RADIATIVE SYMMETRY-BREAKING IN MINIMAL N = 1 SUPERGRAVITY WITH LARGE YUKAWA COUPLINGS

We systematically study the radiative breaking of the electroweak gauge symmetry in minimal N = 1 supergravity models with a heavy top quark, m(t) greater-than-or-equal-to 90 GeV, emphasizing the case of large tan-beta for which the Yukawa couplings for bottom and tau play an important role. We found that three different solutions for tan-beta can exist for fixed values of m(t) and the soft supersymmetry breaking parameters. Two of these solutions have large tan-beta and lead to a large mass splitting and mixing for all third-generation sfermions, as well as a light Higgs spectrum, giving rise to rich phenomenological consequences. The reduced masses of the light b and t-eigenstates lead to large enhancements of gluino branching ratios into b- and t-quarks, which can easily be the dominant gluino decay modes. We also show that combinations of soft breaking parameters that lead to unacceptably large neutralino relic densities for small \tan-beta\ are cosmologically safe if there is a light-tau or a light pseudoscalar Higgs boson; both of these particles can be arbitrarily light for solutions with large \tan-beta\.