Neutrino Mixing: $A_4$ Variations

Abstract

In the context of the non-Abelian discrete symmetry $A_4$, the neutrino mass matrix has been studied extensively. A brief update is presented to focus on the conceptual shift from tribimaximal mixing (${\theta }_{13}=0$, ${\theta }_{23}=\pi /4$, ${\tan }^2{\theta }_{12}=1/2$) to $\underline{\mathrm{cobimaximal}}$ mixing (${\theta }_{13}\ne 0$, ${\theta }_{23}=\pi /4$, ${\delta }_{CP}=\pm \pi /2$) which agrees well with present data. Three specific realistic examples are proposed, two with three and the third with just two parameters.

Comments: 9 pages, no figure, version to appear in PLB