Eur. Phys. J. C (2015) 75: 115
https://doi.org/10.1140/epjc/s10052-015-3337-5

Regular Article - Theoretical Physics

Thermal relics in cosmology with bulk viscosity

¹ Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, 18000, Prague 8, Czech Republic
² Dipartimento di Fisica E.R. Caianiello, Universitá di Salerno, 84084, Fisciano, SA, Italy
³ INFN, Gruppo Collegato di Salerno, Fisciano, Italy

^* e-mail: lambiase@sa.infn.it

Received: 9 December 2014
Accepted: 26 February 2015
Published online: 11 March 2015

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, which cannot be explained by conventional cosmology and particle physics.