SO(3) Gauge model for neutrino masses and oscillations

Abstract

I mainly describe neutrino masses and oscillations in the gauge model with $SO(3)_{F}$ lepton flavor symmetry and with two Higgs triplets. It is shown how the maximal mixing between $\nu_{\mu}$ and $\nu_{\tau}$ neutrinos comes out naturally after spontaneous breaking of the symmetry. The nearly two-flavor mixing scenario is resulted naturally from an approximate permutation symmetry between the two Higgs triplets. The hierarchy between the neutrino mass-squared differences, which is needed for reconciling both solar and atmospheric neutrino data, leads to an almost maximal mixing between $\nu_{e}$ and $\nu_{\mu}$ neutrinos. Thus the model favors the intriguing bi-maximal mixing scenario.The three Majorana neutrino masses are allowed to be nearly degenerate and large enough to play a significant cosmological role. The model can also lead to interesting phenomena on lepton-flavor violations via the $SO(3)_{F}$ gauge interactions.Comment: latex, no figures, invited talk at the Sixth Topical Seminar on Neutrino and Astroparticle Physics, San Miniato, Italy, May 1999, to appear in Nucl. Phys. B (Proc. Suppl.