Viscosity in modified gravity

TL;DR

This paper explores the effects of bulk viscosity in modified gravity theories, deriving solutions for cosmic expansion and addressing potential future singularities through phase transitions.

Contribution

It introduces a formalism for including bulk viscosity in modified gravity and finds solutions that can explain cosmic evolution and singularity avoidance.

Findings

Viscosity can induce a Big Rip singularity in cosmic evolution.

Phase transitions in the cosmic fluid can prevent future singularities.

Abstract

A bulk viscosity is introduced in the formalism of modified gravity. It is shown that, on the basis of a natural scaling law for the viscosity, a simple solution can be found for quantities such as the Hubble parameter and the energy density. These solutions may incorporate a viscosity-induced Big Rip singularity. By introducing a phase transition in the cosmic fluid, the future singularity can nevertheless in principle be avoided.