Unified dark fluid with constant adiabatic sound speed: Including entropic perturbations

Xu, Lixin

doi:10.1103/physrevd.87.043503

Cited by 18 publications

(7 citation statements)

References 65 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…where τ denotes conformal time and h ij denotes the synchronous gauge metric perturbation. Within this gauge and neglecting shear stress, consistently with the earlier work of [146], we can track the evolution of the Fourier space UDF density perturbation δ u and velocity divergence θ u . In the usual notation of Ma & Bertschinger [145], the evolution equations for δ u and θ u are given by:…”

Section: B Evolution Of Perturbationsmentioning

confidence: 85%

Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

Yang

Pan

Vagnozzi

et al. 2019

J. Cosmol. Astropart. Phys.

View full text Add to dashboard Cite

While the origin and composition of dark matter and dark energy remains unknown, it is possible that they might represent two manifestations of a single entity, as occurring in unified dark sector models. On the other hand, advances in our understanding of the dark sector of the Universe might arise from Cosmic Dawn, the epoch when the first stars formed. In particular, the first detection of the global 21-cm absorption signal at Cosmic Dawn from the EDGES experiment opens up a new arena wherein to test models of dark matter and dark energy. Here, we consider generalized and modified Chaplygin gas models as candidate unified dark sector models. We first constrain these models against Cosmic Microwave Background data from the Planck satellite, before exploring how the inclusion of the global 21-cm signal measured by EDGES can improve limits on the model parameters, finding that the uncertainties on the parameters of the Chaplygin gas models can be reduced by a factor between 1.5 and 10. We also find that within the generalized Chaplygin gas model, the tension between the CMB and local determinations of the Hubble constant H0 is reduced from ≈ 4σ to ≈ 1.3σ. In conclusion, we find that the global 21-cm signal at Cosmic Dawn can provide an extraordinary window onto the physics of unified dark sectors.

show abstract

Section: B Evolution Of Perturbationsmentioning

confidence: 85%

Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

Yang

Pan

Vagnozzi

et al. 2019

J. Cosmol. Astropart. Phys.

View full text Add to dashboard Cite

show abstract

“…The main downside of the fundamental approach is that each model has to be studied separately. On the other hand, the phenomenological approach introduces, in a more or less ad-hoc way, some modifications of the ΛCDM model [75][76][77][78][79][80][81][82] that parameterise some basic physical properties shared by a range of fundamental models, but usually without the ability to explicitly map between parameter spaces. Although primarily developed for DE rather than DM, there are also parameterisations that are somewhat in between those two extremes and guarantee a mapping to the parameter space of the fundamental models [83][84][85][86][87][88][89][90].…”

mentioning

confidence: 99%

Extensive investigation of the generalized dark matter model

2016

View full text Add to dashboard Cite

The Cold Dark Matter (CDM) model, wherein the dark matter is treated as a pressureless perfect fluid, provides a good fit to galactic and cosmological data. With the advent of precision cosmology, it should be asked whether this simplest model needs to be extended, and whether doing so could improve our understanding of the properties of dark matter. One established parameterisation for generalising the CDM fluid is the Generalised Dark Matter (GDM) model, in which dark matter is an imperfect fluid with pressure and shear viscosity that fulfill certain postulated closure equations. We investigate these closure equations and the three new parametric functions they contain: the background equation of state w, the speed of sound c 2 s and the viscosity c 2 vis . Taking these functions to be constant parameters, we analyse an exact solution of the perturbed Einstein equations in a flat GDM-dominated universe and discuss the main effects of the three parameters on the Cosmic Microwave Background (CMB). Our analysis suggests that the CMB alone is not able to distinguish between the GDM sound speed and viscosity parameters, but that other observables, such as the matter power spectrum, are required to break this degeneracy. In order to elucidate further the meaning of the GDM closure equations, we also consider other descriptions of imperfect fluids that have a non-perturbative definition and relate these to the GDM model. In particular, we consider scalar fields, an effective field theory (EFT) of fluids, an EFT of Large Scale Structure, non-equilibrium thermodynamics and tightly coupled fluids. These descriptions could be used to extend the GDM model into the nonlinear regime of structure formation, which is necessary if the wealth of data available on those scales is to be employed in constraining the model. We also derive the initial conditions for adiabatic and isocurvature perturbations in the presence of GDM and standard cosmological fluids and provide the result in a form ready for implementation in Einstein-Boltzmann solvers. CONTENTS

show abstract

“…In the presence of entropy perturbation, one can define the effective sound speed c eff for DE which is basically null or positive. In the linear regime (δ ≪ 1), the cosmological observations favor a small effective sound speed c 2 eff ≤ 0.001 for DE (the speed of light c = 1) [104,105].…”

Section: Spherical Collapse In Nade Cosmologiesmentioning

confidence: 99%

Spherical collapse model in agegraphic dark energy cosmologies

Rezaei

Malekjani

2017

Phys. Rev. D

View full text Add to dashboard Cite

Under the commonly used spherical collapse model, we study how dark energy affects the growth of large scale structures of the Universe in the context of agegraphic dark energy models. The dynamics of the spherical collapse of dark matter halos in nonlinear regimes is determined by the properties of the dark energy model. We show that the main parameters of the spherical collapse model are directly affected by the evolution of dark energy in the agegraphic dark energy models. We compute the spherical collapse quantities for different values of agegraphic model parameter $\alpha$ in two different scenarios: first, when dark energy does not exhibit fluctuations on cluster scales, and second, when dark energy inside the overdense region collapses similar to dark matter. Using the Sheth-Tormen and Reed mass functions, we investigate the abundance of dark matter halos in the framework of agegraphic dark energy cosmologies. The model parameter $\alpha$ is a crucial parameter in order to count the abundance of dark matter halos. Specifically, the present analysis suggests that the agegraphic dark energy model with bigger (smaller) value of $\alpha$ predicts less (more) virialized halos with respect to that of $\Lambda$CDM cosmology. We also show that in agegraphic dark energy models, the number of halos strongly depends on clustered or uniformed distributions of dark energy.Comment: 14 pages, 7 figures. Accepted in Physical Review

show abstract

Unified dark fluid with constant adiabatic sound speed: Including entropic perturbations

Cited by 18 publications

References 65 publications

Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

Extensive investigation of the generalized dark matter model

Spherical collapse model in agegraphic dark energy cosmologies

Contact Info

Product

Resources

About