Neutrino masses and mixings are investigated on the basis of a universal seesaw mass matrix model, in which quark (except for top) and charged lepton mass matrices Mf and neutrino mass matrix Mν are given by Mf ≃ mLM F mR and Mν ≃ mLM F mL (F = N), respectively. For a simple model which can successfully describe quark masses and mixings, we find that the observed neutrino data (except for the s...

The solar neutrino problem, atmospheric neutrino problem and the hot dark matter which seems to be required by galaxy formation can all be most economically described by three very degenerate neutrinos with a common mass of a few eV. Such neutrino masses could also be relevant for the recent data on double beta decay. We provide an existence proof for such a scenario by constructing an explicit...

The interpretation of the existing experimental eveidences for oscillations of neu-trinos in schemes with three and four neutrino mixing is reviewed. Forms of the lepton mixing matrix allowed by the neutrino oscillation data are considered. The possible neutrino mass spectra compatible with the observations are analyzed. The possibility to obtain information about the neutrino mass spectrum fro...

We study the neutrino mixing matrix (MNS matrix) in seesaw model. Assuming large mass hierarchy for heavy right-handed Majorana mass, we show that MNS matrix is determined by a unitary matrix which transforms neutrino yukawa term into a triangular form. Large mixing may occur even if yukawa matrix for charged lepton and that for neutrino is simultaneously diagonalized by biunitary transformatio...

We derive a model-independent upper bound on the scale of Majorana-neutrino mass generation. The upper bound is 4pi (nu2)/square root3 m(nu), where nu approximately 246 GeV is the weak scale and m(nu) is the Majorana-neutrino mass. For neutrino masses implied by neutrino oscillation experiments, all but one of these bounds are less than the Planck scale, and they are all within a few orders of ...