L_e + L_\mu - L_ au - L_s Symmetry and a Mixed 2+2 Scenario for Neutrino Oscillations

摘要

Recent results from SuperKamiokande and SNO experiments have set severeconstraints on possible mixings of a light sterile neutrino, \nu_s, with thethree active species required for a simultaneous explanation of the solar,atmospheric and LSND neutrino oscillation data. A consistent scheme has emergedfrom a global analysis of the data wherein two of the neutrinos are nearlydegenerate with a mass of order 1 eV, that mix significantly with the twolighter states. We present realizations of such a mixed 2+2 oscillationscenario based on L_e + L_\mu - L_\tau - L_s symmetry (L_i stands for the ithlepton number). Breaking of of this lepton number symmetry by a small mass termfor \nu_s leads to the required large mixings for both the atmospheric and thesolar neutrino oscillations. Sum rules for the neutrino oscillation parametersare derived within this scheme, and are shown to be consistent with presentdata. These models predict U_{e3} = 0.02-0.03, which can serve as a test ofthis idea. We also present gauge models based on mirror extensions of theStandard Model that naturally lead to a light sterile neutrino with therequired mixing pattern.