Modular $S_{3}$ flavoured Pati-Salam model with two family seesaw

Abstract

We present a unified model of quarks and leptons with modular $S_3$ flavour symmetry, where the two lightest family masses are naturally suppressed via a Pati-Salam version of the type I seesaw mechanism, mediated through heavier vector-like fermions. Majorana neutrino masses are further suppressed through a double seesaw mechanism. The viable parameter space has a preferred range of the modulus field with Im$(\tau) \sim 2 $, leading to successful fermion masses and mixing. The prediction for neutrinoless double beta decay is partly within the reach of the nEXO experiment. In particular, the Dirac CP violating neutrino oscillation phase is predicted to lie in the range $\delta_{\rm CP}^{\nu}\sim 260^o-360^o$.