Group Theory and Dynamics of Neutrino Mixing
  There is a direct group-theoretical connection between neutrino mixing and horizontal symmetry that can be established without any dynamical input. Such a connection is reviewed and expanded in this article. For certain symmetry groups $\G$ including $A_4$ and $S_4$, it is shown that a generic $U(1)\x\G$ Higgs potential of a valon yields exactly the alignments dictated by the group-theoretic approach, but energy can now be used to discriminate different alignments. This mechanism possibly explains why starting from an $A_4$ group, the tribimaximal mixing matrix with an enhanced $S_4$ symmetry is more preferable than the one without it. 
C. S. Lam
hep-ph