Thermal relic abundances of long-lived staus

TL;DR

This paper calculates the relic abundance of long-lived staus in the MSSM, identifying key annihilation processes that can significantly reduce their abundance, with implications for collider searches and gravitino dark matter.

Contribution

It provides a comprehensive analysis of stau annihilation channels in the MSSM, highlighting effects that lead to very low relic abundances, especially near Higgs resonance and with left-right mixing.

Findings

Efficient stau annihilation at Higgs resonance.

Significantly reduced stau abundance due to mixing effects.

Implications for collider searches and gravitino dark matter.

Abstract

In supersymmetric models with a long-lived stau being the lightest Standard Model superpartner, the stau abundance during primordial nucleosynthesis is tightly constrained. Considering the complete set of stau annihilation channels in the minimal supersymmetric Standard Model (MSSM) with real parameters for scenarios in which sparticle coannihilations are negligible, we calculate the decoupling of the lighter stau from the primordial plasma and identify processes which are capable to deplete the resulting stau abundance significantly. We find particularly efficient stau annihilation at the resonance of the heavy CP-even Higgs boson and for a lighter stau with a sizeable left-right mixing due to enhanced stau-Higgs couplings. Even within the constrained MSSM, we encounter both effects leading to exceptionally small values of the resulting stau abundance. Prospects for collider phenomenology are discussed and possible implications of our findings are addressed with emphasis on gravitino dark matter scenarios.