Thermal relics in cosmology with bulk viscosity

TL;DR

This paper explores how bulk viscosity in relativistic imperfect fluids affects early universe processes like nucleosynthesis and particle relic abundance, providing insights into anomalies observed in cosmic positron data.

Contribution

It introduces the impact of bulk viscosity on cosmological models, especially regarding thermal relics and recent positron excess observations.

Findings

Bulk viscosity influences Big Bang Nucleosynthesis outcomes.

It affects the thermal relic abundance of particles.

Provides potential explanations for PAMELA positron excess.

Abstract

In this paper we discuss some consequences of cosmological models in which the primordial cosmic matter is described by a relativistic imperfect fluid. The latter takes into account the dissipative effects (bulk viscosity) arising from different cooling rates of the fluid components in the expanding Universe. We discuss, in particular, the effects of the bulk viscosity on Big Bang Nucleosynthesis and on the thermal relic abundance of particles, looking at recent results of PAMELA experiment. The latter has determined an anomalous excess of positron events, that cannot be explained by the conventional cosmology and particle physics.