Bulk Viscous Cosmology: Unified Dark Matter

Dou, Xu; Meng, Xin-He

doi:10.1155/2011/829340

Cited by 37 publications

(22 citation statements)

References 61 publications

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“…Vanishing sound speed models however evade these constraints [e.g., the silent Chaplygin gas of 50 ]. Other models consider a single fluid with a two-parameter equation of state [e.g 74 ]), models with canonical Lagrangians but a complex scalar field [ 55 ], models with a kinetic term in the energy-momentum tensor [ 379 , 234 ], models based on a DBI action [ 236 ], models which violate the weak equivalence principle [ 375 ] and models with viscosity [ 321 ]. Finally, there are some models which try to unify inflation as well as dark matter and dark energy [ 206 , 688 , 572 , 575 , 430 ].…”

Section: Dark Matter and Neutrinosmentioning

confidence: 99%

Cosmology and Fundamental Physics with the Euclid Satellite

Amendola¹,

Appleby²,

Bacon³

et al. 2013

Living Rev. Relativ.

800

665

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Euclid is a European Space Agency medium-class mission selected for launch in 2019 within the Cosmic Vision 2015–2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the universe. Euclid will explore the expansion history of the universe and the evolution of cosmic structures by measuring shapes and red-shifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky.Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis.This review has been planned and carried out within Euclid’s Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

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Section: Dark Matter and Neutrinosmentioning

confidence: 99%

Cosmology and Fundamental Physics with the Euclid Satellite

Amendola¹,

Appleby²,

Bacon³

et al. 2013

Living Rev. Relativ.

800

665

View full text Add to dashboard Cite

show abstract

“…Any factorization like (20) of an scalar ODE in the form given in (19) allows to find a compatible first order ODE [28]…”

Section: Solving the Differential Equation For The Hubble Ratementioning

confidence: 99%

“…Apart of them, exists the possibility of explain the accelerated expansion of the Universe at late times as an effect of the effective negative pressure, due to bulk viscosity in the cosmic fluids, and was first considered in [16,17]. Several models regarding this approach have been studied and constrained using cosmological data [18][19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Constraining a causal dissipative cosmological model

2019

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In this paper a cosmological solution of polynomial type H ≈ (t + const.) −1 for the causal thermodynamical approach of Isarel-Stewart, found in [1,2], is constrained using the joint of the latest measurements of the Hubble parameter (OHD) and Type Ia Supernovae (SNIa). Since the expansion described by this solution does not present a transition from a decelerated phase to an accelerated one, both phases can be well modeled connecting both phases by requiring the continuity of the Hubble parameter at z = zt, the accelerated-decelerated transition redshift. Our best fit constrains the main free parameters of the model to be A1 = 1.58 +0.08 −0.07 (A2 = 0.84 +0.02 −0.02 ) for the accelerated (decelerated) phase. For both phases we obtain q = −0.37 +0.03 −0.03 (0.19 +0.03 −0.03 ) and ω ef f = −0.58 +0.02 −0.02 (−0.21 +0.02 −0.02 ) for the deceleration parameter and the effective equation of state, respectively. Comparing our model and LCDM statistically through the Akaike information criterion and the Bayesian information criterion we obtain that the LCDM model is preferred by the OHD+SNIa data. Finally, it is shown that the constrained parameters values satisfy the criterion for a consistent fluid description of a dissipative dark matter component, but with a high value of the speed of sound within the fluid, which is a drawback for a consistent description of the structure formation. We briefly discuss the possibilities to overcome this problem with a non-linear generalization of the causal linear thermodynamics of bulk viscosity and also with the inclusion of some form of dark energy.

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“…(99)-(101), 0 represents the differential with respect to η, i.e., d=dη, where η ≡ lnðãðtÞÞ [Eq. (47)]. It should be noted that H and Γ included in Eqs.…”

Section: Bv-h Modelmentioning

confidence: 99%

Evolution of the universe in entropic cosmologies via different formulations

2014

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We study two types of entropic-force models in a homogeneous, isotropic, spatially flat, matterdominated universe. The first type is a ΛðtÞ type similar to ΛðtÞCDM (varying-lambda cold dark matter) models in which both the Friedmann equation and the acceleration equation include an extra driving term. The second type is a BV type similar to bulk viscous models in which the acceleration equation includes an extra driving term but the Friedmann equation does not. In order to examine the two types systematically, we consider an extended entropic-force model that includes a Hubble parameter (H) term and a constant term in entropic-force terms. The H term is derived from a volume entropy, whereas the constant term is derived from an entropy proportional to the square of an area entropy. Based on the extended entropic-force model, we examine four models obtained from combining the H and constant terms with the ΛðtÞ and BV types. The four models agree well with the observed supernova data and describe the background evolution of the late universe properly. However, the evolution of first-order density perturbations is different in each of the four models, especially for low redshift, assuming that an effective sound speed is negligible. The ΛðtÞ type is found to be consistent with the observed growth rate of clustering, in contrast with the BV type examined in this study. A unified formulation is proposed as well, in order to systematically examine density perturbations of the two types.

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Bulk Viscous Cosmology: Unified Dark Matter

Cited by 37 publications

References 61 publications

Cosmology and Fundamental Physics with the Euclid Satellite

Cosmology and Fundamental Physics with the Euclid Satellite

Constraining a causal dissipative cosmological model

Evolution of the universe in entropic cosmologies via different formulations

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