Abstract
The purpose of this short review is to describe cosmological models with a linear inhomogeneous time-dependent equation of state (EoS) for dark energy, when dark fluid is coupled with dark matter. This may lead to a bounce cosmology. We consider equivalent descriptions in terms of the EoS parameters for an exponential, a power-law, or a double-exponential law for the scale factor a. Stability issues are discussed by considering small perturbations around the critical points for the bounce, in the early as well as in the late, universe. The latter part of the paper is concerned with dark energy coupled with dark matter in viscous fluid cosmology. We allow the bulk viscosity ζ = ζ(H, t) to be a function of the Hubble parameter and the time, and consider the Little Rip, the Pseudo Rip, and the bounce universe. Analytic expressions for characteristic properties of these cosmological models are obtained.
Highlights
The current procedure for explaining the observed expansion for the universe [1,2] is to introduce a dark energy fluid with negative pressure and negative entropy [3,4,5]
Concluding this subsection, we have explored the exponential model of bounce cosmology in terms of time-dependent parameters in the equation of state (EoS), taking into account the interaction between dark energy and dark matter
Our second theme of the present review is to describe the theory of dark energy when it is coupled with dark matter in viscous cosmology
Summary
The current procedure for explaining the observed expansion for the universe [1,2] is to introduce a dark energy fluid with negative pressure and negative entropy [3,4,5]. We will study a cosmological system with two coupled fluids: a dark energy component with a linear inhomogeneous EoS, and a dark matter component with a linear homogeneous EoS in a flat homogeneous and isotropic FRW universe. We will explore bounce cosmological models where the scale factor is described by exponential as well as power-law forms and realize them in terms of the parameters of the EoS for the dark fluid. We will consider a bounce cosmological model when the scale factor has a double exponential form The bouncing behavior, both in the early universe and in the late-time universe, will be presented. We find corrections to the thermodynamical parameter, and to the bulk viscosity, in the equation of state for the dark energy
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