Cosmological bulk viscosity, the Burnett regime, and the BGK equation

TL;DR

This paper derives a second-order dissipative stress-energy tensor for matter-dominated cosmological models using the BGK equation, exploring the physical implications of transport coefficients in an isotropic universe.

Contribution

It introduces a novel application of the BGK equation to cosmology, incorporating second-order (Burnett) effects into Einstein's equations for the first time.

Findings

Second-order dissipative effects are significant in low-density cosmological regimes.

Transport coefficients have meaningful physical interpretations in homogeneous isotropic universes.

The model provides new insights into the role of viscosity in cosmic evolution.

Abstract

Einstein's field equations in FRW space-times are coupled to the BGK equation in order to derive the stress energy tensor including dissipative effects up to second order in the thermodynamical forces. The space-time is assumed to be matter-dominated, but in a low density regime for which a second order (Burnett) coefficient becomes relevant. Cosmological implications of the solutions, as well as the physical meaning of transport coefficients in an isotropic homogeneous universe are discussed.