Viscous Bianchi type I universes in brane cosmology

TL;DR

This paper analyzes the evolution of viscous, anisotropic brane universes in a generalized Randall-Sundrum model, showing isotropization and entropy production over time using causal thermodynamics.

Contribution

It provides exact parametric solutions for viscous Bianchi type I brane cosmologies incorporating causal thermodynamics, highlighting entropy generation and isotropization.

Findings

Universe isotropizes at large times

Significant entropy produced in early stages

Solutions describe non-inflationary evolution

Abstract

We consider the dynamics of a viscous cosmological fluid in the generalized Randall-Sundrum model for an anisotropic, Bianchi type I brane. To describe the dissipative effects we use the Israel-Hiscock-Stewart full causal thermodynamic theory. By assuming that the matter on the brane obeys a linear barotropic equation of state, and the bulk viscous pressure has a power law dependence on the energy density, the general solution of the field equations can be obtained in an exact parametric form. The obtained solutions describe generally a non-inflationary brane world. In the large time limit the brane Universe isotropizes, ending in an isotropic and homogeneous state. The evolution of the temperature and of the comoving entropy of the Universe is also considered, and it is shown that due to the viscous dissipative processes a large amount of entropy is created in the early stages of evolution of the brane world.