A New Approach to Cosmological Bulk Viscosity

TL;DR

This paper proposes an alternative bulk viscosity model in cosmology that avoids superluminal signals, leading to distinct evolution dynamics and late-time phantom behavior, with implications for entropy production.

Contribution

It introduces a novel bulk viscosity formulation that differs from Eckart theory and discusses its cosmological implications and entropy considerations.

Findings

Model evolves toward late-time phantom-like behavior

Different evolution of viscous density compared to Eckart theory

Addresses entropy production in the new viscosity framework

Abstract

We examine the cosmological consequences of an alternative to the standard expression for bulk viscosity, one which was proposed to avoid the propagation of superluminal signals without the necessity of extending the space of variables of the theory. The Friedmann equation is derived for this case, along with an expression for the effective pressure. We find solutions for the evolution of the density of a viscous component, which differs markedly from the case of conventional Eckart theory; our model evolves toward late-time phantom-like behavior with a future singularity. Entropy production is addressed, and some similarities and differences to approaches based on the Mueller-Israel-Stewart theory are discussed.