The PMNS neutrino mixing matrix U PMNS is in general a product of two unitary matrices U lep and U ν arising from the diagonalization of the charged lepton and neutrino mass matrices, U PMNS = U † lep U ν . Assuming that U ν is a bimaximal mixing matrix, we investigate the possible forms of U lep . We identify three possible generic structures of U lep , which are compatible with the existing data on neutrino mixing. One corresponds to a hierarchical "CKM-like" matrix. In this case relatively large values of the solar neutrino mixing angle θ sol , and of |U e3 | 2 ≡ |(U PMNS ) e3 | 2 , are typically predicted, tan 2 θ sol > ∼ 0.42, |U e3 | 2 > ∼ 0.02, while the atmospheric neutrino mixing angle θ atm can deviate noticeably from π/4, sin 2 2θ atm > ∼ 0.95. The second corresponds to one of the mixing angles in U lep being equal to π/2, and predicts practically maximal atmospheric neutrino mixing sin 2 2θ atm ≃ 1. Large atmospheric neutrino mixing, sin 2 2θ atm > ∼ 0.95, is naturally predicted by the third possible generic structure of U lep , which corresponds to all three mixing angles in U lep being large. We focus especially on the case of CP-nonconservation, analyzing it in detail. We show how the CP-violating phases, arising from the diagonalization of the neutrino and charged lepton mass matrices, contribute to the measured neutrino mixing observables.

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We have considered short-baseline neutrino oscillations, 3 H β-decay and (ββ) 0ν -decay in two schemes with an inverted mass spectrum and mixing of three and four massive neutrino fields. We have analyzed the results of the latest experiments on the search for oscillations of terrestrial neutrinos and we have discussed the compatibility of the LSND indication in favor of neutrino oscillations with the results of the other experiments. In the framework of the models under consideration, it is shown that the observation of (ββ) 0ν -decay 1 could allow to obtain information about the CP violation in the lepton sector.