Supersymmetric SO(10) simplified

In the context of supersymmetric SO(10) grand unified models, it is shown that the gauge symmetry breaking as well as a natural doublet-triplet splitting can be achieved with a minimal Higgs system consisting of a single adjoint and a pair of vector and spinor multiplets. Such a Higgs spectrum has been shown to arise in the free fermionic formulation of superstrings. Since the symmetry-breaking mechanism relies on nonrenormalizable operators, some of the Higgs particles of the model turn out to have masses somewhat below the GUT scale. As a consequence, the unification scale is raised to about 2×10¹⁷ GeV and sin²θ_W is predicted to be slightly larger than the minimal SUSY SU(5) value. Including threshold uncertainties, which turn out to be surprisingly small in the model, we show that the sin²θ_W prediction is consistent with experiments.