Neutrino masses, anomalous U(1) gauge symmetry and doublet-Triplet splitting

We propose an attractive scenario of grand unified theories in which doublet-triplet splitting is naturally realized in SO(10) unification using the Dimopoulos-Wilczek mechanism. The anomalous U(1)(A) gauge symmetry plays an essential role in the doublet-triplet splitting mechanism. It is interesting that the anomalous U(1)(A) charges determine the unification scale and mass spectrum of additional particles, as well as the order of the Yukawa couplings of quarks and leptons. For the neutrino sector, bi-maximal mixing angles are naturally obtained, and proton decay via dimension 5 operators is suppressed. It is suggestive that the anomalous U(1)(A) gauge symmetry motivated by superstring theory effectively solves the two biggest problems in grand unified theories, the Fermion mass hierarchy problem and doublet-triplet splitting problem.