of SNeIa, direct Hubble data and Gamma Ray Bursts data. Main results are: I. even if constraints on the amplitude are not too strong, we detect a trend of it versus the frequency, i.e. decreasing (and even negatives) amplitudes for higher frequencies; II. the center of oscillation (which corresponds to the present value of the EoS parameter) is very well constrained, and phantom behavior seems statistically disfavored; III. the frequency is hard to constrain, showing similar statistical validity for all the values of the discrete set chosen, but the best fit of all the considered scenarios is associated with a period which is in the redshift range depicted by our cosmological data. The “best” oscillating models are compared with ΛCDM using different dimensionally consistent and Bayesian-based information criteria; the conclusion is reached that at present, data cannot discriminate between a cosmological constant and oscillating equation of state.
Johri, V. B.; Rath, P. K.
2006-12-15
The dynamical age of the universe depends upon the rate of the expansion of the universe, which explicitly involves the dark energy equation of state parameter w(z). Consequently, the evolution of w(z) has a direct imprint on the age of the universe. We have shown that the dynamical age of the universe as derived from CMB data can be used as an authentic criterion, being independent of the prior assumptions likethe present value of the Hubble constant H{sub 0} and the cosmological density parameter {omega}{sub M}{sup 0}, to constrain the range of admissible values of w for quiessence models and to test the physically viable parametrizations of the equation of state w(z) in kinessence models. An upper bound on variation of dark energy density is derived and a relation between cosmological density parameters and the transition redshift is established.
Modeling Dark Matter and Dark Energy
NASA Astrophysics Data System (ADS)
Ludwick, Kevin J.
We study various models of dark matter and dark energy. We first examine the implications of the assumption that black holes act as dark matter. Assuming dark matter in galactic halos is composed solely of black holes, and using observational constraints, we calculate the number of halo black holes and the total entropy due to them. We then study the prospect of dark energy with a non-constant density. We analyze several parameterizations of dark energy density from the literature and one of our own, in particular focusing on the value of redshift at which cosmic acceleration due to dark energy begins. In considering the properties of dark energy densities that monotonically increase over time, we present two new categorizations of dark energy models that we dub "little rip" and "pseudo-rip" models, and both avoid future singularities in the cosmic scale factor. The dark energy density of a little rip model continually increases for all future time, and a pseudo-rip model's dark energy density asymptotically approaches a maximum value. These two types of models, big rip models, and models that have constant dark energy densities comprise all categories of dark energy density with monotonic growth in the future. A little rip leads to the dissociation of all bound structures in the universe, and a pseudo-rip occurs when all bound structures at or below a certain threshold dissociate. We present explicit parameterizations of the little rip and pseudo-rip models that fit supernova data well, and we calculate the times at which particular bound structures rip apart. In looking at different applications of these models, we show that coupling between dark matter and dark energy with an equation of state for a little rip can change the usual evolution of a little rip model into an asymptotic de Sitter expansion. We also give conditions on minimally coupled phantom scalar field models and scalar-tensor models that indicate whether or not they lead to a little rip or a pseudo-rip.
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.
On dark energy isocurvature perturbation
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.
SHOES-Supernovae, HO, for the Equation of State of Dark energy
NASA Astrophysics Data System (ADS)
Riess, Adam
2006-07-01
The present uncertainty in the value of the Hubble constant {resulting in anuncertainty in Omega_M} and the paucity of Type Ia supernovae at redshiftsexceeding 1 are now the leading obstacles to determining the nature of darkenergy. We propose a single, integrated set of observations for Cycle 15 thatwill provide a 40% improvement in constraints on dark energy. This programwill observe known Cepheids in six reliable hosts of Type Ia supernovae withNICMOS, reducing the uncertainty in H_0 by a factor of two because of thesmaller dispersion along the instability strip, the diminished extinction, andthe weaker metallicity dependence in the infrared. In parallel with ACS, atthe same time the NICMOS observations are underway, we will discover andfollow a sample of Type Ia supernovae at z > 1. Together, these measurements,along with prior constraints from WMAP, will provide a great improvement inHST's ability to distinguish between a static, cosmological constant anddynamical dark energy. The Hubble Space Telescope is the only instrument inthe world that can make these IR measurements of Cepheids beyond the LocalGroup, and it is the only telescope in the world that can be used to find andfollow supernovae at z > 1. Our program exploits both of these uniquecapabilities of HST to learn more about one of the greatest mysteries inscience.
Reconstructing and deconstructing dark energy
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.
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.
Measuring the speed of dark: Detecting dark energy perturbations
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.
Entropy bounds and dark energy
NASA Astrophysics Data System (ADS)
Hsu, Stephen D. H.
2004-07-01
Entropy bounds render quantum corrections to the cosmological constant Λ finite. Under certain assumptions, the natural value of Λ is of order the observed dark energy density ~10-10 eV4, thereby resolving the cosmological constant problem. We note that the dark energy equation of state in these scenarios is w≡p/ρ=0 over cosmological distances, and is strongly disfavored by observational data. Alternatively, Λ in these scenarios might account for the diffuse dark matter component of the cosmological energy density. Permanent address: Institute of Theoretical Science and Department of Physics, University of Oregon, Eugene, OR 97403.
Weak lensing and dark energy: The impact of dark energy on nonlinear dark matter clustering
Joudaki, Shahab; Cooray, Asantha; Holz, Daniel E.
2009-07-15
We examine the influence of percent-level dark energy corrections to the nonlinear matter power spectrum on constraints of the dark energy equation of state from future weak lensing probes. We explicitly show that a poor approximation (off by > or approx.10%) to the nonlinear corrections causes a > or approx. 1{sigma} bias on the determination of the dark energy equation of state. Future weak lensing surveys must therefore incorporate dark energy modifications to the nonlinear matter power spectrum accurate to the percent-level, to avoid introducing significant bias in their measurements. For the WMAP5 cosmology, the more accurate power spectrum is more sensitive to dark energy properties, resulting in a factor of 2 improvement in dark energy equation of state constraints. We explore the complementary constraints on dark energy from future weak lensing and supernova surveys. A space-based, Joint Dark Energy Mission-like survey measures the equation of state in five independent redshift bins to {approx}10%, while this improves to {approx}5% for a wide-field ground-based survey like the Large Synoptic Survey Telescope. These constraints are contingent upon our ability to control weak lensing systematic uncertainties to the sub-percent level.
NASA Astrophysics Data System (ADS)
Chamseddine, Ali H.; Mukhanov, Viatcheslav
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.
Direct reconstruction of dark energy.
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. PMID:20867085
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.
Professor Sean Carroll
2010-01-08
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.
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.
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.
Post-Planck dark energy constraints
NASA Astrophysics Data System (ADS)
Hazra, Dhiraj Kumar; Majumdar, Subhabrata; Pal, Supratik; Panda, Sudhakar; Sen, Anjan A.
2015-04-01
We constrain plausible dark energy models using the recently published cosmic microwave background (CMB) temperature anisotropy data from Planck together with WMAP9 low-ℓ polarization data and the data from low redshift surveys. To circumvent the limitations of any particular equation of state toward describing all existing dark energy models, we work with three different equations of state covering a wider class of dark energy models and hence provide more robust and generic constraints on the dark energy behavior. We show that a possible tension exists between constraints from CMB and non-CMB observations when one allows for both phantom and nonphantom behavior for the dark energy. Further, we reconstruct the equation of state of dark energy as a function of redshift using the combined CMB and non-CMB data and show that cosmological constant behavior is disallowed at the 68.3% confidence level. A fully nonphantom history is also disallowed at the 68.3% confidence level, and a considerable fine-tuning is also needed to keep it inside the 95.5% confidence limit. This result might motivate one to construct phantom models for dark energy, which may be achievable in the presence of higher derivative operators as in string theory. However, for a theoretical model that allows only nonphantom behavior, both CMB and non-CMB data sets agree on the dark energy constraint with the mean equation of state being very close to the cosmological constant.
Coupled tachyonic dark energy: A dynamical analysis
NASA Astrophysics Data System (ADS)
Landim, Ricardo C. G.
2015-07-01
In this paper, we present a dynamical analysis for a coupled tachyonic dark energy with dark matter. The tachyonic field ϕ is considered in the presence of barotropic fluids (matter and radiation) and the autonomous system due to the evolution equations is studied. The three cosmological eras (radiation, matter and dark energy) are described through the critical points, for a generic potential V(ϕ).
Constraining dark energy fluctuations with supernova correlations
Blomqvist, Michael; Enander, Jonas; Mörtsell, Edvard E-mail: enander@fysik.su.se
2010-10-01
We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state w≠−1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.
Interacting holographic dark energy with logarithmic correction
Jamil, Mubasher; Farooq, M. Umar E-mail: mufarooq@yahoo.com
2010-03-01
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Employing this new definition, we investigate the model of interacting dark energy and derive its effective equation of state. Finally we establish a correspondence between generalized Chaplygin gas and entropy-corrected holographic dark energy.
Thermodynamics of dark energy interacting with dark matter and radiation
Jamil, Mubasher; Saridakis, Emmanuel N.; Setare, M. R.
2010-01-15
We investigate the validity of the generalized second law of thermodynamics, in the cosmological scenario where dark energy interacts with both dark matter and radiation. Calculating separately the entropy variation for each fluid component and for the apparent horizon itself, we show that the generalized second law is always and generally valid, independently of the specific interaction form, of the fluids equation-of-state parameters and of the background geometry.
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.
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.
Dutta, Sourish; Maor, Irit
2007-03-15
We investigate the clustering properties of a dynamical dark energy component. In a cosmic mix of a pressureless fluid and a light scalar field, we follow the linear evolution of spherical matter perturbations. We find that the scalar field tends to form underdensities in response to the gravitationally collapsing matter. We thoroughly investigate these voids for a variety of initial conditions, explain the physics behind their formation, and consider possible observational implications. Detection of dark energy voids will clearly rule out the cosmological constant as the main source of the present acceleration.
Lincoln, Don
2014-08-07
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.
Dipolar dark matter and dark energy
Blanchet, Luc; Le Tiec, Alexandre
2009-07-15
In previous work [L. Blanchet and A. Le Tiec, Phys. Rev. D 78, 024031 (2008)], a model of dark matter and dark energy based on the concept of gravitational polarization was investigated. This model was shown to recover the concordance cosmological scenario ({lambda}-cold dark matter) at cosmological scales, and the phenomenology of the modified Newtonian dynamics at galactic scales. In this article we prove that the model can be formulated with a simple and physically meaningful matter action in general relativity. We also provide alternative derivations of the main results of the model, and some details on the variation of the action.
NASA Astrophysics Data System (ADS)
Lemoine, Martin; Martin, Jrme; Uzan, Jean-Philippe
2003-05-01
It has recently been proposed by Bastero-Gil, Mersini and co-workers that dark energy could be attributed to the cosmological properties of a scalar field with a nonstandard dispersion relation that decreases exponentially at wave numbers larger than the Planck scale (kphys>MPl). In this scenario, the energy density stored in the modes of trans-Planckian wave numbers but sub-Hubble frequencies produced by amplification of the vacuum quantum fluctuations would account naturally for the dark energy. The present paper examines this model in detail and shows step by step that it does not work. In particular, we show that this model cannot make definite predictions since there is no well-defined vacuum state in the region of wave numbers considered: hence, the initial data cannot be specified unambiguously. We also show that for most choices of initial data this scenario implies the production of a large amount of energy density (of order M4Pl) for modes with momenta MPl, far in excess of the background energy density. We evaluate the amount of fine tuning in the initial data necessary to avoid this back-reaction problem and find it is of order H/MPl. We also argue that the equation of state of the trans-Planckian modes is not vacuumlike. Therefore this model does not provide a suitable explanation for the dark energy.
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.
Thermodynamic aspects of dark energy fluids
NASA Astrophysics Data System (ADS)
Barboza, Edsio M.; Nunes, Rafael C.; Abreu, Everton M. C.; Neto, Jorge Ananias
2015-10-01
In this paper we investigate the limits imposed by thermodynamics on a dark energy fluid. We obtain the heat capacities and the compressibilities for a dark energy fluid. The thermal and mechanical stabilities require these quantities to be positive. We show that dark energy fluids must satisfy the stability conditions and that such a requirement puts difficulties on the cosmic fluid models with negative constant equation-of-state (EoS) parameters. We also show that the observational constraints imposed by type Ia supernova, BAO and H (z ) data on a general dark energy fluid with a time-dependent EoS parameter are in conflict with the constraints imposed by thermodynamics. This result indicates that dark energy fluid models are unphysical.
The dark side of cosmology: dark matter and dark energy.
Spergel, David N
2015-03-01
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. PMID:25745164
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.
Dark soliton solution of Sasa-Satsuma equation
NASA Astrophysics Data System (ADS)
Ohta, Y.
2010-03-01
The Sasa-Satsuma equation is a higher order nonlinear Schrdinger type equation which admits bright soliton solutions with internal freedom. We present the dark soliton solutions for the equation by using Gram type determinant. The dark solitons have no internal freedom and exist for both defocusing and focusing equations.
Dark Matter and Dark Energy Explained
NASA Astrophysics Data System (ADS)
Aisenberg, Sol
2006-03-01
The standard model of the universe has many mysteries and defects requiring the use of large fudge factors such as Dark Matter and Dark Energy. We will show that Dark Matter is needed when we try to extend Newton's law of gravity (based upon observations in our solar system) to galactic distances. Dark Matter was introduced to explain the observed flat velocity rotation curves of the outer parts of spiral galaxies, as observed by Vera. Rubin. Much earlier, the (under appreciated) Fritz Zwicky introduced the need for large amounts of missing invisible matter to explain the surprising observed motion of groups of remote galaxies. In our hypothesis, the modification of Newton's laws by the addition of a linear term to the gravitational constant that increases with distance will eliminate the need for dark matter. Our hypothesis is different from the MOND theory of Milgrom, which depends upon acceleration. The Red shift observations by Hubble as a function of distance, and interpreted as ``apparent Doppler effect'' led to the unproven belief that the universe is expanding, and thus to the Big Bang. In turn the apparent acceleration of the expansion required the introduction of Dark Energy. Actually there are three additional components of the red shift that are solely due to gravity and distance and can be larger than the Doppler contribution.
Dark matter superfluid and DBI dark energy
NASA Astrophysics Data System (ADS)
Cai, Rong-Gen; Wang, Shao-Jiang
2016-01-01
It was shown recently that, without jeopardizing the success of the Λ cold dark matter model on cosmic scales, the modified Newtonian dynamics (MOND) can be derived as an emergent phenomenon when axionlike dark matter particles condense into superfluid on the galactic scales. We propose in this paper a Dirac-Born-Infeld (DBI) scalar field conformally coupled to the matter components. To maintain the success of MOND phenomenon of dark matter superfluid on the galactic scales, the fifth force introduced by the DBI scalar should be screened on the galactic scales. It turns out that the screening effect naturally leads to a simple explanation for a longstanding puzzle that the MOND critical acceleration coincides with present Hubble scale. This galactic coincidence problem is solved, provided that the screened DBI scalar also plays the role of dark energy on the cosmic scales.
Roles of dark energy perturbations in dynamical dark energy models: can we ignore them?
Park, Chan-Gyung; Hwang, Jai-chan; Lee, Jae-heon; Noh, Hyerim
2009-10-01
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. PMID:19905618
Lim, Eugene A.; Sawicki, Ignacy; Vikman, Alexander E-mail: ignacy.sawicki@nyu.edu
2010-05-01
We introduce a novel class of field theories where energy always flows along timelike geodesics, mimicking in that respect dust, yet which possess non-zero pressure. This theory comprises two scalar fields, one of which is a Lagrange multiplier enforcing a constraint between the other's field value and derivative. We show that this system possesses no wave-like modes but retains a single dynamical degree of freedom. Thus, the sound speed is always identically zero on all backgrounds. In particular, cosmological perturbations reproduce the standard behaviour for hydrodynamics in the limit of vanishing sound speed. Using all these properties we propose a model unifying Dark Matter and Dark Energy in a single degree of freedom. In a certain limit this model exactly reproduces the evolution history of ΛCDM, while deviations away from the standard expansion history produce a potentially measurable difference in the evolution of structure.
NASA Astrophysics Data System (ADS)
Sánchez, E.; Des Collaboration
2010-11-01
The Dark Energy Survey (DES) is a next generation optical and near infrared survey that will image 5000 deg2 of the South Galactic Cap in five broad bandpass filters. In order to perform such a survey, a CCD camera of 3 deg2 field of view is being assembled at Fermilab and will be mounted on the Blanco 4m telescope at Cerro Tololo (Chile). The survey will start in the fall of 2011 and will study the dark energy properties using four independent methods: galaxy clusters counts and distributions, weak gravitational lensing tomography, baryon acoustic oscillations and supernovae Ia distances. Obtaining the four measurements from the same data set will allow a strict control of the systematic uncertainties to obtain a robust and precise determination of the cosmological parameters.
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.
Probing the time dependence of dark energy
Barboza Edésio Jr, M.
2012-02-01
A new method to investigate a possible time-dependence of the dark energy equation of state w is proposed. We apply this methodology to a combination of data involving one of the most recent type Ia supernova sample (SNLS3) along with the current baryon acoustic oscillation and H(z) measurements. We show that current observations cannot rule out a non-evolving dark energy component (dw/dz = 0). The approach developed here reduces considerably the so-called smearing effect on w determinations and may be useful to probe a possible evolving dark energy component when applied to upcoming observational data.
NASA Astrophysics Data System (ADS)
Sapone, Domenico
In this paper we review a part of the approaches that have been considered to explain the extraordinary discovery of the late time acceleration of the Universe. We discuss the arguments that have led physicists and astronomers to accept dark energy as the current preferable candidate to explain the acceleration. We highlight the problems and the attempts to overcome the difficulties related to such a component. We also consider alternative theories capable of explaining the acceleration of the Universe, such as modification of gravity. We compare the two approaches and point out the observational consequences, reaching the sad but foresightful conclusion that we will not be able to distinguish between a Universe filled by dark energy or a Universe where gravity is different from General Relativity. We review the present observations and discuss the future experiments that will help us to learn more about our Universe. This is not intended to be a complete list of all the dark energy models but this paper should be seen as a review on the phenomena responsible for the acceleration. Moreover, in a landscape of hardly compelling theories, it is an important task to build simple measurable parameters useful for future experiments that will help us to understand more about the evolution of the Universe.
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 an overdense region, with a low density contrast ~1.
NASA Astrophysics Data System (ADS)
Zhu, Zong-Hong; Fujimoto, Masa-Katsu; He, Xiang-Tao
2004-04-01
Using recent measurements of angular size of high-z milliarcsecond compact radio sources compiled by Gurvits et al. (\\cite{Gurvits99}) and X-ray gas mass fraction of galaxy clusters published by Allen et al. (\\cite{Allen02}, \\cite{Allen03}), we explore their bounds on the equation of state, ωx ≡ px/ρx, of the dark energy, whose existence has been congruously suggested by various cosmological observations. We relax the usual constraint ωx ≥-1, and find that combining the two databases yields a nontrivial lower bound on ωx. Under the assumption of a flat universe, we obtain a bound -2.22 < ωx < -0.62 at 95.4% confidence level. The 95.4% confidence bound goes to -1 ≤ωx < -0.60 when the constraint ωx ≥-1 is imposed.
Dipolar dark matter and dark energy
NASA Astrophysics Data System (ADS)
Blanchet, Luc; Le Tiec, Alexandre
2009-07-01
In previous work [L. Blanchet and A. Le Tiec, Phys. Rev. DPRVDAQ1550-7998 78, 024031 (2008)10.1103/PhysRevD.78.024031], a model of dark matter and dark energy based on the concept of gravitational polarization was investigated. This model was shown to recover the concordance cosmological scenario (Λ-cold dark matter) at cosmological scales, and the phenomenology of the modified Newtonian dynamics at galactic scales. In this article we prove that the model can be formulated with a simple and physically meaningful matter action in general relativity. We also provide alternative derivations of the main results of the model, and some details on the variation of the action.
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.
Probing gravitation, dark energy, and acceleration
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.
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.
Dark Energy Survey Simulations
NASA Astrophysics Data System (ADS)
Lin, Huan; Kuropatkin, N.; Wechsler, R.; Busha, M.; Becker, M.; Rossetto, B.; da Costa, L.; Makler, M.; Dark Energy Survey Collaboration
2010-01-01
The Dark Energy Survey (DES) is a next generation optical imaging survey that will cover 5000 sq. deg. of the southern sky using a new 520 Megapixel CCD camera that will be mounted on the 4m Blanco telescope at the Cerro Tololo Inter-American Observatory. The DES will probe dark energy using the 4 complementary techniques of galaxy clusters, weak gravitational lensing, baryon acoustic oscillations, and Type Ia supernovae. In preparation for the survey, we have been carrying out detailed catalog- and image-level simulations of the DES, as part of annual data challenges that use the simulated data to help develop and test our data management pipelines and science analysis codes. Here we will describe our latest round of simulations for DES "Data Challenge 5" (DC5). Our DC5 catalog simulations include: dark matter from a "Carmen" N-body simulation box; a galaxy catalog derived using the "ADDGALS" method; galaxy shapes based on COSMOS data; weak lensing convergence and shear derived from ray tracing, plus stronly-lensed arcs; and stars based the "Trilegal" model of the Milky Way. The simulated galaxy and stellar catalogs are then used to populate simulated DES images, which account for a wide range of instrumental and observational effects due to the telescope and corrector, the CCD detectors, and the atmosphere and weather. Using grid computing resources at Fermilab, some 3.5 TB of simulated DES imaging data have been generated for DC5, covering the 5 DES filters (grizy) over some 200 sq. deg. of sky.
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.
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.
Can holographic dark energy increase the mass of the wormhole?
NASA Astrophysics Data System (ADS)
Chattopadhyay, Surajit; Momeni, Davood; Altaibayeva, Aziza; Myrzakulov, Ratbay
2015-03-01
Motivated by the quantum essence of wormholes, in this work, we have studied accretion of dark energy (DE) onto Morris-Thorne wormhole with three different forms, namely, holographic dark energy, holographic Ricci dark energy and modified holographic Ricci dark energy. Considering the scale factor in power-law form we have observed that as the holographic dark energy accretes onto wormhole, the mass of the wormhole is decreasing. In the next phase we considered three parameterization schemes that are able to get hold of quintessence as well as phantom phases. Without any choice of scale factor we reconstructed Hubble parameter from conservation equation and dark energy densities and subsequently got the mass of the wormhole separately for accretion of the three dark energy candidates. It was observed that if these dark energies accrete onto the wormhole, then for quintessence stage, wormhole mass decreases up to a certain finite value and then again increases to aggressively during phantom phase of the universe.
Early dark energy and its interaction with dark matter
NASA Astrophysics Data System (ADS)
Pu, Bo-Yu; Xu, Xiao-Dong; Wang, Bin; Abdalla, Elcio
2015-12-01
We study a class of early dark energy models which has a substantial amount of dark energy in the early epoch of the Universe. We examine the impact of the early dark energy fluctuations on the growth of structure and the cosmic microwave background power spectrum in the linear approximation. Furthermore, we investigate the influence of the interaction between the early dark energy and the dark matter and its effect on the structure growth and cosmic microwave background. We finally constrain the early dark energy model parameters and the coupling between dark sectors by confronting different observations.
Dark energy in hybrid inflation
Gong, Jinn-Ouk; Kim, Seongcheol
2007-03-15
The situation that a scalar field provides the source of the accelerated expansion of the Universe while rolling down its potential is common in both the simple models of the primordial inflation and the quintessence-based dark energy models. Motivated by this point, we address the possibility of causing the current acceleration via the primordial inflation using a simple model based on hybrid inflation. We trigger the onset of the motion of the quintessence field via the waterfall field, and find that the fate of the Universe depends on the true vacuum energy determined by choosing the parameters. We also briefly discuss the variation of the equation of state and the possible implementation of our scenario in supersymmetric theories.
Generalized Ghost Pilgrim Scalar Field Models of Dark Energy
NASA Astrophysics Data System (ADS)
Abdul, Jawad; Ujjal, Debnath; Fazal, Batool
2015-11-01
We assume generalized ghost Pilgrim dark energy (GGPDE) model in the presence of cold dark matter in flat FRW universe. With suitable choice of interaction term between GGPDE and cold dark matter, we investigate the nature of equation of state parameter for GGPDE. Also, we investigate the natures of dynamical scalar field models (such as quintessence, tachyon, k-essence, and dilaton dark energy) and concerned potentials through the correspondence phenomenon between GGPDE and these models.
Astrophysical constraints on dark energy
NASA Astrophysics Data System (ADS)
Ho, Chiu Man; Hsu, Stephen D. H.
2016-02-01
Dark energy (i.e., a cosmological constant) leads, in the Newtonian approximation, to a repulsive force which grows linearly with distance and which can have astrophysical consequences. For example, the dark energy force overcomes the gravitational attraction from an isolated object (e.g., dwarf galaxy) of mass 107M⊙ at a distance of 23 kpc. Observable velocities of bound satellites (rotation curves) could be significantly affected, and therefore used to measure or constrain the dark energy density. Here, isolated means that the gravitational effect of large nearby galaxies (specifically, of their dark matter halos) is negligible; examples of isolated dwarf galaxies include Antlia or DDO 190.
NASA Astrophysics Data System (ADS)
Zimdahl, Winfried
Different models of the cosmic substratum which pretend to describe the present stage of accelerated expansion of the Universe, like the ΛCDM model or the Chaplygin gas, can be seen as special realizations of a holographic dark energy cosmology if the option of an interaction between pressureless dark matter and dark energy is taken seriously. The corresponding interaction strength parameter plays the role of a cosmological constant. Differences occur at the perturbative level. In particular, the pressure perturbations are intrinsically nonadiabatic.
Correspondence between Generalized Dark Energy and Scalar Field Dark Energies
NASA Astrophysics Data System (ADS)
Maity, Sayani; Debnath, Ujjal
2015-07-01
In this work, we have considered non-flat FRW universe filled with dark matter (with non-zero pressure) and generalized dark energy (GDE) as motivated by the work of Sharif et al. (Mod. Phys. Lett. A 28, 1350180, 2013). Also the dark matter and the dark energy are considered to be interacting. The energy density, pressure and the EoS of the GDE have been calculated for the interacting scenario. For stability analysis of this model, we have also analyzed the sign of square speed of sound. Next we investigate the correspondence between GDE and different other candidates of dark energies such as DBI-essence, tachyonic field, hessenc and electromagnetic field. Also we have reconstructed the potential functions and the scalar fields in this scenario.
Dark Energy and Dark Matter in a Superfluid Universe
NASA Astrophysics Data System (ADS)
Huang, Kerson
2014-04-01
The vacuum is filled with complex scalar fields, such as the Higgs field. These fields serve as order parameters for superfluidity (quantum phase coherence over oscopic distances), making the entire universe a superfluid. We review a mathematical model consisting of two aspects: (a) emergence of the superfluid during the big bang; (b) observable manifestations of superfluidity in the present universe. The creation aspect requires a self-interacting scalar field that is asymptotically free, i.e. the interaction must grow from zero during the big bang, and this singles out the Halpern-Huang potential, which has exponential behavior for large fields. It leads to an equivalent cosmological constant that decays like a power law, and this gives dark energy without "fine-tuning." Quantum turbulence (chaotic vorticity) in the early universe was able to create all the matter in the universe, fulfilling the inflation scenario. In the present universe, the superfluid can be phenomenologically described by a nonlinear Klein-Gordon equation. It predicts halos around galaxies with higher superfluid density, which is perceived as dark matter through gravitational lensing. In short, dark energy is the energy density of the cosmic superfluid, and dark matter arises from local fluctuations of the superfluid density.
Dark Energy and Dark Matter in a Superfluid Universe
NASA Astrophysics Data System (ADS)
Huang, Kerson
2013-11-01
The vacuum is filled with complex scalar fields, such as the Higgs field. These fields serve as order parameters for superfluidity (quantum phase coherence over macroscopic distances), making the entire universe a superfluid. We review a mathematical model consisting of two aspects: (a) emergence of the superfluid during the big bang; (b) observable manifestations of superfluidity in the present universe. The creation aspect requires a self-interacting scalar field that is asymptotically free, i.e. the interaction must grow from zero during the big bang, and this singles out the Halpern-Huang potential, which has exponential behavior for large fields. It leads to an equivalent cosmological constant that decays like a power law, and this gives dark energy without "fine-tuning." Quantum turbulence (chaotic vorticity) in the early universe was able to create all the matter in the universe, fulfilling the inflation scenario. In the present universe, the superfluid can be phenomenologically described by a nonlinear Klein-Gordon equation. It predicts halos around galaxies with higher superfluid density, which is perceived as dark matter through gravitational lensing. In short, dark energy is the energy density of the cosmic superfluid, and dark matter arises from local fluctuations of the superfluid density.
Optimizing New Dark Energy Experiments
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.
Non-linear dark energy clustering
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.
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.
Dark goo: bulk viscosity as an alternative to dark energy
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.
Fingerprinting dark energy. II. Weak lensing and galaxy clustering tests
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.
Dark Energy Rules the Universe
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
Cosmology from decaying dark energy, primordial at the Planck scale
NASA Astrophysics Data System (ADS)
Besprosvany, Jaime
2005-04-01
The consideration of dark energy's quanta, required also by thermodynamics, introduces its chemical potential into the cosmological equations. Isolating its main contribution, we obtain solutions with dark energy decaying to matter or radiation. When dominant, their energy densities tend asymptotically to a constant ratio, explaining today's dark energy-dark matter coincidence, and in agreement with supernova redshift data, and an age-of-the-universe constraint. This also connects the Planck and today's scales through time. This decay may be manifested in the highest-energy cosmic rays, recently detected.
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).
Thermodynamical description of the ghost dark energy model
NASA Astrophysics Data System (ADS)
Honarvaryan, M.; Sheykhi, A.; Moradpour, H.
2015-04-01
In this paper, we point out thermodynamical description of ghost dark energy (GDE) and its generalization to the early universe. Thereinafter, 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 dark matter (DM) sector is addressed. We will also find the effects of considering the coincidence problem on the mutual interaction between the dark sectors, and thus the equation of state parameter of DE. Finally, we derive a relation between the mutual interaction of the dark components of the universe, accelerated with the either GDE or its generalization, and the thermodynamic fluctuations.
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 region between Superclusters also plays a role in adding extra repulsive gravity force. Note that cosmologist Stephen Hawking comments on his website that ``There is no reason to rule out negative pressure. This is just tension.''
A Dynamic Dark Information Energy Consistent with Planck Data
NASA Astrophysics Data System (ADS)
Gough, Michael
2014-03-01
The 2013 cosmology results from the European Space Agency Planck spacecraft provide new limits to the dark energy equation of state parameter. Here we show that Holographic Dark Information Energy (HDIE), a dynamic dark energy model, achieves an optimal fit to the published datasets where Planck data is combined with other astrophysical measurements. HDIE uses Landauer's principle to account for dark energy by the energy equivalent of information, or entropy, of stellar heated gas and dust. Combining Landauer's principle with the Holographic principle yields an equation of state parameter determined solely by star formation history, effectively solving the 'cosmic coincidence problem'. While HDIE mimics a cosmological constant at low red-shifts, z<1, the small difference from a cosmological constant expected at higher red-shifts will only be resolved by the next generation of dark energy instrumentation. The HDIE model is shown to provide a viable alternative to the main cosmological constant/vacuum energy and scalar field/quintessence explanations.
Dark energy and dark matter from primordial QGP
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.
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.
Planck priors for dark energy surveys
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.
Planck priors for dark energy surveys
NASA Astrophysics Data System (ADS)
Mukherjee, Pia; Kunz, Martin; Parkinson, David; Wang, Yun
2008-10-01
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), la (angular scale of sound horizon at last scattering), Ωbh2 (baryon density fraction) and ns (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.
Reconstructing the interaction between dark energy and dark matter using Gaussian processes
NASA Astrophysics Data System (ADS)
Yang, Tao; Guo, Zong-Kuan; Cai, Rong-Gen
2015-06-01
We present a nonparametric approach to reconstruct the interaction between dark energy and dark matter directly from SNIa Union 2.1 data using Gaussian processes, which is a fully Bayesian approach for smoothing data. In this method, once the equation of state (w ) of dark energy is specified, the interaction can be reconstructed as a function of redshift. For the decaying vacuum energy case with w =-1 , the reconstructed interaction is consistent with the standard Λ CDM model, namely, there is no evidence for the interaction. This also holds for the constant w cases from -0.9 to -1.1 and for the Chevallier-Polarski-Linder (CPL) parametrization case. If the equation of state deviates obviously from -1 , the reconstructed interaction exists at 95% confidence level. This shows the degeneracy between the interaction and the equation of state of dark energy when they get constraints from the observational data.
Neutrino generated dynamical dark energy with no dark energy field
NASA Astrophysics Data System (ADS)
Guendelman, E. I.; Kaganovich, A. B.
2013-02-01
Dynamical dark energy (DE) phenomenon emerges as a geometrical effect accompanying the cosmological expansion of nonrelativistic fermionic matter. This occurs without the need for any fluid, like dynamical scalar field (quintessence, cosmon, etc.), and with conventional form of the Einstein equations in contrast to other known geometrical DE models. The phenomenon results from first principles in the framework of the two measures field theory where, in the Einstein frame, both fermion masses and the cosmological constant (CC) turn into functions of the cold fermion density n. This n dependence becomes negligible in regular (laboratory) conditions, but it may have an important role in cosmology. In the 4D gravity model where the original action involves only CC and massive fermions without self-interaction, for different (but wide) regions in the parameter space, we have found two possible classes of scenarios for the late universe starting from the cold matter domination era. We argue that the fermions which drive the variable CC should be associated with cold neutrinos disposed in voids and supervoids. The cosmological dynamics of the first class practically coincides with that of the ΛCDM model, while the dynamics of the second class is of the phantomlike regime with a pseudo-rip scenario. Crossing the phantom divide happens due to a new type of the neutrino DE effect where neutrinos pass through the state with zero mass and with the vacuumlike EoS Pν=-ρν.
Phase-space analysis of teleparallel dark energy
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.
Non-adiabatic perturbations in Ricci dark energy model
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.
NASA Astrophysics Data System (ADS)
Ohta, Nobuyoshi
2011-01-01
It has been suggested that the dark energy that explains the observed accelerating expansion of the universe may arise due to the contribution to the vacuum energy of the QCD ghost in a time-dependent background. The argument uses a four-dimensional simplified model. In this Letter, we put the discussion in more realistic model keeping all components of the QCD vector ghost and show that indeed QCD ghost produces dark energy proportional to the Hubble parameter H?QCD3 (? is the QCD mass scale) which has the right magnitude (3 eV)4.
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.
Unified dark energy-dark matter model with inverse quintessence
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.
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.
Observing dark energy with SNAP
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.
Structure formation in inhomogeneous Early Dark Energy models
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.
