Leptogenesis, Gravitino Dark Matter and Entropy Production

TL;DR

This paper explores how entropy production from decaying particles like the saxion can reconcile thermal leptogenesis with Big Bang Nucleosynthesis constraints in models with gravitino dark matter.

Contribution

It provides a general analysis of entropy production mechanisms, focusing on the saxion, to address BBN constraints in supersymmetric models with gravitino dark matter.

Findings

Entropy production can help reconcile leptogenesis with BBN.

Saxion decay can generate sufficient entropy without spoiling BBN.

Constraints on entropy-producing particles are derived.

Abstract

Many extensions of the Standard Model predict super-weakly interacting particles, which typically have to decay before Big Bang Nucleosynthesis (BBN). The entropy produced in the decays may help to reconcile thermal leptogenesis and BBN in scenarios with gravitino dark matter, which is usually difficult due to late decays of the next-to-lightest supersymmetric particle (NLSP) spoiling the predictions of BBN. We study this possibility for a general neutralino NLSP. We elaborate general properties of the scenario and strong constraints on the entropy-producing particle. As an example, we consider the saxion from the axion multiplet and show that, while enabling a solution of the strong CP problem, it can also produce a suitable amount of entropy.