Hierarchical quark-lepton masses and intermediate mass scale

A mechanism of generating hierarchical fermion masses is proposed for the SO(10) x U(1)PQ x GH model with an intermediate mass scale of the symmetry breakdown, where GH is assumed to be a global horizontal symmetry. A light Higgs field responsible for producing quark-lepton masses is taken as a GH singlet in order to assure the absence of the flavour-changing neutral-current couplings.The generation pattern arises from the leakage of the GH 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 mt≅43 Gev. (orig.)