Dodging the dark matter degeneracy while determining the dynamics of dark energy
NASA Astrophysics Data System (ADS)
Busti, Vinicius C.; Clarkson, Chris
2016-05-01
One of the key issues in cosmology is to establish the nature of dark energy, and to determine whether the equation of state evolves with time. When estimating this from distance measurements there is a degeneracy with the matter density. We show that there exists a simple function of the dark energy equation of state and its first derivative which is independent of this degeneracy at all redshifts, and so is a much more robust determinant of the evolution of dark energy than just its derivative. We show that this function can be well determined at low redshift from supernovae using Gaussian Processes, and that this method is far superior to a variety of parameterisations which are also subject to priors on the matter density. This shows that parametrised models give very biased constraints on the evolution of dark energy.
Dark energy in perturbative string cosmology
NASA Astrophysics Data System (ADS)
Banks, Tom; Dine, Michael
2001-10-01
The apparent observation of dark energy poses problems for string theory. In de Sitter space, or in quintessence models, one cannot define a gauge-invariant S-matrix. We argue that eternal quintessence does not arise in weakly coupled string theory, but point out that it is difficult to define an S-matrix even in the presence of perturbative potentials for the moduli. The solutions of the Fischler-Susskind equations all have Big Bang or Big Crunch Singularities. We believe that an S-matrix (or S-vector) exists in this context but cannot be calculated by purely perturbative methods. We study the possibility of metastable de Sitter vacua in such weakly coupled scenarios, and conclude that the S-matrix of the extreme weak coupling region cannot probe de Sitter physics. We also consider proposed explanations of the dark energy from the perspective of string theory, and find that most are implausible. We note that it is possible that the axion constitutes both the dark matter and the dark energy.
The Hubble constant and dark energy from cosmological distance measures
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.
Cosmological anisotropy from non-comoving dark matter and dark energy
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 plausible and viable working hypothesis.
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.
Simple implementation of general dark energy models
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.
Dark energy as a kinematic effect
NASA Astrophysics Data System (ADS)
Jennen, H.; Pereira, J. G.
2016-03-01
We present a generalization of teleparallel gravity that is consistent with local spacetime kinematics regulated by the de Sitter group SO(1 , 4) . The mathematical structure of teleparallel gravity is shown to be given by a nonlinear Riemann-Cartan geometry without curvature, which inspires us to build the generalization on top of a de Sitter-Cartan geometry with a cosmological function. The cosmological function is given its own dynamics and naturally emerges nonminimally coupled to the gravitational field in a manner akin to teleparallel dark energy models or scalar-tensor theories in general relativity. New in the theory here presented, the cosmological function gives rise to a kinematic contribution in the deviation equation for the world lines of adjacent free-falling particles. While having its own dynamics, dark energy manifests itself in the local kinematics of spacetime.
Probing dark energy via galaxy cluster outskirts
NASA Astrophysics Data System (ADS)
Morandi, Andrea; Sun, Ming
2016-04-01
We present a Bayesian approach to combine Planck data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters (0.056 < z < 1.24, kT ≳ 3 keV) observed with Chandra. We exploited the high level of similarity of the emission measure in the cluster outskirts as cosmology proxy. The cosmological parameters are thus constrained assuming that the emission measure profiles at different redshift are weakly self-similar, that is their shape is universal, explicitly allowing for temperature and redshift dependence of the gas fraction. This cosmological test, in combination with Planck+SNIa data, allows us to put a tight constraint on the dark energy models. For a constant-w model, we have w = -1.010 ± 0.030 and Ωm = 0.311 ± 0.014, while for a time-evolving equation of state of dark energy w(z) we have Ωm = 0.308 ± 0.017, w0 = -0.993 ± 0.046 and wa = -0.123 ± 0.400. Constraints on the cosmology are further improved by adding priors on the gas fraction evolution from hydrodynamic simulations. Current data favour the cosmological constant with w ≡ -1, with no evidence for dynamic dark energy. We checked that our method is robust towards different sources of systematics, including background modelling, outlier measurements, selection effects, inhomogeneities of the gas distribution and cosmic filaments. We also provided for the first time constraints on which definition of cluster boundary radius is more tenable, namely based on a fixed overdensity with respect to the critical density of the Universe. This novel cosmological test has the capacity to provide a generational leap forward in our understanding of the equation of state of dark energy.
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.
Dark energy from discrete spacetime.
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. PMID:24312502
Dark Energy from Discrete Spacetime
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
Josephson junctions and dark energy
NASA Astrophysics Data System (ADS)
Jetzer, Philippe; Straumann, Norbert
2006-08-01
In a recent paper Beck and Mackey [C. Beck, M.C. Mackey, astro-ph/0603397] argue that the argument we gave in our paper [Ph. Jetzer, N. Straumann, Phys. Lett. B 606 (2005) 77, astro-ph/0411034] to disprove their claim that dark energy can be discovered in the Lab through noise measurements of Josephson junctions is incorrect. In particular, they emphasize that the measured noise spectrum in Josephson junctions is a consequence of the fluctuation dissipation theorem, while our argument was based on equilibrium statistical mechanics. In this note we show that the fluctuation dissipation relation does not depend upon any shift of vacuum (zero-point) energies, and therefore, as already concluded in our previous paper, dark energy has nothing to do with the proposed measurements.
The Dark Energy Camera (DECam)
NASA Astrophysics Data System (ADS)
DePoy, D. L.; Abbott, T.; Annis, J.; Antonik, M.; Barceló, M.; Bernstein, R.; Bigelow, B.; Brooks, D.; Buckley-Geer, E.; Campa, J.; Cardiel, L.; Castander, F.; Castilla, J.; Cease, H.; Chappa, S.; Dede, E.; Derylo, G.; Diehl, H. T.; Doel, P.; DeVicente, J.; Estrada, J.; Finley, D.; Flaugher, B.; Gaztanaga, E.; Gerdes, D.; Gladders, M.; Guarino, V.; Gutierrez, G.; Hamilton, J.; Haney, M.; Holland, S.; Honscheid, K.; Huffman, D.; Karliner, I.; Kau, D.; Kent, S.; Kozlovsky, M.; Kubik, D.; Kuehn, K.; Kuhlmann, S.; Kuk, K.; Leger, F.; Lin, H.; Martinez, G.; Martinez, M.; Merritt, W.; Mohr, J.; Moore, P.; Moore, T.; Nord, B.; Ogando, R.; Olsen, J.; Onal, B.; Peoples, J.; Qian, T.; Roe, N.; Sanchez, E.; Scarpine, V.; Schmidt, R.; Schmitt, R.; Schubnell, M.; Schultz, K.; Selen, M.; Shaw, T.; Simaitis, V.; Slaughter, J.; Smith, C.; Spinka, H.; Stefanik, A.; Stuermer, W.; Talaga, R.; Tarle, G.; Thaler, J.; Tucker, D.; Walker, A.; Worswick, S.; Zhao, A.
2008-07-01
We describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey. DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a large mosaic CCD focal plane, a five element optical corrector, five filters (g,r,i,z,Y), 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 roughly 2.2 degree diameter field of view. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms, and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.
Unified dark energy and dark matter from a scalar field different from quintessence
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.
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.
Figures of merit for present and future dark energy probes
Mortonson, Michael J.; Huterer, Dragan; Hu, Wayne
2010-09-15
We compare current and forecasted constraints on dynamical dark energy models from Type Ia supernovae and the cosmic microwave background using figures of merit based on the volume of the allowed dark energy parameter space. For a two-parameter dark energy equation of state that varies linearly with the scale factor, and assuming a flat universe, the area of the error ellipse can be reduced by a factor of {approx}10 relative to current constraints by future space-based supernova data and CMB measurements from the Planck satellite. If the dark energy equation of state is described by a more general basis of principal components, the expected improvement in volume-based figures of merit is much greater. While the forecasted precision for any single parameter is only a factor of 2-5 smaller than current uncertainties, the constraints on dark energy models bounded by -1{<=}w{<=}1 improve for approximately 6 independent dark energy parameters resulting in a reduction of the total allowed volume of principal component parameter space by a factor of {approx}100. Typical quintessence models can be adequately described by just 2-3 of these parameters even given the precision of future data, leading to a more modest but still significant improvement. In addition to advances in supernova and CMB data, percent-level measurement of absolute distance and/or the expansion rate is required to ensure that dark energy constraints remain robust to variations in spatial curvature.
Studies of dark energy with x-ray observatories
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
Studies of dark energy with X-ray observatories.
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. PMID:20404207
Do neutrinos contribute to total dark energy
NASA Astrophysics Data System (ADS)
Manihar Singh, Koijam; Mahanta, K. L.
2016-02-01
From a critical study of our present universe it is found that dark energy, and of course, dark matter are there in the universe from the beginning of its evolution manifesting in one form or the other. The different forms contained in our model are found to be generalized Chaplygin gas, quintessence and phantom energy; of course, the generalized Chaplygin gas can explain the origin of dark energy as well as dark matter in our universe simultaneously. However the more beauty in our study is that there is high possibility of the energy produced from the neutrinos might contribute to the dark energy prevalent in this universe.
The Dark Energy Survey: more than dark energy - an overview
NASA Astrophysics Data System (ADS)
Dark Energy Survey Collaboration; Abbott, T.; Abdalla, F. B.; Allam, S.; Aleksić, J.; Amara, A.; Bacon, D.; Balbinot, E.; Banerji, M.; Bechtol, K.; Benoit-Lévy, A.; Bernstein, G. M.; Bertin, E.; Blazek, J.; Dodelson, S.; Bonnett, C.; Brooks, D.; Bridle, S.; Brunner, R. J.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Caminha, G. B.; 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.; Doel, P.; Drlica-Wagner, A.; Etherington, J.; Estrada, J.; Evrard, A. E.; Fabbri, J.; Finley, D. A.; Flaugher, B.; Fosalba, P.; Foley, R. J.; 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.; Peoples, J.; Plazas, A. A.; Percival, W. J.; Reed, S. L.; 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.; Wester, W.; Weller, J.; Whiteway, L.; Wilcox, H.; Yanny, B.; Zhang, Y.; Zuntz, J.
2016-03-01
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 Λ + Cold Dark Matter (LCDM) 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).
The Dark Energy Survey: More than dark energy - An overview
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
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
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.
Tachyon dark energy models: Dynamics and constraints
Calcagni, Gianluca; Liddle, Andrew R.
2006-08-15
We explore the dynamics of dark energy models based on a Dirac-Born-Infeld (DBI) tachyonic action, studying a range of potentials. We numerically investigate the existence of tracking behavior and determine the present-day value of the equation of state parameter and its running, which are compared with observational bounds. We find that tachyon models have quite similar phenomenology to canonical quintessence models. While some potentials can be selected amongst many possibilities and fine-tuned to give viable scenarios, there is no apparent advantage in choosing a DBI scalar field instead of a Klein-Gordon one.
Testable anthropic predictions for dark energy
NASA Astrophysics Data System (ADS)
Garriga, J.; Vilenkin, A.
2003-02-01
In the context of models where the dark energy density ρD is a random variable, anthropic selection effects may explain both the “old” cosmological constant problem and the “time coincidence.” We argue that this type of solution to both cosmological constant problems entails a number of definite predictions, which can be checked against upcoming observations. In particular, the anthropic approach predicts that the dark energy equation of state is pD=-ρD with a very high accuracy, and that the dark energy density is greater than the currently favored value ΩD≈0.7. Another prediction, which may be testable with an improved understanding of galactic properties, is that the conditions for civilizations to emerge arise mostly in galaxies completing their formation at low redshift, z≈1. Finally, there is a prediction which is not likely to be tested observationally: our part of the universe is going to recollapse eventually, but it will take more than a trillion years of accelerated expansion before this happens.
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.
Dark energy anisotropic stress and large scale structure formation
Koivisto, Tomi; Mota, David F.
2006-04-15
We investigate the consequences of an imperfect dark energy fluid on the large scale structure. A phenomenological three parameter fluid description is used to study the effect of dark energy on the cosmic microwave background radiation (CMBR) and matter power spectrum. In addition to the equation of state and the sound speed, we allow a nonzero viscosity parameter for the fluid. Then anisotropic stress perturbations are generated in dark energy. In general, we find that this possibility is not excluded by the present day cosmological observations. In the simplest case when all of the three parameters are constant, we find that the observable effects of the anisotropic stress can be closely mimicked by varying the sound speed of perfect dark energy. However, now also negative values for the sound speed, as expected for adiabatic fluid model, are tolerable and in fact could explain the observed low quadrupole in the CMBR spectrum. We investigate also structure formation of imperfect fluid dark energy characterized by an evolving equation of state. In particular, we study models unifying dark energy with dark matter, such as the Chaplygin gas or the Cardassian expansion, with a shear perturbation included. This can stabilize the growth of inhomogeneities in these models, thus somewhat improving their compatibility with large scale structure observations.
Generalized ghost dark energy in Horava-Lifshitz cosmology
NASA Astrophysics Data System (ADS)
Borah, Bharat; Ansari, M.
2015-12-01
Purpose of this paper is to study generalized quantum chromodynamics ghost dark energy (GDE) in the frame work of Horava-Lifshitz cosmology. Considering interacting and non-interacting scenario of GDE with dark matter in a spatially non-flat universe, we investigate the cosmological implications of this model in detail. We obtain equation of state parameter, deceleration parameter and the evolution of dark energy density to explain the expansion of the universe. Also, we show that the results we calculate have a good compatibility with previous work and restore it in limiting case. Further, we investigate validity of generalized second law of thermodynamics in this scenario. Finally, we find out a cosmological application of our work by evaluating a relation for the equation of state of dark energy for law redshifts.
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.
Bistable dark solitons of a cubic-quintic Helmholtz equation
NASA Astrophysics Data System (ADS)
Christian, J. M.; McDonald, G. S.; Chamorro-Posada, P.
2010-05-01
We provide a report on exact analytical bistable dark spatial solitons of a nonlinear Helmholtz equation with a cubic-quintic refractive-index model. Our analysis begins with an investigation of the modulational instability characteristics of Helmholtz plane waves. We then derive a dark soliton by mapping the desired asymptotic form onto a uniform background field and obtain a more general solution by deploying rotational invariance laws in the laboratory frame. The geometry of the new soliton is explored in detail, and a range of new physical predictions is uncovered. Particular attention is paid to the unified phenomena of arbitrary-angle off-axis propagation and nondegenerate bistability. Crucially, the corresponding solution of paraxial theory emerges in a simultaneous multiple limit. We conclude with a set of computer simulations that examine the role of Helmholtz dark solitons as robust attractors.
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.
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.
Dark energy, matter creation and curvature
NASA Astrophysics Data System (ADS)
Cárdenas, Víctor H.
2012-09-01
The most studied way to explain the current accelerated expansion of the universe is to assume the existence of dark energy; a new component that fills the universe, does not form clumps, currently dominates the evolution, and has a negative pressure. In this work I study an alternative model proposed by Lima et al. (Abramo and Lima in Class. Quantum Gravity 13:2953, 1996; Zimdahl in Phys. Rev. D 53:5483, 1996; Zimdahl and Pavón in Mon. Not. R. Astron. Soc. 266:872, 1994), which does not need an exotic equation of state, but assumes instead the existence of gravitational particle creation. Because this model fits the supernova observations as well as the ΛCDM model, I perform in this work a thorough study of this model, considering an explicit spatial curvature. I found that in this scenario we can alleviate the cosmic coincidence problem, basically showing that these two components, dark matter and dark energy, are of the same nature, but they act at different scales. I also shown the inadequacy of some particle creation models, and I study a previously proposed new model that overcomes these difficulties.
Correspondence of pilgrim dark energy with scalar field models
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Majeed, Asim
2015-04-01
In this paper, we consider interacting pilgrim dark energy (Hubble horizon as an infrared cutoff) with cold dark matter in flat universe. We develop the equation of state parameter in this scenario which shows the consistency with pilgrim dark energy phenomenon. In this framework, we analyze the behavior of scalar field and corresponding scalar potentials (which describe the dynamics of the scalar fields) of various scalar field models, graphically. The dynamics of scalar fields and potentials indicate accelerated expansion of the universe which is consistent with the current observations.
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.
Dune: the dark energy explorer
NASA Astrophysics Data System (ADS)
Douspis, Marian
The Dark UNiverse Explorer (DUNE) is a wide-field space imager whose primary goal is the study of dark energy and dark matter with unprecedented precision. The mission is optimised for weak gravitational lensing, and also uses Baryon Accoustic Oscillations, cluster counts and the Integrated Sachs Wolfe effect as complementary cosmological probes. Immediate secondary goals concern the evolution of galaxies, the detailed structure of the Milky Way and nearby galaxies, and the demographics of Earth-mass planet. DUNE is an Medium-class mission with limited risks and costs consisting of a 1.2m telescope with a combined visible/NIR field-of-view of 1 sq. deg. DUNE will carry out an all-sky survey in one visible and three NIR bands which will form a unique legacy for astronomy and will make full use of synergies with ground based facilities. DUNE is a realisation of the wide-field imaging mission recommended by the ESO/ESA Working Group on Fundamental Cosmology. DUNE has recently been selected by ESA as one of the concept to be studied for an Assessment Phase within its Cosmic Vision programme. DUNE addresses multiple goals of this programme, including fundamental cosmology, galaxy evolution, and extrasolar planet search, and will yield major advances in a broad range of fields in astrophysics and cosmology.
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.
Spherical collapse of dark energy with an arbitrary sound speed
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.
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. PMID:19113691
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.
Holographic dark energy with varying gravitational constant in Hořava-Lifshitz cosmology
Setare, M.R.; Jamil, Mubasher E-mail: mjamil@camp.nust.edu.pk
2010-02-01
We investigate the holographic dark energy scenario with a varying gravitational constant in a flat background in the context of Hořava-Lifshitz gravity. We extract the exact differential equation determining the evolution of the dark energy density parameter, which includes G variation term. Also we discuss a cosmological implication of our work by evaluating the dark energy equation of state for low redshifts containing varying G corrections.
Leptogenesis, Dark Energy, Dark Matter and the neutrinos
Sarkar, Utpal
2007-10-03
In this review we discuss how the models of neutrino masses can accommodate solutions to the problem of matter-antimatter asymmetry in the universe, dark energy or cosmological constant problem and dark matter candidates. The matter-antimatter asymmetry is explained by leptogenesis, originating from the lepton number violation associated with the neutrino masses. The dark energy problem is correlated with a mass varying neutrinos, which could originate from a pseudo-Nambu-Goldstone boson. In some radiative models of neutrino masses, there exists a Higgs doublet that does not acquire any vacuum expectation value. This field could be inert and the lightest inert particle could then be a dark matter candidate. We reviewed these scenarios in connection with models of neutrino masses with right-handed neutrinos and with triplet Higgs scalars.
A two measure model of dark energy and dark matter
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.
A new class of parametrization for dark energy without divergence
Feng, Chao-Jun; Shen, Xian-Yong; Li, Ping; Li, Xin-Zhou E-mail: 1000304237@smail.shnu.edu.cn E-mail: kychz@shnu.edu.cn
2012-09-01
A new class of parametrization of the equation of state of dark energy is proposed in this paper. In contrast with the famous CPL parametrization, the equation of state with this new kind of parametrization does not divergent during the evolution of the Universe even in the future. By using the Markov Chain Monte Carlo (MCMC) method, we perform an observational constraint on two simplest dark energy models belonging to this new class of parametrization with the combined latest observational data from the type Ia supernova compilations including Union2(557), cosmic microwave background, and baryon acoustic oscillation.
Reconstruction of dark energy and expansion dynamics using Gaussian processes
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.
Constraining dark energy with clusters: Complementarity with other probes
Cunha, Carlos; Huterer, Dragan; Frieman, Joshua A.
2009-09-15
The Figure of Merit Science Working Group recently forecast the constraints on dark energy that will be achieved prior to the Joint Dark Energy Mission by ground-based experiments that exploit baryon acoustic oscillations, type Ia supernovae, and weak gravitational lensing. We show that cluster counts from ongoing and near-future surveys should provide robust, complementary dark energy constraints. In particular, we find that optimally combined optical and Sunyaev-Zel'dovich effect cluster surveys should improve the Dark Energy Task Force figure of merit for pre-Joint Dark Energy Mission projects by a factor of 2 even without prior knowledge of the nuisance parameters in the cluster mass-observable relation. Comparable improvements are achieved in the forecast precision of parameters specifying the principal component description of the dark energy equation of state parameter, as well as in the growth index {gamma}. These results indicate that cluster counts can play an important complementary role in constraining dark energy and modified gravity even if the associated systematic errors are not strongly controlled.
Dark matter and dark energy from quark bag model
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.
Probing Dark Energy in the Accelerating Universe with SNAP
NASA Astrophysics Data System (ADS)
Schubnell, Michael
2004-02-01
It has now been firmly established that the Universe is expanding at an accelerated rate, driven by a presently unknown form of dark energy that appears to dominate our Universe today. A dedicated satellite mission has been designed to precisely map out the cosmological expansion history of the Universe and thereby determine the properties of the dark energy. The SuperNova / Acceleration Probe (SNAP) will study thousands of distant supernovae, each with unprecedented precision, using a 2-meter aperture telescope with a wide field, large-area optical-to-near-IR imager and high-throughput spectrograph. SNAP can not only determine the amount of dark energy with high precision, but test the nature of the dark energy by examining how its equation of state evolves. The images produced by SNAP will have an unprecedented combination of depth, solid-angle, angular resolution, and temporal sampling and will provide a rich program of auxiliary science.
Holographic dark energy from minimal supergravity
NASA Astrophysics Data System (ADS)
Landim, Ricardo C. G.
2016-02-01
We embed models of holographic dark energy (HDE) coupled to dark matter (DM) in minimal supergravity plus matter, with one chiral superfield. We analyze two cases. The first one has the Hubble radius as the infrared (IR) cutoff and the interaction between the two fluids is proportional to the energy density of the DE. The second case has the future event horizon as IR cutoff while the interaction is proportional to the energy density of both components of the dark sector.
Massive photon and dark energy
NASA Astrophysics Data System (ADS)
Kouwn, Seyen; Oh, Phillial; Park, Chan-Gyung
2016-04-01
We investigate the cosmology of massive electrodynamics and explore the possibility whether the massive photon could provide an explanation of dark energy. The action is given by the scalar-vector-tensor theory of gravity, which is obtained by nonminimal coupling of the massive Stueckelberg QED with gravity; its cosmological consequences are studied by paying particular attention to the role of photon mass. We find that the theory allows for cosmological evolution where the radiation- and matter-dominated epochs are followed by a long period of virtually constant dark energy that closely mimics a Λ CDM model. We also find that the main source of the current acceleration is provided by the nonvanishing photon mass governed by the relation Λ ˜m2 . A detailed numerical analysis shows that the nonvanishing photon mass on the order of ˜1 0-34 eV is consistent with current observations. This magnitude is far less than the most stringent limit on the photon mass available so far, which is on the order of m ≤1 0-27 eV .
Reconstruction of the interaction term between dark matter and dark energy using SNe Ia
Solano, Freddy Cueva; Nucamendi, Ulises E-mail: ulises@ifm.umich.mx
2012-04-01
We apply a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of dark energy (DE) with constant equation of state (EOS) parameter interacting with dark matter (DM)\\@. The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which form a complete set orthonormal functions. This interaction term describes an exchange of energy flow between the DE and DM within dark sector. To show how the method works we do the reconstruction of the interaction function expanding it in terms of only the first six Chebyshev polynomials and obtain the best estimation for the coefficients of the expansion assuming three models: (a) a DE equation of the state parameter w = −1 (an interacting cosmological Λ), (b) a DE equation of the state parameter w = constant with a dark matter density parameter fixed, (c) a DE equation of the state parameter w = constant with a free constant dark matter density parameter to be estimated, and using the Union2 SNe Ia data set from ''The Supernova Cosmology Project'' (SCP) composed by 557 type Ia supernovae. In both cases, the preliminary reconstruction shows that in the best scenario there exist the possibility of a crossing of the noninteracting line Q = 0 in the recent past within the 1σ and 2σ errors from positive values at early times to negative values at late times. This means that, in this reconstruction, there is an energy transfer from DE to DM at early times and an energy transfer from DM to DE at late times. We conclude that this fact is an indication of the possible existence of a crossing behavior in a general interaction coupling between dark components.
Reconstruction of the interaction term between dark matter and dark energy using SNe Ia
NASA Astrophysics Data System (ADS)
Cueva Solano, Freddy; Nucamendi, Ulises
2012-04-01
We apply a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of dark energy (DE) with constant equation of state (EOS) parameter interacting with dark matter (DM)\\@. The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which form a complete set orthonormal functions. This interaction term describes an exchange of energy flow between the DE and DM within dark sector. To show how the method works we do the reconstruction of the interaction function expanding it in terms of only the first six Chebyshev polynomials and obtain the best estimation for the coefficients of the expansion assuming three models: (a) a DE equation of the state parameter w = -1 (an interacting cosmological Λ), (b) a DE equation of the state parameter w = constant with a dark matter density parameter fixed, (c) a DE equation of the state parameter w = constant with a free constant dark matter density parameter to be estimated, and using the Union2 SNe Ia data set from ``The Supernova Cosmology Project'' (SCP) composed by 557 type Ia supernovae. In both cases, the preliminary reconstruction shows that in the best scenario there exist the possibility of a crossing of the noninteracting line Q = 0 in the recent past within the 1σ and 2σ errors from positive values at early times to negative values at late times. This means that, in this reconstruction, there is an energy transfer from DE to DM at early times and an energy transfer from DM to DE at late times. We conclude that this fact is an indication of the possible existence of a crossing behavior in a general interaction coupling between dark components.
Disformal dark energy at colliders
NASA Astrophysics Data System (ADS)
Brax, Philippe; Burrage, Clare; Englert, Christoph
2015-08-01
Disformally coupled, light scalar fields arise in many of the theories of dark energy and modified gravity that attempt to explain the accelerated expansion of the Universe. They have proved difficult to constrain with precision tests of gravity because they do not give rise to fifth forces around static nonrelativistic sources. However, because the scalar field couples derivatively to standard model matter, measurements at high-energy particle colliders offer an effective way to constrain and potentially detect a disformally coupled scalar field. Here we derive new constraints on the strength of the disformal coupling from LHC run 1 data and provide a forecast for the improvement of these constraints from run 2. We additionally comment on the running of disformal and standard model couplings in this scenario under the renormalization group flow.
Nonparametric dark energy reconstruction from supernova data.
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. PMID:21231517
Dark energy and supermassive black holes
Gonzalez-Diaz, Pedro F.
2004-09-15
This paper deals with a cosmological model in which the universe is filled with tachyon dark energy in order to describe current and future accelerating expansion. We obtain that the simplest condition for the regime of phantom energy to occur in this scenario is that the scalar field be Wick rotated to imaginary values which correspond to an axionic field classically. By introducing analytical expressions for the scale factor or the Hubble parameter that satisfy all constraint equations of the used models we show that such models describe universes which may develop a big rip singularity in the finite future. It is argued that, contrary to a recent claim, the entropy for a universe filled with dark energy is definite positive even on the phantom regime where the universe would instead acquire a negative temperature. It is also seen that, whichever the fate of the tachyonic accelerating universe, it will be stable to any fluctuations of the scalar field, and that since the considered models have all an imaginary sound speed, any overdense regions will undergo an accelerated collapse leading rapidly to formation of giant black holes. Finally the conjecture is advanced that these black holes may be the supermassive black holes that most galaxies harbor at their center.
Imperfect dark energy from kinetic gravity braiding
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.
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 /? ) and the ratio of their perturbations in its rest frame (cs2=? p /? ? ). 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)?m . We did not find any strong evidence for the existence of this matter-sourced anisotropic stress, even in the 1 ? region.
Reconstruction of interacting dark energy models from parametrizations
Rosenfeld, R.
2007-04-15
Models with interacting dark energy can alleviate the cosmic coincidence problem by allowing dark matter and dark energy to evolve in a similar fashion. At a fundamental level, these models are specified by choosing a functional form for the scalar potential and for the interaction term. However, in order to compare to observational data it is usually more convenient to use parametrizations of the dark energy equation of state and the evolution of the dark matter energy density. Once the relevant parameters are fitted, it is important to obtain the shape of the fundamental functions. In this paper I show how to reconstruct the scalar potential and the scalar interaction with dark matter from general parametrizations. I give a few examples and show that it is possible for the effective equation of state for the scalar field to cross the phantom barrier when interactions are allowed. I analyze the uncertainties in the reconstructed potential arising from foreseen errors in the estimation of fit parameters and point out that a Yukawa-like linear interaction results from a simple parametrization of the coupling.
Thermodynamics of interacting holographic dark energy
NASA Astrophysics Data System (ADS)
Arevalo, Fabiola; Cifuentes, Paulo; Peña, Francisco
2016-01-01
The thermodynamics of a scheme of dark matter-dark energy interaction is studied considering a holographic model for the dark energy in a flat Friedmann-Lemaitre-Robertson-Walker background. We obtain a total entropy rate for a general horizon and we study the Generalized Second Law of Thermodynamics for a cosmological interaction as a free function. Additionally, we discuss two horizons related to the Ricci and Ricci-like model and its effect on an interacting system.
[Dark matter and dark energy of the universe].
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. PMID:16463572
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.
Topology and dark energy: testing gravity in voids.
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. PMID:24483641
Physical evidence for dark energy
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.
The Dark Energy Survey instrument design
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.
Examining the evidence for dynamical dark energy.
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. PMID:23215174
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,…
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,
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.
Constraining dark energy through the stability of cosmic structures
Pavlidou, V.; Tetradis, N.; Tomaras, T.N. E-mail: ntetrad@phys.uoa.gr
2014-05-01
For a general dark-energy equation of state, we estimate the maximum possible radius of massive structures that are not destabilized by the acceleration of the cosmological expansion. A comparison with known stable structures constrains the equation of state. The robustness of the constraint can be enhanced through the accumulation of additional astrophysical data and a better understanding of the dynamics of bound cosmic structures.
Computing model independent perturbations in dark energy and modified gravity
Battye, Richard A.; Pearson, Jonathan A. E-mail: jonathan.pearson@durham.ac.uk
2014-03-01
We present a methodology for computing model independent perturbations in dark energy and modified gravity. This is done from the Lagrangian for perturbations, by showing how field content, symmetries, and physical principles are often sufficient ingredients for closing the set of perturbed fluid equations. The fluid equations close once ''equations of state for perturbations'' are identified: these are linear combinations of fluid and metric perturbations which construct gauge invariant entropy and anisotropic stress perturbations for broad classes of theories. Our main results are the proof of the equation of state for perturbations presented in a previous paper, and the development of the required calculational tools.
GALAXY CLUSTERS AS A PROBE OF EARLY DARK ENERGY
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.
On cosmic acceleration without dark energy
Kolb, E.W.; Matarrese, S.; Riotto, A.; ,
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.
NASA Astrophysics Data System (ADS)
Mattsson, Teppo
2010-03-01
Motivated by the observed cosmic matter distribution, we present the following conjecture: due to the formation of voids and opaque structures, the average matter density on the path of the light from the well-observed objects changes from Ω M ≃ 1 in the homogeneous early universe to Ω M ≃ 0 in the clumpy late universe, so that the average expansion rate increases along our line of sight from EdS expansion Ht ≃ 2/3 at high redshifts to free expansion Ht ≃ 1 at low redshifts. To calculate the modified observable distance-redshift relations, we introduce a generalized Dyer-Roeder method that allows for two crucial physical properties of the universe: inhomogeneities in the expansion rate and the growth of the nonlinear structures. By treating the transition redshift to the void-dominated era as a free parameter, we find a phenomenological fit to the observations from the CMB anisotropy, the position of the baryon oscillation peak, the magnitude-redshift relations of type Ia supernovae, the local Hubble flow and the nucleosynthesis, resulting in a concordant model of the universe with 90% dark matter, 10% baryons, no dark energy, 15 Gyr as the age of the universe and a natural value for the transition redshift z 0 = 0.35. Unlike a large local void, the model respects the cosmological principle, further offering an explanation for the late onset of the perceived acceleration as a consequence of the forming nonlinear structures. Additional tests, such as quantitative predictions for angular deviations due to an anisotropic void distribution and a theoretical derivation of the model, can vindicate or falsify the interpretation that light propagation in voids is responsible for the perceived acceleration.
Possible dark energy imprints in the gravitational wave spectrum of mixed neutron-dark-energy stars
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.
Sussman, Roberto A.
2009-01-15
A numerical approach is considered for spherically symmetric spacetimes that generalize Lemaitre-Tolman-Bondi dust solutions to nonzero pressure ('LTB spacetimes'). We introduce quasilocal (QL) variables that are covariant LTB objects satisfying evolution equations of Friedman-Lemaitre-Robertson-Walker (FLRW) cosmologies. We prove rigorously that relative deviations of the local covariant scalars from the QL scalars are nonlinear, gauge invariant and covariant perturbations on a FLRW formal background given by the QL scalars. The dynamics of LTB spacetimes is completely determined by the QL scalars and these exact perturbations. Since LTB spacetimes are compatible with a wide variety of ''equations of state,'' either single fluids or mixtures, a large number of known solutions with dark matter and dark energy sources in a FLRW framework (or with linear perturbations) can be readily examined under idealized but nontrivial inhomogeneous conditions. Coordinate choices and initial conditions are derived for a numerical treatment of the perturbation equations, allowing us to study nonlinear effects in a variety of phenomena, such as gravitational collapse, nonlocal effects, void formation, dark matter and dark energy couplings, and particle creation. In particular, the embedding of inhomogeneous regions can be performed by a smooth matching with a suitable FLRW solution, thus generalizing the Newtonian 'top hat' models that are widely used in astrophysical literature. As examples of the application of the formalism, we examine numerically the formation of a black hole in an expanding Chaplygin gas FLRW universe, as well as the evolution of density clumps and voids in an interactive mixture of cold dark matter and dark energy.
Holographic dark energy in a vector field cosmology
NASA Astrophysics Data System (ADS)
Sadatian, S. Davood
2015-08-01
We obtain interacting holographic dark energy density in the framework of vector field cosmology (LIV). We consider possible modification of equation of state for the holographic energy density in lorentz invariance violation cosmology. In this case we select Jeans length as the IR cut-off in the holographic model. Then we consider the interaction between holographic energy densities ρΛ and ρm in this framework.
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.
DBI models for the unification of dark matter and dark energy
NASA Astrophysics Data System (ADS)
Chimento, Luis P.; Lazkoz, Ruth; Sendra, Irene
2010-06-01
We propose a model based on a DBI action for the unification of dark matter and dark energy. This is supported by the results of the study of its background behavior at early and late times, and reinforced by the analysis of the evolution of perturbations. We also perform a Bayesian analysis to set observational constraints on the parameters of the model using type Ia SN, CMB shift and BAO data. Finally, to complete the study we investigate its kinematics aspects, such as the effective equation of state parameter, acceleration parameter and transition redshift. Particularizing them for the best fit one appreciates that an effective phantom behavior is preferred.
