The degenerate gravitino scenario

TL;DR

This paper investigates a scenario where a small mass difference between the gravitino and the LSP reduces decay energy, relaxing cosmological constraints and allowing higher reheating temperatures compatible with thermal leptogenesis.

Contribution

It introduces the 'degenerate gravitino' scenario, showing how small mass splittings can mitigate constraints and enable higher reheating temperatures in supersymmetric models.

Findings

Reheating temperatures of 10^9 GeV are achievable with small splittings for neutralino LSP.

Temperatures up to 4x10^9 GeV are possible with stau NLSPs even for larger splittings.

The scenario offers a solution to the gravitino problem in thermal leptogenesis.

Abstract

In this work, we explore the "degenerate gravitino" scenario where the mass difference between the gravitino and the lightest MSSM particle is much smaller than the gravitino mass itself. In this case, the energy released in the decay of the next to lightest sypersymmetric particle (NLSP) is reduced. Consequently the cosmological and astrophysical constraints on the gravitino abundance, and hence on the reheating temperature, become softer than in the usual case. On the other hand, such small mass splittings generically imply a much longer lifetime for the NLSP. We find that, in the constrained MSSM (CMSSM), for neutralino LSP or NLSP, reheating temperatures compatible with thermal leptogenesis are reached for small splittings of order 10^{-2} GeV. While for stau NLSP, temperatures of 4x10^9 GeV can be obtained even for splittings of order of tens of GeVs. This "degenerate gravitino" scenario offers a possible way out to the gravitino problem for thermal leptogenesis in supersymmetric theories.