Inverse Seesaw Model in Non-holomorphic Modular $A_4$ Flavor Symmetry

Abstract: We investigate an inverse seesaw model of neutrino masses based on non-holomorphic modular $A_4$ symmetry, by extending the framework of modular-invariant flavor models beyond the conventional holomorphic paradigm. After establishing the general theoretical framework, we analyze three concrete model realizations distinguished by their $A_4$ representation assignments and modular weight configurations for the matter fields. Focusing on these three specific realizations, we perform a comprehensive analysis of neutrino phenomenology. By constraining the modulus parameter $\tau$ to the fundamental domain and systematically scanning the parameter space, we identify regions compatible with current neutrino oscillation data. Our numerical results provide predictions for currently unmeasured quantities, including the absolute neutrino mass scale, Dirac CP-violating phase, and Majorana phases. These predictions establish specific, testable signatures for upcoming neutrino experiments, particularly in neutrinoless double beta decay and precision oscillation measurements. The framework offers a well-defined target for future experimental verification or exclusion, while demonstrating the phenomenological viability of non-holomorphic modular symmetry approaches to flavor structure.