On deviations from bimaximal neutrino mixing
Abstract
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 "CKMlike" 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}2 θ_{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}2 θ_{atm}≃1. Large atmospheric neutrino mixing, sin ^{2}2 θ_{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 CPnonconservation, analyzing it in detail. We show how the CPviolating phases, arising from the diagonalization of the neutrino and charged lepton mass matrices, contribute to the measured neutrino mixing observables.
 Publication:

Nuclear Physics B
 Pub Date:
 May 2004
 DOI:
 10.1016/j.nuclphysb.2004.03.014
 arXiv:
 arXiv:hepph/0401206
 Bibcode:
 2004NuPhB.687...31F
 Keywords:

 High Energy Physics  Phenomenology
 EPrint:
 26 pages, 6 figures. Typos corrected, references added, to appear in NPB