Yukawa unification, b→sγ and bino-stau coannihilation

The minimal supersymmetric standard model with universal boundary conditions and "asymptotic" Yukawa unification is considered. The full one-loop effective potential for radiative electroweak symmetry breaking as well as the one-loop corrections to the charged Hi,ags boson, b-quark and tau-lepton masses are included. The CP-even Higgs boson masses are corrected to two-loops. The relic abundance of the lightest supersymmetric particle (bino) is calculated by including its coannihilations with the next-to-lightest supersymmetric particle (lightest stau) consistently with Yukawa unification. The branching ratio of b --> s gamma is evaluated by incorporating all the applicable next-to-leading order QCD corrections. The bino-stau coannihilations reduce the bino relic abundance below the upper bound from cold dark matter 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 acceptable b-quark mass, is perfectly compatible with data. (C) 2000 Elsevier Science B.V. All rights reserved.