Unified Dark Fluid with Constant Adiabatic Sound Speed: Including Entropic Perturbations

Abstract

In this paper, we continue to study a unified dark fluid model with a constant adiabatic sound speed but with the entropic perturbations. When the entropic perturbations are included, an effective sound speed, which reduces to the adiabatic sound speed when the entropic perturbations are zero, has to be specified as an additional free model parameter. Due to the relations between the adiabatic sound speed and equations of state (EoS) $c_{s,ad}^2(a)=w(a)-d\ln (1+w(a))/3d\ln a$, the equation of state can be determined up to an integration constant in principle when an adiabatic sound speed is given. Then there are two degrees of freedom to describe the linear perturbations for a fluid. Its micro-scale properties are characterized by its EoS or adiabatic sound speed and an effective sound speed. We take the effective sound speed and adiabatic sound speed as free model parameters and then use the currently available cosmic observational data sets, which include type Ia supernova Union 2.1, baryon acoustic oscillation and WMAP 7-year data of cosmic background radiation, to constrain the possible entropic perturbations and the adiabatic sound speed via the Markov Chain Monte Carlo method. The results show that the cosmic observations favor a small effective sound speed $c_{s,eff}^2=0.00155_{-0.00155}^{+0.000319}$ in $1\sigma$ region.

7 pages, 5 figures, to appear in Phys. Rev. D

References in corpus (20)

• Dark energy cosmology: the equivalent description via different theoretical models and cosmography tests
• Constraints on modified Chaplygin gas from recent observations and a comparison of its status with other models
• Generalized Chaplygin gas model: constraints from Hubble parameter versus Redshift Data
• Gauge-invariant analysis of perturbations in Chaplygin gas unified models of dark matter and dark energy
• Inflation, dark matter and dark energy in the string landscape
• The dark degeneracy and interacting cosmic components
• Revisiting Generalized Chaplygin Gas as a Unified Dark Matter and Dark Energy Model
• $\Lambda \alpha$DM: Observational constraints on unified dark matter with constant speed of sound
• WMAP5 constraints on the unified model of dark energy and dark matter
• Affine equation of state from quintessence and k-essence fields
• Constraints on the generalized Chaplygin gas model including gamma-ray bursts via a Markov Chain Monte Carlo approach
• Cosmological constraints on generalized Chaplygin gas model: Markov Chain Monte Carlo approach
• Unified Dark Fluid with Constant Adiabatic Sound Speed and Cosmic Constraints
• Constraining the dark fluid
• Linear and non-Linear Instabilities in Unified Dark Energy Models
• Affine parameterization of the dark sector: costraints from WMAP5 and SDSS
• Dark matter from dark energy-baryonic matter couplings
• Testing the (generalized) Chaplygin gas model with the Lookback time-Redshift data
• Cosmological dark fluid from five-dimensional vacuum
• Probing Ricci dark energy model with perturbations by using WMAP seven-year cosmic microwave background measurements, BAO and Type Ia supernovae

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• Cosmic constraint on massive neutrinos in viable f(R) gravity with producing LCDM background expansion
• Reduced modified Chaplygin gas cosmology
• Spherical collapse model in agegraphic dark energy cosmologies
• Accelerating Cosmological Models in $f(T,B)$ Gravitational Theory
• Linearized modified gravity theories and gravitational waves physics in the GBD theory
• Stability analysis of two-fluid dark energy models
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