Bimaximal neutrino mixing from a localSU(2)horizontal symmetry

Abstract

Freedom from global anomalies in the presence of a local ${\mathrm{SU}(2)}_{H}$ horizontal symmetry under which right-handed charged leptons transform nontrivially requires that there be at least two right-handed neutrinos with masses of order of the horizontal symmetry breaking scale. If a third right-handed neutrino is introduced to satisfy quark lepton symmetry, it is unprotected by the horizontal symmetry, becomes superheavy with a Planck scale mass, and decouples from lower-energy physics. The resulting seesaw mechanism with two right-handed neutrinos in combination with the horizontal symmetry leads naturally to a near bimaximal pattern for the neutrino mixing with an inverted mass hierarchy and is compatible with all data. It predicts a correlation between the solar mixing angle and ${U}_{e3}$ that is testable in the proposed long baseline experiments.