Broken SU(3) Flavor Symmetry and Tribimaximal Neutrino Mixing

Understand

Recent work on a lepton mass matrix model based on an SU(3) flavor symmetry which is broken into S_4 is reviewed.

• The flavor structures of the masses and mixing are caused by VEVs of SU(2)_L-singlet scalars \phi which are nonets ({\bf 8}+{\bf 1}) of the SU(3) flavor symmetry, and which are broken into {\bf 2}+{\bf 3}+{\bf 3}' and {\bf 1} of S_4.
• If we require the invariance under the transformation (\phi^{(8)},\phi^{(1)}) \to (-\phi^{(8)},+\phi^{(1)}) for the superpotential of the nonet field \phi^{(8+1)}, the model leads to a beautiful relation for the charged lepton masses.
• The observed tribimaximal neutrino mixing is understood by assuming two SU(3) singlet right-handed neutrinos \nu_R^{(\pm)} and an SU(3) triplet scalar \chi.