REDUCTION OF COUPLINGS AND HEAVY TOP-QUARK IN THE MINIMAL SUSY GUT

Out of 256 independent reduction solutions that can be found within the minimal supersymmetric SU(5) GUT, there are exactly two asymptotically free solutions which can restrict the top quark mass m(t) and do not contradict the observed mass spectrum of the first two fermion generations. A numerical analysis shows that these two solutions lie on the same renormalization group invariant surface on which m(t) and the bottom quark mass m(b), assume relatively stable values for a given supersymmetry breaking scale m(SUSY). For m(SUSY) = 200 GeV with alpha(S) (M(Z)) = 0.12, alpha(em) (M(Z)) = (127.9)(-1) and m(tau) = 1.78 GeV fixed, we find that on this surface m(t) and m(b) vary 2% and 3% around their central values 182 GeV and 5.3 GeV, respectively.