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×${10}^{17}$ GeV and ${\sin }^2$ ${\mathrm{\theta }}_{\mathit{W}}$ 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 ${\sin }^2$ ${\mathrm{\theta }}_{\mathit{W}}$ prediction is consistent with experiments.