Grand Unification in High-scale Supersymmetry

A constraint on masses of superheavy gauge and Higgs multiplets at the grand unification (GUT) scale is obtained from the gauge coupling unification in the case of high-scale supersymmetry. We found that all of the particles may lie around a scale of 10^16 GeV so that the threshold corrections to the gauge coupling constants at the GUT scale are smaller than those in the case of the low-energy supersymmetry. In addition, the GUT scale tends to be slightly lower when the gauginos are heavier and, thus, the proton decay rate via the X-boson exchange process is expected to be enhanced.