TOP-QUARK-MASS PREDICTION FROM SUPERSYMMETRIC GRAND UNIFIED THEORIES

We consider a supersymmetric grand-unified-theory (GUT) framework motivated by SO(10) or E6 unification in which the parameter tan-beta(= upsilon-2/upsilon-1) of the minimal supersymmetric standard model is con-strained by the condition that the Yukawa couplings h(t),h(b), and h-tau are all equal at the GUT scale. With alpha-s (M(Z)) = 0. 106 +/- 0.006, the estimate for the b-quark mass, which depends on tan-beta, lies in the "observed" range m(b)(m(b)) = 4.25 +/- 0.10 GeV, provided that the top-quark mass is 142(-49)+26 GeV.