Proton decay suppression in a supersymmetric SO(10) model

We propose a mechanism for sufficient suppression of dimension-5 operators for proton decay in a supersymmetric SO(10) model. This mechanism is analogue to the double seesaw mechanism in studying neutrino masses. Only an intermediate VEV instead of an intermediate scale is required so that gauge coupling unification is maintained. The VEV is generated by introducing an anomalous U(1) symmetry whose breaking is at higher scale. The proton decay amplitudes are suppressed by this VEV over the GUT scale. We use 45+54 in breaking GUT symmetry. 120 is included so that fermion sector is fully realistic. Assuming a minimal fine-tuning in the Higgs doublet sector, tan beta of order one is predicted.