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 collaboration-wide treatment of the data. The science measurements themselves are also detailed. We verified DES's capabilities for performing weak lensing analyses by measuring the masses of four galaxy clusters, finding consistency with previous measurements, and utilized DECam's wide field-of-view for a photometric study of filament-like structures in the fields. Finally, my recent work with Balrog is presented. Balrog is a simulation toolkit for embedding fake objects into real survey images in order to correct for systematic biases. We have used Balrog to extend DES galaxy clustering measurements down to fainter limits than previously possible, finding results consistent with higher-resolution space-based data. The methodology used in this analysis generalizes beyond galaxy clustering alone, and promises to be useful in future imaging survey measurements.
Instability of Interacting Ghost Dark Energy Model in an Anisotropic Universe
NASA Astrophysics Data System (ADS)
Azimi, N.; Barati, F.
2016-02-01
A new dark energy model called "ghost dark energy" was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, ρ Λ = α H, where α is a constant of order {Λ }3_{QCD} and Λ Q C D ˜ 100M e V is QCD mass scale. In this paper, we investigate about the stability of generalized QCD ghost dark energy model against perturbations in the anisotropic background. At first, the ghost dark energy model of the universe with spatial BI model with/without the interaction between dark matter and dark energy is discussed. In particular, the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy model are obtained. Then, we use the squared sound speed {vs2} the sign of which determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. In conclusion, we find evidence that the ghost dark energy might can not lead to a stable universe favored by observations at the present time in BI universe.
Can a galaxy redshift survey measure dark energy clustering?
Takada, Masahiro
2006-08-15
A wide-field galaxy redshift survey allows one to probe galaxy clustering at largest spatial scales, which carries invaluable information on horizon-scale physics complementarily to the cosmic microwave background (CMB). Assuming the planned survey consisting of z{approx}1 and z{approx}3 surveys with areas of 2000 and 300 deg.{sup 2}, respectively, we study the prospects for probing dark energy clustering from the measured galaxy power spectrum, assuming the dynamical properties of dark energy are specified in terms of the equation of state and the effective sound speed c{sub e} in the context of an adiabatic cold dark dominated matter model. The dark energy clustering adds a power to the galaxy power spectrum amplitude at spatial scales greater than the sound horizon, and the enhancement is sensitive to redshift evolution of the net dark energy density, i.e. the equation of state. We find that the galaxy survey, when combined with CMB expected from the Planck satellite mission, can distinguish dark energy clustering from a smooth dark energy model such as the quintessence model (c{sub e}=1), when c{sub e} < or approx. 0.04 (0.02) in the case of the constant equation of state w{sub 0}=-0.9 (-0.95). An ultimate full-sky survey of z{approx}1 galaxies allows the detection when c{sub e}(less-or-similar sign)0.08 (0.04) for w{sub 0}=0.9 (-0.95). These forecasts show a compatible power with an all-sky CMB and galaxy cross correlation that probes the integrated Sachs-Wolfe effect. We also investigate a degeneracy between the dark energy clustering and the nonrelativistic neutrinos implied from the neutrino oscillation experiments, because the two effects both induce a scale-dependent modification in the galaxy power spectrum shape at largest spatial scales accessible from the galaxy survey. It is shown that a wider redshift coverage can efficiently separate the two effects by utilizing the different redshift dependences, where dark energy clustering is apparent only at low redshifts z < or approx. 1.
Cosmological neutrino mass limit and the dynamics of dark energy
Xia Junqing; Zhao Gongbo; Zhang Xinmin
2007-05-15
We investigate the correlation between the neutrino mass limit and dark energy with the time evolving equation of state. Parametrizing dark energy as w=w{sub 0}+w{sub 1}*z/(1+z), we make a global fit using Markov Chain Monte Carlo technique to determine w{sub 0}, w{sub 1}, neutrino mass as well as other cosmological parameters simultaneously. We pay particular attention to the correlation between neutrino mass {sigma}m{sub {nu}} and w{sub 1} using current cosmological observations as well as the future simulated data sets such as PLANCK, SNAP, and LAMOST.
Quintom dark energy models with nearly flat potentials
Setare, M. R.; Saridakis, E. N.
2009-02-15
We examine quintom dark energy models, produced by the combined consideration of a canonical and a phantom field, with nearly flat potentials and dark energy equation-of-state parameter w{sub DE} close to -1. We find that all such models converge to a single expression for w{sub DE}(z), depending only on the initial field values and their derivatives. We show that this quintom paradigm allows for a description of the transition through -1 in the near cosmological past. In addition, we provide the necessary conditions for the determination of the direction of the -1 crossing.
Constraining neutrinos and dark energy with galaxy clustering in the Dark Energy Survey
NASA Astrophysics Data System (ADS)
Zablocki, Alan
We determine the forecast errors on the absolute neutrino mass scale and the equation of state of dark energy by combining synthetic data from the Dark Energy Survey (DES) and the Cosmic Microwave Background (CMB) Planck surveyor. We use angular clustering of galaxies for DES in 7 redshift shells up to z ~ 1.7 including cross-correlations between different redshift shells. We study models with massless and massive neutrinos and three different dark energy models: LambdaCDM(w = --1), wCDM (constant w), and waCDM (evolving equation of state parameter w(a) = w 0 +wa(1 --- a)). We include the impact of uncertainties in modelling galaxy bias using a constant and a redshift-evolving bias model. Combining DES galaxy clustering with CMB data improves the errors on summv and w by an order of magnitude, relative to a CMB only analysis. For the LambdaCDM model we obtain the best upper limit for the sum of neutrino masses from DES+Planck of summv < 0.08 eV (95% C.L.) for a fiducial mass of summv = 0.047 eV with a 1sigma error of 0.02 eV, assuming perfect knowledge of galaxy bias. For the wCDM model the limit is summv< 0.10 eV. For a wCDM model where galaxy bias evolves with redshift, the upper limit on the sum of neutrino masses increases to 0.19 eV. The upper limit onsummv does not change much when we allow w to vary with redshift, once we include a redshift-evolving galaxy bias model, with a limit of summv < 0.20 eV. DES will be able to place competitive upper limits on the sum of neutrino masses of 0.1-0.2 eV and could therefore strongly constrain the inverted mass hierarchy of neutrinos. In a wCDM model the 1sigma error on constant w is Deltaw = 0.03 from DES galaxy clustering and Planck. Allowing summv as a free parameter increases the error on w by a factor of 2, with Deltaw = 0.06. In a waCDM model, in which the dark energy equation of state varies with time, the errors are Deltaw0 = 0.2 and Delta wa = 0.42. Including neutrinos and redshift dependent galaxy bias increases the errors to Deltaw0 = 0.35 and Deltawa = 0.89. The resulting uncertainty in galaxy bias parameters varies between 3-5% for all our cosmological models that include massive neutrinos.
The Dark Energy Survey Pipeline
NASA Astrophysics Data System (ADS)
Morganson, Eric; Dark Energy Survey Data Management Team
2016-01-01
The Dark Energy Survey (DES) is a large optical survey that is intended to study cosmology using Type Ia supernovae, baryon acoustic oscillations, galaxy cluster counting and gravitational lensing. DES comprises two five year surveys (roughly 100 nights per year) on the Blanco 4-m telescope at the Cerro Tololo Interamerican Observatory (CTIO) in Chile. The first is a 5,000 square degree survey of the high Galactic latitude Southern sky to roughly 24th magnitude in the g, r, i, z and Y filters. The second is a set of ten 3 square degree fields that are observed roughly once every five nights as a supernova survey. DES will be significantly deeper than and have superior image quality to previous wide field surveys like SDSS and Pan-STARRS1. Reduced DES images are made public at NOAO roughly one year after the images are taken. DES plans to release its first two years of data (images and catalogs) in 2017 and its entire dataset after it finishes taking data in 2018. The National Center for Supercomputing Applications (NCSA) at the University of Illinois is leading the DES data processing. I describe this data processing, the DES pipeline and the DES data in this poster.
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.
The scale factor in a Universe with dark energy
NASA Astrophysics Data System (ADS)
Sazhin, M. V.; Sazhina, O. S.
2016-04-01
The solution of the Friedmann cosmological equations for the scale factor in a model of the Universe containing matter having the equation of state of dust and dark energy is considered. The equation-of-state parameter of the dark energy is taken to be an arbitrary constant w = -1.006 ± 0.045, whose value is constrained by the current observational limits. An exact solution for the scale factor as a function of physical time and conformal time is obtained. Approximate solutions have been found for the entire admissible conformal time interval with an accuracy better than 1%, which exceeds the accuracy of the determined global parameters of our Universe. This is the first time an exact solution for the scale factor describing the evolution of the Universe in a unified way, beginning with the matter-dominated epoch and ending with the infinitely remote future, has been obtained.
Dark Energy as Extra-Dimensional Gravity
NASA Astrophysics Data System (ADS)
Burgess, C. P.
The nature of dark energy, which presently dominates the universal energy budget, remains a complete mystery. Models in which it is currently evolving tend to be overly sensitive to initial conditions, and necessarily involve a very light degree of freedom which is very difficult to obtain from realistic microscopic physics. This essay describes recent progress in understanding how the dark energy can arise as a residue of extra-dimensional gravitation, leading to new insights into how dark-energy cosmology might work. This picture produces dark energy dynamics within which couplings slowly run (or: 'walk') over cosmological times. It also has several unusual experimental predictions, including measurable modifications to Newton's Law on sub-millimeter scales and dramatic implications at next-generation collider experiments.
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.
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.
Phenomenology of hybrid scenarios of neutrino dark energy
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.
Dark matter from dark energy-baryonic matter couplings
Aviles, Alejandro; Cervantes-Cota, Jorge L.
2011-01-15
We present a scenario in which a scalar field dark energy is coupled to the trace of the energy momentum tensor of the baryonic matter fields. In the slow-roll regime, this interaction could give rise to the cosmological features of dark matter. We work out the cosmological background solutions and fit the parameters of the model using the Union 2 supernovae data set. Then, we develop cosmological perturbations up to linear order, and we find that the perturbed variables have an acceptable behavior, in particular, the density contrast of baryonic matter grows similar to that in the {Lambda}CDM model for a suitable choice of the strength parameter of the coupling.
What We Know About Dark Energy From Supernovae
Filippenko, Alex [University of California, Berkeley, California, United States
2010-01-08
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.
Voids as a precision probe of dark energy
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.
Fine-structure constant constraints on dark energy
NASA Astrophysics Data System (ADS)
Martins, C. J. A. P.; Pinho, A. M. M.
2015-05-01
We use astrophysical and atomic clock tests of the stability of the fine-structure constant α , together with type Ia supernova and Hubble parameter data, to constrain the simplest class of dynamical dark energy models where the same degree of freedom is assumed to provide both the dark energy and (through a dimensionless coupling ζ to the electromagnetic sector) the α variation. We show how current data tightly constrain a combination of ζ and the dark energy equation of state w0. At the 95% confidence level and marginalizing over w0 we find |ζ |<5 ×10-6, with the atomic clock tests dominating the constraints. The forthcoming generation of high-resolution ultrastable spectrographs will enable significantly tighter constraints.
Estimating the uncorrelated dark energy evolution in the Planck era
NASA Astrophysics Data System (ADS)
Wang, F. Y.; Dai, Z. G.
2014-01-01
The equation of state (EOS), w(z), is the most important parameter of dark energy. We reconstruct the evolution of this EOS in a model-independent way using the latest cosmic microwave background (CMB) data from Planck and other observations, such as type Ia supernovae, the baryonic acoustic oscillation measurements (SDSS, 6dF, BOSS, and WiggleZ), and the Hubble parameter value H(z). The results show that the EOS is consistent with the cosmological constant at the 2σ confidence level, not preferring a dynamical dark energy. The uncorrelated EOS of dark energy constraints from Planck CMB data are much tighter than those from the WMAP 9-year CMB data.
a Comprehensive Model of Dark Energy, Inflation and Black Holes
NASA Astrophysics Data System (ADS)
Biermann, Peter L.; Harms, Benjamin C.
2015-01-01
We derive two new equations of quantum gravity and combine them with reinterpretations of previously proposed concepts of dark energy, black holes, inflation, the arrow of time and the energy at which rest-mass first manifests itself into a theory which may be a first step toward a comprehensive description of all these phenomena. The resulting theory also predicts new tests which can be experimentally checked within a few years.
Essential building blocks of dark energy
Gleyzes, Jerome; Vernizzi, Filippo; Langlois, David; Piazza, Federico E-mail: langlois@apc.univ-paris7.fr E-mail: filippo.vernizzi@cea.fr
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.
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.
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.
Probing dark energy through scale dependence
NASA Astrophysics Data System (ADS)
Motta, Mariele; Sawicki, Ignacy; Saltas, Ippocratis D.; Amendola, Luca; Kunz, Martin
2013-12-01
We consider the consequences of having no prior knowledge of the true dark energy model for the interpretation of cosmological observations. The magnitude of redshift-space distortions and weak-lensing shear is determined by the metric on the geodesics of which galaxies and light propagate. We show that, given precise enough observations, we can use these data to completely reconstruct the metric on our past light cone and therefore to measure the scale and time dependence of the anisotropic stress and the evolution of the gravitational potentials in a model-independent manner. Since both dark matter and dark energy affect the visible sector only through the gravitational field they produce, they are inseparable without a model for dark energy: galaxy bias cannot be measured and therefore the distribution of dark matter determined; the peculiar velocity of dark matter can be identified with that of the galaxies only when the equivalence principle holds. Given these limitations, we show how one can nonetheless build tests for classes of dark energy models which depend on making measurements at multiple scales at a particular redshift. They are null tests on the model-independent observables, do not require modeling evolution in time, and do not require any parametrization of the free functions of these models—such as the sound speed. We show that one in principle could rule out or constrain the whole class of the most general scalar-tensor theories even without assuming the quasistatic limit.
Readout electronics for the Dark Energy Camera
NASA Astrophysics Data System (ADS)
Castilla, Javier; Ballester, Otger; Cardiel, Laia; Chappa, Steve; de Vicente, Juan; Holm, Scott; Huffman, David; Kozlovsky, Mark; Martinez, Gustavo; Olsen, Jamieson; Shaw, Theresa; Stuermer, Walter
2010-07-01
The goal of the Dark Energy Survey (DES) is to measure the dark energy equation of state parameter with four complementary techniques: galaxy cluster counts, weak lensing, angular power spectrum and type Ia supernovae. DES will survey a 5000 sq. degrees area of the sky in five filter bands using a new 3 deg2 mosaic camera (DECam) mounted at the prime focus of the Blanco 4-meter telescope at the Cerro-Tololo International Observatory (CTIO). DECam is a ~520 megapixel optical CCD camera that consists of 62 2k x 4k science sensors plus 4 2k x 2k sensors for guiding. The CCDs, developed at the Lawrence Berkeley National Laboratory (LBNL) and packaged and tested at Fermilab, have been selected to obtain images efficiently at long wavelengths. A front-end electronics system has been developed specifically to perform the CCD readout. The system is based in Monsoon, an open source image acquisition system designed by the National Optical Astronomy Observatory (NOAO). The electronics consists mainly of three types of modules: Control, Acquisition and Clock boards. The system provides a total of 132 video channels, 396 bias levels and around 1000 clock channels in order to readout the full mosaic at 250 kpixel/s speed with 10 e- noise performance. System configuration and data acquisition is done by means of six 0.8 Gbps optical links. The production of the whole system is currently underway. The contribution will focus on the testing, calibration and general performance of the full system in a realistic environment.
Hessence: a new view of quintom dark energy
NASA Astrophysics Data System (ADS)
Wei, Hao; Cai, Rong-Gen; Zeng, Ding-Fang
2005-08-01
Recently a lot of attention has been given to building a dark energy model in which the equation-of-state parameter w can cross the phantom divide w = -1. One of the models to realize crossing the phantom divide is called the quintom model, in which two real scalar fields appear, one is a normal scalar field and the other is a phantom-type scalar field. In this paper we propose a non-canonical complex scalar field as the dark energy, which we dub 'hessence', to implement crossing the phantom divide, in a similar sense as the quintom dark energy model. In the hessence model, the dark energy is described by a single field with an internal degree of freedom rather than two independent real scalar fields. However, the hessence is different from an ordinary complex scalar field, we show that the hessence can avoid the difficulty of the Q-ball formation which gives trouble to the spintessence model (an ordinary complex scalar field acts as the dark energy). Furthermore, we find that, by choosing a proper potential, the hessence could correspond to a Chaplygin gas at late times.
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.
On dark energy models of single scalar field
Li, Mingzhe; Qiu, Taotao; Cai, Yifu; Zhang, Xinmin E-mail: xsjqiu@gmail.com E-mail: xmzhang@ihep.ac.cn
2012-04-01
In this paper we revisit the dynamical dark energy model building based on single scalar field involving higher derivative terms. By imposing a degenerate condition on the higher derivatives in curved spacetime, one can select the models which are free from the ghost mode and the equation of state is able to cross the cosmological constant boundary smoothly, dynamically violate the null energy condition. Generally the Lagrangian of this type of dark energy models depends on the second derivatives linearly. It behaves like an imperfect fluid, thus its cosmological perturbation theory needs to be generalized. We also study such a model with explicit form of degenerate Lagrangian and show that its equation of state may cross -1 without any instability.
Report of the Dark Energy Task Force
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.; ,
2006-09-01
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.
Coupling dark energy with standard model states
NASA Astrophysics Data System (ADS)
Bento, M. C.; Bernardini, A. E.; Bertolami, O.
2009-06-01
In this contribution one examines the coupling of dark energy to the gauge fields to neutrinos, and to the Higgs field. In the first case, one show how a putative evolution of the fundamental couplings of strong and weak interactions via coupling to dark energy through a generalized Bekenstein-type model may cause deviation on the statistical nuclear decay Rutherford-Soddy law. Existing bounds for the weak interaction exclude any significant deviation. For neutrinos, a perturbative approach is developed which allows for considering viable varying mass neutrino models coupled to any quintessence-type field. The generalized Chaplygin model is considered as an example. For the coupling with the Higgs field one obtains an interesting cosmological solution which includes the unification of dark energy and dark matter.
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.
Dark energy as double N-flation - observational predictions
NASA Astrophysics Data System (ADS)
Gott, J. Richard; Slepian, Zachary
2011-09-01
We propose a simple model for dark energy useful for comparison with observations. It is based on the idea that dark energy and inflation should be caused by the same physical process. As motivation, we note that Linde's simple chaotic inflation ? produces values of ns= 0.967 and r= 0.13, which are consistent with the Wilkinson Microwave Anisotropy Probe (WMAP) 1? error bars. We therefore propose ? with m1 10-5 and m2? 10-60, where c= 1 =? and the reduced Planck mass is set to unity. The field ?1 drives inflation and has damped by now (?1, 0= 0), while ?2 is currently rolling down its potential to produce dark energy. Using this model, we derive the formula ?w(z) ?w(z) + 1 =?w0(H0/H(z))2 via the slow-roll approximation. Our numerical results from exact and self-consistent solution of the equations of motion for ?2 and the Friedmann equations support this formula, and it should hold for any slow-roll dark energy. Our potential can be easily realized in N-flation models with many fields, and is easily falsifiable by upcoming experiments - for example, if Linde's chaotic inflation is ruled out. But if r values consistent with Linde's chaotic inflation are detected then one should take this model seriously indeed.
Bianchi type I Universe and instability of new agegraphic dark energy in Brans-Dicke theories
NASA Astrophysics Data System (ADS)
Fayaz, V.
2016-02-01
In this paper, we consider the new agegraphic dark energy (NADE) in a Bianchi type-I metric (which is a spatially homogeneous and anisotropic) in the framework of Brans-Dicke theory. For this purpose, we use the squared sound speed vs2 whose sign determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. The equation of state and the deceleration parameter of the new agegraphic dark energy in a anisotropic Universe is obtained. We show that the combination of Brans-Dicke field and new agegraphic dark energy can accommodate ω_{\\varLambda}=-1 crossing for the equation of state of noninteracting dark energy. When an interaction between dark energy and dark matter is taken into account, the transition of ω_{\\varLambda} to phantom regime can be more easily accounted when the Einstein field equations is being resort. In conclusion, we find evidences that the new agegraphic dark energy in BD theory can not lead to a stable Universe favored by observations at the present time. The anisotropy of the Universe decreases and the Universe transits to an isotropic flat FRW Universe accommodating the present acceleration.
Dark energy constraints after the new Planck data
NASA Astrophysics Data System (ADS)
Xia, Jun-Qing; Li, Hong; Zhang, Xinmin
2013-09-01
The Planck Collaboration has recently published maps of the cosmic microwave background radiation with the highest precision. In the standard flat Λ cold dark matter framework, Planck data show that the Hubble constant H0 is in tension with that measured by the several direct probes on H0. In this paper, we perform a global analysis from the current observational data in the general dark energy models and find that resolving this tension requires the dark energy model with its equation of state (EOS) w≠-1. Firstly, assuming the w to be a constant, the Planck data favor w<-1 at about 2σ confidence level when combining with the supernovae “supernova legacy survey” compilation. Consequently the value derived on H0, H0=71.3±2.0kms-1Mpc-1 (68% C.L.) is consistent with that from direct H0 probes. We then investigate the dark energy model with a time-evolving w, and obtain the 68% C.L. constraints w0=-0.81±0.19 and wa=-1.9±1.1 from the Planck data and the “supernova legacy survey” compilation. Current data still slightly favor the quintom dark energy scenario with EOS across the cosmological constant boundary w≡-1.
A dynamical system analysis of holographic dark energy models with different IR cutoff
NASA Astrophysics Data System (ADS)
Mahata, Nilanjana; Chakraborty, Subenoy
2015-07-01
The paper deals with a dynamical system analysis of the cosmological evolution of an holographic dark energy (HDE) model interacting with dark matter (DM) which is chosen in the form of dust. The infrared cutoff of the holographic model is considered as future event horizon or Ricci length scale. The interaction term between dark energy (DE) and DM is chosen of following three types: (i) proportional to the sum of the energy densities of the two dark components, (ii) proportional to the product of the matter energy densities and (iii) proportional to DE density. The dynamical equations are reduced to an autonomous system for the three cases and corresponding phase space is analyzed.
Evolution of perturbations in distinct classes of canonical scalar field models of dark energy
Jassal, H. K.
2010-04-15
Dark energy must cluster in order to be consistent with the equivalence principle. The background evolution can be effectively modeled by either a scalar field or by a barotropic fluid. The fluid model can be used to emulate perturbations in a scalar field model of dark energy, though this model breaks down at large scales. In this paper we study evolution of dark energy perturbations in canonical scalar field models: the classes of thawing and freezing models. The dark energy equation of state evolves differently in these classes. In freezing models, the equation of state deviates from that of a cosmological constant at early times. For thawing models, the dark energy equation of state remains near that of the cosmological constant at early times and begins to deviate from it only at late times. Since the dark energy equation of state evolves differently in these classes, the dark energy perturbations too evolve differently. In freezing models, since the equation of state deviates from that of a cosmological constant at early times, there is a significant difference in evolution of matter perturbations from those in the cosmological constant model. In comparison, matter perturbations in thawing models differ from the cosmological constant only at late times. This difference provides an additional handle to distinguish between these classes of models and this difference should manifest itself in the integrated Sachs-Wolfe effect.
"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.
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 coincidence problem. At the same time, this model reproduces to high accuracy the distance measurements performed with the aid of the supernovae (SNe) Type Ia standard candles, and most naturally interprets, not only when, but also why the Universe transits from deceleration to acceleration, thus arising as a mighty contestant for a DE model.
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.
Clarifying spherical collapse in coupled dark energy cosmologies
Wintergerst, Nico; Pettorino, Valeria
2010-11-15
The spherical collapse model is often used to follow the evolution of overdensities into the nonlinear regime. We describe the correct approach to be used in coupled dark energy cosmologies, where a fifth force, different from gravity and mediated by the dark energy scalar field, influences the collapse. We reformulate the spherical collapse description by deriving it directly from the set of nonlinear hydrodynamical Navier-Stokes equations. By comparing with the corresponding relativistic equations, we show how the fifth force should be taken into account within the spherical collapse picture and clarify the problems arising when an inhomogeneous scalar field is considered within a spherical collapse picture. We then apply our method to the case of coupled quintessence, where the fifth force acts among cold dark matter particles, and to growing neutrino quintessence, where the fifth force acts between neutrinos. Furthermore, we review this method within standard cosmologies and apply our analysis to minimally coupled quintessence. We also check past results for early dark energy parametrizations.
Ghost Dark Energy with Non-Linear Interaction Term
NASA Astrophysics Data System (ADS)
Ebrahimi, E.
2016-01-01
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.
Reconstruction of generalized ghost pilgrim dark energy in gravity
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Rani, Shamaila
2015-09-01
In this paper, we study the reconstruction scenario of a dark energy model in the framework of modified Horava-Lifshitz gravity or gravity. We assume generalized ghost pilgrim dark energy model in flat universe. We consider three well-known scale factors to analyze the behavior of reconstructed model. These scale factors include bouncing and intermediate scale factors as well as scale factor representing the unification of matter and accelerated phases. The graphical representation is adopted to analyze the behavior of reconstructed model and equation of state parameter for different values of model parameter. The reconstructed model represents increasing and decreasing behavior with respect to time in all cases. The equation of state parameter represents phantom-like universe after transition for intermediate scale factor while quintessence behavior for bouncing and unified scale factors. We also found that the squared speed of sound exhibits the stability of all reconstructed models.
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.
Dark energy: Vacuum fluctuations, the effective phantom phase, and holography
Elizalde, E.; Nojiri, S.; Odintsov, S. D.; Wang Peng
2005-05-15
We aim at the construction of dark energy models without exotic matter but with a phantomlike equation of state (an effective phantom phase). The first model we consider is decaying vacuum cosmology where the fluctuations of the vacuum are taken into account. In this case, the phantom cosmology (with an effective, observational {omega} being less than -1 ) emerges even for the case of a real dark energy with a physical equation of state parameter {omega} larger than -1. The second proposal is a generalized holographic model, which is produced by the presence of an infrared cutoff. It also leads to an effective phantom phase, which is not a transient one as in the first model. However, we show that quantum effects are able to prevent its evolution towards a big rip singularity.
f (R ) gravity as a dark energy fluid
NASA Astrophysics Data System (ADS)
Battye, Richard A.; Bolliet, Boris; Pearson, Jonathan A.
2016-02-01
We study the equations for the evolution of cosmological perturbations in f (R ) and conclude that this modified gravity model can be expressed as a dark energy fluid at background and linearized perturbation order. By eliminating the extra scalar degree of freedom known to be present in such theories, we are able to characterize the evolution of the perturbations in the scalar sector in terms of equations of state for the entropy perturbation and anisotropic stress which are written in terms of the density and velocity perturbations of the dark energy fluid and those in the matter, or the metric perturbations. We also do the same in the much simpler vector and tensor sectors. In order to illustrate the simplicity of this formulation, we numerically evolve perturbations in a small number of cases.
Coupled dark energy with perturbed Hubble expansion rate
NASA Astrophysics Data System (ADS)
Yang, Weiqiang; Xu, Lixin
2014-10-01
The coupling between dark sectors provides a possible approach to mitigate the coincidence problem of the 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 proportional the Hubble parameter and energy density of dark energy, that is, Q =3 ?xH ? x . In particular, we consider the Hubble expansion rate to be perturbed in the perturbation evolutions of dark sectors. Using joint data sets which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and redshift-space distortions, we perform a full Markov chain Monte Carlo likelihood analysis for the coupled model. The results show that the mean value with errors of the interaction rate is ?x=0.0030 5-0.00305-0.00305 -0.00305 +0.000645 +0.00511 +0.00854 for QA??uc? and ?x=0.0031 7-0.00317-0.00317 -0.00317 +0.000628 +0.00547 +0.00929 for QA??ux?, which means that the recent cosmic observations favor a small interaction rate which is up to the order of 10-3. Moreover, in contrast to the coupled model with an unperturbed expansion rate, we find the perturbed Hubble expansion rate can bring about a negligible impact on the model parameter space.
Topics in microlensing and dark energy
NASA Astrophysics Data System (ADS)
Yashar, Mark
In this dissertation we describe two separate research projects. The first project involves the utilization and development of reddening models, color magnitude diagrams (CMDs), and microlensing population models of the Large Magellanic Cloud (LMC) to constrain the locations of micro-lensing source stars and micro-lensing objects in the Large Magellanic Cloud and the Milky Way (MW) halo using data of 13 microlensing source stars obtained by the MACHO (massive compact halo objects) collaboration with the Hubble Space Telescope. This analysis suggests that the source stars are located in the LMC disk and the lenses are located in the MW halo. For the second project, we report on the results of a Markov Chain Monte Carlo (MCMC) analysis of an inverse power law (IPL) quintessence model using the Dark Energy Task Force (DETF) simulated data models as a representation of future dark energy experiments. Simulated data sets were generated for a Lambda cold dark matter (L CDM ) background cosmology as well as a case where the dark energy is provided by a specific IPL fiducial model. The results are presented in the form of error contours generated by these two background cosmologies which are then used to consider the effects of future dark energy projects on IPL scalar field models and are able to demonstrate the power of DETF Stage 4 data sets in the context of the IPL model. We find that the respective increase in constraining power with higher quality data sets produced by our analysis gives results that are broadly consistent with the DETF results for the w 0 - w a parameterization of dark energy. Finally, using our simulated data sets constructed around a fiducial IPL model, we find that for a universe containing dark energy described by such a scalar field, a cosmological constant can be excluded by Stage 4 data at the 3s level.
Cosmological implications of dark energy model in DGP braneworld
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Salako, Ines G.
2015-10-01
This paper is devoted to study the cosmic acceleration in the presence of pilgrim dark energy with conformal age of the universe in the framework of DGP braneworld. We explore different cosmological parameters such as Hubble, equation of state and squared speed of sound parameters. Also, we develop the ω ϑ - ω' ϑ . We observe that these parameters as well as plane provide consistent results with the observational data.
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.
QCD Ghost Dark Energy in RS II Braneworld with Bulk-Brane Interaction
NASA Astrophysics Data System (ADS)
Yousefi, Leila; Sheykhi, Ahmad
2014-05-01
We investigate the QCD ghost model of dark energy in the framework of RS II braneworld. We assume there is an energy flow between the brane and bulk, and hence the continuity equation for the ghost dark energy is violated, while it is still preserved for the dark matter on the brane. We find that with the brane-bulk interaction, the equation of state parameter of ghost dark energy on the brane, can cross the phantom line w D =-1 at the present time, which confirms by some cosmological evidences. This result is in contrast to the standard cosmology where w D of ghost dark energy never cross the phantom line and the universe enters a de Sitter phase at the late time.
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.
2016-05-01
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 percent 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.
Emergent cosmology, inflation and dark energy
NASA Astrophysics Data System (ADS)
Guendelman, Eduardo; Herrera, Ramón; Labrana, Pedro; Nissimov, Emil; Pacheva, Svetlana
2015-02-01
A new class of gravity-matter models defined in terms of two independent non-Riemannian volume forms (alternative generally covariant integration measure densities) on the space-time manifold are studied in some detail. These models involve an additional (square of the scalar curvature) term as well as scalar matter field potentials of appropriate form so that the pertinent action is invariant under global Weyl-scale symmetry. Scale invariance is spontaneously broken upon integration of the equations of motion for the auxiliary volume-form degrees of freedom. After performing transition to the physical Einstein frame we obtain: (1) an effective potential for the scalar field with two flat regions which allows for a unified description of both early universe inflation as well as of present dark energy epoch; (2) for a definite parameter range the model possesses a non-singular "emergent universe" solution which describes an initial phase of evolution that precedes the inflationary phase; (3) for a reasonable choice of the parameters the present model conforms to the Planck Collaboration data.
Transient and late time attractor tachyon dark energy: Can we distinguish it from quintessence?
Ali, Amna; Sami, M.; Sen, A. A.
2009-06-15
The string inspired tachyon field can serve as a candidate of dark energy. Its equation of state parameter w varies from 0 to -1. In the case of tachyon field potential V({phi}){yields}0 slower (faster) than 1/{phi}{sup 2} at infinity, dark energy (dark matter) is a late time attractor. We investigate the tachyon dark energy models under the assumption that w is close to -1. We find that all the models exhibit unique behavior around the present epoch which is exactly the same as that of the thawing quintessence.
Testing coupled dark energy with large scale structure observation
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.
Testing coupled dark energy with large scale structure observation
NASA Astrophysics Data System (ADS)
Yang, Weiqiang; Xu, Lixin
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 bar Q=3Hξxbar rhox. 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 fσ8(z) data points from redshift-space distortion. The results show the interaction rate in σ regions: ξx = 0.00328-0.00328-0.00328-0.00328+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 10-2, meanwhile, the measurement of redshift-space distortion could rule out the large interaction rate in the σ region.
Gravity resonance spectroscopy constrains dark energy and dark matter scenarios.
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.). PMID:24785025
New Perspectives: Wave Mechanical Interpretations of Dark Matter, Baryon and Dark Energy
NASA Astrophysics Data System (ADS)
Russell, Esra
We model the cosmic components: dark matter, dark energy and baryon distributions in the Cosmic Web by means of highly nonlinear Schrodinger type and reaction diffusion type wave mechanical descriptions. The construction of these wave mechanical models of the structure formation is achieved by introducing the Fisher information measure and its comparison with highly nonlinear term which has dynamical analogy to infamous quantum potential in the wave equations. Strikingly, the comparison of this nonlinear term and the Fisher information measure provides a dynamical distinction between lack of self-organization and self-organization in the dynamical evolution of the cosmic components. Mathematically equivalent to the standard cosmic fluid equations, these approaches make it possible to follow the evolution of the matter distribution even into the highly nonlinear regime by circumventing singularities. Also, numerical realizations of the emerging web-like patterns are presented from the nonlinear dynamics of the baryon component while dark energy component shows Gaussian type dynamics corresponding to soliton-like solutions.
Singularity problem in teleparallel dark energy models
NASA Astrophysics Data System (ADS)
Geng, Chao-Qiang; Gu, Je-An; Lee, Chung-Chi
2013-07-01
We study future singularity in teleparallel dark energy models, particularly its behavior and its (non)occurrence in the observationally viable models. For the models with a general self-potential of the scalar field, we point out that both at early times and in the future near the singularity the behavior of dark energy can be described by the analytic solutions of the scalar field we obtained for the model with no self-potential. As to the (non)occurrence in the viable models, we consider a natural binding-type self-potential, the quadratic potential, when fitting observational data, and illustrate the constraining region up to the 3σ confidence level as well as the region where a singularity will occur. As a result, the singularity region is outside the 3σ constraint. Thus, although the future singularity problem potentially exists in teleparallel dark energy models, the observationally viable models may not suffer this problem.
Probing dark energy with lensing magnification in photometric surveys.
Schneider, Michael D
2014-02-14
I present an estimator for the angular cross correlation of two tracers of the cosmological large-scale structure that utilizes redshift information to isolate separate physical contributions. The estimator is derived by solving the Limber equation for a reweighting of the foreground tracer that nulls either clustering or lensing contributions to the cross correlation function. Applied to future photometric surveys, the estimator can enhance the measurement of gravitational lensing magnification effects to provide a competitive independent constraint on the dark energy equation of state. PMID:24580685
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.
