Hierarchical quark-lepton masses and intermediate mass scale

Abstract

A mechanism of generating hierarchical fermion masses is proposed for the SO(10) ⊗ U(1) PQ ⊗ G H model with an intermediate mass scale of the symmetry breakdown, where G H is assumed to be a global horizontal symmetry. A light Higgs field responsible for producing quark-lepton masses is taken as a G H singlet in order to assure the absence of the flavour-changing neutral-current couplings. The generation pattern arises from the leakage of the G H non-singlet structure at the intermediate mass scale. No new heavy fermions are introduced. The realistic mass matrices are obtained and the top-quark mass is predicted as m t ⋍ 43 GeV .