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

Abstract

We propose an attractive scenario of grand unified theories in which doublet-triplet splitting is beautifully realized in SO(10) unification using Dimopoulos-Wilczek mechanism. The anomalous U(1)_A gauge symmetry plays essential roles 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 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 excellently solves the two biggest problems in grand unified theories, fermion mass hierarchy problem and doublet-triplet splitting problem.