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

In the democratic universal seesaw model, the mass matrices are given by (f) over bar (L)m(L)F(R)+(F) over bar (L)m(R)f(R)+(F) over bar LMFFR (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.