Yukawa unification, b -> s gamma and bino-stau coannihilation

The minimal supersymmetric standard model with universal boundary condition s and "asymptotic" Yukawa unification is considered. The full one-loop effe ctive potential for radiative electroweak symmetry breaking as well as the one-loop corrections to the charged Hi,ags boson, b-quark and tau-lepton ma sses are included. The CP-even Higgs boson masses are corrected to two-loop s. The relic abundance of the lightest supersymmetric particle (bino) is ca lculated by including its coannihilations with the next-to-lightest supersy mmetric particle (lightest stau) consistently with Yukawa unification. The branching ratio of b --> s gamma is evaluated by incorporating all the appl icable next-to-leading order QCD corrections. The bino-stau coannihilations reduce the bino relic abundance below the upper bound from cold dark matte r considerations in a sizable fraction of the parameter space allowed by b --> s gamma for mu > 0. Thus, the mu > 0 case, which also predicts an accep table b-quark mass, is perfectly compatible with data. (C) 2000 Elsevier Sc ience B.V. All rights reserved.