Lepton and quark mass matrices

We propose a model that all quark and lepton mass matrices have the same zero texture. Namely, their (1,1), (1,3), and (3,1) components are zeros. The mass matrices are classified into two types. Type I is consistent with experimental data in the quark sector. For the lepton sector, if the seesaw mechanism is not used, type II allows a large nu(mu)-nu(tau) mixing angle. However, severe compatibility with all neutrino oscillation experiments forces us to use the seesaw mechanism. If we adopt the seesaw mechanism, it turns out that type I instead of type II can be consistent with experimental data in the lepton sector too. [S0556-2821(99)05613-1].