Supersymmetric Cold Dark Matter with Yukawa Unification

TL;DR

This paper calculates the relic density of the lightest supersymmetric particle in the minimal supersymmetric standard model, emphasizing the importance of coannihilation with the lightest stau for dark matter compatibility.

Contribution

It demonstrates that coannihilation with the lightest stau is essential for achieving acceptable relic densities in Yukawa-unified supersymmetric models.

Findings

The lightest supersymmetric particle is mainly bino.

Coannihilation with the stau reduces relic density.

Stau mass must be 2-8% larger than bino mass.

Abstract

The cosmological relic density of the lightest supersymmetric particle of the minimal supersymmetric standard model is calculated under the assumption of gauge and Yukawa coupling unification. We employ radiative electroweak breaking with universal boundary conditions from gravity-mediated supersymmetry breaking. Coannihilation of the lightest supersymmetric particle, which turns out to be an almost pure bino, with the next-to-lightest supersymmetric particle (the lightest stau) is crucial for reducing its relic density to an acceptable level. Agreement with the mixed or the pure cold (in the presence of a nonzero cosmological constant) dark matter scenarios for large scale structure formation in the universe requires that the lightest stau mass is about 2-8% larger than the bino mass, which can be as low as 222 GeV. The smallest allowed value of the lightest stau mass turns out to be about 232 GeV.