Universal Seesaw Mass Matrix Model with Three Light Pseudo-Dirac Neutrinos

A universal seesaw mass matrix model, which gives successful description of quark mass matrix in terms of lepton masses, yields three "sterile" neutrinos \nu^s_{i}, which compose pseudo-Dirac neutrinos \nu_{i\pm}^{ps}\simeq (\nu_{i} \pm \nu^s_{i})/\sqrt{2} together with the active neutrinos \nu_{i} (i=e,\mu,\tau). The solar and atmospheric neutrino data are explained by the mixings \nu_{e}\leftrightarrow \nu^s_{e} and \nu_{\mu}\leftrightarrow \nu^s_{\mu}, respectively. In spite of such observations of the large mixing \sin^2 2\theta\simeq 1 in the disappearance experiments, effective mixing parameters \sin^2 2\theta^{\alpha\beta} in appearance experiments \nu_\alpha\to\nu_\beta (\alpha, \beta = e, \mu, \tau) are highly suppressed.