INFRARED FIXED-POINT SOLUTION FOR THE TOP-QUARK MASS AND UNIFICATION OF COUPLINGS IN THE MSSM

We analyze the implications of the infrared quasi fixed point solution for the top quark mass in the Minimal Supersymmetric Standard Model. This solution could explain in a natural way the relatively large valu e of the top quark mass and, if confirmed experimentally, may be sugge stive of the onset of nonperturbative physics at very high energy scal es. In the framework of grand unification, the expected bottom quark-t au lepton Yukawa coupling unification is very sensitive to the fixed p oint structure of the top quark mass. For the presently allowed values of the electroweak parameters and the bottom quark mass, the Yukawa c oupling unification implies that the top quark mass must be within ten percent of its fixed point values.