One diagonal texture or cofactor zero of the neutrino mass matrix

Abstract

In view of the recent measurement of nonzero ${\ensuremath{\theta}}_{13}$, we carry out a systematic study of a simple class of neutrino models that has one diagonal texture or cofactor zero in the mass matrix. There are seven free parameters in the model, and five of them are already measured by neutrino oscillation experiments; some cases for the normal or inverted hierarchy are excluded, and for the rest we obtain the preferred values for the lightest neutrino mass and Dirac $CP$ phase. We find that there are strong similarities between one diagonal texture zero models with one mass hierarchy and one diagonal cofactor zero models with the opposite mass hierarchy. We also make predictions for neutrinoless double beta decay for these models. For the one cofactor zero models, we present a simple realization based on a new $U(1)$ gauge symmetry.