Supersymmetric cold dark matter with Yukawa unification - art. no. 123512

The cosmological relic density of the lightest supersymmetric particle of t he 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 supersymm etry breaking. Coannihilation of the lightest supersymmetric particle, whic h turns out to be an almost pure B-ino, with the next-to-lightest supersymm etric particle (the lightest stau) is crucial for reducing its relic densit y to an acceptable level. Agreement with the mixed or the pure cold (in the presence of a nonzero cosmological constant) dark matter scenarios for la- ge scale structure formation in the universe requires that the lightest sta u mass is about 2 - 8 % larger than the B-ino 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.