Dark Energy: A Crisis for Fundamental Physics
Stubbs, Christopher [Harvard University, Cambridge, Massachusetts, USA
2010-09-01
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.
Spectroscopic needs for imaging dark energy experiments
NASA Astrophysics Data System (ADS)
Newman, Jeffrey A.; Abate, Alexandra; Abdalla, Filipe B.; Allam, Sahar; Allen, Steven W.; Ansari, Réza; 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 L.; Cheu, Elliott; Chisari, Nora Elisa; Colless, Matthew; Comparat, Johan; Coupon, Jean; Cunha, Carlos E.; de la Macorra, Axel; Dell'Antonio, Ian P.; Frye, Brenda L.; Gawiser, Eric J.; Gehrels, Neil; Grady, Kevin; Hagen, Alex; Hall, Patrick B.; Hearin, Andew P.; Hildebrandt, Hendrik; Hirata, Christopher M.; Ho, Shirley; Honscheid, Klaus; Huterer, Dragan; Ivezić, Željko; Kneib, Jean-Paul; Kruk, Jeffrey W.; Lahav, Ofer; Mandelbaum, Rachel; Marshall, Jennifer L.; Matthews, Daniel J.; Ménard, Brice; Miquel, Ramon; Moniez, Marc; Moos, H. W.; Moustakas, John; Myers, Adam D.; Papovich, Casey; Peacock, John A.; Park, Changbom; Rahman, Mubdi; Rhodes, Jason; Ricol, Jean-Stephane; Sadeh, Iftach; Slozar, Anže; Schmidt, Samuel J.; Stern, Daniel K.; Anthony Tyson, J.; von der Linden, Anja; Wechsler, Risa H.; Wood-Vasey, W. M.; Zentner, Andrew R.
2015-03-01
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.
Fermions, scalars and dark energy
McKellar, Bruce H. J.; Alsing, P.; Stephenson, G. J. Jr.; Goldman, T.
2010-07-27
We present a model in which neutral fermions, weakly interacting with light scalars, can lead to a regime in which the equation of state parameter is near (but above)-1 for a range of values of the red shift z. Our model is distinguished from many scalar field models which give a cosmic acceleration by requiring that the equation of state parameter approaches 0 as the density of our fermions approaches zero, and approaches the value for a relativistic gas in the early universe.
Dark Energy and The Dark Matter Relic Abundance
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.
Dark energy properties from large future galaxy surveys
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 finite temperature effects can be probed with 1σ precision for the first time.
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.
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.
Advanced Dark Energy Physics Telescope (ADEPT)
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 Digital Sky Survey (SDSS) data. A measurement of the BAO standard ruler as a function of time (or redshift) would provide powerful and reliable observational data to shed light on dark energy. In particular, the BAO data provide the angular diameter distance to each redshift, and directly give the expansion rate, H(z), at each redshift. The SNe measurements provide luminosity distances. A space mission is required to obtain the three-dimensional position of enormous numbers of galaxies at high redshift. As recognized by the Dark Energy Task Force, BAO systematic errors are naturally low. The following are the key findings: (1) The BAO method is robust. (2) Separation of the spectral and imaging detection focal planes vastly improves spectral identifications. (3) Prisms instead of grisms provide higher throughput and cleaner spectra. Prisms are clearly superior. (4) Lower prism dispersions improve signal-to-noise but high prism dispersions improve systematic. To ensure that the experiment is not systematic limited, a high dispersion should be used. (5) Counter-dispersion of the spectra reduces systematic errors on the redshift determination and assists in the reduction of confusion. (6) Small rolls are very effective for the reduction of confusion. (7) Interlopers can be recognized by a variety of methods, which combine to produce a sufficiently 'clean' survey data set so as not to limit the dark energy results. (8) A space mission can measure the BAO signature to the cosmic variance limit, limited only by statistics and not by systematic. (9) Density field reconstruction allows for significant BAO accuracy improvements, well beyond that assumed by the Dark Energy Task Force. (10) The BAO method is statistically powerful. It is more powerful than previously estimated, and far more powerful than high redshift Type 1a supernovae, for which the ultimate distance accuracy is limited by flux calibration accuracy. (11) The BAO technique is far simpler than the weak lensing technique and likely to produce more robust dark energy solutions.
Stringy Model of Cosmological Dark Energy
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.
Stringy Model of Cosmological Dark Energy
NASA Astrophysics Data System (ADS)
Aref'eva, Irina Ya.
2007-11-01
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.
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.
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.
The Dark Energy Spectroscopic Instrument (DESI)
NASA Astrophysics Data System (ADS)
Flaugher, Brenna; Bebek, Chris
2014-07-01
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-field (3.2 deg. linear field of view) corrector plus a multi-object spectrometer with up to 5000 robotically positioned optical fibers and will be installed at prime focus on the Mayall 4m telescope at Kitt Peak, Arizona. The fibers 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).
Correspondence Between Einstein-Aether Gravity and Scalar Field Dark Energies
NASA Astrophysics Data System (ADS)
Debnath, Ujjal
2015-07-01
Here we briefly discuss the Einstein-Aether gravity theory by modification of Einstein-Hilbert action. We find the modified Friedmann equations and then we find the effective energy density and pressure for Einstein-Aether gravity sector. These can be treated as dark energy provided some restrictions on the free function F( K), where K is proportional to H 2. Subsequently, we study the correspondence between the effective dark energy coming from Einstein-Aether gravity with other dark energies like k-essence, tachyon, dilaton, hessence and DBI-essence dark energy and construct the scalar field and corresponding scalar potentials which describe the dynamics of the scalar fields graphically. So finally, if the Einstein-Aether gravity behaves like other dark energy models, in this situation, the scalar field increases and potential decreases.
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 development to slow down." Vikhlinin and his colleagues used Chandra to observe the hot gas in dozens of galaxy clusters, which are the largest collapsed objects in the universe. Some of these clusters are relatively close and others are more than halfway across the universe. The results show the increase in mass of the galaxy clusters over time aligns with a universe dominated by dark energy. It is more difficult for objects like galaxy clusters to grow when space is stretched, as caused by dark energy. Vikhlinin and his team see this effect clearly in their data. The results are remarkably consistent with those from the distance measurements, revealing general relativity applies, as expected, on large scales. "For years, scientists have wanted to start testing how gravity works on large scales and now, we finally have," said William Forman, a co-author of the study from the Smithsonian Astrophysical Observatory. "This is a test that general relativity could have failed." When combined with other clues -- supernovas, the study of the cosmic microwave background, and the distribution of galaxies -- this new X-ray result gives scientists the best insight to date on the properties of dark energy. The study strengthens the evidence that dark energy is the cosmological constant. Although it is the leading candidate to explain dark energy, theoretical work suggests it should be about 10 raised to the power of 120 times larger than observed. Therefore, alternatives to general relativity, such as theories involving hidden dimensions, are being explored. "Putting all of this data together gives us the strongest evidence yet that dark energy is the cosmological constant, or in other words, that 'nothing weighs something'," said Vikhlinin. "A lot more testing is needed, but so far Einstein's theory is looking as good as ever." These results have consequences for predicting the ultimate fate of the universe. If dark energy is explained by the cosmological constant, the expansion of the universe will continue to accelerate, and the Milky Way and its neighbor galaxy, Andromeda, never will merge with the Virgo cluster. In that case, about a hundred billion years from now, all other galaxies ultimately would disappear from the Milky Way's view and, eventually, the local superclusters of galaxies also would disintegrate. The work by Vikhlinin and his colleagues will be published in two separate papers in the Feb. 10 issue of The Astrophysical Journal. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.
Constraints on the coupling between dark energy and dark matter from CMB data
NASA Astrophysics Data System (ADS)
Murgia, R.; Gariazzo, S.; Fornengo, N.
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 H0 and σ8, already present for standard cosmology, increases: this model in fact predicts lower H0 and higher σ8, 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 H0 and σ8 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.
NASA Astrophysics Data System (ADS)
Dymnikova, Irina
2016-01-01
The Petrov classification of stress-energy tensors provides a model-independent definition of a vacuum by the algebraic structure of its stress-energy tensor and implies the existence of vacua whose symmetry is reduced as compared with the maximally symmetric de Sitter vacuum associated with the Einstein cosmological term. This allows to describe a vacuum in general setting by dynamical vacuum dark fluid, presented by a variable cosmological term with the reduced symmetry which makes vacuum dark fluid essentially anisotropic and allows it to be evolving and clustering. The relevant regular solutions to the Einstein equations describe regular cosmological models with time-evolving and spatially inhomogeneous vacuum dark energy, and compact vacuum objects generically related to a dark energy through the de Sitter vacuum interior: regular black holes, their remnants and self-gravitating vacuum solitons — which can be responsible for observational effects typically related to a dark matter. The mass of objects with de Sitter interior is generically related to vacuum dark energy and to breaking of space-time symmetry.
Observational constraints on dark energy and cosmic curvature
Wang Yun; Mukherjee, Pia
2007-11-15
Current observational bounds on dark energy depend on our assumptions about the curvature of the universe. We present a simple and efficient method for incorporating constraints from cosmic microwave background (CMB) anisotropy data and use it to derive constraints on cosmic curvature and dark energy density as a free function of cosmic time using current CMB, Type Ia supernova (SN Ia), and baryon acoustic oscillation data. We show that there are two CMB shift parameters, R{identical_to}{radical}({omega}{sub m}H{sub 0}{sup 2})r(z{sub CMB}) (the scaled distance to recombination) and l{sub a}{identical_to}{pi}r(z{sub CMB})/r{sub s}(z{sub CMB}) (the angular scale of the sound horizon at recombination), with measured values that are nearly uncorrelated with each other. Allowing nonzero cosmic curvature, the three-year WMAP (Wilkinson Microwave Anisotropy Probe) data give R=1.71{+-}0.03, l{sub a}=302.5{+-}1.2, and {omega}{sub b}h{sup 2}=0.02173{+-}0.00082, independent of the dark energy model. The corresponding bounds for a flat universe are R=1.70{+-}0.03, l{sub a}=302.2{+-}1.2, and {omega}{sub b}h{sup 2}=0.022{+-}0.00082. We give the covariance matrix of (R,l{sub a},{omega}{sub b}h{sup 2}) from the three-year WMAP data. We find that (R,l{sub a},{omega}{sub b}h{sup 2}) provide an efficient and intuitive summary of CMB data as far as dark energy constraints are concerned. Assuming the Hubble Space Telescope (HST) prior of H{sub 0}=72{+-}8 (km/s) Mpc{sup -1}, using 182 SNe Ia (from the HST/GOODS program, the first year Supernova Legacy Survey, and nearby SN Ia surveys), (R,l{sub a},{omega}{sub b}h{sup 2}) from WMAP three-year data, and SDSS (Sloan Digital Sky Survey) measurement of the baryon acoustic oscillation scale, we find that dark energy density is consistent with a constant in cosmic time, with marginal deviations from a cosmological constant that may reflect current systematic uncertainties or true evolution in dark energy. A flat universe is allowed by current data: {omega}{sub k}=-0.006{sub -0.012-0.025}{sup +0.013+0.025} for assuming that the dark energy equation of state w{sub X}(z) is constant, and {omega}{sub k}=-0.002{sub -0.018-0.032}{sup +0.018+0.041} for w{sub X}(z)=w{sub 0}+w{sub a}(1-a) (68% and 95% confidence levels). The bounds on cosmic curvature are less stringent if dark energy density is allowed to be a free function of cosmic time, and are also dependent on the assumption about the early time property of dark energy. We demonstrate this by studying two examples. Significant improvement in dark energy and cosmic curvature constraints is expected as a result of future dark energy and CMB experiments.
Entanglement in holographic dark energy models
NASA Astrophysics Data System (ADS)
Horvat, R.
2010-10-01
We study a process of equilibration of holographic dark energy (HDE) with the cosmic horizon around the dark-energy dominated epoch. This process is characterized by a huge amount of information conveyed across the horizon, filling thereby a large gap in entropy between the system on the brink of experiencing a sudden collapse to a black hole and the black hole itself. At the same time, even in the absence of interaction between dark matter and dark energy, such a process marks a strong jump in the entanglement entropy, measuring the quantum-mechanical correlations between the horizon and its interior. Although the effective quantum field theory (QFT) with a peculiar relationship between the UV and IR cutoffs, a framework underlying all HDE models, may formally account for such a huge shift in the number of distinct quantum states, we show that the scope of such a framework becomes tremendously restricted, devoid virtually any application in other cosmological epochs or particle-physics phenomena. The problem of negative entropies for the non-phantom stuff is also discussed.
The Dark Energy Survey Data Management System and its Applications
NASA Astrophysics Data System (ADS)
Desai, Shantanu; Mohr, J.; Armstrong, R.; Bertin, E.; Cai, D.; Darnell, T.; Daues, G.; Gower, M.; Hadji, L.; Kotwani, K.; Lin, H.; Myers, J.; Neilsen, E.; Ngeow, C.; Tucker, D.; Zenteno, A.; Adams, D.; Beldica, C.; Freemon, M.; Bazin, G.; Song, J.
2010-01-01
The Dark Energy Survey (DES) collaboration will map out the dark energy equation of state by doing a 5000 degree griZY survey with the Blanco 4 meter telescope, which begins in 2011. The DES data management (DESDM) system will be used to analyze and archive this data and the various science products whose total volume will exceed 1 PB. DESDM consists of several components : astronomy codes to process the data, processing framework to perform automated and high performance data parallel processing, catalog database to support various science analysis, and web portals to monitor data processing and downloading of data. DESDM has been used to be process simulated DES data since 2005 as well as real data from Blanco Cosmology Survey (BCS), which is a 45 night NOAO survey program on the Blanco 4m telescope. We describe various components of the DESDM and present some preliminary photometry and astrometry results obtained by using this system.
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.
Quantum gravity and the holographic dark energy cosmology
NASA Astrophysics Data System (ADS)
Nastase, Horatiu
2016-04-01
The holographic dark energy model is obtained from a cosmological constant generated by generic quantum gravity effects giving a minimum length. By contrast, the usual bound for the energy density to be limited by the formation of a black hole simply gives the Friedmann equation. The scale of the current cosmological constant relative to the inflationary scale is an arbitrary parameter characterizing initial conditions, which however can be fixed by introducing a physical principle during inflation, as a function of the number of e-folds and the inflationary scale.
Analysis of Generalized Ghost Dark Energy in LQC and Galileon Gravity
NASA Astrophysics Data System (ADS)
Mahasweta, Biswas; Ujjal, Debnath
2016-01-01
A so-called ghost dark energy was recently proposed to explain the present acceleration of the universe. The energy density of ghost dark energy, which originates from Veneziano ghost of Quantum Chromodynamics (QCD), in a time dependent background, can be written in the form, ρD = (αH + βH2) where H is the Hubble parameter. We investigate the generalized ghost dark energy (GGDE) model in the setup of loop quantum Cosmology (LQC) and Galileon Cosmology. We study the cosmological implications of the models. We also obtain the equation of state and the deceleration parameters and differential equations governing the evolution of this dark energy model for LQC and Galileon Cosmology.
A geometric measure of dark energy with pairs of galaxies.
Marinoni, Christian; Buzzi, Adeline
2010-11-25
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 (Ω(X)) and equation of state (W(X)) 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 Ω(k)≡0 and the dark energy equation-of-state parameter at W(X)≡-1, and using the results of baryon acoustic oscillations, we can establish at the 68.3% confidence level that and -0.85>W(X)>-1.12 and 0.60<Ω(X)<0.80. PMID:21107424
Evolution of spherical overdensities in holographic dark energy models
NASA Astrophysics Data System (ADS)
Naderi, Tayebe; Malekjani, Mohammad; Pace, Francesco
2015-02-01
In this work, we investigate the spherical collapse model in flat Friedmann-Robertson-Walker (FRW) dark energy universes. We consider the holographic dark energy (HDE) model as a dynamical dark energy scenario with a slowly time-varying equation-of-state parameter wde in order to evaluate the effects of the dark energy component on structure formation in the universe. We first calculate the evolution of density perturbations in the linear regime for both phantom and quintessence behaviour of the HDE model and compare the results with standard Einstein-de Sitter and Λ cold dark matter (ΛCDM) models. We then calculate the evolution of two characterizing parameters in the spherical collapse model, i.e. the linear density threshold δc and the virial overdensity parameter Δvir. We show that in HDE cosmologies the growth factor g(a) and the linear overdensity parameter δc fall behind the values for a ΛCDM universe while the virial overdensity Δvir is larger in HDE models than in the ΛCDM model. We also show that the ratio between the radius of the spherical perturbations at the virialization and turn-around time is smaller in HDE cosmologies than that predicted in a ΛCDM universe. Hence, the growth of structures starts earlier in HDE models than in ΛCDM cosmologies and more concentrated objects can form in this case. It has been shown that the non-vanishing surface pressure leads to smaller virial radius and larger virial overdensity Δvir. We compare the predicted number of haloes in HDE cosmologies and find out that in general this value is smaller than for ΛCDM models at higher redshifts and we compare different mass function prescriptions. Finally, we compare the results of the HDE models with observations.
Probing the Dark Energy by the Solar-system experiments
NASA Astrophysics Data System (ADS)
Dumin, Yu. V.
According to the recent astronomical data the most part of energy density in the Universe 73 is in the dark form which is effectively described by Lambda -term in the Einstein equations All arguments in favor of the Dark Energy were obtained so far from the observational data related to very large intergalactic scales The aim of the present report is to show that Lambda -dominated cosmology can be efficiently tested via the Solar-system experiments seeking for the effect of local Hubble expansion if the Dark Energy really exists it should increase the mean Earth--Moon distance by 2 div 3 cm per year which is comparable with the effect of geophysical tides and well measurable by the lunar laser ranging 1 After exclusion of the tidal effects the local Hubble constant was found to be H 0loc 56 pm 8 km s Mpc Assuming that rate of the Hubble expansion is determined at local scales only by the perfectly-uniform Dark Energy while at the global scales it involves also a contribution from the irregularly-distributed cold Dark Matter it can be shown that the total Hubble constant should be H 0 59 pm 8 km s Mpc 2 which is in agreement with the commonly-accepted WMAP value 71 pm 4 km s Mpc on the edge of the confidence intervals Moreover our result is in excellent agreement with the recent data on SN Ia distribution which gave the value of Hubble constant about 60 km s Mpc 3 i e a bit less than WMAP The above general coincidence shows that high-precision measurements
Symmetron dark energy in laboratory experiments.
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. PMID:23373910
Cosmological dynamics of tachyonic teleparallel dark energy
NASA Astrophysics Data System (ADS)
Otalora, G.
2013-09-01
A detailed dynamical analysis of the tachyonic teleparallel dark energy model, in which a noncanonical scalar field (tachyon field) is nonminimally coupled to gravitation, is performed. It is found that, when the nonminimal coupling is ruled by a dynamically changing coefficient α≡f,ϕ/f, with f(ϕ) an arbitrary function of the scalar field ϕ, the Universe may experience a field-matter-dominated era “ϕMDE,” in which it has some portions of the energy density of ϕ in the matter dominated era. This is the most significant difference in relation to the so-called teleparallel dark energy scenario, in which a canonical scalar field (quintessence) is nonminimally coupled to gravitation.
Inflationary and dark energy regimes in 2+1 dimensions
NASA Astrophysics Data System (ADS)
Christmann, M. H.; Devecchi, F. P.; Kremer, G. M.; Zanetti, C. M.
2006-02-01
In this work we investigate the behavior of three-dimensional (3D) cosmological models. The simulation of inflationary and dark-energy-dominated eras are among the possible results in these 3D formulations; taking as starting point the results obtained by Cornish and Frankel. Motivated by those results, we investigate, first, the inflationary case where we consider a two-constituent cosmological fluid: the scalar field represents the hypothetical inflaton which is in gravitational interaction with a matter/radiation contribution. For the description of an old universe, it is possible to simulate its evolution starting with a matter dominated universe that faces a decelerated/accelerated transition due to the presence of the additional constituent (simulated by the scalar field or ruled by an exotic equation of state) that plays the role of dark energy. We obtain, through numerical analysis, the evolution in time of the scale factor, the acceleration, the energy densities, and the hydrostatic pressure of the constituents. The alternative scalar cosmology proposed by Cornish and Frankel is also under investigation in this work. In this case an inflationary model can be constructed when another non-polytropic equation of state (the van der Waals equation) is used to simulate the behavior of an early 3D universe.
Dark Energy and Type Ia Supernovae: Present and Future
NASA Astrophysics Data System (ADS)
Phillips, Mark
2005-04-01
Since the pioneering work of Baade and Zwicky in the 1930s, astronomers have been aware of the possibility of using Type Ia supernovae to probe the expansion of the universe. However, only in the last 15 years has this potential been fully realized. After briefly recounting the discovery and calibration of the peak luminosity vs. decline rate relation for Type Ia supernovae which has allowed distance measurements to host galaxies to be made with a precision of 10% or better, I review recent results from high-redshift observations which confirm that the universe is currently being accelerated by a mysterious dark energy which comprises approximately 70% of the present energy density of the universe. Current research is focussed on measuring the equation of state parameter `w' of the dark energy to determine if it is consistent with a cosmological constant (w = -1). This effort is reviewed, along with the observational problems which must be overcome to achieve this objective. Finally, the potential of future ground- and space-based programs for probing the nature of the dark energy is discussed.
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 time-variable source gives the angular diameter distance through measured time delays of multiple images. Finally, the growth of structure can also be constrained by measuring the mass of the largest galaxy clusters over cosmic time. HST has contributed to the study of dark energy through SN1a and gravitational lensing, as discussed above. HST has also helped to characterize galaxy clusters and the HST-measured constraints on the current Hubble constant H(sub 0) are relevant to the interpretation of dark energy measurements (Riess et al 2009a). HST has not been used to constrain BAO as the large number of galaxy redshifts required, of order 100 million, is poorly matched to HST's capabilities. As the successor to HST, the James Webb Space Telescope (JWST; Gardner et al 2006) will continue and extend HST's dark energy work in several ways.
New cosmographic constraints on the dark energy and dark matter coupling
NASA Astrophysics Data System (ADS)
Bolotin, Yu. L.; Cherkaskiy, V. A.; Lemets, O. A.
2016-03-01
We propose a novel approach to obtain limitations on the dark energy (DE) and dark matter (DM) coupling. The suggested approach allows us to express the coupling constant in terms of the cosmographic parameters (CPs). It enables us to find constraints on the coupling constant directly based on observational data and to restrict number of numerous models describing interaction in the dark sector.
Cosmological evolution of generalized ghost pilgrim dark energy in f(T) gravity
NASA Astrophysics Data System (ADS)
Sharif, M.; Nazir, Kanwal
2015-12-01
We explore the phenomenon that phantom-like dark energy prevents the formation of black holes by assuming the generalized ghost version of pilgrim dark energy in the background of generalized teleparallel gravity. In this scenario, we construct f(T) model for explaining the evolutionary behavior of equation of state parameter, ω_{\\varLambda}-ω'_{\\varLambda} and r-s planes. We discuss these cosmological parameters graphically by taking different values of redshift parameter and pilgrim dark energy parameter. It is found that the equation of state parameter shows phantom like behavior while ω_{\\varLambda}-ω'_{\\varLambda} plane possesses thawing region for some particular values of pilgrim dark energy parameter. The statefinder parameters in r-s plane indicate the behavior of quintessence and phantom models. Finally, we discuss the first and second laws of thermodynamics and investigate the behavior of entropy production term.
Constraining competing models of dark energy with cosmological observations
NASA Astrophysics Data System (ADS)
Pavlov, Anatoly
The last decade of the 20th century was marked by the discovery of the accelerated expansion of the universe. This discovery puzzles physicists and has yet to be fully understood. It contradicts the conventional theory of gravity, i.e. Einstein's General Relativity (GR). According to GR, a universe filled with dark matter and ordinary matter, i.e. baryons, leptons, and photons, can only expand with deceleration. Two approaches have been developed to study this phenomenon. One attempt is to assume that GR might not be the correct description of gravity, hence a modified theory of gravity has to be developed to account for the observed acceleration of the universe's expansion. This approach is known as the "Modified Gravity Theory". The other way is to assume that the energy budget of the universe has one more component which causes expansion of space with acceleration on large scales. Dark Energy (DE) was introduced as a hypothetical type of energy homogeneously filling the entire universe and very weakly or not at all interacting with ordinary and dark matter. Observational data suggest that if DE is assumed then its contribution to the energy budget of the universe at the current epoch should be about 70% of the total energy density of the universe. In the standard cosmological model a DE term is introduced into the Einstein GR equations through the cosmological constant, a constant in time and space, and proportional to the metric tensor gmunu. While this model so far fits most available observational data, it has some significant conceptual shortcomings. Hence there are a number of alternative cosmological models of DE in which the dark energy density is allowed to vary in time and space.
Coupled dark energy: a dynamical analysis with complex scalar field
NASA Astrophysics Data System (ADS)
Landim, Ricardo C. G.
2016-01-01
The dynamical analysis for coupled dark energy with dark matter is presented, where a complex scalar field is taken into account and it is considered in the presence of a barothropic fluid. We consider three dark-energy candidates: quintessence, phantom, and tachyon. The critical points are found and their stabilities analyzed, leading to the three cosmological eras (radiation, matter, and dark energy), for a generic potential. The results presented here extend the previous analyses found in the literature.
Atom-interferometry constraints on dark energy
NASA Astrophysics Data System (ADS)
Hamilton, P.; Jaffe, M.; Haslinger, P.; Simmons, Q.; Mller, H.; Khoury, J.
2015-08-01
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.
Dark energy from the string axiverse.
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. PMID:25554872
The WiggleZ Dark Energy Survey
NASA Astrophysics Data System (ADS)
Blake, Chris; Brough, Sarah; Couch, Warrick; Glazebrook, Karl; Poole, Greg; Davis, Tamara; Drinkwater, Michael; Jurek, Russell; Pimbblet, Kevin; Colless, Matthew; Sharp, Rob; Croom, Scott; Pracy, Michael; Woods, David; Madore, Barry; Martin, Chris; Wyder, Ted
2008-10-01
The accelerating expansion of the universe, attributed to ``dark energy'', has no accepted theoretical explanation. The origin of this phenomenon unambiguously implicates new physics via a novel form of matter exerting negative pressure or an alteration to Einstein's general relativity. These profound consequences have inspired a new generation of cosmological surveys that will measure the influence of dark energy using various techniques. One of the forerunners is the WiggleZ Survey at the Anglo-Australian Telescope, a new large-scale high-redshift galaxy survey that is now 50% complete and scheduled to finish in 2010. The WiggleZ project is aiming to map the cosmic expansion history using delicate features in the galaxy clustering pattern imprinted 13.7 billion years ago. In this article we outline the survey design and context, and predict the science highlights. Chris Blake and the WiggleZ team highlight the design and targets of this innovative survey.
Dark energy simulacrum in nonlinear electrodynamics
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.
Ten scenarios from early radiation to late time acceleration with a minimally coupled dark energy
Fay, Stéphane
2013-09-01
We consider General Relativity with matter, radiation and a minimally coupled dark energy defined by an equation of state w. Using dynamical system method, we find the equilibrium points of such a theory assuming an expanding Universe and a positive dark energy density. Two of these points correspond to classical radiation and matter dominated epochs for the Universe. For the other points, dark energy mimics matter, radiation or accelerates Universe expansion. We then look for possible sequences of epochs describing a Universe starting with some radiation dominated epoch(s) (mimicked or not by dark energy), then matter dominated epoch(s) (mimicked or not by dark energy) and ending with an accelerated expansion. We find ten sequences able to follow this Universe history without singular behaviour of w at some saddle points. Most of them are new in dark energy literature. To get more than these ten sequences, w has to be singular at some specific saddle equilibrium points. This is an unusual mathematical property of the equation of state in dark energy literature, whose physical consequences tend to be discarded by observations. This thus distinguishes the ten above sequences from an infinity of ways to describe Universe expansion.
Detecting dark energy with wavelets on the sphere
NASA Astrophysics Data System (ADS)
McEwen, Jason D.
2007-09-01
Dark energy dominates the energy density of our Universe, yet we know very little about its nature and origin. Although strong evidence in support of dark energy is provided by the cosmic microwave background, the relic radiation of the Big Bang, in conjunction with either observations of supernovae or of the large scale structure of the Universe, the verification of dark energy by independent physical phenomena is of considerable interest. We review works that, through a wavelet analysis on the sphere, independently verify the existence of dark energy by detecting the integrated Sachs-Wolfe effect. The effectiveness of a wavelet analysis on the sphere is demonstrated by the highly statistically significant detections of dark energy that are made. Moreover, the detection is used to constrain properties of dark energy. A coherent picture of dark energy is obtained, adding further support to the now well established cosmological concordance model that describes our Universe.
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.
Planck Oscillators in the Background Dark Energy
NASA Astrophysics Data System (ADS)
Sidharth, B. G.
2010-10-01
We consider a model for an underpinning of the universe: there are oscillators at the Planck scale in the background dark energy. Starting from a coherent array of such oscillators it is possible to get a description from elementary particles to Black Holes including the usual Hawking-Beckenstein theory. There is also a description of Gravitation in the above model which points to a unified description with electromagnetism.
Electromagnetic dark energy and gravitoelectrodynamics of superconductors
NASA Astrophysics Data System (ADS)
de Matos, Clovis Jacinto
2008-02-01
It is shown that Beck and Mackey electromagnetic model of dark energy in superconductors can account for the non-classical inertial properties of superconductors, which have been conjectured by the author to explain the Cooper pair’s mass excess reported by Cabrera and Tate. A new fundamental scale of nature (the Planck-Einstein scale) for gravitation in low temperature condensed matter is proposed to host the gravitoelectrodynamic properties of superconductors.
A scalar field dark energy model: Noether symmetry approach
NASA Astrophysics Data System (ADS)
Dutta, Sourav; Panja, Madan Mohan; Chakraborty, Subenoy
2016-04-01
Scalar field dark energy cosmology has been investigated in the present paper in the frame work of Einstein gravity. In the context of Friedmann-Lemaitre-Robertson-Walker space time minimally coupled scalar field with self interacting potential and non-interacting perfect fluid with barotropic equation of state (dark matter) is chosen as the matter context. By imposing Noether symmetry on the Lagrangian of the system the symmetry vector is obtained and the self interacting potential for the scalar field is determined. Then we choose a point transformation (a, φ )→ (u, v) such that one of the transformation variable (say u) is cyclic for the Lagrangian. Subsequently, using conserved charge (corresponding to the cyclic co-ordinate) and the constant of motion, solutions are obtained. Finally, the cosmological implication of the solutions in the perspective of recent observation has been examined.
The continuous tower of scalar fields as a system of interacting dark matter-dark energy
NASA Astrophysics Data System (ADS)
Santos, Paulo
2015-10-01
This paper aims to introduce a new parameterisation for the coupling Q in interacting dark matter and dark energy models by connecting said models with the Continuous Tower of Scalar Fields model. Based upon the existence of a dark matter and a dark energy sectors in the Continuous Tower of Scalar Fields, a simplification is considered for the evolution of a single scalar field from the tower, validated in this paper. This allows for the results obtained with the Continuous Tower of Scalar Fields model to match those of an interacting dark matter-dark energy system, considering that the energy transferred from one fluid to the other is given by the energy of the scalar fields that start oscillating at a given time, rather than considering that the energy transference depends on properties of the whole fluids that are interacting.
NASA Astrophysics Data System (ADS)
Ghosh, Rahul; Chattopadhyay, Surajit; Debnath, Ujjal
2012-02-01
This work is motivated by the work of Kim et al. (Mod. Phys. Lett. A 23:3049, 2008), which considered the equation of state parameter for the new agegraphic dark energy based on generalized uncertainty principle coexisting with dark matter without interaction. In this work, we have considered the same dark energy interacting with dark matter in emergent, intermediate and logamediate scenarios of the universe. Also, we have investigated the statefinder, kerk and lerk parameters in all three scenarios under this interaction. The energy density and pressure for the new agegraphic dark energy based on generalized uncertainty principle have been calculated and their behaviors have been investigated. The evolution of the equation of state parameter has been analyzed in the interacting and non-interacting situations in all the three scenarios. The graphical analysis shows that the dark energy behaves like quintessence era for logamediate expansion and phantom era for emergent and intermediate expansions of the universe.
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.
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.
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.
General Astrophysics with TPF: Not Just Dark Energy
NASA Technical Reports Server (NTRS)
Kuchner, Marc
2006-01-01
Besides searching for Earth-LIke Planets, TPF can study Jupiters, Neptunes, and all sorts of exotic planets. It can image debris-disks, YSO disks, AGN disks, maybe even AGB disks. And you are probably aware that a large optical space telescope like TPF-C or TPF-O can be a fantastic tool for studying the equation of state of the Dark Energy. I will review some of the future science of TPF-C, TPF-I and TPF-O, focusing on the applications of TPF to the study of objects in our Galaxy: especially circumstellar disks and planets other than exo-Earths.
Perturbed dark energy: Classical scalar field versus tachyon
Sergijenko, Olga; Novosyadlyj, Bohdan
2009-10-15
The evolution of scalar linear perturbations is studied in gauge-invariant approach for 2-component models with nonrelativistic matter and minimally coupled scalar fields, the potentials of which were constructed for either constant dark energy equation of state parameter w or its adiabatic sound speed c{sub a}{sup 2} equal to zero. The numerical solutions show that such fields are almost smoothed out on subhorizon scales. However, they cause the scale dependent suppression of the nonrelativistic matter density perturbations and the decay of gravitational potential, which can be used for choice of the dark energy model. We discuss two types of the Lagrangian: classical and tachyonic ones. As our results show, the fields with w=const are almost indistinguishable, while for fields with c{sub a}{sup 2}=0 the difference of dark energy effective sound speeds c{sub s}{sup 2}, which is caused by the shape of Lagrangian, affects the evolution of perturbations significantly. We present also the transfer functions for both components.
Effective field theory of dark energy: a dynamical analysis
NASA Astrophysics Data System (ADS)
Frusciante, Noemi; Raveri, Marco; Silvestri, Alessandra
2014-02-01
The effective field theory (EFT) of dark energy relies on three functions of time to describe the dynamics of background cosmology. The viability of these functions is investigated here by means of a thorough dynamical analysis. While the system is underdetermined, and one can always find a set of functions reproducing any expansion history, we are able to determine general compatibility conditions for these functions by requiring a viable background cosmology. In particular, we identify a set of variables that allows us to transform the non-autonomous system of equations into an infinite-dimensional one characterized by a significant recursive structure. We then analyze several autonomous sub-systems, obtained truncating the original one at increasingly higher dimension, that correspond to increasingly general models of dark energy and modified gravity. Furthermore, we exploit the recursive nature of the system to draw some general conclusions on the different cosmologies that can be recovered within the EFT formalism and the corresponding compatibility requirements for the EFT functions. The machinery that we set up serves different purposes. It offers a general scheme for performing dynamical analysis of dark energy and modified gravity models within the model independent framework of EFT; the general results, obtained with this technique, can be projected into specific models, as we show in one example. It also can be used to determine appropriate anstze for the three EFT background functions when studying the dynamics of cosmological perturbations in the context of large scale structure tests of gravity.
