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On the Unification of Couplings in the Minimal Supersymmetric Standard Model
The unification of gauge and Yukawa couplings within the minimal
supersymmetric standard model is studied at the two loop level. We derive an
expression for the effective scale, , which characterizes the
supersymmetric particle threshold corrections to the gauge couplings, and
demonstrate that is only slightly dependent on the squark and
slepton masses, and strongly dependent on the Higgsino masses as well as on the
mass ratio of the gauginos of the strong and weak interactions. Moreover, the
value of the top quark Yukawa coupling necessary to achieve the unification of
bottom and tau Yukawa couplings is also governed by , and it yields
predictions for the top quark mass which are close to the quasi infrared fixed
point results associated with the triviality bounds on this quantity. From the
requirement of perturbative consistency of the top quark Yukawa sector of the
theory, we obtain constraints on the allowed splitting of the supersymmetric
spectrum, which, for certain values of the running bottom quark mass, are
stronger than those ones coming from the experimental constraints on the strong
gauge coupling.Comment: 40 pages, MPI-Ph/93-1