An A4 model to accommodate maximal theta23 and maximal delta consistent with mu-tau reflection symmetry

Abstract

In this work, we construct an A4-based flavor symmetry model within the framework of the type-I seesaw mechanism to realize a light neutrino mass matrix consistent with mu-tau reflection symmetry. The entire framework is based on the Standard Model gauge symmetry extended by the discrete group A4 x Z2 x Z4. In general, the elements of the light Majorana neutrino mass matrix are complex. The mu-tau reflection symmetric texture of the mass matrix can be realized in a generalized CP symmetry limit. In this symmetry limit, the model predicts a maximal atmospheric mixing angle theta23 = pi/4 and a maximal Dirac CP phase delta = pi/2 or 3pi/2. These features are consistent with current experimental observations, including a near-maximal value of theta23, a non-zero reactor angle, and a preference for delta close to 270 degrees, as indicated by the T2K and NOvA experiments. Non-maximal values of theta23 and delta can be accommodated when one does not restrict to the CP symmetry limit. The model predictions for the mixing angles and the Dirac CP phase delta are then controlled by two parameters. We perform a numerical analysis to identify the allowed values of the model parameters consistent with current global three-neutrino oscillation data. The model successfully reproduces the desired deviations of theta23 and delta from their maximal values, consistent with global fit data, while simultaneously accommodating the observed values of theta12 and theta13.