Cold dark matter and b -> s gamma in the Horava-Witten theory

The minimal supersymmetric standard model with complete, partial or no Yuka wa unification and radiative electroweak breaking with boundary conditions from the Horava-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 correcti ons and the branching ratio of b --> s gamma to be compatible with data. Co mplete Yukawa unification can be excluded. Also, t-b Yukawa unification is strongly disfavored since it requires almost degenerate lightest and next-t o-lightest sparticle masses. However, the b-tau or no Yukawa unification ca ses avoid this degeneracy. The latter with mu < 0 is the most natural case. The lightest sparticle mass, in this case, can be as low as about 77 GeV. (C) 2001 Elsevier Science B.V. All rights reserved.