PROBING THE GRAND-UNIFICATION-SCALE MASS-SPECTRUM THROUGH PRECISION-MEASUREMENTS ON THE WEAK-SCALE PARAMETERS

We study the renormalization-group evolution of gauge coupling constants including mass threshold effects of both light and heavy particles, in the minimal supersymmetric SU(5) grand unified model assuming supersymmetry breaking at less than or similar to 1 TeV. We show that a certain combination of superheavy masses M(V)2M(SIGMA) is tightly constrained, while the mass of the color-triplet Higgs boson, M(H), can vary from 2 x 10(13) to 2 x 10(17) GeV. With a relatively heavy color-triplet mass (M(H) is similar to 10(17) GeV), the present nucleon-decay experiments still allow superparticles below 1 TeV. The importance of a precise measurement on alpha-3 is stressed.