Viscosity in modified gravity

Abstract

A bulk viscosity is introduced in the formalism of modified gravity. It is shown that, based on 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 cosmicfluid, the future singularity can nevertheless in principle be avoided. © 2012 by the author; licensee MDPI, Basel, Switzerland.