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

Out of 256 independent reduction solutions that can be found within th e minimal supersymmetric SU(5) GUT, there are exactly two asymptotical ly free solutions which can restrict the top quark mass m(t) and do no t contradict the observed mass spectrum of the first two fermion gener ations. A numerical analysis shows that these two solutions lie on the same renormalization group invariant surface on which m(t) and the bo ttom quark mass m(b), assume relatively stable values for a given supe rsymmetry 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 fi xed, 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.