Gluino Coannihilation Revisited

TL;DR

This paper recalculates the relic density of neutralino dark matter in the MSSM along the gluino coannihilation strip, incorporating bound-state effects and Sommerfeld enhancement, revealing the potential for very heavy LSPs up to 8 TeV.

Contribution

It provides a detailed calculation of relic density in the MSSM considering bound-state effects and large squark masses, extending the viable LSP mass range significantly.

Findings

Bound-state effects can increase the maximum LSP mass by ~50%.

LSP mass can reach up to ~8 TeV in the gluino coannihilation scenario.

Relic density calculations depend on squark to gluino mass ratio.

Abstract

Some variants of the MSSM feature a strip in parameter space where the lightest neutralino is identified as the lightest supersymmetric particle (LSP), the gluino is the next-to-lightest supersymmetric particle (NLSP) and is nearly degenerate with the LSP, and the relic cold dark matter density is brought into the range allowed by astrophysics and cosmology by coannihilation with the gluino NLSP. We calculate the relic density along this gluino coannihilation strip in the MSSM, including the effects of gluino-gluino bound states and initial-state Sommerfeld enhancement, and taking into account the decoupling of the gluino and LSP densities that occurs for large values of the squark mass. We find that bound-state effects can increase the maximum LSP mass for which the relic cold dark matter density lies within the range favoured by astrophysics and cosmology by as much as ~ 50% if the squark to gluino mass ratio is 1.1, and that the LSP may weigh up to ~ 8 TeV for a wide range of the squark to gluino mass ratio \lesssim 100.