Calculations of Neutralino-Stau Coannihilation Channels and the Cosmologically Relevant Region of MSSM Parameter Space

TL;DR

This paper investigates neutralino-stau coannihilation processes within the MSSM, providing analytical and numerical insights, and shows how these processes significantly extend the allowed mass range of the neutralino consistent with cosmological data.

Contribution

It offers a detailed analysis of coannihilation channels, including new calculations and their impact on the viable MSSM parameter space, especially on the neutralino mass limit.

Findings

Neutralino mass upper limit increased from 200 GeV to 600 GeV due to coannihilations.

Including selectron and smuon coannihilations broadens the cosmologically allowed parameter space.

Coannihilations significantly affect relic density calculations in the CMSSM.

Abstract

Assuming that the lightest supersymmetric particle (LSP) is the lightest neutralino, we present a detailed exploration of neutralino-stau coannihilation channels, including analytical expressions and numerical results. We also include neutralino coannihilations with the selectron and smuon. We evaluate the implications of coannihilations for the cosmological relic density of the LSP, which is assumed to be stable, in the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the soft supersymmetry-breaking parameters are universal at the supergravity GUT scale. We evaluate the changes due to coannihilations in the region of the MSSM parameter space that is consistent with the cosmological upper limit on the relic LSP density. In particular, we find that the upper limit on the mass of the neutralino is increased from about 200 GeV to about 600 GeV in the CMSSM, and estimate a qualitatively similar increase for gauginos in the general MSSM.