Unified description of quark and lepton mass matrices in a universal seesaw model

Abstract

In the democratic universal seesaw model, the mass matrices are given by ${f}_{L}{m}_{L}{F}_{R}+{F}_{L}{m}_{R}{f}_{R}+{F}_{L}{M}_{F}{F}_{R}$ $(f:$ quarks and leptons; F: hypothetical heavy fermions), ${m}_{L}$ and ${m}_{R}$ are universal for up and down fermions, and ${M}_{F}$ has the structure $(1{+b}_{f}X){(b}_{f}$ is a flavor-dependent parameter, and X is a democratic matrix). The model can successfully explain the quark masses and Cabibbo-Kobayashi-Maskawa mixing parameters in terms of the charged lepton masses by adjusting only one parameter ${b}_{f}.$ However, so far, the model has not been able to give the observed bimaximal mixing for the neutrino sector. In the present paper, we consider that ${M}_{F}$ in the quark sectors are still ``fully'' democratic, while ${M}_{F}$ in the lepton sectors are partially democratic. Then the revised model can reasonably give a nearly bimaximal mixing without spoiling the previous success in the quark sectors.