Effective field theory of dark energy: a dynamical analysis
Frusciante, Noemi; Raveri, Marco; Silvestri, Alessandra E-mail: mraveri@sissa.it
2014-02-01
The effective field theory (EFT) of dark energy relies on three functions of time to describe the dynamics of background cosmology. The viability of these functions is investigated here by means of a thorough dynamical analysis. While the system is underdetermined, and one can always find a set of functions reproducing any expansion history, we are able to determine general compatibility conditions for these functions by requiring a viable background cosmology. In particular, we identify a set of variables that allows us to transform the non-autonomous system of equations into an infinite-dimensional one characterized by a significant recursive structure. We then analyze several autonomous sub-systems, obtained truncating the original one at increasingly higher dimension, that correspond to increasingly general models of dark energy and modified gravity. Furthermore, we exploit the recursive nature of the system to draw some general conclusions on the different cosmologies that can be recovered within the EFT formalism and the corresponding compatibility requirements for the EFT functions. The machinery that we set up serves different purposes. It offers a general scheme for performing dynamical analysis of dark energy and modified gravity models within the model independent framework of EFT; the general results, obtained with this technique, can be projected into specific models, as we show in one example. It also can be used to determine appropriate ansätze for the three EFT background functions when studying the dynamics of cosmological perturbations in the context of large scale structure tests of gravity.
Present and future evidence for evolving dark energy
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.
DARK FLUID: A UNIFIED FRAMEWORK FOR MODIFIED NEWTONIAN DYNAMICS, DARK MATTER, AND DARK ENERGY
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.
NASA Astrophysics Data System (ADS)
2008-01-01
Using ESO's Very Large Telescope Interferometer, astronomers have probed the inner parts of the disc of material surrounding a young stellar object, witnessing how it gains its mass before becoming an adult. ESO PR Photo 03/08 ESO PR Photo 03a/08 The disc around MWC 147 (Artist's Impression) The astronomers had a close look at the object known as MWC 147, lying about 2,600 light years away towards the constellation of Monoceros ('the Unicorn'). MWC 147 belongs to the family of Herbig Ae/Be objects. These have a few times the mass of our Sun and are still forming, increasing in mass by swallowing material present in a surrounding disc. MWC 147 is less than half a million years old. If one associated the middle-aged, 4.6 billion year old Sun with a person in his early forties, MWC 147 would be a 1-day-old baby [1]. The morphology of the inner environment of these young stars is however a matter of debate and knowledge of it is important to better understand how stars and their cortège of planets form. The astronomers Stefan Kraus, Thomas Preibisch, and Keiichi Ohnaka have used the four 8.2-m Unit Telescopes of ESO's Very Large Telescope to this purpose, combining the light from two or three telescopes with the MIDI and AMBER instruments. "With our VLTI/MIDI and VLTI/AMBER observations of MWC147, we combine, for the first time, near- and mid-infrared interferometric observations of a Herbig Ae/Be star, providing a measurement of the disc size over a wide wavelength range [2]," said Stefan Kraus, lead-author of the paper reporting the results. "Different wavelength regimes trace different temperatures, allowing us to probe the disc's geometry on the smaller scale, but also to constrain how the temperature changes with the distance from the star." The near-infrared observations probe hot material with temperatures of up to a few thousand degrees in the innermost disc regions, while the mid-infrared observations trace cooler dust further out in the disc. The 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").
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.
Interacting vacuum energy in the dark sector
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.
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.
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.
Growth of cosmic structure: Probing dark energy beyond expansion
NASA Astrophysics Data System (ADS)
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, Ane; 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. One way to explain the acceleration of the Universe is invoke dark energy parameterized by an equation of state w. Distance measurements provide one set of constraints on w, but dark energy also affects how rapidly structure grows; the greater the acceleration, the more suppressed the growth of structure. Upcoming surveys are therefore designed to probe w with direct observations of the distance scale and the growth of structure, each complementing the other on systematic errors and constraints on dark energy. A consistent set of results will greatly increase the reliability of the final answer. Another possibility is that there is no dark energy, but that General Relativity does not describe the laws of physics accurately on large scales. While the properties of gravity have been measured with exquisite precision at stellar system scales and densities, within our solar system and by binary pulsar systems, its properties in different environments are poorly constrained. To fully understand if General Relativity is the complete theory of gravity we must test gravity across a spectrum of scales and densities. Rapid developments in gravitational wave astronomy and numerical relativity are directed at testing gravity in the high curvature, high density regime. Cosmological evolution provides a polar opposite test bed, probing how gravity behaves in the lowest curvature, low density environments. There are a number of different implementations of astrophysically relevant modifications of gravity. Generically, the models are able to reproduce the distance measurements while at the same time altering the growth of structure. In particular, as detailed below, the Poisson equation relating over-densities to gravitational potentials is altered, and the potential that determines the geodesics of relativistic particles (such as photons) differs from the potential that determines the motion of non-relativistic particles. Upcoming surveys will exploit these differences to determine whether the acceleration of the Universe is due to dark energy or to modified gravity. To realize this potential, both wide field imaging and spectroscopic redshift surveys play crucial roles. Projects including DES, eBOSS, DESI, PFS, LSST, Euclid, and WFIRST are in line to map more than a 1000 cubic-billion-light-year volume of the Universe. These will map the cosmic structure growth rate to 1% in the redshift range 0
Observational constraints on holographic tachyonic dark energy in interaction with dark matter
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.
Anisotropic modified holographic Ricci dark energy cosmological model with hybrid expansion law
NASA Astrophysics Data System (ADS)
Das, Kanika; Sultana, Tazmin
2015-11-01
Here in this paper we present a locally rotationally symmetric Bianchi type-II metric filled with dark matter and anisotropic modified holographic Ricci dark energy. To solve the Einstein's field equations we have taken the hybrid expansion law (HEL) which exhibits a cosmic transition of the universe from decelerating to accelerating phase. We have investigated the physical and geometrical properties of the model. It is observed that the anisotropy of the universe and that of the modified holographic Ricci dark energy tends to zero at later times and the universe becomes homogeneous, isotropic and flat. We have also studied the cosmic jerk parameter.
The Einstein-Klein-Gordon Equations, Wave Dark Matter, and the Tully-Fisher Relation
NASA Astrophysics Data System (ADS)
Goetz, Andrew S.
2015-01-01
We examine the Einstein equation coupled to the Klein-Gordon equation for a complex-valued scalar field. These two equations together are known as the Einstein-Klein-Gordon system. In the low-field, non-relativistic limit, the Einstein-Klein-Gordon system reduces to the Poisson-Schrodinger system. We describe the simplest solutions of these systems in spherical symmetry, the spherically symmetric static states, and some scaling properties they obey. We also describe some approximate analytic solutions for these states. The EKG system underlies a theory of wave dark matter, also known as scalar field dark matter (SFDM), boson star dark matter, and Bose-Einstein condensate (BEC) dark matter. We discuss a possible connection between the theory of wave dark matter and the baryonic Tully-Fisher relation, which is a scaling relation observed to hold for disk galaxies in the universe across many decades in mass. We show how fixing boundary conditions at the edge of the spherically symmetric static states implies Tully-Fisher-like relations for the states. We also catalog other ``scaling conditions'' one can impose on the static states and show that they do not lead to Tully-Fisher-like relations--barring one exception which is already known and which has nothing to do with the specifics of wave dark matter.
Kunz, Martin; Liddle, Andrew R.; Parkinson, David; Gao Changjun
2009-10-15
Cosmological observations are normally fit under the assumption that the dark sector can be decomposed into dark matter and dark energy components. However, as long as the probes remain purely gravitational, there is no unique decomposition and observations can only constrain a single dark fluid; this is known as the dark degeneracy. We use observations to directly constrain this dark fluid in a model-independent way, demonstrating, in particular, that the data cannot be fit by a dark fluid with a single constant equation of state. Parametrizing the dark fluid equation of state by a variety of polynomials in the scale factor a, we use current kinematical data to constrain the parameters. While the simplest interpretation of the dark fluid remains that it is comprised of separate dark matter and cosmological constant contributions, our results cover other model types including unified dark energy/matter scenarios.
Limits on dark radiation, early dark energy, and relativistic degrees of freedom
Calabrese, Erminia; Melchiorri, Alessandro; Huterer, Dragan; Linder, Eric V.; Pagano, Luca
2011-06-15
Recent cosmological data analyses hint at the presence of an extra relativistic energy component in the early universe. This component is often parametrized as an excess of the effective neutrino number N{sub eff} over the standard value of 3.046. The excess relativistic energy could be an indication for an extra (sterile) neutrino, but early dark energy and barotropic dark energy also contribute to the relativistic degrees of freedom. We examine the capabilities of current and future data to constrain and discriminate between these explanations, and to detect the early dark energy density associated with them. We find that while early dark energy does not alter the current constraints on N{sub eff}, a dark radiation component, such as that provided by barotropic dark energy models, can substantially change current constraints on N{sub eff}, bringing its value back to agreement with the theoretical prediction. Both dark energy models also have implications for the primordial mass fraction of Helium Y{sub p} and the scalar perturbation index n{sub s}. The ongoing Planck satellite mission will be able to further discriminate between sterile neutrinos and early dark energy.
Wang, Y. T.; Xu, L. X.; Gui, Y. X.
2010-10-15
In this paper, we investigate the integrated Sachs-Wolfe effect in the quintessence cold dark matter model with constant equation of state and constant speed of sound in dark energy rest frame, including dark energy perturbation and its anisotropic stress. Comparing with the {Lambda}CDM model, we find that the integrated Sachs-Wolfe (ISW)-power spectrums are affected by different background evolutions and dark energy perturbation. As we change the speed of sound from 1 to 0 in the quintessence cold dark matter model with given state parameters, it is found that the inclusion of dark energy anisotropic stress makes the variation of magnitude of the ISW source uncertain due to the anticorrelation between the speed of sound and the ratio of dark energy density perturbation contrast to dark matter density perturbation contrast in the ISW-source term. Thus, the magnitude of the ISW-source term is governed by the competition between the alterant multiple of (1+3/2xc-circumflex{sub s}{sup 2}) and that of {delta}{sub de}/{delta}{sub m} with the variation of c-circumflex{sub s}{sup 2}.
Dark energy properties in DBI theory
Ahn, Changrim; Kim, Chanju; Linder, Eric V.
2009-12-15
The Dirac-Born-Infeld (DBI) action from string theory provides several new classes of dark energy behavior beyond quintessence due to its relativistic kinematics. We constrain parameters of natural potentials and brane tensions with cosmological observations as well as showing how to design these functions for a desired expansion history. We enlarge the attractor solutions, including new ways of obtaining cosmological constant behavior, to the case of generalized DBI theory with multiple branes. An interesting novel signature of DBI attractors is that the sound speed is driven to zero, unlike for quintessence where it is the speed of light.
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.
Neutron interferometry constrains dark energy chameleon fields
NASA Astrophysics Data System (ADS)
Lemmel, H.; Brax, Ph.; Ivanov, A. N.; Jenke, T.; Pignol, G.; Pitschmann, M.; Potocar, T.; Wellenzohn, M.; Zawisky, M.; Abele, H.
2015-04-01
We present phase shift measurements for neutron matter waves in vacuum and in low pressure Helium using a method originally developed for neutron scattering length measurements in neutron interferometry. We search for phase shifts associated with a coupling to scalar fields. We set stringent limits for a scalar chameleon field, a prominent quintessence dark energy candidate. We find that the coupling constant ? is less than 1.9 107 for n = 1 at 95% confidence level, where n is an input parameter of the self-interaction of the chameleon field ? inversely proportional to ?n.
The Dark Energy Survey CCD imager design
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.
Observational constraints on teleparallel dark energy
Geng, Chao-Qiang; Lee, Chung-Chi; Saridakis, Emmanuel N. E-mail: g9522545@oz.nthu.edu.tw
2012-01-01
We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB) observations to constrain the recently proposed teleparallel dark energy scenario based on the teleparallel equivalent of General Relativity, in which one adds a canonical scalar field, allowing also for a nonminimal coupling with gravity. Using the power-law, the exponential and the inverse hyperbolic cosine potential ansatzes, we show that the scenario is compatible with observations. In particular, the data favor a nonminimal coupling, and although the scalar field is canonical the model can describe both the quintessence and phantom regimes.
NASA Astrophysics Data System (ADS)
Reddy, D. R. K.; Raju, P.; Sobhanbabu, K.
2016-04-01
Five dimensional spherically symmetric space-time filled with two minimally interacting fields; matter and holographic dark energy components is investigated in a scalar tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). To obtain a determinate solution of the highly non-linear field equations we have used (i) a relation between metric potentials and (ii) an equation of state which represents disordered radiation in five dimensional universe. The solution obtained represents a minimally interacting and radiating holographic dark energy model in five dimensional universe. Some physical and Kinematical properties of the model are, also, studied.
De-Santiago, Josue; Cervantes-Cota, Jorge L.
2011-03-15
We study a unification model for dark energy, dark matter, and inflation with a single scalar field with noncanonical kinetic term. In this model, the kinetic term of the Lagrangian accounts for the dark matter and dark energy, and at early epochs, a quadratic potential accounts for slow roll inflation. The present work is an extension to the work by Bose and Majumdar [Phys. Rev. D 79, 103517 (2009).] with a more general kinetic term that was proposed by Chimento in Phys. Rev. D 69, 123517 (2004). We demonstrate that the model is viable at the background and linear perturbation levels.
Dark energy from primordial inflationary quantum fluctuations.
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. PMID:20867625
Interacting new agegraphic dark energy in nonflat Brans-Dicke cosmology
Sheykhi, Ahmad
2010-01-15
We construct a cosmological model of late acceleration based on the new agegraphic dark energy model in the framework of Brans-Dicke cosmology where the new agegraphic energy density {rho}{sub D}=3n{sup 2}m{sub p}{sup 2}/{eta}{sup 2} is replaced with {rho}{sub D}=3n{sup 2{phi}2}/(4{omega}{eta}{sup 2}). We show that the combination of the Brans-Dicke field and agegraphic dark energy can accommodate a w{sub D}=-1 crossing for the equation of state of noninteracting dark energy. When an interaction between dark energy and dark matter is taken into account, the transition of w{sub D} to the phantom regime can be more easily accounted for than when we resort to the Einstein field equations. In the limiting case {alpha}=0 ({omega}{yields}{infinity}), all previous results of the new agegraphic dark energy in Einstein gravity are restored.
New agegraphic dark energy in Hořava-Lifshitz cosmology
Jamil, Mubasher; Saridakis, Emmanuel N. E-mail: msaridak@phys.uoa.gr
2010-07-01
We investigate the new agegraphic dark energy scenario in a universe governed by Hořava-Lifshitz gravity. We consider both the detailed and non-detailed balanced version of the theory, we impose an arbitrary curvature, and we allow for an interaction between the matter and dark energy sectors. Extracting the differential equation for the evolution of the dark energy density parameter and performing an expansion of the dark energy equation-of-state parameter, we calculate its present and its low-redshift value as functions of the dark energy and curvature density parameters at present, of the Hořava-Lifshitz running parameter λ, of the new agegraphic dark energy parameter n, and of the interaction coupling b. We find that w{sub 0} = −0.82{sup +0.08}{sub −0.08} and w{sub 1} = 0.08{sup +0.09}{sub −0.07}. Although this analysis indicates that the scenario can be compatible with observations, it does not enlighten the discussion about the possible conceptual and theoretical problems of Hořava-Lifshitz gravity.
Can the Existence of Dark Energy be Directly Detected?
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?
An accelerating cosmology without dark energy
Steigman, G.; Santos, R.C.; Lima, J.A.S. E-mail: cliviars@astro.iag.usp.br
2009-06-01
The negative pressure accompanying gravitationally-induced particle creation can lead to a cold dark matter (CDM) dominated, accelerating Universe (Lima et al. 1996 [1]) without requiring the presence of dark energy or a cosmological constant. In a recent study, Lima et al. 2008 [2] (LSS) demonstrated that particle creation driven cosmological models are capable of accounting for the SNIa observations [3] of the recent transition from a decelerating to an accelerating Universe, without the need for Dark Energy. Here we consider a class of such models where the particle creation rate is assumed to be of the form Γ = βH+γH{sub 0}, where H is the Hubble parameter and H{sub 0} is its present value. The evolution of such models is tested at low redshift by the latest SNe Ia data provided by the Union compilation [4] and at high redshift using the value of z{sub eq}, the redshift of the epoch of matter — radiation equality, inferred from the WMAP constraints on the early Integrated Sachs-Wolfe (ISW) effect [5]. Since the contributions of baryons and radiation were ignored in the work of LSS, we include them in our study of this class of models. The parameters of these more realistic models with continuous creation of CDM are constrained at widely-separated epochs (z{sub eq} ≈ 3000 and z ≈ 0) in the evolution of the Universe. The comparison of the parameter values, (β, γ), determined at these different epochs reveals a tension between the values favored by the high redshift CMB constraint on z{sub eq} from the ISW and those which follow from the low redshift SNIa data, posing a potential challenge to this class of models. While for β = 0 this conflict is only at ∼< 2σ, it worsens as β increases from zero.
Early-matter-like dark energy and the cosmic microwave background
NASA Astrophysics Data System (ADS)
Aurich, R.; Lustig, S.
2016-01-01
Early-matter-like dark energy is defined as a dark energy component whose equation of state approaches that of cold dark matter (CDM) at early times. Such a component is an ingredient of unified dark matter (UDM) models, which unify the cold dark matter and the cosmological constant of the ΛCDM concordance model into a single dark fluid. Power series expansions in conformal time of the perturbations of the various components for a model with early-matter-like dark energy are provided. They allow the calculation of the cosmic microwave background (CMB) anisotropy from the primordial initial values of the perturbations. For a phenomenological UDM model, which agrees with the observations of the local Universe, the CMB anisotropy is computed and compared with the CMB data. It is found that a match to the CMB observations is possible if the so-called effective velocity of sound ceff of the early-matter-like dark energy component is very close to zero. The modifications on the CMB temperature and polarization power spectra caused by varying the effective velocity of sound are studied.
Quintessence interacting dark energy and a scalar dark fluid from 5D vacuum
NASA Astrophysics Data System (ADS)
Reyes, L. M.; Madriz Aguilar, José Edgar
2011-11-01
Considering a five-dimensional (5D) spacetime empty of matter, we develop a procedure from which an interacting scalar field and its potential are induced on our 4D spacetime by the 5D geometry. We use the procedure to derive a new 4D interacting quintessence scenario, where the quintessence field, its potential and the interaction between the dark matter and dark energy components have a geometrical origin. The mass of the interacting quintessence field depends on the extra dimension, thus giving more freedom to avoid conflicts with nucleosynthesis. Then, inspired from some scalar dark matter models, we extend the geometrical formalism to derive a novel 4D late-time cosmological scenario, where the whole dark sector of the universe (scalar dark matter plus dark energy) admits a unified description by a single geometrical scalar field.
The effective field theory of dark energy
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.
HUBBLE PARAMETER MEASUREMENT CONSTRAINTS ON DARK ENERGY
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.
Probing Dark Energy with Constellation-X
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.
The Dark Energy Camera readout system
NASA Astrophysics Data System (ADS)
Shaw, Theresa; Ballester, Otger; Cardiel-Sas, Laia; Castilla, Javier; Chappa, Steve; de Vicente, Juan; Holm, Scott; Huffman, Dave; Kozlovsky, Mark; Martínez, Gustavo; Moore, Todd; Olsen, Jamieson; Simaitis, Vaidas; Stuermer, Walter
2012-07-01
The Dark Energy Camera (DECam) was developed for use by the Dark Energy Survey (DES). The camera will be installed in the Blanco 4M telescope at the Cerro Tololo Inter-American Observatory (CTIO) and be ready for observations in the second half of 2012. The focal plane consists of 62 2×4K and 12 2×2K fully depleted CCDs. The camera provides a 3 sq. degree view and the survey will cover a 5000 sq. degree area. The camera cage and corrector have already been installed. The development of the electronics to readout the focal plane was a collaborative effort by multiple institutions in the United States and in Spain. The goal of the electronics is to provide readout at 250 kpixels/second with less than 15erms noise. Integration of these efforts and initial testing took place at Fermi National Accelerator Laboratory. DECam currently resides at CTIO and further testing has occurred in the Coudé room of the Blanco. In this paper, we describe the development of the readout system, test results and the lessons learned.
On the holographic dark energy in chameleon scalar-tensor cosmology
NASA Astrophysics Data System (ADS)
Saaidi, K.; Sheikhahmadi, H.; Golanbari, T.; Rabiei, S. W.
2013-11-01
We study the holographic dark energy (HDE) model in generalized Brans-Dicke scenario with a non-minimal coupling between the scalar field and matter Lagrangian namely Chameleon Brans Dicke (CBD) mechanism. In this study we consider the interacting and non-interacting cases for two different cutoffs. The physical quantities of the model such as, equation of state (EoS) parameter, deceleration parameter and the evolution equation of dimensionless parameter of dark energy are obtained. We shall show that this model can describe the dynamical evolution of fraction parameter of dark energy in all epochs. Also we find the EoS parameter can cross the phantom divide line by suitable choices of parameters without any mines kinetic energy term.
On the growth of perturbations in interacting dark energy and dark matter fluids
NASA Astrophysics Data System (ADS)
Koshelev, N. A.
2011-05-01
The covariant generalizations of the background dark sector coupling suggested in Mangano, Miele and Pettorino (Mod Phys Lett A 18:831, 2003) are considered. The evolution of perturbations is studied with detailed attention to interaction rate that is proportional to the product of dark matter and dark energy densities. It is shown that some classes of models with coupling of this type do not suffer from early time instabilities in strong coupling regime.
Inflation, Dark Energy and the AFTA: Survey Evaluation Tools
NASA Astrophysics Data System (ADS)
Bennett, Charles
We propose to address these questions about the Astrophysics Focused Telescope Assets (AFTA) implementation of the Wide-Field Infra-Red Survey Telescope (WFIRST): (1) What constraints does WFIRST/AFTA place on inflationary and dark energy cosmological parameters for a given set of nominal instrument design and observing parameters? (2) How do these constraints change with variations in mission parameters (sky area, observing duration, sensitivity, purity, astrophysical assumptions, etc.)? and (3) How should requirements or capabilities be included in the design to ensure the dark energy and inflation parameter estimates can be met? To answer these questions we propose to develop a set of simulation tools to better understand the dependencies of the cosmological results on the mission design. We emphasize that it is not our intent to argue for particular changes to the mission, but rather to provide the WFIRST/AFTA Study Office with insights, specific numbers, and functional dependencies so that the Study Office can make informed decisions. Early time accelerated expansion (inflation) and late time accelerated expansion (from dark energy) have physical similarities and differences. They are both, in their simplest form, exponential expansions with the equation of state parameter w = -1, yet they appear unrelated in the sense that they occur on vastly different energy scales. Neither is well understood, hence the strong desire for improved measurements. In a practical sense, the interpretation of future measurements are interdependent. Flatness (Omega_k=0) is often assumed to deduce limits on w, or alternatively w = -1 is assumed to deduce limits on flatness. Baryon acoustic oscillations (BAO) are effectively differential and hence approximately independent of the detailed shape of the power spectrum, P(k), but if the AFTA galaxy redshift survey is used to deduce P(k), then there is a strong interaction between the interpretation of P(k) and inflation, including its assumptions and parameters. We propose to explore this interaction, and the mission's ability to place constraints for a range of instrumental, astrophysical, and observational conditions. The Science Definition Team's AFTA report (Spergel et al. 2013) states, "The broad-band shape of the galaxy power spectrum P(k) provides a second 'standard ruler' for geometrical measurements via the turnover scale imprinted by the transition from radiation to matter domination in the early universe, as well as a diagnostic for neutrino masses, extra radiation components, and the physics of inflation." It further notes that to constrain dark energy it is necessary to also constrain other cosmological parameters such as the Hubble constant and the matter density (both values were recently reported by Bennett et al. (2014)), as well as "the curvature Omega_k, and the amplitude and spectral index of the inflationary fluctuation spectrum." Rather than only treating these latter parameters as uncertainties to marginalize over to get dark energy constraints, we seek to study the constraints AFTA places on these inflationary parameters, both separately and jointly with dark energy constraints. Fortunately the AFTA survey design does not require a strong trade-off between achieving dark energy and inflation constraints; both tend to be strengthened or weakened together by varying survey parameters. We begin with tools we have already developed and propose to build increasingly detailed simulation and analysis tools to evaluate the AFTA galaxy redshift survey cosmological results as a function of mission specific input parameters.
Interacting new agegraphic version of pilgrim dark energy
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Abbas, G.
2015-05-01
We discuss the cosmological evolution of the interacting pilgrim dark energy (DE) with conformal age of the universe in flat FRW universe. We evaluate the equation of state (EoS) parameter for three different values of interacting parameter which evolutes the universe from matter dominated to phantom-like eras by evolving quintessence as well as vacuum DE eras. We also give the correspondence of the present DE model with quintessence, tachyon, k-essence, dilaton and DBI-essence scalar field models. We discuss the dynamics of scalar field and corresponding potentials. We find that the behavior of scalar field, corresponding potentials and kinetic energy terms (in k-essence and dilaton field) consistent with the present day observations. Also, cosmological planes such as ω ǎrtheta-ω ǎrtheta' and r - s planes corresponds to ΛCDM limit.
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 models are treated in great detail, as expected from a volume covering an estimated four thousand papers. This much needed volume fills a gap in the literature and is a must-have in the library of young and seasoned researchers alike.
Chameleon dark energy models with characteristic signatures
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.
Testing the interaction between dark energy and dark matter with Planck data
NASA Astrophysics Data System (ADS)
Costa, André A.; Xu, Xiao-Dong; Wang, Bin; Ferreira, Elisa G. M.; Abdalla, E.
2014-05-01
Interacting dark energy and dark matter is used to go beyond the standard cosmology. We base our arguments on Planck data and conclude that an interaction is compatible with the observations and can provide a strong argument towards consistency of different values of cosmological parameters.
The traces of anisotropic dark energy in light of Planck
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.
NASA Astrophysics Data System (ADS)
Bamba, Kazuharu; Capozziello, Salvatore; Nojiri, Shin'ichi; Odintsov, Sergei D.
2012-11-01
We review different dark energy cosmologies. In particular, we present the ΛCDM cosmology, Little Rip and Pseudo-Rip universes, the phantom and quintessence cosmologies with Type I, II, III and IV finite-time future singularities and non-singular dark energy universes. In the first part, we explain the ΛCDM model and well-established observational tests which constrain the current cosmic acceleration. After that, we investigate the dark fluid universe where a fluid has quite general equation of state (EoS) [including inhomogeneous or imperfect EoS]. All the above dark energy cosmologies for different fluids are explicitly realized, and their properties are also explored. It is shown that all the above dark energy universes may mimic the ΛCDM model currently, consistent with the recent observational data. Furthermore, special attention is paid to the equivalence of different dark energy models. We consider single and multiple scalar field theories, tachyon scalar theory and holographic dark energy as models for current acceleration with the features of quintessence/phantom cosmology, and demonstrate their equivalence to the corresponding fluid descriptions. In the second part, we study another equivalent class of dark energy models which includes F( R) gravity as well as F( R) Hořava-Lifshitz gravity and the teleparallel f( T) gravity. The cosmology of such models representing the ΛCDM-like universe or the accelerating expansion with the quintessence/phantom nature is described. Finally, we approach the problem of testing dark energy and alternative gravity models to general relativity by cosmography. We show that degeneration among parameters can be removed by accurate data analysis of large data samples and also present the examples.
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.
Scaling attractors in interacting teleparallel dark energy
Otalora, G.
2013-07-01
It has been proposed recently the existence of a non-minimal coupling between a canonical scalar field (quintessence) and gravity in the framework of teleparallel gravity, motivated by similar constructions in the context of General Relativity. The dynamics of the model, known as teleparallel dark energy, has been further developed, but no scaling attractor has been found. Here we consider a model in which the non-minimal coupling is ruled by a dynamically changing coefficient α≡f{sub ,φ}/(f){sup 1/2}, with f(φ) an arbitrary function of the scalar field φ. It is shown that in this case the existence of scaling attractors is possible, which means that the universe will eventually enter these scaling attractors, regardless of the initial conditions. As a consequence, the cosmological coincidence problem could be alleviated without fine-tunings.
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.
Calibration Monitor for Dark Energy Experiments
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.
CONSTRAINTS ON DARK ENERGY FROM BARYON ACOUSTIC PEAK AND GALAXY CLUSTER GAS MASS MEASUREMENTS
Samushia, Lado; Ratra, Bharat E-mail: ratra@phys.ksu.ed
2009-10-01
We use baryon acoustic peak measurements by Eisenstein et al. and Percival et al., together with the Wilkinson Microwave Anisotropy Probe (WMAP) measurement of the apparent acoustic horizon angle, and galaxy cluster gas mass fraction measurements of Allen et al., to constrain a slowly rolling scalar field dark energy model, phiCDM, in which dark energy's energy density changes in time. We also compare our phiCDM results with those derived for two more common dark energy models: the time-independent cosmological constant model, LAMBDACDM, and the XCDM parameterization of dark energy's equation of state. For time-independent dark energy, the Percival et al. measurements effectively constrain spatial curvature and favor a close to the spatially flat model, mostly due to the WMAP cosmic microwave background prior used in the analysis. In a spatially flat model the Percival et al. data less effectively constrain time-varying dark energy. The joint baryon acoustic peak and galaxy cluster gas mass constraints on the phiCDM model are consistent with but tighter than those derived from other data. A time-independent cosmological constant in a spatially flat model provides a good fit to the joint data, while the alpha parameter in the inverse power-law potential phiCDM model is constrained to be less than about 4 at 3sigma confidence level.
Dynamics of minimally coupled dark energy in spherical halos of dark matter
NASA Astrophysics Data System (ADS)
Novosyadlyj, Bohdan; Tsizh, Maksym; Kulinich, Yurij
2016-03-01
We analyse the evolution of scalar field dark energy in the spherical halos of dark matter at the late stages of formation of gravitationally bound systems in the expanding Universe. The dynamics of quintessential dark energy at the center of dark matter halo strongly depends on the value of effective sound speed c_s (in units of speed of light). If c_s˜ 1 (classical scalar field) then the dark energy in the gravitationally bound systems is only slightly perturbed and its density is practically the same as in cosmological background. The dark energy with small value of sound speed (c_s<0.1), on the contrary, is important dynamical component of halo at all stages of their evolution: linear, non-linear, turnaround, collapse, virialization and later up to current epoch. These properties of dark energy can be used for constraining the value of effective sound speed c_s by comparison the theoretical predictions with observational data related to the large scale gravitationally bound systems.
Observatory conceptual development for the Joint Dark Energy Mission
NASA Astrophysics Data System (ADS)
Sholl, Michael J.; Bernstein, Gary M.; Content, David A.; Dittman, Michael G.; Howard, Joseph M.; Lampton, Michael L.; Lehan, John P.; Mentzell, J. Eric; Woodruff, Robert A.
2009-08-01
The Joint Dark Energy Mission (JDEM)1,2 is a proposed dark energy space mission that will measure the expansion history of the universe and the growth of its large scale structure. It is intended to provide tight constraints on the equation of state of the universe and test the validity of general relativity. Three complementary observational analyses will be employed: Baryon Acoustic Oscillations, Type 1a Supernovae and Gravitational Weak Lensing. An observatory designed for efficient accommodation of these techniques combines wide-field, diffraction-limited observations, ultra-stable point spread function, and spectroscopy. In this paper we discuss optical configurations capable of simultaneous wide-field imaging and spectroscopy, using either afocal or focal telescope configurations. Spectroscopy may be performed by an integral field unit (IFU), grism or prism spectrometer. We present a flowdown of weak lensing image stability requirements (the most demanding technique optically) to telescope thermo-mechanical stability limits, based on variations in the optical transfer function of combinations of Zernike modes, and the sensitivity of these mode combinations to thermo-mechanical drift of the telescope. We apply our formalism to a representative threemirror anastigmat telescope and find quantitative relations between the second moments of the image and the required stability of the telescope over a typical weak lensing observation.
Observational constraints on a variable dark energy model
Movahed, M. Sadegh; Rahvar, Sohrab
2006-04-15
We study the effect of a phenomenological parameterized quintessence model on low, intermediate and high redshift observations. At low and intermediate redshifts, we use the Gold sample of supernova Type Ia (SNIa) data and recently observed size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), to put constraint on the parameters of the quintessence model. At the high redshift, the same fitting procedure is done using WAMP data, comparing the location of acoustic peak with that obtain from the dark energy model. As a complementary analysis in a flat universe, we combine the results from the SNIa, CMB and SDSS. The best fit values for the model parameters are {omega}{sub m}=0.27{sub -0.02}{sup +0.02} (the present matter content) and w{sub 0}=-1.45{sub -0.60}{sup +0.35} (dark energy equation of state). Finally we calculate the age of universe in this model and compare it with the age of old stars and high redshift objects.
Is the effective field theory of dark energy effective?
NASA Astrophysics Data System (ADS)
Linder, Eric V.; Sengör, Gizem; Watson, Scott
2016-05-01
The effective field theory of cosmic acceleration systematizes possible contributions to the action, accounting for both dark energy and modifications of gravity. Rather than making model dependent assumptions, it includes all terms, subject to the required symmetries, with four (seven) functions of time for the coefficients. These correspond respectively to the Horndeski and general beyond Horndeski class of theories. We address the question of whether this general systematization is actually effective, i.e. useful in revealing the nature of cosmic acceleration when compared with cosmological data. The answer is no and yes: there is no simple time dependence of the free functions—assumed forms in the literature are poor fits, but one can derive some general characteristics in early and late time limits. For example, we prove that the gravitational slip must restore to general relativity in the de Sitter limit of Horndeski theories, and why it doesn't more generally. We also clarify the relation between the tensor and scalar sectors, and its important relation to observations; in a real sense the expansion history H(z) or dark energy equation of state w(z) is 1/5 or less of the functional information! In addition we discuss the de Sitter, Horndeski, and decoupling limits of the theory utilizing Goldstone techniques.
Analysis of dark energy models in DGP braneworld
NASA Astrophysics Data System (ADS)
Jawad, Abdul
2015-12-01
In this paper, we reconsider the accelerated expansion phenomenon in the DGP braneworld scenario which leads to an accelerated universe without cosmological constant or other form of dark energy for the positive branch (ɛ= +1) which is not more attractive model. Thus, we assume the DGP braneworld scenario with (ɛ= -1) and also interacting Hubble and event horizons pilgrim dark energy models. We extract various cosmological parameters in this scenario and displayed our results with respect to redshift parameter. It is found that the ranges of Hubble parameter are coincided with observational results. The equation of state parameter lies within the suggested ranges of different observational schemes. The squared speed of sound shows stability for all present models in DGP braneworld scenario. The ω_{\\vartheta}-ω'_{\\vartheta} planes lie in the range (ω_{\\vartheta}=-1.13^{+0.24}_{-0.25},ω'_{\\vartheta}<1.32) which has been obtained through different observational schemes. It is remarked that our results of various cosmological parameters shows consistency with different observational data like Planck, WP, BAO, H0 and SNLS.
