Trimaximal TM1 neutrino mixing in S4 with spontaneous CP violation

TL;DR

This paper develops a model based on S4 symmetry that explains neutrino mixing angles, including CP violation effects, aligning well with recent experimental data and moving beyond the tri-bimaximal paradigm.

Contribution

It introduces a direct S4-based model for TM1 neutrino mixing with spontaneous CP violation, explaining deviations from tri-bimaximal mixing and accommodating recent experimental results.

Findings

Solar angle decreased by about one degree from tri-bimaximal value.

Atmospheric angle depends on CP phase and can deviate from maximal mixing.

Model aligns with latest global fit data on neutrino mixing angles.

Abstract

The measurement of the reactor angle by the Daya Bay and RENO experiments in 2012 has ruled out the tri-bimaximal paradigm. Adopting an S4 family symmetry, we propose direct models of the trimaximal type TM1 in which the tri-bimaximal Klein symmetry of the neutrino sector is broken to a residual Z2 symmetry. In such a scenario, the solar mixing angle is decreased compared to its tri-bimaximal value by about one degree, thus bringing it in excellent agreement with experimental observation. The atmospheric mixing angle, on the other hand, depends on the CP violating Dirac phase delta. Imposing CP conservation in the family symmetry limit, we show how to break the CP symmetry via flavon VEVs with well-defined complex phases, so that sizable deviations of the atmospheric angle from maximal mixing, consistent with the latest global fits, are produced.