Proton lifetime in the SO(10) grand unified model

The Grand Unified Model based on the orthogonal group SO(10) is treated. The symmetry breaks down to the standard group SU(3)/sub C/ x SU(2)/sub L/ x U(1)/sub Y/ in two stages through the vacuum expectation values of the 45 and 126 Higgs fields. The scales M/sub X/ of SO(10) symmetry breaking and M/sub R/ of left-right symmetry breaking are calculated making use of the renormalization group equations in the two-loop approximation. It is shown that the proton lifetime in the SO(10) model can be sufficiently high under available experimental constraints on the Weinberg angle to be consistent with recent proton-decay data. Possible constraints on the neutrino masses which arise in the model are treated as well