Observational constraints on holographic dark energy with varying gravitational constant
Lu, Jianbo; Xu, Lixin; Saridakis, Emmanuel N.; Setare, M.R. E-mail: msaridak@phys.uoa.gr E-mail: lxxu@dlut.edu.cn
2010-03-01
We use observational data from Type Ia Supernovae (SN), Baryon Acoustic Oscillations (BAO), Cosmic Microwave Background (CMB) and observational Hubble data (OHD), and the Markov Chain Monte Carlo (MCMC) method, to constrain the cosmological scenario of holographic dark energy with varying gravitational constant. We consider both flat and non-flat background geometry, and we present the corresponding constraints and contour-plots of the model parameters. We conclude that the scenario is compatible with observations. In 1σ we find Ω{sub Λ0} = 0.72{sup +0.03}{sub −0.03}, Ω{sub k0} = −0.0013{sup +0.0130}{sub −0.0040}, c = 0.80{sup +0.19}{sub −0.14} and Δ{sub G}≡G'/G = −0.0025{sup +0.0080}{sub −0.0050}, while for the present value of the dark energy equation-of-state parameter we obtain w{sub 0} = −1.04{sup +0.15}{sub −0.20}.
Modified Holographic Dark Energy and Phantom Behaviour of Randall-Sundrum Brane
NASA Astrophysics Data System (ADS)
Bandyopadhyay, Tanwi
2011-10-01
In this work, we discuss the evolution of modified Holographic Dark Energy (HDE) derived from the UV/IR cutoff in the Randall-Sundrum II (RS-II) braneworld scenario. Choosing future event horizon as the IR cutoff, it is seen that the equation of state parameter for the modified HDE can cross the phantom crossing line ω=-1.
WzBinned: Binned and uncorrelated estimates of dark energy EOS extractor
NASA Astrophysics Data System (ADS)
Sullivan, Scott; Cooray, Asantha; Holz, Daniel E.
2016-01-01
WzBinned extracts binned and uncorrelated estimates of dark energy equation of state w(z) using Type Ia supernovae Hubble diagram and other cosmological probes and priors. It can handle an arbitrary number of input distance modulus data (entered as an input file SNdata.dat) and various existing cosmological information.
Baryon acoustic oscillation intensity mapping of dark energy.
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 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. PMID:18352692
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.
The CHASE laboratory search for chameleon dark energy
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.
Anisotropic cosmologies with ghost dark energy models in f (R, T) gravity
NASA Astrophysics Data System (ADS)
Fayaz, V.; Hossienkhani, H.; Zarei, Z.; Azimi, N.
2016-02-01
In this work, the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity is investigated. For this purpose, we use the squared sound speed vs2 whose sign determines the stability of the model. At first, the non-interacting ghost dark energy in a Bianchi type-I (BI) background is discussed. Then the equation-of-state parameter, ω_D=pD/ρD, the deceleration parameter, and the evolution equation of the generalized ghost dark energy are obtained. It is shown that the equation-of-state parameter of the ghost dark energy can cross the phantom line ( ω=-1 in some range of the parameter spaces. Then, this investigation was extended to the general scheme for modified f(R,T) gravity reconstruction from a realistic case in an anisotropic Bianchi type-I cosmology, using the dark matter and ghost dark energy. Special attention is taken into account for the case in which the function f is given by f(R,T)=f1(R) +f2(T). We consider a specific model which permits the standard continuity equation in this modified theory. Besides Ω_{Λ} and Ω in standard Einstein cosmology, another density parameter, Ω_{σ}, is expected by the anisotropy. This theory implies that if Ω_{σ} is zero then it yields the FRW universe model. Interestingly enough, we find that the corresponding f ( R, T) gravity of the ghost DE model can behave like phantom or quintessence of the selected models which describe the accelerated expansion of the universe.
Anti-dark and Mexican-hat solitons in the Sasa-Satsuma equation on the continuous wave background
NASA Astrophysics Data System (ADS)
Xu, Tao; Li, Min; Li, Lu
2015-02-01
In this letter, via the Darboux transformation method we construct new analytic soliton solutions for the Sasa-Satsuma equation which describes the femtosecond pulses propagation in a monomode fiber. We reveal that two different types of femtosecond solitons, i.e., the anti-dark (AD) and Mexican-hat (MH) solitons, can form on a continuous wave (CW) background, and numerically study their stability under small initial perturbations. Different from the common bright and dark solitons, the AD and MH solitons can exhibit both the resonant and elastic interactions, as well as various partially/completely inelastic interactions which are composed of such two fundamental interactions. In addition, we find that the energy exchange between some interacting soliton and the CW background may lead to one AD soliton changing into an MH one, or one MH soliton into an AD one.
Exact solutions in a scalar-tensor model of dark energy
Granda, L.N.; Loaiza, E. E-mail: edwin.loaiza@correounivalle.edu.co
2012-09-01
We consider a model of scalar field with non minimal kinetic and Gauss Bonnet couplings as a source of dark energy. Based on asymptotic limits of the generalized Friedmann equation, we impose restrictions on the kinetic an Gauss-Bonnet couplings. This restrictions considerable simplify the equations, allowing for exact solutions unifying early time matter dominance with transitions to late time quintessence and phantom phases. The stability of the solutions in absence of matter has been studied.
Basilakos, Spyros; Sanchez, Juan Carlos Bueno; Perivolaropoulos, Leandros
2009-08-15
We generalize the small scale dynamics of the Universe by taking into account models with an equation of state which evolves with time, and provide a complete formulation of the cluster virialization attempting to address the nonlinear regime of structure formation. In the context of the current dark energy models, we find that galaxy clusters appear to form at z{approx}1-2, in agreement with previous studies. Also, we investigate thoroughly the evolution of spherical matter perturbations, as the latter decouple from the background expansion and start to 'turn around' and finally collapse. Within this framework, we find that the concentration parameter depends on the choice of the considered dark energy (homogeneous or clustered). In particular, if the distribution of the dark energy is clustered then we produce more concentrated structures with respect to the homogeneous dark energy. Finally, comparing the predicted concentration parameter with the observed concentration parameter, measured for four massive galaxy clusters, we find that the scenario which contains a pure homogeneous dark energy is unable to reproduce the data. The situation becomes somewhat better in the case of an inhomogeneous (clustered) dark energy.
Induced gravity and the attractor dynamics of dark energy/dark matter
Cervantes-Cota, Jorge L.; Putter, Roland de; Linder, Eric V. E-mail: rdeputter@berkeley.edu
2010-12-01
Attractor solutions that give dynamical reasons for dark energy to act like the cosmological constant, or behavior close to it, are interesting possibilities to explain cosmic acceleration. Coupling the scalar field to matter or to gravity enlarges the dynamical behavior; we consider both couplings together, which can ameliorate some problems for each individually. Such theories have also been proposed in a Higgs-like fashion to induce gravity and unify dark energy and dark matter origins. We explore restrictions on such theories due to their dynamical behavior compared to observations of the cosmic expansion. Quartic potentials in particular have viable stability properties and asymptotically approach general relativity.
Mega-masers, Dark Energy and the Hubble Constant
Lo, Fred K.Y.
2007-10-15
Powerful water maser emission (water mega-masers) can be found in accretion disks in the nuclei of some galaxies. Besides providing a measure of the mass at the nucleus, such mega-masers can be used to determine the distance to the host galaxy, based on a kinematic model. We will explain the importance of determining the Hubble Constant to high accuracy for constraining the equation of state of Dark Energy and describe the Mega-maser Cosmology Project that has the goal of determining the Hubble Constant to better than 3%. Time permitting, we will also present the scientific capabilities of the current and future NRAO facilities: ALMA, EVLA, VLBA and GBT, for addressing key astrophysical problems
Cosmic slowing down of acceleration for several dark energy parametrizations
Magaña, Juan; Cárdenas, Víctor H.; Motta, Verónica E-mail: victor.cardenas@uv.cl
2014-10-01
We further investigate slowing down of acceleration of the universe scenario for five parametrizations of the equation of state of dark energy using four sets of Type Ia supernovae data. In a maximal probability analysis we also use the baryon acoustic oscillation and cosmic microwave background observations. We found the low redshift transition of the deceleration parameter appears, independently of the parametrization, using supernovae data alone except for the Union 2.1 sample. This feature disappears once we combine the Type Ia supernovae data with high redshift data. We conclude that the rapid variation of the deceleration parameter is independent of the parametrization. We also found more evidence for a tension among the supernovae samples, as well as for the low and high redshift data.
Pilgrim dark energy in f( T, T G ) cosmology
NASA Astrophysics Data System (ADS)
Chattopadhyay, Surajit; Jawad, Abdul; Momeni, Davood; Myrzakulov, Ratbay
2014-09-01
We work on the reconstruction scenario of pilgrim dark energy (PDE) in f( T, T G ). In PDE model it is assumed that a repulsive force that is accelerating the Universe is phantom type with ( w DE <-1) and it is so strong that prevents formation of the black hole. We construct the f( T, T G ) models and correspondingly evaluate equation of state parameter for various choices of scale factor. Also, we assume polynomial form of f( T, T G ) in terms of cosmic time and reconstruct H and w DE in this manner. Through discussion, it is concluded that PDE shows aggressive phantom-like behavior for s=-2 in f( T, T G ) gravity.
Binary Mixture of Perfect Fluid and Dark Energy in Modified Theory of Gravity
NASA Astrophysics Data System (ADS)
Shaikh, A. Y.
2016-02-01
A self consistent system of Plane Symmetric gravitational field and a binary mixture of perfect fluid and dark energy in a modified theory of gravity are considered. The gravitational field plays crucial role in the formation of soliton-like solutions, i.e., solutions with limited total energy, spin, and charge. The perfect fluid is taken to be the one obeying the usual equation of state, i.e., p = γρ with γ∈ [0, 1] whereas, the dark energy is considered to be either the quintessence like equation of state or Chaplygin gas. The exact solutions to the corresponding field equations are obtained for power-law and exponential volumetric expansion. The geometrical and physical parameters for both the models are studied.
Technically natural dark energy from Lorentz breaking
Blas, D.
2011-07-01
We construct a model of dark energy with a technically natural small contribution to cosmic acceleration, i.e. this contribution does not receive corrections from other scales in the theory. The proposed acceleration mechanism appears generically in the low-energy limit of gravity theories with violation of Lorentz invariance that contain a derivatively coupled scalar field Θ. The latter may be the Goldstone field of a broken global symmetry. The model, that we call ΘCDM, is a valid effective field theory up to a high cutoff just a few orders of magnitude below the Planck scale. Furthermore, it can be ultraviolet-completed in the context of Hořava gravity. We discuss the observational predictions of the model. Even in the absence of a cosmological constant term, the expansion history of the Universe is essentially indistinguishable from that of ΛCDM. The difference between the two theories appears at the level of cosmological perturbations. We find that in ΘCDM the matter power spectrum is enhanced at subhorizon scales compared to ΛCDM. This property can be used to discriminate the model from ΛCDM with current cosmological data.
Effects of ghost dark energy perturbations on the evolution of spherical overdensities
NASA Astrophysics Data System (ADS)
Malekjani, Mohammad; Naderi, Tayebe; Pace, Francesco
2015-11-01
While in the standard cosmological model the accelerated expansion of the Universe is explained by invoking the presence of the cosmological constant term, it is still unclear the true origin of this stunning observational fact. It is therefore interesting to explore alternatives to the simplest scenario, in particular by assuming a more general framework where the fluid responsible for the accelerated expansion is characterized by a time-dependent equation of state. Usually these models, dubbed dark energy models, are purely phenomenological, but in this work we concentrate on a theoretically justified model, the ghost dark energy model. Within the framework of the spherical collapse model, we evaluate effects of dark energy perturbations both at the linear and non-linear level and transfer these results into an observable quantity, the mass function, by speculatively taking into account contributions of dark energy to the mass of the haloes. We showed that the growth rate is higher in ghost models and that perturbations enhance the number of structures with respect to the Λ cold dark matter model, with stronger effects when the total mass takes into account dark energy clumps.
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 Union2.1 data set is consistent with these three data sets, but the combination Union2.1+BAO+HST is in tension with Plank+WP+lensing, corresponding to a large Δχ2 that is equal to 8.6 (1.4% probability). Thus, combining internal inconsistent data sets (SNIa+BAO+HST with Plank+WP+lensing) can lead to ambiguous results, and it is necessary to perform the HDE data analysis for each independent data sets. Our tightest self-consistent constraint is c = 0.495 ± 0.039 obtained from Plank+WP+BAO+HST+lensing.
Planck constraints on holographic dark energy
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 6.4, 3.5 and 4.1, respectively. As a comparison, the Union2.1 data set is consistent with these three data sets, but the combination Union2.1+BAO+HST is in tension with Plank+WP+lensing, corresponding to a large Δχ{sup 2} that is equal to 8.6 (1.4% probability). Thus, combining internal inconsistent data sets (SNIa+BAO+HST with Plank+WP+lensing) can lead to ambiguous results, and it is necessary to perform the HDE data analysis for each independent data sets. Our tightest self-consistent constraint is c = 0.495 ± 0.039 obtained from Plank+WP+BAO+HST+lensing.
Abramo, L. R.; Batista, R. C.; Liberato, L.; Rosenfeld, R.
2009-01-15
The abundance and distribution of collapsed objects such as galaxy clusters will become an important tool to investigate the nature of dark energy and dark matter. Number counts of very massive objects are sensitive not only to the equation of state of dark energy, which parametrizes the smooth component of its pressure, but also to the sound speed of dark energy, which determines the amount of pressure in inhomogeneous and collapsed structures. Since the evolution of these structures must be followed well into the nonlinear regime, and a fully relativistic framework for this regime does not exist yet, we compare two approximate schemes: the widely used spherical collapse model and the pseudo-Newtonian approach. We show that both approximation schemes convey identical equations for the density contrast, when the pressure perturbation of dark energy is parametrized in terms of an effective sound speed. We also make a comparison of these approximate approaches to general relativity in the linearized regime, which lends some support to the approximations.
Chemical potential and the nature of dark energy: The case of a phantom field
Lima, J. A. S.; Pereira, S. H.
2008-10-15
The influence of a possible nonzero chemical potential {mu} on the nature of dark energy is investigated by assuming that the dark energy is a relativistic perfect simple fluid obeying the equation of state, p={omega}{rho} ({omega}<0, constant). The entropy condition, S{>=}0, implies that the possible values of {omega} are heavily dependent on the magnitude, as well as on the sign of the chemical potential. For {mu}>0, the {omega} parameter must be greater than -1 (vacuum is forbidden) while for {mu}<0 not only the vacuum but even a phantomlike behavior ({omega}<-1) is allowed. In any case, the ratio between the chemical potential and temperature remains constant, that is, {mu}/T={mu}{sub 0}/T{sub 0}. Assuming that the dark energy constituents have either a bosonic or fermionic nature, the general form of the spectrum is also proposed. For bosons {mu} is always negative and the extended Wien's law allows only a dark component with {omega}<-1/2, which includes vacuum and the phantomlike cases. The same happens in the fermionic branch for {mu}<0. However, fermionic particles with {mu}>0 are permitted only if -1<{omega}<-1/2. The thermodynamics and statistical arguments constrain the equation-of-state parameter to be {omega}<-1/2, a result surprisingly close to the maximal value required to accelerate a Friedmann-Robertson-Walker-type universe dominated by matter and dark energy ({omega} < or approx. -10/21)
Some cosmological solutions of 5D Einstein equations with dark spinor condensate
NASA Astrophysics Data System (ADS)
Lee, Tae Hoon
2012-05-01
We study the 5D Einstein gravity equations with dark spinor condensate, and under the cylinder condition we find an exponentially expanding cosmological solution for the scale factor of our universe, even without a cosmological constant. The stability condition for the solution is given. Some power-law cosmological solutions are also derived when bulk matter sources in the form of a perfect fluid are additionally introduced.
Crosta, M.; Fratalocchi, A.; Trillo, S.
2011-12-15
We characterize the full family of soliton solutions sitting over a background plane wave and ruled by the cubic-quintic nonlinear Schroedinger equation in the regime where a quintic focusing term represents a saturation of the cubic defocusing nonlinearity. We discuss the existence and properties of solitons in terms of catastrophe theory and fully characterize bistability and instabilities of the dark-antidark pairs, revealing mechanisms of decay of antidark solitons into dispersive shock waves.
Separating Dark Physics from Physical Darkness: Minimalist Modified Gravity vs. Dark Energy
Huterer, Dragan; Linder, Eric V.
2007-01-31
The acceleration of the cosmic expansion may be due to a new component of physical energy density or a modification of physics itself. Mapping the expansion of cosmic scales and the growth of large scale structure in tandem can provide insights to distinguish between the two origins. Using Minimal Modified Gravity (MMG) - a single parameter gravitational growth index formalism to parameterize modified gravity theories - we examine the constraints that cosmological data can place on the nature of the new physics. For next generation measurements combining weak lensing, supernovae distances, and the cosmic microwave background we can extend the reach of physics to allow for fitting gravity simultaneously with the expansion equation of state, diluting the equation of state estimation by less than 25percent relative to when general relativity is assumed, and determining the growth index to 8percent. For weak lensing we examine the level of understanding needed of quasi- and nonlinear structure formation in modified gravity theories, and the trade off between stronger precision but greater susceptibility to bias as progressively more nonlinear information is used.
NEW LIMITS ON EARLY DARK ENERGY FROM THE SOUTH POLE TELESCOPE
Reichardt, C. L.; De Putter, R.; Zahn, O.; Hou, Z.
2012-04-10
We present new limits on early dark energy (EDE) from the cosmic microwave background (CMB) using data from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite on large angular scales and South Pole Telescope on small angular scales. We find a strong upper limit on the EDE density of {Omega}{sub e} < 0.018 at 95% confidence, a factor of three improvement over WMAP data alone. We show that adding lower-redshift probes of the expansion rate to the CMB data improves constraints on the dark energy equation of state, but not the EDE density. We also explain how small-scale CMB temperature anisotropy constrains EDE.
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.
Black Hole Universe Model and Dark Energy
NASA Astrophysics Data System (ADS)
Zhang, Tianxi
2011-01-01
Considering black hole as spacetime and slightly modifying the big bang theory, the author has recently developed a new cosmological model called black hole universe, which is consistent with Mach principle and Einsteinian general relativity and self consistently explains various observations of the universe without difficulties. According to this model, the universe originated from a hot star-like black hole and gradually grew through a supermassive black hole to the present universe by accreting ambient material and merging with other black holes. The entire space is infinitely and hierarchically layered and evolves iteratively. The innermost three layers are the universe that we lives, the outside space called mother universe, and the inside star-like and supermassive black holes called child universes. The outermost layer has an infinite radius and zero limits for both the mass density and absolute temperature. All layers or universes are governed by the same physics, the Einstein general relativity with the Robertson-Walker metric of spacetime, and tend to expand outward physically. When one universe expands out, a new similar universe grows up from its inside black holes. The origin, structure, evolution, expansion, and cosmic microwave background radiation of black hole universe have been presented in the recent sequence of American Astronomical Society (AAS) meetings and published in peer-review journals. This study will show how this new model explains the acceleration of the universe and why dark energy is not required. We will also compare the black hole universe model with the big bang cosmology.
Cooling the dark energy camera instrument
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.
Cooling the Dark Energy Camera instrument
NASA Astrophysics Data System (ADS)
Schmitt, R. L.; Cease, H.; DePoy, D.; Diehl, H. T.; Estrada, J.; Flaugher, B.; Kuhlmann, S.; Onal, Birce; Stefanik, A.
2008-07-01
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.
Probing Dark Energy models with neutrons
NASA Astrophysics Data System (ADS)
Pignol, Guillaume
2015-07-01
There is a deep connection between cosmology — the science of the infinitely large — and particle physics — the science of the infinitely small. This connection is particularly manifest in neutron particle physics. Basic properties of the neutron — its Electric Dipole Moment and its lifetime — are intertwined with baryogenesis and nucleosynthesis in the early Universe. I will cover this topic in the first part, that will also serve as an introduction (or rather a quick recap) of neutron physics and Big Bang cosmology. Then, the rest of the paper will be devoted to a new idea: using neutrons to probe models of Dark Energy. In the second part, I will present the chameleon theory: a light scalar field accounting for the late accelerated expansion of the Universe, which interacts with matter in such a way that it does not mediate a fifth force between macroscopic bodies. However, neutrons can alleviate the chameleon mechanism and reveal the presence of the scalar field with properly designed experiments. In the third part, I will describe a recent experiment performed with a neutron interferometer at the Institut Laue Langevin that sets already interesting constraints on the chameleon theory. Last, the chameleon field can be probed by measuring the quantum states of neutrons bouncing over a mirror. In the fourth part, I will present the status and prospects of the GRANIT experiment at the ILL.
Galaxy Clustering in the Dark Energy Survey
NASA Astrophysics Data System (ADS)
Ross, Ashley; Dark Energy Survey Large-Scale Structure Working Group
2016-01-01
I will present the status of galaxy clustering results in the Dark Energy Survey (DES).DES will image the sky over 5000 deg2 in five photometric bands (grizY) to a nominal depth (iAB ~ 24), enabling the structure of the Universe to be studied to redshift 1.2 and beyond. I will present results of the clustering analyses performed to date, including those from Crocce et al. (2015), who studied the clustering of DES data over five tomographic bins, with photometric redshifts, z, in the range 0.2 < z < 1.2, and those from the `redMaGiC' sample (Rozo et al. 2015), which provides accurate (better than 2%) photometric redshifts for luminous red galaxies. I will describe how these measurements can be combined with weak lensing analyses to probe the growth of structure. Finally, I will report on how DES data can provide a 2% measurement of the angular diameter distance to z~0.9 by measuring the position of baryon acoustic oscillation feature in the clustering of DES galaxies.
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.
NASA Astrophysics Data System (ADS)
Väliviita, Jussi; Palmgren, Elina
2015-07-01
We employ the Planck 2013 CMB temperature anisotropy and lensing data, and baryon acoustic oscillation (BAO) data to constrain a phenomenological wCDM model, where dark matter and dark energy interact. We assume time-dependent equation of state parameter for dark energy, and treat dark matter and dark energy as fluids whose energy-exchange rate is proportional to the dark-matter density. The CMB data alone leave a strong degeneracy between the interaction rate and the physical CDM density parameter today, ωc, allowing a large interaction rate |Γ| ~ H0. However, as has been known for a while, the BAO data break this degeneracy. Moreover, we exploit the CMB lensing potential likelihood, which probes the matter perturbations at redshift z ~ 2 and is very sensitive to the growth of structure, and hence one of the tools for discerning between the ΛCDM model and its alternatives. However, we find that in the non-phantom models (wde>-1), the constraints remain unchanged by the inclusion of the lensing data and consistent with zero interaction, -0.14 < Γ/H0 < 0.02 at 95% CL. On the contrary, in the phantom models (wde<-1), energy transfer from dark energy to dark matter is moderately favoured over the non-interacting model; 0-0.57 < Γ/H0 < -0.1 at 95% CL with CMB+BAO, while addition of the lensing data shifts this to -0.46 < Γ/H0 < -0.01.
Large format filter changer mechanism for the dark energy survey
NASA Astrophysics Data System (ADS)
Tarlé, G.; Bigelow, B.; Boprie, D.; Cooper, C.; Dede, E.; Lorenzon, W.; Nord, B.; Schubnell, M.; Weaverdyck, C.
2010-07-01
The Dark Energy Survey is a Stage III Dark Energy Experiment that will obtain cosmological parameters by combining four observational techniques; Galaxy Clusters, Weak Lensing, Type Ia Supernovae and Baryon Acoustic Oscillations. The observations will be performed with a new wide field camera (DECam) that will be placed on the Blanco 4 m telescope at CTIO. Here we describe the large format (600 mm clear aperture) Filter Changer Mechanism (FCM) for the Dark Energy Survey Camera (DECam). The FCM, based on the Pan-STARRS design, is the largest ever constructed. Fabrication of the filter changer has been completed and it has been tested under realistic conditions.
The distinguishability of interacting dark energy from modified gravity
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.
Spectroscopic Needs for Imaging Dark Energy Experiments
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.; et al
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 scatter further, enhancing the science return from planned experiments greatly (increasing the Dark Energy Task Force figure of merit by up to ~50%); Options: This spectroscopy will most efficiently be done by covering as much of the optical and near-infrared spectrum as possible at modestly high spectral resolution (λ/Δλ > ~3000), while maximizing the telescope collecting area, field of view on the sky, and multiplexing of simultaneous spectra. The most efficient instrument for this would likely be either the proposed GMACS/MANIFEST spectrograph for the Giant Magellan Telescope or the OPTIMOS spectrograph for the European Extremely Large Telescope, depending on actual properties when built. The PFS spectrograph at Subaru would be next best and available considerably earlier, c. 2018; the proposed ngCFHT and SSST telescopes would have similar capabilities but start later. Other key options, in order of increasing total time required, are the WFOS spectrograph at TMT, MOONS at the VLT, and DESI at the Mayall 4 m telescope (or the similar 4MOST and WEAVE projects); of these, only DESI, MOONS, and PFS are expected to be available before 2020. Table 2-3 of this white paper summarizes the observation time required at each facility for strawman training samples. To attain secure redshift measurements for a high fraction of targeted objects and cover the full redshift span of future experiments, additional near-infrared spectroscopy will also be required; this is best done from space, particularly with WFIRST-2.4 and JWST; Calibration: The first several moments of redshift distributions (the mean, RMS redshift dispersion, etc.), must be known to high accuracy for cosmological constraints not to be systematics-dominated (equivalently, the moments of the distribution of differences between photometric and true redshifts could be determined instead). The ultimate goal of calibration is to characterize these moments for every subsample used in analyses - i.e., to minimize the uncertainty in their mean redshift, RMS dispersion, etc. – rather than to make the moments themselves small. Calibration may be done with the same spectroscopic dataset used for training if that dataset is extremely high in redshift completeness (i.e., no populations of galaxies to be used in analyses are systematically missed). Accurate photo-z calibration is necessary for all imaging experiments; Requirements: If extremely low levels of systematic incompleteness (<~0.1%) are attained in training samples, the same datasets described above should be sufficient for calibration. However, existing deep spectroscopic surveys have failed to yield secure redshifts for 30–60% of targets, so that would require very large improvements over past experience. This incompleteness would be a limiting factor for training, but catastrophic for calibration. If <~0.1% incompleteness is not attainable, the best known option for calibration of photometric redshifts is to utilize cross-correlation statistics in some form. The most direct method for this uses cross-correlations between positions on the sky of bright objects of known spectroscopic redshift with the sample of objects that we wish to calibrate the redshift distribution for, measured as a function of spectroscopic z. For such a calibration, redshifts of ~100,000 objects over at least several hundred square degrees, spanning the full redshift range of the samples used for dark energy, would be necessary; and Options: The proposed BAO experiment eBOSS would provide sufficient spectroscopy for basic calibrations, particularly for ongoing and near-future imaging experiments. The planned DESI experiment would provide excellent calibration with redundant cross-checks, but will start after the conclusion of some imaging projects. An extension of DESI to the Southern hemisphere would provide the best possible calibration from cross-correlation methods for DES and LSST. We thus anticipate that our two primary needs for spectroscopy – training and calibration of photometric redshifts – will require two separate solutions. For ongoing and future projects to reach their full potential, new spectroscopic samples of faint objects will be needed for training; those new samples may be suitable for calibration, but the latter possibility is uncertain. In contrast, wide-area samples of bright objects are poorly suited for training, but can provide high-precision calibrations via cross-correlation techniques. Additional training/calibration redshifts and/or host galaxy spectroscopy would enhance the use of supernovae and galaxy clusters for cosmology. We also summarize additional work on photometric redshift techniques that will be needed to prepare for data from ongoing and future dark energy experiments.« less
Spectroscopic Needs for Imaging Dark Energy Experiments
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 further, enhancing the science return from planned experiments greatly (increasing the Dark Energy Task Force figure of merit by up to ~50%); Options: This spectroscopy will most efficiently be done by covering as much of the optical and near-infrared spectrum as possible at modestly high spectral resolution (λ/Δλ > ~3000), while maximizing the telescope collecting area, field of view on the sky, and multiplexing of simultaneous spectra. The most efficient instrument for this would likely be either the proposed GMACS/MANIFEST spectrograph for the Giant Magellan Telescope or the OPTIMOS spectrograph for the European Extremely Large Telescope, depending on actual properties when built. The PFS spectrograph at Subaru would be next best and available considerably earlier, c. 2018; the proposed ngCFHT and SSST telescopes would have similar capabilities but start later. Other key options, in order of increasing total time required, are the WFOS spectrograph at TMT, MOONS at the VLT, and DESI at the Mayall 4 m telescope (or the similar 4MOST and WEAVE projects); of these, only DESI, MOONS, and PFS are expected to be available before 2020. Table 2-3 of this white paper summarizes the observation time required at each facility for strawman training samples. To attain secure redshift measurements for a high fraction of targeted objects and cover the full redshift span of future experiments, additional near-infrared spectroscopy will also be required; this is best done from space, particularly with WFIRST-2.4 and JWST; Calibration: The first several moments of redshift distributions (the mean, RMS redshift dispersion, etc.), must be known to high accuracy for cosmological constraints not to be systematics-dominated (equivalently, the moments of the distribution of differences between photometric and true redshifts could be determined instead). The ultimate goal of calibration is to characterize these moments for every subsample used in analyses - i.e., to minimize the uncertainty in their mean redshift, RMS dispersion, etc. – rather than to make the moments themselves small. Calibration may be done with the same spectroscopic dataset used for training if that dataset is extremely high in redshift completeness (i.e., no populations of galaxies to be used in analyses are systematically missed). Accurate photo-z calibration is necessary for all imaging experiments; Requirements: If extremely low levels of systematic incompleteness (<~0.1%) are attained in training samples, the same datasets described above should be sufficient for calibration. However, existing deep spectroscopic surveys have failed to yield secure redshifts for 30–60% of targets, so that would require very large improvements over past experience. This incompleteness would be a limiting factor for training, but catastrophic for calibration. If <~0.1% incompleteness is not attainable, the best known option for calibration of photometric redshifts is to utilize cross-correlation statistics in some form. The most direct method for this uses cross-correlations between positions on the sky of bright objects of known spectroscopic redshift with the sample of objects that we wish to calibrate the redshift distribution for, measured as a function of spectroscopic z. For such a calibration, redshifts of ~100,000 objects over at least several hundred square degrees, spanning the full redshift range of the samples used for dark energy, would be necessary; and Options: The proposed BAO experiment eBOSS would provide sufficient spectroscopy for basic calibrations, particularly for ongoing and near-future imaging experiments. The planned DESI experiment would provide excellent calibration with redundant cross-checks, but will start after the conclusion of some imaging projects. An extension of DESI to the Southern hemisphere would provide the best possible calibration from cross-correlation methods for DES and LSST. We thus anticipate that our two primary needs for spectroscopy – training and calibration of photometric redshifts – will require two separate solutions. For ongoing and future projects to reach their full potential, new spectroscopic samples of faint objects will be needed for training; those new samples may be suitable for calibration, but the latter possibility is uncertain. In contrast, wide-area samples of bright objects are poorly suited for training, but can provide high-precision calibrations via cross-correlation techniques. Additional training/calibration redshifts and/or host galaxy spectroscopy would enhance the use of supernovae and galaxy clusters for cosmology. We also summarize additional work on photometric redshift techniques that will be needed to prepare for data from ongoing and future dark energy experiments.
Spectroscopic Needs for Imaging Dark Energy Experiments
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; DellAntonio, 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-zs): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-zs 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 further, enhancing the science return from planned experiments greatly (increasing the Dark Energy Task Force figure of merit by up to ~50%); Options: This spectroscopy will most efficiently be done by covering as much of the optical and near-infrared spectrum as possible at modestly high spectral resolution (?/?? > ~3000), while maximizing the telescope collecting area, field of view on the sky, and multiplexing of simultaneous spectra. The most efficient instrument for this would likely be either the proposed GMACS/MANIFEST spectrograph for the Giant Magellan Telescope or the OPTIMOS spectrograph for the European Extremely Large Telescope, depending on actual properties when built. The PFS spectrograph at Subaru would be next best and available considerably earlier, c. 2018; the proposed ngCFHT and SSST telescopes would have similar capabilities but start later. Other key options, in order of increasing total time required, are the WFOS spectrograph at TMT, MOONS at the VLT, and DESI at the Mayall 4 m telescope (or the similar 4MOST and WEAVE projects); of these, only DESI, MOONS, and PFS are expected to be available before 2020. Table 2-3 of this white paper summarizes the observation time required at each facility for strawman training samples. To attain secure redshift measurements for a high fraction of targeted objects and cover the full redshift span of future experiments, additional near-infrared spectroscopy will also be required; this is best done from space, particularly with WFIRST-2.4 and JWST; Calibration: The first several moments of redshift distributions (the mean, RMS redshift dispersion, etc.), must be known to high accuracy for cosmological constraints not to be systematics-dominated (equivalently, the moments of the distribution of differences between photometric and true redshifts could be determined instead). The ultimate goal of calibration is to characterize these moments for every subsample used in analyses - i.e., to minimize the uncertainty in their mean redshift, RMS dispersion, etc. rather than to make the moments themselves small. Calibration may be done with the same spectroscopic dataset used for training if that dataset is extremely high in redshift completeness (i.e., no populations of galaxies to be used in analyses are systematically missed). Accurate photo-z calibration is necessary for all imaging experiments; Requirements: If extremely low levels of systematic incompleteness (<~0.1%) are attained in training samples, the same datasets described above should be sufficient for calibration. However, existing deep spectroscopic surveys have failed to yield secure redshifts for 3060% of targets, so that would require very large improvements over past experience. This incompleteness would be a limiting factor for training, but catastrophic for calibration. If <~0.1% incompleteness is not attainable, the best known option for calibration of photometric redshifts is to utilize cross-correlation statistics in some form. The most direct method for this uses cross-correlations between positions on the sky of bright objects of known spectroscopic redshift with the sample of objects that we wish to calibrate the redshift distribution for, measured as a function of spectroscopic z. For such a calibration, redshifts of ~100,000 objects over at least several hundred square degrees, spanning the full redshift range of the samples used for dark energy, would be necessary; and Options: The proposed BAO experiment eBOSS would provide sufficient spectroscopy for basic calibrations, particularly for ongoing and near-future imaging experiments. The planned DESI experiment would provide excellent calibration with redundant cross-checks, but will start after the conclusion of some imaging projects. An extension of DESI to the Southern hemisphere would provide the best possible calibration from cross-correlation methods for DES and LSST. We thus anticipate that our two primary needs for spectroscopy training and calibration of photometric redshifts will require two separate solutions. For ongoing and future projects to reach their full potential, new spectroscopic samples of faint objects will be needed for training; those new samples may be suitable for calibration, but the latter possibility is uncertain. In contrast, wide-area samples of bright objects are poorly suited for training, but can provide high-precision calibrations via cross-correlation techniques. Additional training/calibration redshifts and/or host galaxy spectroscopy would enhance the use of supernovae and galaxy clusters for cosmology. We also summarize additional work on photometric redshift techniques that will be needed to prepare for data from ongoing and future dark energy experiments.
