ELECTROWEAK SYMMETRY-BREAKING AND BOTTOM-TOP YUKAWA UNIFICATION

The condition of unification of gauge couplings in the minimal supersymmetric standard model provides successful predictions for the weak mixing angle as a function of the strong gauge coupling and the supersymmetric threshold scale. In addition, in some scenarios, e.g. in the minimal SO(10) model, the tau lepton and the bottom and top quark Yukawa couplings unify at the grand unification scale. The condition of Yukawa unification naturally leads to large values of tan beta, implying a proper top quark-bottom quark mass hierarchy. In this work, we investigate the feasibility of unification of the Yukawa couplings, in the framework of the minimal supersymmetric standard model with (assumed) universal mass parameters at the unification scale and with radiative breaking of the electroweak symmetry. We show that strong correlations between the parameters mu(0), M1/2 and delta = B-0 - (6r/7)A(0) appear within this scheme, where r is the ratio of the Yukawa coupling of the top quark to its infrared fixed-point value. These correlations have relevant implications for the sparticle spectrum, which presents several characteristic features. In addition, we show that due to large corrections to the running bottom quark mass induced through the supersymmetry breaking sector of the theory, the predicted top quark mass and tan beta values are significantly lower than those previously estimated in the literature.