A causal viscous cosmology without singularities

TL;DR

This paper proposes a viscous relativistic fluid cosmological model that avoids singularities and can describe an accelerating universe with dark energy, analyzing conditions for different causal correction parameters.

Contribution

It introduces a causal viscous cosmology model that satisfies key physical conditions and distinguishes between phantom and k-essence sectors based on the sign of the transport coefficient.

Findings

Model satisfies non-singular energy density over time.

Accelerating universe condition is met in both cases.

Entropy increases in the k-essence sector, favoring that case.

Abstract

An isotropic and homogeneous cosmological model with a source of dark energy is studied. That source is simulated with a viscous relativistic fluid with minimal causal correction. In this model the restrictions on the parameters coming from the following conditions are analized: a) energy density without singularities along time, b) scale factor increasing with time, c) universe accelerated at present time, d) state equation for dark energy with "w" bounded and close to -1. It is found that those conditions are satified for the following two cases. i) When the transport coefficient ({\tau}_{{\Pi}}), associated to the causal correction, is negative, with the aditional restriction {\zeta}|{\tau}_{{\Pi}}|>2/3, where {\zeta} is the relativistic bulk viscosity coefficient. The state equation is in the "phantom" energy sector. ii) For {\tau}_{{\Pi}} positive, in the "k-essence" sector. It is performed an exact calculation for the case where the equation of state is constant, finding that option (ii) is favored in relation to (i), because in (ii) the entropy is always increasing, while this does no happen in (i).