Coupled dark matter-dark energy in light of near universe observations
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.
Cosmological constraints on interacting dark energy with redshift-space distortion after Planck data
NASA Astrophysics Data System (ADS)
Yang, Weiqiang; Xu, Lixin
2014-04-01
The interacting dark energy model could propose a effective way to avoid the coincidence problem. In this paper, dark energy is taken as a fluid with a constant equation-of-state parameter wx. In a general gauge, we could obtain two sets of different perturbation equations when the momentum transfer potential is vanished in the rest frame of dark matter or dark energy. There are many kinds of interacting forms from the phenomenological considerations; here, we choose Q =3Hξxρx, which owns the stable perturbations in most cases. Then, 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 fσ8(z) data points from redshift-space distortion. Jointing the geometry tests with the large scale structure information, the results show a tighter constraint on the interacting model than the case without fσ8(z) data. We find the interaction rate in 3σ regions: ξx=0.00372-0.00372-0.00372-0.00372+0.000768+0.00655+0.0102. It means that the recently cosmic observations favor a small interaction rate between the dark sectors, snf at the same time, the measurement of redshift-space distortion could rule out a large interaction rate in the 1σ region.
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
NASA Astrophysics Data System (ADS)
Fu, Xiangyun; Wu, Puxun; Yu, Hongwei; Zhou, Bingju
2013-05-01
The effect of spatial curvature in reconstructing the cosmic expansion history and the property of dark energy is studied in this paper by smoothing the noise of the Union2.1 Type Ia Supernovae (SNIa) data with a Gaussian smoothing function. We find that the spatial curvature induces an apparent effect in reconstructing the Hubble parameter H(z), the deceleration parameter q(z), and especially on the equation of state w(z) of dark energy. Thus, when one probes the dark energy property, an assumption of a flat universe may induce critical bias and it is imperative to take account of the spatial curvature.
Testing for dynamical dark energy models with redshift-space distortions
Tsujikawa, Shinji; Felice, Antonio De; Alcaniz, Jailson E-mail: antoniod@nu.ac.th
2013-01-01
The red-shift space distortions in the galaxy power spectrum can be used to measure the growth rate of matter density perturbations δ{sub m}. For dynamical dark energy models in General Relativity we provide a convenient analytic formula of f(z)σ{sub 8}(z) written as a function of the redshift z, where f = dln δ{sub m}/dln a (a is the cosmological scale factor) and σ{sub 8} is the rms amplitude of over-density at the scale 8 h{sup −1} Mpc. Our formula can be applied to the models of imperfect fluids, quintessence, and k-essence, provided that the dark energy equation of state w does not vary significantly and that the sound speed is not much smaller than 1. We also place observational constraints on dark energy models of constant w and tracking quintessence from the recent data of red-shift space distortions.
Belmonte-Beitia, J.; Cuevas, J.
2011-03-15
In this paper, we give a proof of the existence of stationary dark soliton solutions or heteroclinic orbits of nonlinear equations of Schroedinger type with periodic inhomogeneous nonlinearity. The result is illustrated with examples of dark solitons for cubic and photorefractive nonlinearities.
Variable modified Chaplygin gas in the holographic dark energy scenario
NASA Astrophysics Data System (ADS)
Chattopadhyay, Surajit; Debnath, Ujjal
2012-07-01
The holographic principle emerged in the context of black-holes, where it was noted that a local quantum field theory can not fully describe the black holes [1]. Some long standing debates regarding the time evolution of a system, where a black hole forms and then evaporates, played the key role in the development of the holographic principle [2,3,4]. The Chaplygin gas is characterized by an exotic equation of state p=-B/ρ. where B is a positive constant. Role of Chaplygin gas in the accelerated universe has been studied by several authors. The above mentioned equation of state has been modified to p=-B/ρ^{α}, where α lies between 0 and 1. This equation has been further modified to p=-A+B/ρ^{α}. This is called the modified Chaplygin gas. Debnath [5] introduced a variable modified Chaplygin gas by considering B as a function of scale factor a. In this work, we have considered that the universe is filled with normal matter and variable modified Chaplygin gas. Also we have considered the interaction between normal matter and variable modified Chaplygin gas in FRW universe. Then we have considered a correspondence between the holographic dark energy density and interacting variable modified Chaplygin gas energy density. Then we have reconstructed the potential of the scalar field which describes the variable modified Chaplygin cosmology References: [1] K. Enqvist, S. Hannested and M. S. Sloth, JCAP 2, 004 (2005). [2] L. Thorlocius, hep-th/0404098. [3] G. T. Hooft, gr-qc/9310026. [4] L. Susskind, J. Math. Phys. 36, 6377 (1995). [5] U. Debnath, Astrophys. Space Sci. 312, 295 (2007).
Constraining cold dark matter halo merger rates using the coagulation equations
NASA Astrophysics Data System (ADS)
Benson, Andrew J.
2008-08-01
We place additional constraints on the three parameters of the dark matter halo merger rate function recently proposed by Parkinson, Cole & Helly by utilizing Smoluchowski's coagulation equation, which must be obeyed by any binary merging process which conserves mass. We find that the constraints from Smoluchowski's equation are degenerate, limiting to a thin plane in the three-dimensional parameter space. This constraint is consistent with those obtained from fitting to N-body measures of progenitor mass functions, and provides a better match to the evolution of the overall dark matter halo mass function, particularly for the most massive haloes. We demonstrate that the proposed merger rate function does not permit an exact solution of Smoluchowski's equation and, therefore, the choice of parameters must reflect a compromise between fitting various parts of the mass function. The techniques described herein are applicable to more general merger rate functions, which may permit a more accurate solution of Smoluchowski's equation. The current merger rate solutions are most probably sufficiently accurate for the vast majority of applications.
Turbulence kinetic energy equation for dilute suspensions
NASA Technical Reports Server (NTRS)
Abou-Arab, T. W.; Roco, M. C.
1989-01-01
A multiphase turbulence closure model is presented which employs one transport equation, namely the turbulence kinetic energy equation. The proposed form of this equation is different from the earlier formulations in some aspects. The power spectrum of the carrier fluid is divided into two regions, which interact in different ways and at different rates with the suspended particles as a function of the particle-eddy size ratio and density ratio. The length scale is described algebraically. A mass/time averaging procedure for the momentum and kinetic energy equations is adopted. The resulting turbulence correlations are modeled under less retrictive assumptions comparative to previous work. The closures for the momentum and kinetic energy equations are given. Comparisons of the predictions with experimental results on liquid-solid jet and gas-solid pipe flow show satisfactory agreement.
Difficulties distinguishing dark energy from modified gravity via redshift distortions
NASA Astrophysics Data System (ADS)
Simpson, Fergus; Peacock, John A.
2010-02-01
The bulk motion of galaxies induced by the growth of cosmic structure offers a rare opportunity to test the validity of general relativity across cosmological scales. However, modified gravity can be degenerate in its effect with the unknown values of cosmological parameters. More seriously, even the “observed” value of the redshift-space distortions used to measure the fluctuation growth rate depends on the assumed cosmological parameters (the Alcock-Paczynski effect). We give a full analysis of these issues, showing how to combine redshift-space distortions with baryon acoustic oscillations and CMB data, in order to obtain joint constraints on deviations from general relativity and on the equation of state of dark energy while allowing for factors such as nonzero curvature. In particular we note that the evolution of Ωm(z), along with the Alcock-Paczynski effect, produces a degeneracy between the equation of state w and the modified growth parameter γ. Typically, the total marginalized error on either of these parameters will be larger by a factor ≃2 compared to the conditional error where one or the other is held fixed. We argue that future missions should be judged by their figure of merit as defined in the wp-γ plane, and note that the inclusion of spatial curvature can degrade this value by an order of magnitude.
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.
Phantom dark energy, cosmic doomsday, and the coincidence problem
NASA Astrophysics Data System (ADS)
Scherrer, Robert J.
2005-03-01
Phantom dark-energy models, with w<-1, are characterized by a future singularity and therefore a finite lifetime for the universe. Because the future singularity is triggered by the onset of dark-energy domination, the universe spends a significant fraction of its total lifetime in a state for which the dark-energy and matter densities are roughly comparable. We calculate, as a function of w, the fraction of the total lifetime of the universe for which the dark-energy and matter densities differ by less than the ratio r0 in either direction. For r0=10, this fraction varies from 1/3 to 1/8 as w varies from -1.5 to -1.1; the fraction is smaller for smaller values of r0. This result indicates that the coincidence problem is significantly ameliorated in phantom-dominated cosmologies with a future singularity.
Phantom dark energy, cosmic doomsday, and the coincidence problem
Scherrer, Robert J.
2005-03-15
Phantom dark-energy models, with w<-1, are characterized by a future singularity and therefore a finite lifetime for the universe. Because the future singularity is triggered by the onset of dark-energy domination, the universe spends a significant fraction of its total lifetime in a state for which the dark-energy and matter densities are roughly comparable. We calculate, as a function of w, the fraction of the total lifetime of the universe for which the dark-energy and matter densities differ by less than the ratio r{sub 0} in either direction. For r{sub 0}=10, this fraction varies from 1/3 to 1/8 as w varies from -1.5 to -1.1; the fraction is smaller for smaller values of r{sub 0}. This result indicates that the coincidence problem is significantly ameliorated in phantom-dominated cosmologies with a future singularity.
Cosmological viability conditions for f(T) dark energy models
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.
"CosmoMicroPhysics" Approach to Study the Dark Matter and Dark Energy
NASA Astrophysics Data System (ADS)
Vavilova, Iryna; Shulga, Valery M.
In 2007-2009 the Complex Research Program of the NAS of Ukraine titled "Study of the Structure of the Universe, Dark Matter and Dark Energy" (CosmoMicroPhysics) was con-ducted with the aim to join efforts of the Ukrainian scientists for resolving this actual task (http://www.nas.gov.ua/ResearchActivities/ComplexProgram/Pages/17.aspx). Our research team is presented by the scientists and post-graduated students from 15 institutes and univer-sities of Ukraine ()about 70 persons) working in the different fields (astrophysics, mathematics, theoretical physics, and nuclear physics). The main scientific goals, which were put forwards on the observational and theoretical revelations of dark matter/dark energy, were the follow-ing: -Observational base of the astronomical revelations of dark matter and dark energy as well as candidates to the different baryonic components of the hidden mass of the Universe; -Observational base of the earlier evolution of the Universe and properties of the large-scale structure; -Theoretical support for such observational data and creation of the cosmological models; -Experimental search of the WIMPs and study of the neutrino properties as one of the main components of a dark matter; -Theoretical research of the classical and quantum fields in astrophysics and cosmology. We will discuss the main results obtained by our team as the essential contribution to resolve this problem: * Observations, data analysis, and estimation as regarding the various LMS components of the Universe, at the first turn as the candidates to the dark matter (AGNs, black holes in double stars, halo of galaxies and galaxy groups/clusters, mass-to-luminosity estimation for isolated galaxies and galaxies in clusters/groups, brawn dwarfs etc.); * Gravitational lenses as the sources of the mass distribution data in the Universe; *Theoretical models of the Universe with cosmological fields, Dark energy models, and research of the dark energy impact on the evolution of the Universe; *Experimental limits for the WIMPs cross-section with nuclei, as well as a study of the neutrino properties in the experiments on the double beta-decay; *Development of the modifications of the Relativity Theory, including in spaces with the additional dimensions; *Study of the role of quantum effects in cosmology and astrophysics, as well as the cosmological and astrophysical revelations at the phase transitions in super dense matter. The most part of these researches is conducting in the tight international cooperation. Focusing an attention at the NASU "CosmoMicroPhysics" program, we will discuss also our proposals for the further cooperation, including the experiments for space missions..
Model of dark matter and dark energy based on gravitational polarization
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.
Model independent early expansion history and dark energy
NASA Astrophysics Data System (ADS)
Samsing, Johan; Linder, Eric V.; Smith, Tristan L.
2012-12-01
We examine model independent constraints on the high redshift and prerecombination expansion history from upcoming cosmic microwave background observations, using a combination of principal component analysis and other techniques. This can be translated to model independent limits on early dark energy and the number of relativistic species Neff. Models such as scaling (Doran-Robbers), dark radiation (ΔNeff), and barotropic aether fall into distinct regions of eigenspace and can be easily distinguished from each other. Incoming CMB data will map the expansion history from z=0-105, achieving subpercent precision around recombination, and enable determination of the amount of early dark energy and valuable guidance to its nature.
Pathfinder for a HI Dark Energy Survey
NASA Astrophysics Data System (ADS)
Bandura, Kevin; Cylindrical Radio Telescope Team
2011-05-01
The 21cm Hydrogen spin flip transition has great potential to constrain the standard model of cosmology. A standard galaxy survey requires high resolution and sensitivity to identify individual galaxies. Instead using 21-cm emission, a low-resolution intensity mapping technique that resolves only large-scale linear cosmic structure will be much more efficient. At the frequencies 500-1000MHz redshifted 21cm emission can be used to study dark energy. At these frequencies, neither a standard phased array nor single dish is optimal. The Pittsburgh Cylindrical Prototype Telescope (PCPT) is a hybrid of these designs, close spaced parabolic cylinders. A cylinder views a strip of the sky, broken into as many beams as there are feeds along the focal line. This hybrid allows for much higher survey speed than a single dish, and a much larger collecting area than a traditional synthesis array. The PCPT is comprised of two 10m by 25m cylinders, centers spaced 25m apart. The telescope is a fixed drift-scan design. The cylinders are oriented N-S, such that the entire sky is swept through its 2o by 90o primary beam every day. Each feed line has 16 dipoles for each polarization spaced by 0.7λ, giving a 2o by 5o resolution after digital beam-forming. The dipoles directly feed a room temperature low noise amplifier made on the same circuit board. These LNA's have a measured noise temperature of 20K. Since the radio environment of Pittsburgh is full of strong terrestrial sources, a filter was added in front of the LNA, which raised the system temperature to about 100 Kelvin. We present continuum maps as well as 21cm maps of the galaxy made with the PCPT.
The Dark Energy Survey Data Management System
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.
The Dark Energy Survey data management system
NASA Astrophysics Data System (ADS)
Mohr, Joseph J.; Adams, Darren; Barkhouse, Wayne; Beldica, Cristina; Bertin, Emmanuel; Cai, Y. Dora; da Costa, Luiz A. Nicolaci; Darnell, J. Anthony; Daues, Gregory E.; Jarvis, Michael; Gower, Michelle; Lin, Huan; Martelli, Leandro; Neilsen, Eric; Ngeow, Chow-Choong; Ogando, Ricardo L. C.; Parga, Alex; Sheldon, Erin; Tucker, Douglas; Kuropatkin, Nikolay; Stoughton, Chris
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.
NASA Astrophysics Data System (ADS)
Duorah, H. L.
2015-08-01
The bound on the cosmological constant energy density produced by big bang nucleosynthesis,0.786≤ΩΛ≤0.844 has been used to study the growth rate of large scale structure. The equation of state of dark energy is found to vary with a rate, △ω/△t≈10-14yr-1 since the time of decoupling and it levels off at about ω≈-0.996 for all the values of ΩΛ permitted by nucleosynthesis. This equation of state along with spectral index, n≈0.9 permitted by WMAP data yields growth rate which saturates at about z≈0.4 . The growth is suppressed below z≈0.4 . Observed growth data satisfies the trend of evolution. It strengthens the case for ΛCDM with nucleosynthesis bound on dark energy consistent with structure formation. The minute departure from scale invariance in presence of dark energy generates a mass scale M18=434.53-817.71 and a length scale λpeak=935.02-1283.94 Mpc. This elevation of structure mass and length may be a new feature of the ΛCDM model. The results may call for a serious look into the nature of dark energy and gravity itself.
Yang-Mills condensate as dark energy: A nonperturbative approach
NASA Astrophysics Data System (ADS)
Donà, Pietro; Marcianò, Antonino; Zhang, Yang; Antolini, Claudia
2016-02-01
Models based on the Yang-Mills condensate (YMC) have been advocated for in the literature and claimed as successful candidates for explaining dark energy. Several variations on this simple idea have been considered, the most promising of which are reviewed here. Nevertheless, the previously attained results relied heavily on the perturbative approach to the analysis of the effective Yang-Mills action, which is only adequate in the asymptotically free limit, and were extended into a regime, the infrared limit, in which confinement is expected. We show that if a minimum of the effective Lagrangian in θ =-Fμν aFa μ ν/2 exists, a YMC forms that drives the Universe toward an accelerated de Sitter phase. The details of the models depend weakly on the specific form of the effective Yang-Mills Lagrangian. Using nonperturbative techniques mutated from the functional renormalization-group procedure, we finally show that the minimum in θ of the effective Lagrangian exists. Thus, a YMC can actually take place. The nonperturbative model has properties similar to the ones in the perturbative model. In the early stage of the Universe, the YMC equation of state has an evolution that resembles the radiation component, i.e., wy→1 /3 . However, in the late stage, wy naturally runs to the critical state with wy=-1 , and the Universe transitions from a matter-dominated into a dark energy dominated stage only at latest time, at a redshift whose value depends on the initial conditions that are chosen while solving the dynamical system.
New Light on Dark Energy (LBNL Science at the Theater)
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.
New Light on Dark Energy (LBNL Science at the Theater)
Linder, Eric; Ho, Shirly; Aldering, Greg; Fraiknoi, Andrew
2011-06-08
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.
Cosmological effects of scalar-photon couplings: dark energy and varying-α Models
Avgoustidis, A.; Martins, C.J.A.P.; Monteiro, A.M.R.V.L.; Vielzeuf, P.E.; Luzzi, G. E-mail: Carlos.Martins@astro.up.pt E-mail: up110370652@alunos.fc.up.pt
2014-06-01
We study cosmological models involving scalar fields coupled to radiation and discuss their effect on the redshift evolution of the cosmic microwave background temperature, focusing on links with varying fundamental constants and dynamical dark energy. We quantify how allowing for the coupling of scalar fields to photons, and its important effect on luminosity distances, weakens current and future constraints on cosmological parameters. In particular, for evolving dark energy models, joint constraints on the dark energy equation of state combining BAO radial distance and SN luminosity distance determinations, will be strongly dominated by BAO. Thus, to fully exploit future SN data one must also independently constrain photon number non-conservation arising from the possible coupling of SN photons to the dark energy scalar field. We discuss how observational determinations of the background temperature at different redshifts can, in combination with distance measures data, set tight constraints on interactions between scalar fields and photons, thus breaking this degeneracy. We also discuss prospects for future improvements, particularly in the context of Euclid and the E-ELT and show that Euclid can, even on its own, provide useful dark energy constraints while allowing for photon number non-conservation.
Dark energy in the three-body problem: Wide triple galaxies
NASA Astrophysics Data System (ADS)
Emel'yanov, N. V.; Kovalev, M. Yu.; Chernin, A. D.
2016-04-01
The structure and evolution of triple galaxy systems in the presence of the cosmic dark-energy background is studied in the framework of the three-body problem. The dynamics of wide triple systems are determinedmainly by the competition between the mutual gravitational forces between the three bodies and the anti-gravity created by the dark-energy background. This problem can be solved via numerical integration of the equations of motion with initial conditions that admit various types of evolutionary behavior of the system. Such dynamical models show that the anti-gravity created by dark energy makes a triple system less tightly bound, thereby facilitating its decay, with a subsequent transition to motion of the bodies away from each other in an accelerating regime with a linear Hubble-law dependence of the velocity on distance. The coefficient of proportionality between the velocity and distance in this asymptotic relation corresponds to the universal value H Λ = 61 km s-1 Mpc-1, which depends only on the dark-energy density. The similarity of this relation to the large-scale recession of galaxies indicates that double and triple galaxies represent elementary dynamical cells realizing the overall behavior of a system dominated by dark energy on their own scale, independent of their masses and dimensions.
Fine-structure constant constraints on dark energy. II. Extending the parameter space
NASA Astrophysics Data System (ADS)
Martins, C. J. A. P.; Pinho, A. M. M.; Carreira, P.; Gusart, A.; López, J.; Rocha, C. I. S. A.
2016-01-01
Astrophysical tests of the stability of fundamental couplings, such as the fine-structure constant α , are a powerful probe of new physics. Recently these measurements, combined with local atomic clock tests and Type Ia supernova and Hubble parameter data, were used to constrain the simplest class of dynamical dark energy models where the same degree of freedom is assumed to provide both the dark energy and (through a dimensionless coupling, ζ , to the electromagnetic sector) the α variation. One caveat of these analyses was that it was based on fiducial models where the dark energy equation of state was described by a single parameter (effectively its present day value, w0). Here we relax this assumption and study broader dark energy model classes, including the Chevallier-Polarski-Linder and early dark energy parametrizations. Even in these extended cases we find that the current data constrains the coupling ζ at the 1 0-6 level and w0 to a few percent (marginalizing over other parameters), thus confirming the robustness of earlier analyses. On the other hand, the additional parameters are typically not well constrained. We also highlight the implications of our results for constraints on violations of the weak equivalence principle and improvements to be expected from forthcoming measurements with high-resolution ultrastable spectrographs.
Dark energy domination in the local flow of giant galaxies
NASA Astrophysics Data System (ADS)
Chernin, A. D.; Emelyanov, N. V.; Karachentsev, I. D.
2015-05-01
A dozen of the most luminous galaxies, at distances of up to 10 Mpc from the Local Group, move away from the group, forming the local expansion flow of giants. We use recent Hubble Space Telescope data on local giants and their numerous fainter companions to study the dynamical structure and evolutionary trends of the flow. An N-body computer model, which reproduces the observed kinematics of the flow, is constructed under the assumption that the flow is embedded in the universal dark energy background. In the model, the motions of the flow members are controlled by their mutual attraction force and the repulsion force produced by the dark energy. It is found that the dark energy repulsion dominates the force field of the flow. Because of this, the flow expands with acceleration. The dark energy domination is enhanced by the environment effect of the low mean matter density on the spatial scale of 50 Mpc in the local Universe. The dark energy domination increases with time and introduces to the flow an asymptotically linear velocity-distance relation with the universal time-rate that depends on the dark energy density only.
Reconstruction of the dark matter-vacuum energy interaction
NASA Astrophysics Data System (ADS)
Wang, Yuting; Zhao, Gong-Bo; Wands, David; Pogosian, Levon; Crittenden, Robert G.
2015-11-01
An interaction between the vacuum energy and dark matter is an intriguing possibility which may offer a way of solving the cosmological constant problem. Adopting a general prescription for momentum exchange between the two dark components, we reconstruct α (a ), the temporal evolution of the coupling strength between dark matter and vacuum energy, in a nonparametric Bayesian approach using combined observational data sets from the cosmic microwave background, supernovae and large scale structure. An evolving interaction between the vacuum energy and dark matter removes some of the tensions between different data sets. However, it is not preferred over Λ CDM in the Bayesian sense, as improvement in the fit is not sufficient to compensate for the increase in the volume of the parameter space.
Modified holographic Ricci dark energy model with sign-changeable interaction
NASA Astrophysics Data System (ADS)
Das, Kanika; Sultana, Tazmin
2016-02-01
In this paper we present a spatially homogeneous and anisotropic Bianchi type-VI0 space-time filled with interacting dark matter and modified holographic Ricci dark energy. We have taken here a sign-changeable interaction. Assuming the relation between the shear scalar and expansion scalar with a particular form of Hubble parameter we have obtained the exact solution of the Einstein's field equations. The geometric and kinematic properties of the model have been investigated. Under suitable conditions it is observed that the universe becomes spatially homogeneous, isotropic and flat. The results are found to be consistent with the recent day observations.
Explaining the dark energy, baryon and dark matter coincidence via domain-dependent random densities
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.
Dark energy from quantum uncertainty of distant clock
NASA Astrophysics Data System (ADS)
Luo, M. J.
2015-06-01
The observed cosmic acceleration was attributed to an exotic dark energy in the framework of classical general relativity. The dark energy behaves very similar with vacuum energy in quantum mechanics. However, once the quantum effects are seriously taken into account, it predicts a completely wrong result and leads to a severe fine-tuning. To solve the problem, the exact meaning of time in quantum mechanics is reexamined. We abandon the standard interpretation of time in quantum mechanics that time is just a global parameter, replace it by a quantum dynamical variable playing the role of physical clock. We find that synchronization of two spatially separated clocks can not be precisely realized at quantum level. There is an intrinsic quantum uncertainty of distant clock time, which implies an apparent vacuum energy fluctuation and gives an observed dark energy density at tree level approximation, where L P and L H are the Planck and Hubble scale cutoffs. The fraction of the dark energy is given by , which does not evolve with the internal clock time. The "dark energy" as a quantum cosmic variance is always seen comparable with the matter energy density by an observer using the internal clock time. The corrected distance-redshift relation of cosmic observations due to the distant clock effect are also discussed, which again gives a redshift independent fraction . The theory is consistent with current cosmic observations.
The abnormally weighting energy hypothesis: the missing link between dark matter and dark energy
Alimi, J-M; Fuezfa, A E-mail: andre.fuzfa@fundp.ac.be; Groupe d'Application des MAthematiques aux Sciences du COsmos , University of Namur
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.
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.
The Higgs Portal and AN Unified Model for Dark Energy and Dark Matter
NASA Astrophysics Data System (ADS)
Bertolami, O.; Rosenfeld, R.
We examine a scenario where the Higgs boson is coupled to an additional Standard Model singlet scalar field from a hidden sector. We show that, in the case where this field is very light and has already relaxed to its nonzero vacuum expectation value, one gets a very stringent limit on the mixing angle between the hidden sector scalar and the Higgs field from fifth force experiments. However, this limit does not imply in a small coupling due to the large difference of vacuum expectation values. In the case that the hidden sector scalar is identified with the quintessence field, responsible for the recent acceleration of the universe, the most natural potential describing the interaction is disfavored since it results in a time-variation of the Fermi scale. We show that an ad hoc modification of the potential describing the Higgs interaction with the quintessence field may result in an unified picture of dark matter and dark energy, where dark energy is the zero-mode classical field rolling the usual quintessence potential and the dark matter candidate is the quantum excitation (particle) of the field, which is produced in the universe due to its coupling to the Higgs boson. This coupling also generates a mass for the new particle that, contrary to usual quintessence models, does not have to be small, since it does not affect the evolution of classical field. In this scenario, a feasible dark matter density can be, under conditions, obtained.
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 ability of X-ray observations to detect and study the hot gas in galaxy clusters. From these data, the ratio of the mass of the hot gas and the mass of the dark matter in a cluster can be determined. The observed values of the gas fraction depend on the assumed distance to the cluster, which in turn depends on the curvature of space and the amount of dark energy in the universe. Galaxy Cluster Animation Galaxy Cluster Animation Because galaxy clusters are so large, they are thought to represent a fair sample of the matter content in the universe. If so, then relative amounts of hot gas and dark matter should be the same for every cluster. Using this assumption, Allen and colleagues adjusted the distance scale to determine which one fit the data best. These distances show that the expansion of the Universe was first decelerating and then began to accelerate about six billion years ago. Chandra's observations agree with supernova results including those from the Hubble Space Telescope (HST), which first showed dark energy's effect on the acceleration of the Universe. Chandra's results are completely independent of the supernova technique - both in wavelength and the objects observed. Such independent verification is a cornerstone of science. In this case it helps to dispel any remaining doubts that the supernova technique is flawed. "Our Chandra method has nothing to do with other techniques, so they're definitely not comparing notes, so to speak," said Robert Schmidt of University of Potsdam in Germany, another coauthor on the study. Energy Distribution of the Universe Energy Distribution of the Universe Better limits on the amount of dark energy and how it varies with time are obtained by combining the X-ray results with data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), which used observations of the cosmic microwave background radiation to discover evidence for dark energy in the very early Universe. Using the combined data, Allen and his colleagues found that dark energy makes up about 75% of the Universe, dark matter about 21%, and visible matter about 4%. Allen and his colleagues stress that the uncertainties in the measurements are such that the data are consistent with dark energy having a constant value. The present Chandra data do, however, allow for the possibility that the dark energy density is increasing with time. More detailed studies with Chandra, HST, WMAP and with the future mission Constellation-X should provide much more precise constraints on dark energy. Expansion of the Universe Expansion of the Universe at Constant Acceleration "Until we better understand cosmic acceleration and the nature of the dark energy we cannot hope to understand the destiny of the Universe," said independent commentator Michael Turner, of the University of Chicago. The team conducting the research also included Harald Ebeling of the University of Hawaii and the late Leon van Speybroeck of the Harvard-Smithsonian Center for Astrophysics. These results will appear in an upcoming issue of the Monthly Notices of the Royal Astronomy Society. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA's Office of Space Science, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. Press Kit: Galaxy Clusters and Dark Energy Press Kit Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov
Gravitational Energy as Dark Energy: Concordance of Cosmological Tests
NASA Astrophysics Data System (ADS)
Leith, Ben M.; Ng, S. C. Cindy; Wiltshire, David L.
2008-01-01
We provide preliminary quantitative evidence that a new solution to averaging the observed inhomogeneous structure of matter in the universe may lead to an observationally viable cosmology without exotic dark energy. We find parameters which simultaneously satisfy three independent tests: the match to the angular scale of the sound horizon detected in the cosmic microwave background anisotropy spectrum; the effective comoving baryon acoustic oscillation scale detected in galaxy clustering statistics; and Type Ia supernova luminosity distances. Independently of the supernova data, concordance is obtained for a value of the Hubble constant which agrees with the measurement of the Hubble Key team of Sandage and coworkers. Best-fit parameters include a global average Hubble constant H0 = 61.7‑1.1+1.2 km s‑1 Mpc‑1, a present epoch void volume fraction of fv 0 = 0.76‑0.09+0.12, and an age of the universe of 14.7‑0.5+0.7 billion years as measured by observers in galaxies. The mass ratio of nonbaryonic dark matter to baryonic matter is 3.1‑2.4+2.5, computed with a baryon-to-photon ratio that is in concordance with primordial lithium abundances.
On dark degeneracy and interacting models
Carneiro, S.; Borges, H.A. E-mail: humberto@ufba.br
2014-06-01
Cosmological background observations cannot fix the dark energy equation of state, which is related to a degeneracy in the definition of the dark sector components. Here we show that this degeneracy can be broken at perturbation level by imposing two observational properties on dark matter. First, dark matter is defined as the clustering component we observe in large scale structures. This definition is meaningful only if dark energy is unperturbed, which is achieved if we additionally assume, as a second condition, that dark matter is cold, i.e. non-relativistic. As a consequence, dark energy models with equation-of-state parameter −1 ≤ ω < 0 are reduced to two observationally distinguishable classes with ω = −1, equally competitive when tested against observations. The first comprises the ΛCDM model with constant dark energy density. The second consists of interacting models with an energy flux from dark energy to dark matter.
Generation of switchable domain wall and Cubic-Quintic nonlinear Schrödinger equation dark pulse
NASA Astrophysics Data System (ADS)
Tiu, Z. C.; Suthaskumar, M.; Zarei, A.; Tan, S. J.; Ahmad, H.; Harun, S. W.
2015-10-01
A switchable domain-wall (DW) and Cubic-Quintic nonlinear Schrödinger equation (CQNLSE) dark soliton pulse generation are demonstrated in Erbium-doped fiber laser (EDFL) for the first time. The DW pulse train operates at 1575 nm with a fundamental repetition rate of 1.52 MHz and pulse width of 203 ns as the pump power is increased above the threshold pump power of 80 mW. The highest pulse energy of 2.24 nJ is obtained at the maximum pump power of 140 mW. CQNLSE pulse can also be realized from the same cavity by adjusting the polarization state but at a higher threshold pump power of 104 mW. The repetition rate and pulse width of the CQNLSE dark pulses are obtained at 1.52 MHz and 219 ns, respectively. The highest energy of 0.58 nJ is obtained for the CQNLSE pulse at pump power of 140 mW.
Inflation and dark energy arising from geometrical tachyons
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.
Higgs seesaw mechanism as a source for dark energy.
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. PMID:23971559
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.
A possible connection between massive fermions and dark energy
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.
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.
The Relative Abundance of Isolated Clusters as a Probe of Dark Energy
NASA Astrophysics Data System (ADS)
Lee, Jounghun
2012-06-01
Those galaxy clusters that do not belong to superclusters are referred to as isolated clusters. Their relative abundance at a given epoch may be a powerful constraint of the dark energy equation of state since it depends strongly on how fast the structures grow on the largest scale in the universe. We note that the mass function of isolated clusters can be separately evaluated through modification of the recently developed Corasaniti-Achitouv (CA) theory according to which the stochastic collapse barrier is quantified by two coefficients: the drifting average coefficient (β) and the diffusion coefficient (DB ). Regarding β in the CA formalism as an adjustable parameter and assuming that the formation of isolated clusters corresponds to the case of DB = 0, we determine the mass function of isolated clusters by fitting the numerical results from the MICE simulations to the modified CA formula. It is found that the best-fit value of β changes with redshift and that the CA mass function with DB = 0 agrees very well with the numerical results at various redshifts. Defining the relative abundance of isolated clusters, ξ I , as the ratio of the cumulative mass function of isolated clusters to that of non-isolated clusters at a given epoch, we finally show how sensitively ξ I changes with the dark energy equation of state. It is also discussed how ξ I can help break the degeneracy between the dark energy equation of state and the other key cosmological parameters.
Constraints on interacting Dark Energy models from galaxy rotation curves
Baldi, Marco; Salucci, Paolo E-mail: salucci@sissa.it
2012-02-01
Interacting Dark Energy models have been introduced as a possible alternative to the standard ΛCDM concordance cosmological scenario in order to ease the fine-tuning problems of the cosmological constant. However, the interaction of the Dark Energy field with other massive particles in the universe induces also an effective modification of structure formation processes, leading to a different dynamical behavior of density perturbations with respect to the standard scenario. In particular, high-resolution N-body simulations have recently shown that also the structural properties of highly nonlinear objects, as e.g. their average concentration at a given mass, could be significantly modified in the presence of an interaction between Dark Energy and Dark Matter. While a constant interaction strength leads to less concentrated density profiles, a steep growth in time of the coupling function has been shown to determine a large increase of halo concentrations over a wide range of masses, including the typical halos hosting luminous spiral galaxies. This determines a substantial worsening of the 'cusp-core' tension arising in the standard ΛCDM model and provides a direct way to constrain the form of the Dark Energy interaction. In the present paper we make use of the outcomes of some high-resolution N-body simulations of a specific class of interacting Dark Energy models to compare the predicted rotation curves of luminous spiral galaxies forming in these cosmologies against real observational data. Our results show how some specific interacting Dark Energy scenarios featuring a steep growth in time of the coupling function — which are virtually indistinguishable from ΛCDM in the background — cannot fit the observed rotation curves of luminous spiral galaxies and can therefore be ruled out only on the basis of dynamical properties of small-scale structures. Our study is a pilot investigation of the effects of a Dark Energy interaction at small scales, and demonstrates how the dynamical properties of visible galaxies can in some cases provide direct constraints on the nature of Dark Energy.
