Bimaximal Neutrino Mixixing from a Local SU(2) Horizontal Symmetry
  Freedom from global anomalies in the presence of a local 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. 
R. Kuchimanchi and R.N. Mohapatra