Yukawa Unification , b → sγ and Bino - Stau Coannihilation

The minimal supersymmetric standard model with universal boundary conditions and 'asymptotic' Yukawa coupling unification is considered. The full one-loop effective potential for radiative electroweak symmetry breaking as well as the one-loop corrections to all the Higgs boson, b-quark and τ-lepton masses are included. The relic abundance of the lightest su-persymmetric particle (bino) is calculated by including its coannihilations with the next-to-lightest supersymmetric particle (lightest stau) consistently with Yukawa unification. Although these coannihilations drastically reduce the bino relic abundance, they do not quite succeed to bring it below the upper bound from cold dark matter considerations in the region of the parameter space allowed by b → sγ for µ > 0. Thus, the µ > 0 case remains excluded even after including bino-stau coannihilations despite the fact that, in contrast to the µ < 0 case, it leads to an experimentally acceptable value of the b-quark mass after supersymmetric corrections.