Constraining Dark Energy with the DEEP2 Redshift Survey
NASA Astrophysics Data System (ADS)
Davis, M.; Gerke, B. F.; Newman, J. A.; Deep2 Team
2005-08-01
The DEEP2 survey has now completed half of its planned 3-year life-span, and we have collected approximately 50% of the data, putting us exactly on schedule. The survey plan calls for spectroscopic coverage by July 2005 of ˜60,000 galaxies over 3.5 deg2 to a limiting magnitude of RAB = 24.1 ; the great majority of these objects are at 0.7
Dark Energy: Measurement by the DEEP2 Redshift Survey
NASA Astrophysics Data System (ADS)
Davis, Marc
2005-04-01
The DEEP2 redshift survey has now covered ˜2.5 degrees^2 of sky and obtained nearly 40,000 spectra; the survey is nearly finished, and I shall describe what has been accomplished with all that Keck time! One of our fields is the Extended Groth Strip (EGS), a region where deep imaging is being obtained with Chandra, Spitzer, GALEX, VLA, and HST/ACS and will be the subject of Sunyaev-Zel'dovich observations. We will eventually provide 17,000 redshifts. In three other regions, we have used three-color imaging to efficiently select galaxies with magnitude RAB<24.1 and redshifts in the range 0.7
Reconstructing the history of dark energy using maximum entropy
NASA Astrophysics Data System (ADS)
Zunckel, Caroline; Trotta, Roberto
2007-09-01
We present a Bayesian technique based on a maximum-entropy method to reconstruct the dark energy equation of state (EOS) w(z) in a non-parametric way. This Maximum Entropy (MaxEnt) technique allows to incorporate relevant prior information while adjusting the degree of smoothing of the reconstruction in response to the structure present in the data. After demonstrating the method on synthetic data, we apply it to current cosmological data, separately analysing Type Ia supernova measurement from the HST/GOODS programme and the first-year Supernovae Legacy Survey (SNLS), complemented by cosmic microwave background and baryonic acoustic oscillation data. We find that the SNLS data are compatible with w(z) = -1 at all redshifts 0 <= z <~ 1100, with error bars of the order of 20 per cent for the most-constraining choice of priors. The HST/GOODS data exhibit a slight (about 1σ significance) preference for w > -1 at z ~ 0.5 and a drift towards w > -1 at larger redshifts which, however, is not robust with respect to changes in our prior specifications. We employ both a constant EOS prior model and a slowly varying w(z) and find that our conclusions are only mildly dependent on this choice at high redshifts. Our method highlights the danger of employing parametric fits for the unknown EOS, that can potentially miss or underestimate real structure in the data.
The Nature of Dark Energy from Type Ia Supernovae
NASA Astrophysics Data System (ADS)
Hook, Isobel
2007-02-01
Type Ia supernovae (SNe Ia) currently provide the most direct evidence for an accelerating Universe and for the existence of an unknown "dark energy". The 5-year Supernova Legacy Survey (SNLS) is generating a definitive dataset with well-sampled g'r'i'z' light curves and spectroscopic confirmation, which together allow precise measurement of the cosmological parameters. We are now entering the final 18 months of this highly successful survey. With the full, final sample we expect to determine the cosmological equation of state parameter "w" to a statistical precision of +/-0.05 or better, testing theories for the origin of the universal acceleration. The amount of spectroscopic follow-up performed is central to the success of the survey. Approximately 500 SNe Ia will be spectroscopically confirmed in a coherent program involving Gemini, VLT and Keck. Nod-and-shuffle observations at Gemini play a pivotal role. The goal for Gemini this semester is to obtain types and redshifts for 30 SN Ia candidates with redshifts 0.6-0.9, contributing to a dataset superior to any existing - or planned - sample. This is a continuing QR (quick response) proposal for GMOS-N.
Dark energy parametrization motivated by scalar field dynamics
NASA Astrophysics Data System (ADS)
de la Macorra, Axel
2016-05-01
We propose a new dark energy (DE) parametrization motivated by the dynamics of a scalar field ϕ. We use an equation of state w parametrized in terms of two functions L and y, closely related to the dynamics of scalar fields, which is exact and has no approximation. By choosing an appropriate ansatz for L we obtain a wide class of behavior for the evolution of DE without the need to specify the scalar potential V. We parametrize L and y in terms of only four parameters, giving w a rich structure and allowing for a wide class of DE dynamics. Our w can either grow and later decrease, or it can happen the other way around; the steepness of the transition is not fixed and it contains the ansatz w={w}o+{w}a(1-a). Our parametrization follows closely the dynamics of a scalar field, and the function L allows us to connect it with the scalar potential V(φ ). While the Universe is accelerating and the slow roll approximation is valid, we get L≃ {({V}\\prime /V)}2. To determine the dynamics of DE we also calculate the background evolution and its perturbations, since they are important to discriminate between different DE models.
Determination of Dark Matter Properties at High-Energy Collider
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.
Determination of Dark Matter Properties at High-Energy Colliders
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.
Revisit of the interaction between holographic dark energy and dark matter
Zhang, Zhenhui; Li, Xiao-Dong; Li, Song; Li, Miao; Zhang, Xin E-mail: sli@itp.ac.cn E-mail: zhangxin@mail.neu.edu.cn
2012-06-01
In this paper we investigate the possible direct, non-gravitational interaction between holographic dark energy (HDE) and dark matter. Firstly, we start with two simple models with the interaction terms Q∝ρ{sub dm} and Q∝ρ{sub de}, and then we move on to the general form Q∝ρ{sub m}{sup α}ρ{sub de}{sup β}. The cosmological constraints of the models are obtained from the joint analysis of the present Union2.1+BAO+CMB+H{sub 0} data. We find that the data slightly favor an energy flow from dark matter to dark energy, although the original HDE model still lies in the 95.4% confidence level (CL) region. For all models we find c < 1 at the 95.4% CL. We show that compared with the cosmic expansion, the effect of interaction on the evolution of ρ{sub dm} and ρ{sub de} is smaller, and the relative increment (decrement) amount of the energy in the dark matter component is constrained to be less than 9% (15%) at the 95.4% CL. By introducing the interaction, we find that even when c < 1 the big rip still can be avoided due to the existence of a de Sitter solution at z→−1. We show that this solution can not be accomplished in the two simple models, while for the general model such a solution can be achieved with a large β, and the big rip may be avoided at the 95.4% CL.
Precision Photometry to Study the Nature of Dark Energy
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.
New limits on coupled dark energy from Planck
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.
Can we distinguish early dark energy from a cosmological constant?
NASA Astrophysics Data System (ADS)
Shi, Difu; Baugh, Carlton M.
2016-04-01
Early dark energy (EDE) models are a class of quintessence dark energy with a dynamically evolving scalar field which display a small but non-negligible amount of dark energy at the epoch of matter-radiation equality. Compared with a cosmological constant, the presence of dark energy at early times changes the cosmic expansion history and consequently the shape of the linear theory power spectrum and potentially other observables. We constrain the cosmological parameters in the EDE cosmology using recent measurements of the cosmic microwave background and baryon acoustic oscillations. The best-fitting models favour no EDE; here we consider extreme examples which are in mild tension with current observations in order to explore the observational consequences of a maximally allowed amount of EDE. We study the non-linear evolution of cosmic structure in EDE cosmologies using large volume N-body simulations. Many large-scale structure statistics are found to be very similar between the Λ cold dark matter (ΛCDM) and EDE models. We find that EDE cosmologies predict fewer massive halos in comparison to ΛCDM, particularly at high redshifts. The most promising way to distinguish EDE from ΛCDM is to measure the power spectrum on large scales, where differences of up to 15% are expected.
New limits on coupled dark energy from Planck
NASA Astrophysics Data System (ADS)
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 H0 probes from HST.
What can gamma ray bursts teach us about dark energy?
Hooper, Dan; Dodelson, Scott; /Fermilab /Chicago U., Astron. Astrophys. Ctr.
2005-12-01
It has been suggested that Gamma Ray Bursts (GRB) may enable the expansion rate of our Universe to be measured out to very high redshifts (z {approx}> 5) just as type Ia supernovae have done at z {approx} 1-1.5. We explore this possibility here, and find that GRB have the potential to detect dark energy at high statistical significance, but they are unlikely to be competitive with future supernovae missions, such as SNAP, in measuring the properties of the dark energy. The exception to this conclusion is if there is appreciable dark energy at early times, in which case the information from GRB's will provide an excellent complement to the z {approx} 1 information from supernovae.
Dark energy, scalar-tensor gravity, and large extra dimensions
Kainulainen, Kimmo; Sunhede, Daniel
2006-04-15
We explore in detail a dilatonic scalar-tensor theory of gravity inspired by large extra dimensions, where a radion field from compact extra dimensions gives rise to quintessence in our 4-dimensional world. We show that the model can give rise to other types of cosmologies as well, some more akin to k-essence and possibly variants of phantom dark energy. In our model the field (or radius) stabilization arises from quantum corrections to the effective 4D Ricci scalar. We then show that various constraints nearly determine the model parameters, and give an example of a quintessence-type cosmology consistent with observations. We show that the upcoming SNAP-experiment would easily distinguish the present model from a constant {lambda} model with an equal amount of dark energy, but that the SNAP-data alone will not be able distinguish it from a {lambda} model with about 5% less dark energy.
Low redshift universe and a varying ghost dark energy
NASA Astrophysics Data System (ADS)
Khurshudyan, M.
2016-03-01
Recently, a phenomenological modification of ghost dark energy has been suggested and appropriate models of low redshift universe have been constructed. In this paper, we will consider a model of low redshift universe in General Relativity containing another model of varying ghost dark energy. In this model, an effective fluid is a radiation-like fluid in an early universe and evolves to quintessence dark energy in large scale universe. Cosmographic analysis of new model is performed and appropriate constraints on the parameters of the model are obtained. We have a look at suggested model via statefinder hierarchy in addition to thermodynamical description of it. We also study massless particle creation possibility in a radiation dominated universe of our cosmological model. According to our theoretical results, massless particle production is possible. To study particle creation, a straight analogy between quantization in Minkowski background and canonical quantization of a scalar field in curved dynamical backgrounds is taken into account.
Dark energy cosmology with the alternative cosmic microwave background data
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.
Status of the Dark Energy Survey Camera (DECam) Project
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.
Gauss-Bonnet dark energy by Lagrange multipliers
NASA Astrophysics Data System (ADS)
Capozziello, Salvatore; Makarenko, Andrey N.; Odintsov, Sergei D.
2013-04-01
A string-inspired effective theory of gravity, containing Gauss-Bonnet invariant interacting with a scalar field, is considered in view of obtaining cosmological dark energy solutions. A Lagrange multiplier is inserted into the action in order to achieve the cosmological reconstruction by selecting suitable forms of couplings and potentials. Several cosmological exact solutions (including dark energy of quintessence, phantom, or Little Rip type) are derived in the presence and in the absence of the Lagrange multiplier showing the difference in the two dynamical approaches. In the models that we consider, the Lagrange multiplier behaves as a sort of dust fluid that realizes the transitions between matter-dominated and dark energy epochs. The relation between Lagrange multipliers and Noether symmetries is discussed.
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.
New Agegraphic Pilgrim Dark Energy in f(T, TG) Gravity
NASA Astrophysics Data System (ADS)
Abdul, Jawad; Ujjal, Debnath
2015-08-01
In this work, we briefly discuss a novel class of modified gravity like f(T, TG) gravity. In this background, we assume the new agegraphic version of pilgrim dark energy and reconstruct f(T, TG) models for two specific values of s. We also discuss the equation of state parameter, squared speed of sound and wDE-w?DE plane for these reconstructed f(T, TG) models. The equation of state parameter provides phantom-like behavior of the universe. The wDE-w?DE plane also corresponds to ?CDM limit, thawing and freezing regions for both models.
NASA Astrophysics Data System (ADS)
Dasu Naidu, K.; Naidu, R. L.; Sobhan babu, K.
2015-09-01
In this paper, we have investigated Kantowski-Sachs space-time in the presence of anisotropic fluid with variable equation of state (EoS) parameter and constant deceleration parameter in the scale covariant theory of gravitation proposed by Canuto et al. (Phys. Rev. Lett. 39:429, 1977). We have found a determinate solution of the field equations of the theory using variation law for Hubble's parameter given by Bermann (Nuvo Cimento 74:182, 1983). Our solution represents Kantowski-Sachs dark energy model in this theory. The physical and kinematical properties of the model are also discussed.
NASA Astrophysics Data System (ADS)
de Vega, H. J.; Sanchez, N. G.
2016-05-01
We find the distribution function f(E) for dark matter (DM) halos in galaxies and the corresponding equation of state from the (empirical) DM density profiles derived from observations. We solve for DM in galaxies the analogous of the Eddington equation originally used for the gas of stars in globular clusters. The observed density profiles are a good realistic starting point and the distribution functions derived from them are realistic. We do not make any assumption about the DM nature, the methods developed here apply to any DM kind, though all results are consistent with warm dark matter (WDM). With these methods we find: (i) Cored density profiles behaving quadratically for small distances ρ(r)= r → 0ρ(0) ‑ Kr2 produce distribution functions which are finite and positive at the halo center while cusped density profiles always produce divergent distribution functions at the center. (ii) Cored density profiles produce approximate thermal Boltzmann distribution functions for r ≲ 3rh where rh is the halo radius. (iii) Analytic expressions for the dispersion velocity and the pressure are derived yielding at each halo point an ideal DM gas equation of state with local temperature T(r) ≡ mv2(r)/3. T(r) turns out to be constant in the same region where the distribution function is thermal and exhibits the same temperature within the percent. The self-gravitating DM gas can thermalize despite being collisionless because it is an ergodic system. (iv) The DM halo can be consistently considered at local thermal equilibrium with: (a) a constant temperature T(r) = T0 for r ≲ 3rh, (b) a space dependent temperature T(r) for 3rh < r ≲ Rvirial, which slowly decreases with r. That is, the DM halo is realistically a collisionless self-gravitating thermal gas for r ≲ Rvirial. (v) T(r) outside the halo radius nicely follows the decrease of the circular velocity squared.
A New Viewpoint (The expanding universe, Dark energy and Dark matter)
NASA Astrophysics Data System (ADS)
Cwele, Daniel
2011-10-01
Just as the relativity paradox once threatened the validity of physics in Albert Einstein's days, the cosmos paradox, the galaxy rotation paradox and the experimental invalidity of the theory of dark matter and dark energy threaten the stability and validity of physics today. These theories and ideas and many others, including the Big Bang theory, all depend almost entirely on the notion of the expanding universe, Edwin Hubble's observations and reports and the observational inconsistencies of modern day theoretical Physics and Astrophysics on related subjects. However, much of the evidence collected in experimental Physics and Astronomy aimed at proving many of these ideas and theories is ambiguous, and can be used to prove other theories, given a different interpretation of its implications. The argument offered here is aimed at providing one such interpretation, attacking the present day theories of dark energy, dark matter and the Big Bang, and proposing a new Cosmological theory based on a modification of Isaac Newton's laws and an expansion on Albert Einstein's theories, without assuming any invalidity or questionability on present day cosmological data and astronomical observations.
Unified dark energy and dust dark matter dual to quadratic purely kinetic K-essence
NASA Astrophysics Data System (ADS)
Guendelman, Eduardo; Nissimov, Emil; Pacheva, Svetlana
2016-02-01
We consider a modified gravity plus single scalar-field model, where the scalar Lagrangian couples symmetrically both to the standard Riemannian volume-form (spacetime integration measure density) given by the square root of the determinant of the Riemannian metric, as well as to another non-Riemannian volume-form in terms of an auxiliary maximal-rank antisymmetric tensor gauge field. As shown in a previous paper, the pertinent scalar-field dynamics provides an exact unified description of both dark energy via dynamical generation of a cosmological constant, and dark matter as a "dust" fluid with geodesic flow as a result of a hidden Noether symmetry. Here we extend the discussion by considering a non-trivial modification of the purely gravitational action in the form of f(R) = R - α R^2 generalized gravity. Upon deriving the corresponding "Einstein-frame" effective action of the latter modified gravity-scalar-field theory we find explicit duality (in the sense of weak versus strong coupling) between the original model of unified dynamical dark energy and dust fluid dark matter, on one hand, and a specific quadratic purely kinetic "k-essence" gravity-matter model with special dependence of its coupling constants on only two independent parameters, on the other hand. The canonical Hamiltonian treatment and Wheeler-DeWitt quantization of the dual purely kinetic "k-essence" gravity-matter model is also briefly discussed.
Reducing Zero-point Systematics in Dark Energy Supernova Experiments
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.
CMB anisotropy induced by tachyonic perturbations of dark energy
Libanov, M. V.; Rubakov, V. A.; Sazhina, O. S. Sazhin, M. V.
2009-02-15
We consider the effects of possible tachyonic perturbations of dark energy on the CMB anisotropy. Such perturbations emerge, in particular, in models with phantom dark energy violating Lorentz invariance. Therefore, we discuss tachyonic perturbations with a Lorentz-violating dispersion relation. We show that the corresponding contribution to the CMB anisotropy can have an appreciable amplitude, while the angular spectrum has a distinct maximum. These predictions are compared with observational data. The tachyonic contribution slightly improves the agreement between the theory and observations, but this improvement is statistically insignificant and our analysis gives constraints on the tachyonic perturbation amplitude.
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.
Quintessence and phantom dark energy from ghost D-branes
Saridakis, Emmanuel N.; Ward, John
2009-10-15
We present a novel dark-energy candidate, based upon the existence and dynamics of ghost D-branes in a warped compactification of type IIB string theory. Gp-branes cancel the combined BPS sectors of the Dp-branes, while they preserve the same supersymmetries. We show that this scenario can naturally lead to either quintessence or phantomlike behaviors, depending on the form of the involved potentials and brane tension. As a specific example we investigate the static, dark-energy dominated solution subclass.
Quantisation of the holographic Ricci dark energy model
NASA Astrophysics Data System (ADS)
Albarran, Imanol; Bouhmadi-López, Mariam
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.
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.
What do we really know about dark energy?
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. PMID:22084297
Clusters of Galaxies in the Dark Energy Survey
NASA Astrophysics Data System (ADS)
Jeltema, Tesla E.; DES Collaboration
2016-01-01
The growth rate of clusters of galaxies is highly sensitive to the underlying cosmology. In fact, clusters will provide one of the most precise methods of constraining dark energy with large-area optical surveys like the Dark Energy Survey (DES). However, extracting precision cosmology from cluster surveys necessarily depends on having a well-understood method of selecting clusters and accurately translating their observed properties to underlying mass. I will discuss the status of the DES cluster survey as well as efforts to calibrate the cluster richness-mass relation.
NASA Astrophysics Data System (ADS)
Azizur Rahman, M.; Ansari, M.
2014-12-01
In this paper, we have investigated a spatially homogeneous and anisotropic universe where dark energy interacts with dark matter. To obtain the exact solutions of Einstein's field equations, we consider a hybrid expansion law (HEL) which exhibits a transition of the universe from decelerating phase to the present accelerating phase. We observe that the model of the universe approaches isotropy under suitable condition and the coincidence parameter is found to be an increasing function of time. The physical and geometrical properties of the universe have been discussed which are found to be consistent with recent observations. Moreover, a correspondence between the holographic dark energy and polytropic gas model of dark energy is established. This correspondence allows us to reconstruct the potential and the dynamics for the scalar field of the polytropic gas which describes the accelerated expansion of the universe. We have also studied the statefinder parameters to characterize different phases of the evolution of the universe.
f(T) theories from holographic dark energy models within Bianchi type I universe
NASA Astrophysics Data System (ADS)
Fayaz, V.; Hossienkhani, H.; Pasqua, A.; Amirabadi, M.; Ganji, M.
2015-02-01
Recently, the teleparallel Lagrangian density described by the torsion scalar T has been extended to a function of T. The f( T) modified teleparallel gravity has been proposed as the natural gravitational alternative for dark energy to explain the late time acceleration of the universe. We consider spatially homogenous and anisotropic Bianchi type I universe in the context of f( T) gravity. The purpose of this work is to develop a reconstruction of the f( T) gravity model according to the holographic dark energy model. We have considered an action, of the form T + g( T) + L m, describing Einstein's gravity plus a function of the torsion scalar. In the framework of the said modified gravity theory, we have considered the equation of state of the holographic dark energy density. Subsequently, we have developed a reconstruction scheme for modified gravity with f( T) action. Finally, we have also studied the de Sitter and power-law solutions when the universe enters a phantom phase and shown that such solutions may exist for some f( T) solutions with the holographic and new agegraphic dark energy scenario.
Generalized Chaplygin gas as a unified scenario of dark matter/energy: Observational constraints
NASA Astrophysics Data System (ADS)
Zhu, Z.-H.
2004-08-01
Although various cosmological observations congruously suggest that our universe is dominated by two dark components, the cold dark matter without pressure and the dark energy with negative pressure, the nature and origin of these components is yet unknow. The generalized Chaplygin gas (gCg), parametrized by an equation of state, p = -A/ρgCg\\alpha, was recently proposed to be a candidate of the unified dark matter/energy (UDME) scenarios. In this work, we investigate some observational constraints on it. We mainly focus our attention on the constraints from recent measurements of the X-ray gas mass fractions in clusters of galaxies published by Allen et al. (\\cite{Allen02}, MNRAS, 334, L11; \\cite{Allen03}, 342, 257) and the dimensionless coordinate distances to type Ia supernovae and Fanaroff-Riley type IIb radio galaxies compiled by Daly & Djorgovski (\\cite{Daly03}, ApJ, 597, 9). We obtain the confidence region on the two parameters fully characterizing gCg, As ≡ A/ρgCg0(1+α) and α, from a combined analysis of these databases, where ρgCg0 is the energy density of gCg at present. It is found that As= 0.70+0.16-0.17 and α= -0.09+0.54-0.33, at a 95% confidence level, which is consistent within the errors with the standard dark matter + dark energy model, i.e., the case of α = 0. Particularly, the standard Chaplygin gas (α=1) is ruled out as a feasible UDME by the data at a 99% confidence level.
LSST Dark Energy Science Final Report
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.
Dynamical behavior of the extended holographic dark energy with the Hubble horizon
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.
Generalized Chaplygin gas as geometrical dark energy
Heydari-Fard, M.; Sepangi, H. R.
2007-11-15
The generalized Chaplygin gas provides an interesting candidate for the present accelerated expansion of the universe. We explore a geometrical explanation for the generalized Chaplygin gas within the context of brane world theories where matter fields are confined to the brane by means of the action of a confining potential. We obtain the modified Friedmann equations, deceleration parameter, and age of the universe in this scenario and show that they are consistent with the present observational data.
A cosmographic analysis of holographic dark energy models
NASA Astrophysics Data System (ADS)
Pan, Supriya; Chakraborty, Subenoy
2014-11-01
The present work deals with a detailed study of interacting holographic dark energy model for three common choices of the interaction term. Also, two standard choices of IR cut-off, namely, Ricci length scale and radius of the event horizon are considered here. Finally, the cosmographic parameters are presented both analytically and graphically.
The solutions and thermodynamic dark energy in the accelerating universe
NASA Astrophysics Data System (ADS)
Demirel, E. C. Günay
2016-03-01
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.
Decoherent neutrino mixing, dark energy, and matter-antimatter asymmetry
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.
Impacts of dark energy on weighing neutrinos after Planck 2015
NASA Astrophysics Data System (ADS)
Zhang, Xin
2016-04-01
We investigate how dark energy properties impact the cosmological limits on the total mass of active neutrinos. We consider two typical, simple dark energy models (that have only one more additional parameter than Λ CDM ), i.e., the w CDM model and the holographic dark energy (HDE) model, as examples, to make an analysis. In the cosmological fits, we use the Planck 2015 temperature and polarization data, in combination with other low-redshift observations, including the baryon acoustic oscillations, type Ia supernovae, and Hubble constant measurement, as well as the Planck lensing measurements. We find that, once dynamical dark energy is considered, the degeneracy between ∑mν and H0 will be changed, i.e., in the Λ CDM model, ∑mν is anticorrelated with H0, but in the w CDM and HDE models, ∑mν becomes positively correlated with H0. Compared to Λ CDM , in the w CDM model the limit on ∑mν becomes much looser, but in the HDE model the limit becomes much tighter. In the HDE model, we obtain ∑mν<0.113 eV (95% C.L.) with the combined data sets, which is perhaps the most stringent upper limit by far on neutrino mass. Thus, our result in the HDE model is nearly ready to diagnose the neutrino mass hierarchy with the current cosmological observations.
Dark Energy as a Holographic Ricci Component of the Universe
NASA Astrophysics Data System (ADS)
Belkacemi, Moulay-Hicham; Bouhmadi-Lpez, Mariam; Errahmani, Ahmed; Ouali, Taoufiq
2014-01-01
The holographic Ricci dark energy model is a very interesting proposal to describe the present acceleration of the universe. However, it turns out that a Friedmann-Lematre-Robertson-Walker filled with this kind of fluid might face a big rip singularity in its future. Here we propose a way to smooth such a future doomsday on this kind of model.
Accretion of dark energy onto stringy electrically charged black hole
NASA Astrophysics Data System (ADS)
Geng, Jin-Ling; Zhang, Yu; Li, En-Kun; Duan, Peng-Fei
2015-11-01
This paper studies the accretion of dark energy onto a stringy electrically charged black hole. Solution for a general spherical accretion of the ideal fluid onto a black hole is given first. It is shown that the location of the critical point lies inside the event horizon. In our paper, two solvable models of dark energy are considered. For the linearized model, the expression for the mass of the black hole is derived. And for the Chaplygin gas model, the change rate of the black hole mass is obtained. The results show that the mass of the stringy electrically charged black hole is fixed when ρ+ p = 0, but decreases at ρ+ p < 0 and increases at ρ+ p >0. Then, we conclude that the accretion of phantom-like dark energy makes the mass of the black hole decrease, and the accretion of the quintessence-like dark energy can increase the black hole mass. The bigger the absolute value of the pressure is, the faster the black hole mass decreases.
Has dark energy really been discovered in the Lab?
NASA Astrophysics Data System (ADS)
Jetzer, Philippe; Straumann, Norbert
2005-01-01
We show that dark energy contributions can not be determined from noise measurements of Josephson junctions, as was recently suggested in a paper by C. Beck and M.C. Mackey [Phys. Lett. B 605 (2005) 295, http://arXiv.org/astro-ph/0406504].
Generalized dark-bright vector soliton solution to the mixed coupled nonlinear Schrödinger equations
NASA Astrophysics Data System (ADS)
Manikandan, N.; Radhakrishnan, R.; Aravinthan, K.
2014-08-01
We have constructed a dark-bright N-soliton solution with 4N+3 real parameters for the physically interesting system of mixed coupled nonlinear Schrödinger equations. Using this as well as an asymptotic analysis we have investigated the interaction between dark-bright vector solitons. Each colliding dark-bright one-soliton at the asymptotic limits includes more coupling parameters not only in the polarization vector but also in the amplitude part. Our present solution generalizes the dark-bright soliton in the literature with parametric constraints. By exploiting the role of such coupling parameters we are able to control certain interaction effects, namely beating, breathing, bouncing, attraction, jumping, etc., without affecting other soliton parameters. Particularly, the results of the interactions between the bound state dark-bright vector solitons reveal oscillations in their amplitudes under certain parametric choices. A similar kind of effect was also observed experimentally in the BECs. We have also characterized the solutions with complicated structure and nonobvious wrinkle to define polarization vector, envelope speed, envelope width, envelope amplitude, grayness, and complex modulation. It is interesting to identify that the polarization vector of the dark-bright one-soliton evolves on a spherical surface instead of a hyperboloid surface as in the bright-bright case of the mixed coupled nonlinear Schrödinger equations.
Searching for Milky Way Satellites with the Dark Energy Survey
NASA Astrophysics Data System (ADS)
Drlica-Wagner, Alex
2015-04-01
We currently know of roughly two dozen satellite galaxies surrounding the Milky Way. Nearly half of these satellites were discovered in the last decade with the Sloan Digital Sky Survey (SDSS). As the nearest and most dark-matter dominated galaxies known, Milky Way satellites are unique laboratories for fundamental physics. Milky Way satellite galaxies probe the low-mass end of the matter power spectrum, provide a unique testing ground for CDM, and are pristine targets for indirect searches for dark matter annihilation. Due to the limited magnitude range and sky coverage of SDSS, the census of these objects is far from complete. We present results from a recent search for new satellite galaxies in the first year of Dark Energy Survey data and briefly discuss some implications for tests of fundamental physics. on behalf of the DES Collaboration.
Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion
Huterer, Dragan; Kirkby, David; Bean, Rachel; Connolly, Andrew; Dawson, Kyle; Dodelson, Scott; Evrard, August; Jain, Bhuvnesh; Jarvis, Michael; Linder, Eric; et al
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
Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion
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.
High-energy neutrino signatures of dark matter
NASA Astrophysics Data System (ADS)
Buckley, Matthew R.; Spolyar, Douglas; Freese, Katherine; Hooper, Dan; Murayama, Hitoshi
2010-01-01
It has been suggested that the excesses of high-energy cosmic ray electrons and positrons seen by PAMELA and the Fermi Gamma Ray Space Telescope are evidence of dark matter annihilation or decay in the Galactic halo. To accommodate these signals however, the final states must be predominantly muons or taus. These leptonic final states will produce neutrinos, which are potentially detectable with the IceCube neutrino observatory. We find that with five years of data, IceCube (supplemented by DeepCore) can significantly constrain the relevant parameter space for both annihilating or decaying dark matter, and may be capable of discovering leptophilic dark matter in the halo of the Milky Way.
Cosmological constraints on Lorentz violating dark energy
Audren, B.; Lesgourgues, J.; Sibiryakov, S. E-mail: Diego.Blas@cern.ch E-mail: Sergey.Sibiryakov@cern.ch
2013-08-01
The role of Lorentz invariance as a fundamental symmetry of nature has been lately reconsidered in different approaches to quantum gravity. It is thus natural to study whether other puzzles of physics may be solved within these proposals. This may be the case for the cosmological constant problem. Indeed, it has been shown that breaking Lorentz invariance provides Lagrangians that can drive the current acceleration of the universe without experiencing large corrections from ultraviolet physics. In this work, we focus on the simplest model of this type, called ΘCDM, and study its cosmological implications in detail. At the background level, this model cannot be distinguished from ΛCDM. The differences appear at the level of perturbations. We show that in ΘCDM, the spectrum of CMB anisotropies and matter fluctuations may be affected by a rescaling of the gravitational constant in the Poisson equation, by the presence of extra contributions to the anisotropic stress, and finally by the existence of extra clustering degrees of freedom. To explore these modifications accurately, we modify the Boltzmann code class. We then use the parameter inference code Monte Python to confront ΘCDM with data from WMAP-7, SPT and WiggleZ. We obtain strong bounds on the parameters accounting for deviations from ΛCDM. In particular, we find that the discrepancy between the gravitational constants appearing in the Poisson and Friedmann equations is constrained at the level of 1.8%.
Dark energy from large-scale structure lensing information
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.
Comparison of thawing and freezing dark energy parametrizations
NASA Astrophysics Data System (ADS)
Pantazis, G.; Nesseris, S.; Perivolaropoulos, L.
2016-05-01
Dark energy equation of state w (z ) parametrizations with two parameters and given monotonicity are generically either convex or concave functions. This makes them suitable for fitting either freezing or thawing quintessence models but not both simultaneously. Fitting a data set based on a freezing model with an unsuitable (concave when increasing) w (z ) parametrization [like Chevallier-Polarski-Linder (CPL)] can lead to significant misleading features like crossing of the phantom divide line, incorrect w (z =0 ), incorrect slope, etc., that are not present in the underlying cosmological model. To demonstrate this fact we generate scattered cosmological data at both the level of w (z ) and the luminosity distance DL(z ) based on either thawing or freezing quintessence models and fit them using parametrizations of convex and of concave type. We then compare statistically significant features of the best fit w (z ) with actual features of the underlying model. We thus verify that the use of unsuitable parametrizations can lead to misleading conclusions. In order to avoid these problems it is important to either use both convex and concave parametrizations and select the one with the best χ2 or use principal component analysis thus splitting the redshift range into independent bins. In the latter case, however, significant information about the slope of w (z ) at high redshifts is lost. Finally, we propose a new family of parametrizations w (z )=w0+wa(z/1 +z )n which generalizes the CPL and interpolates between thawing and freezing parametrizations as the parameter n increases to values larger than 1.
Evolution of non-interacting entropic dark energy and its phantom nature
NASA Astrophysics Data System (ADS)
Mathew, Titus K.; Murali, Chinthak; Shejeelammal, J.
2016-04-01
Assuming the form of the entropic dark energy (EDE) as it arises from the surface term in the Einstein-Hilbert’s action, its evolution was analyzed in an expanding flat universe. The model parameters were evaluated by constraining the model using the Union data on Type Ia supernovae. We found that in the non-interacting case, the model predicts an early decelerated phase and a later accelerated phase at the background level. The evolutions of the Hubble parameter, dark energy (DE) density, equation of state parameter and deceleration parameter were obtained. The model hardly seems to be supporting the linear perturbation growth for the structure formation. We also found that the EDE shows phantom nature for redshifts z < 0.257. During the phantom epoch, the model predicts big rip effect at which both the scale factor of expansion and the DE density become infinitely large and the big rip time is found to be around 36 Giga years from now.
Fate of the phantom dark energy universe in semiclassical gravity. II. Scalar phantom fields
NASA Astrophysics Data System (ADS)
de Haro, Jaume; Amoros, Jaume; Elizalde, Emilio
2012-10-01
Quantum corrections coming from massless fields conformally coupled with gravity are studied, in order to see if they can lead to avoidance of the annoying big rip singularity which shows up in a flat Friedmann-Robertson-Walker universe filled with dark energy and modeled by a scalar phantom field. The dynamics of the model are discussed for all values of the two parameters, named α>0 and β<0, corresponding to the regularization process. The new results are compared with the ones obtained in [J. Haro J. Amoros, and E. Elizalde, Phys. Rev. D 83, 123528 (2011)] previously, where dark energy was modeled by means of a phantom fluid with equation of state P=ωρ, with ω<-1.
Shafieloo, Arman
2012-05-01
By introducing Crossing functions and hyper-parameters I show that the Bayesian interpretation of the Crossing Statistics [1] can be used trivially for the purpose of model selection among cosmological models. In this approach to falsify a cosmological model there is no need to compare it with other models or assume any particular form of parametrization for the cosmological quantities like luminosity distance, Hubble parameter or equation of state of dark energy. Instead, hyper-parameters of Crossing functions perform as discriminators between correct and wrong models. Using this approach one can falsify any assumed cosmological model without putting priors on the underlying actual model of the universe and its parameters, hence the issue of dark energy parametrization is resolved. It will be also shown that the sensitivity of the method to the intrinsic dispersion of the data is small that is another important characteristic of the method in testing cosmological models dealing with data with high uncertainties.
Clustering GCG: a viable option for unified dark matter-dark energy?
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.