E6 Unification, Doublet-Triplet Splitting and Anomalous U(1)A Symmetry

We propose a natural Higgs sector in E6 grand unified theory (GUT) with anomalous U(1)A gauge symmetry. In this scenario, the doublet-triplet splitting can be realized, while proton decay via dimension 5 operators is suppressed. Gauge coupling unification is also realized without fine-tuning. The GUT scale obtained in this scenario is generally lower than the usual GUT scale, 2×1016 GeV, and therefore it should be possible to observe proton decay via dimension 6 operators in near future experiments. The lifetime of a nucleon in this model is roughly estimated as τp(p→e+π0)⋃3×1033 years. It is shown that the Higgs sector is compatible with the matter sector proposed by one of the present authors, which reproduces realistic quark and lepton mass matrices, including a bi-large neutrino mixing angle. Combining the Higgs sector and the matter sector, we can obtain a completely consistent E6 GUT. The input parameters for this model are only eight integer anomalous U(1)A charges (+3 for singlet Higgs) for the Higgs sector and three (half) integer charges for the matter sector.