New modular fixed point models and their phenomenological implications for JUNO, T2HK and DUNE

TL;DR

This paper explores minimal modular fixed point models with two right-handed neutrinos and three fixed points, revealing highly predictive models based on $S_4'$ and $A_5$ symmetries that have specific implications for neutrino oscillation experiments.

Contribution

It introduces a new class of highly predictive modular fixed point models with generalized Dirac columns, expanding the Littlest Seesaw framework and deriving new sum rule relations for neutrino mixing angles.

Findings

Models are based on $S_4'$ and $A_5$ symmetries.

New sum rule relations for solar and reactor angles.

Predictions for atmospheric angle and CP phase compared to experimental sensitivities.

Abstract

We perform a general analysis of minimal modular fixed point models based on two right-handed neutrinos (2RHNs) and three modular fixed points, and find that the only viable possibilities are based on modular $S_4'$ and $A_5$ symmetry. Such models are highly predictive, with neutrino masses and the lepton mixing mixing matrix being fixed by three real parameters, as in the Littlest Seesaw Models. We perform an exhaustive scan over all possible models in this class and find many viable fixed points and modular form alignments, after confronting them with the latest neutrino oscillation global fits. The resulting models have the new feature that the two Dirac columns take more general forms than traditional Littlest Seesaw models, resulting in new sum rule relations between the solar and reactor angles, beyond those associated with TM1 (where the first column of the tri-bimaximal mixing matrix is preserved), which are compared to present and future projected JUNO results. We also compare the predictions of these models for the atmospheric angle and CP violating phase to current global fits and future T2HK and DUNE sensitivities.