A general analysis is made of the question of whether the $d=5\mathrm{}$ proton-decay operators coming from the exchange of colored Higgsinos can be completely eliminated in a natural way in supersymmetric (SUSY) grand unified models. It is shown that they can indeed be in SO(10) while at the same time naturally solving the doublet-triplet splitting problem, having only two light Higgs doublets, and using no more than a single adjoint Higgs field. Accomplishing all of this requires that the vacuum expectation value of the adjoint Higgs field be proportional to the generator $I_{3R}$ rather than to $B-L,$ as is usually assumed. It is shown that such models can give realistic quark and lepton masses. We also point out a new mechanism for solving the μ problem in the context of SO(10) SUSY grand unified theories.

• Received 3 February 2002

DOI:https://doi.org/10.1103/PhysRevD.65.095009