2 research outputs found
Bilarge Neutrino Mixing and \mu - \tau Permutation Symmetry for Two-loop Radiative Mechanism
The presence of approximate electron number conservation and \mu-\tau
permutation symmetry of S_2 is shown to naturally provide bilarge neutrino
mixing. First, the bimaximal neutrino mixing together with U_{e3}=0 is
guaranteed to appear owing to S_2 and, then, the bilarge neutrino mixing
together with |U_{e3}|<<1 arises as a result of tiny violation of S_2. The
observed mass hierarchy of \Delta m^2_{\odot}<<\Delta m^2_{atm} is subject to
another tiny violation of the electron number conservation. This scenario is
realized in a specific model based on SU(3)_L x U(1)_N with two-loop radiative
mechanism for neutrino masses. The radiative effects from heavy leptons
contained in lepton triplets generate the bimaximal structure and those from
charged leptons, which break S_2, generate the bilarge structure together with
|U_{e3}|<<1. To suppress dangerous flavor-changing neutral current interactions
due to Higgs exchanges especially for quarks, this S_2 symmetry is extended to
a discrete Z_8 symmetry, which also ensures the absence of one-loop radiative
mechanism.Comment: 18 pages, 7 figures, to appear in Phys. Rev.