Unified Dark Fluid with Constant Adiabatic Sound Speed and Cosmic Constraints

Abstract

As is known above 90% of the energy content in Universe is made of unknown dark component. Usually this dark fluid is separated into two parts: dark matter and dark energy. However, it may be a mixture of these two energy components, or just one exotic unknown fluid. This property is dubbed as dark degeneracy. With this motivation, in this paper, a unified dark fluid having constant adiabatic sound speed $c_s^2=\alpha$, which is in the range $[0,1]$, is studied. At first, via the energy conservation equation, its energy density, ${\rho }_d/{\rho }_{d0}=(1-B_s)+B_s{a}^{-3(1+\alpha )}$ where $B_s$ is related to integration constant from energy conservation equation as another model parameter, is presented. Then by using Markov Chain Monte Carlo method with currently available cosmic observational data sets which include type Ia supernova Union 2, baryon acoustic oscillation and WMAP 7-year data of cosmic background radiation, we show that small values of $\alpha$ are favored in this unified dark fluid model. Furthermore, we show that smaller values of $\alpha <10^{-5}$ are required to match matter (baryon) power spectrum from SDSS DR7.

9 pages, 5 figures

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• Dark Energy and Dark Matter from an additional adiabatic fluid
• Unified dark fluid in Brans-Dicke theory
• Extending the generalized Chaplygin gas model by using geometrothermodynamics
• Polytropic dark matter flows illuminate dark energy and accelerated expansion
• Viscous Generalized Chaplygin Gas as a Unified Dark Fluid: Including Perturbation of Bulk Viscosity
• Constraints on a decomposed dark fluid with constant adiabatic sound speed by jointing the geometry test and growth rate after Planck data
• Dark Energy: The Shadowy Reflection of Dark Matter?
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• Role of Extended Gravity Theory in Matter Bounce Dynamics
• Inclusive Constraints on Unified Dark Matter Models from Future Large-Scale Surveys
• Generalized models of unification of dark matter and dark energy
• Stability analysis of two-fluid dark energy models
• Cosmological perturbations in the $\Lambda$CDM-like limit of a polytropic dark matter model
• Spherical top-hat Collapse of a Viscous Unified Dark Fluid
• Cosmological Model with Cosmic transit behaviour in Brans-Dicke Theory
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