Vacuum stability in stau-neutralino coannihilation in MSSM

TL;DR

This paper investigates the upper limits of stau mass in MSSM under coannihilation conditions, considering vacuum stability and dark matter relic density, and finds that stau mass can be significantly higher than previously thought.

Contribution

It introduces a detailed analysis of stau mass bounds in MSSM considering large mixing, vacuum stability, and dark matter constraints, extending previous limits.

Findings

Stau mass upper bound can reach about 1.4 TeV with large mixing.

Vacuum stability constraints reduce the stau mass limit to about 0.9 TeV.

Stau pair annihilation into dibosons relaxes previous mass bounds.

Abstract

The stau-neutralino coannihilation provides a feasible way to accommodate the observed cosmological dark matter (DM) relic density in the minimal supersymmetric standard model (MSSM). In such a coannihilation mechanism the stau mass usually has an upper bound since its annihilation rate becomes small with the increase of DM mass. Inspired by this observation, we examine the upper limit of stau mass in the parameter space with a large mixing of staus. We find that the stau pair may dominantly annihilate into dibosons and hence the upper bound on the stau mass ($\sim400$ GeV) obtained from the $f\bar{f}$ final states can be relaxed. Imposing the DM relic density constraint and requiring a long lifetime of the present vacuum, we find that the lighter stau mass can be as heavy as about 1.4 TeV for the stau maximum mixing. However, if requiring the present vacuum to survive during the thermal history of the universe, this mass limit will reduce to about 0.9 TeV. We also discuss the complementarity of vacuum stability and direct detections in probing this stau coannihilation scenario.