Cold Dark Matter and b → sγ in the Hořava - Witten Theory

The minimal supersymmetric standard model with complete, partial or no Yukawa unification and radiative electroweak breaking with boundary conditions from the Hořava-Witten theory is considered. The parameters are restricted by constraining the lightest sparticle relic abundance by cold dark matter considerations and requiring the b-quark mass after supersym-metric corrections and the branching ratio of b → sγ to be compatible with data. Complete Yukawa unification can be excluded. Also, t − b Yukawa unification is strongly disfavored since it requires almost degenerate lightest and next-to-lightest sparticle masses. However, the b − τ or no Yukawa unification cases avoid this degeneracy. The latter with µ < 0 is the most natural case. The lightest sparticle mass, in this case, can be as low as about 77 GeV.