Cosmological solutions with nonlinear bulk viscosity

TL;DR

This paper explores nonlinear bulk viscosity in cosmological models, analyzing stability of solutions and discovering new singular solutions that could describe late-time inflation.

Contribution

It introduces a nonlinear transport equation for bulk viscosity in cosmology and investigates the stability of de Sitter and Friedmann solutions, finding new solutions for specific viscosity regimes.

Findings

De Sitter solution is stable for viscosity index q<1.

Friedmann solution is stable for q>1.

New singular solutions are found for q=1, some indicating late-time inflation.

Abstract

A recently proposed nonlinear transport equation is used to model bulk viscous cosmologies that may be far from equilibrium, as happens during viscous fluid inflation or during reheating. The asymptotic stability of the de Sitter and Friedmann solutions is investigated. The former is stable for bulk viscosity index $q<1$ and the latter for $q>1$. New solutions are obtained in the weakly nonlinear regime for $q=1$. These solutions are singular and some of them represent a late-time inflationary era.