Cosmology with bulk viscosity and the gravitino problem

TL;DR

This paper explores how bulk viscosity in the early universe's cosmic fluid can resolve the gravitino problem by reducing gravitino abundance independently of the reheating temperature.

Contribution

It demonstrates that dissipative effects from bulk viscosity can prevent gravitino overproduction, offering a novel solution within cosmological models with imperfect fluids.

Findings

Bulk viscosity reduces gravitino abundance.

Gravitino abundance becomes independent of reheating temperature.

Model parameters can be tuned to avoid gravitino overproduction.

Abstract

The gravitino problem is revisited in the framework of cosmological models in which the primordial cosmic matter is described by a relativistic imperfect fluid. Dissipative effects (or bulk viscosity effects) arise owing to the different cooling rates of the fluid components. We show that the effects of the bulk viscosity allow to avoid the late abundance of gravitinos. In particular, we found that for a particular choice of the parameters characterizing the cosmological model, the gravitino abundance turns out to be independent on the reheating temperature.