Two-loop renormalization group analysis of supersymmetric SO(10) models with 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 generation Yukawa couplings are studied. The unification scale, the intermediate scale and the value of the unification gauge coupling in these models are calculated and the gauge boson mediated proton decay rates are estimated. In some cases the predicted proton lifetime turns out to be in the border-line of experimental limit. The predictions of the top quark mass, the mass ratio $m_b(m_b)/ m_\tau(m_\tau)$ from the two-loop evolution of Yukawa couplings and the mass of the left handed neutrino via see-saw mechanism are summarized. The lower bounds on the ratio of the VEVs of the two low energy doublets ($\tan\beta$) from the requirement of the perturbative unitarity of the top quark Yukawa coupling up to the grand unification scale are also presented. All the predictions have been compared with those of the one-step unified theory.