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 supersymmetric 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.