We construct phenomenologically viable models of lepton masses and mixing based on modular A 4 invariance broken to residual symmetries Z 3T or Z 3ST and Z 2S respectively in the charged lepton and neutrino sectors. In these models the neutrino mixing matrix is of trimaximal mixing form. In addition to successfully describing the charged lepton masses, neutrino mass-squared differences and the atmospheric and reactor neutrino mixing angles θ 23 and θ 13 , these models predict the values of the lightest neutrino mass (i.e., the absolute neutrino mass scale), of the Dirac and Majorana CP violation (CPV) phases, as well as the existence of specific correlations between i) the values of the solar neutrino mixing angle θ 12 and the angle θ 13 (which determines θ 12 ), ii) the values of the Dirac CPV phase δ and of the angles θ 23 and θ 13 , iii) the sum of the neutrino masses and θ 23 , iv) the neutrinoless double beta decay effective Majorana mass and θ 23 , and v) between the two Majorana phases.
Novichkov, P. P., Petcov, S. T., & Tanimoto, M. (2019). Trimaximal neutrino mixing from modular A 4 invariance with residual symmetries. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 793, 247–258. https://doi.org/10.1016/j.physletb.2019.04.043