2-LOOP RENORMALIZATION-GROUP ANALYSIS OF SUPERSYMMETRIC SO(10) MODELSWITH AN INTERMEDIATE SCALE

Two-loop evolutions of the gauge couplings in a class of intermediate- scale supersymmetric SO(10) models including the effect of third gener ation Yukawa couplings are studied. The unification scale, the interme diate scale and the value of the unification gauge coupling in these m odels are calculated and the gauge boson mediated proton decay rates a re estimated. In some cases the predicted proton lifetime turns out to be on the borderline of experimental limit. The predictions of the to p quark mass, the mass ratio m(b)(m(b))/m(tau)(m(tau)) from the two-lo op evolution of Yukawa couplings and the mass of the left-handed neutr ino via a see-saw mechanism are summarized. The lower bounds on the ra tio of the VEVs of the two low energy doublets (tan beta) from the req uirement of the perturbative unitarity of the top quark Yukawa couplin g up to the grand unification scale are also presented. All the predic tions have been compared with those of the one-step unified theory.