Modular-symmetry-protected seesaw

TL;DR

This paper explores how modular flavor symmetries can naturally generate fermion mass hierarchies and neutrino masses in a low-scale seesaw model, with testable predictions for future heavy neutral lepton experiments.

Contribution

It introduces a novel mechanism linking modular symmetry deviations to lepton number breaking and neutrino mass generation in a low-scale seesaw framework.

Findings

Mass hierarchies arise from small deviations in the modular parameter.

Lepton number breaking is connected to charged-lepton mass hierarchies.

Models predict observable signals in future heavy neutral lepton searches.

Abstract

In the presence of a finite modular flavour symmetry, fermion mass hierarchies may be generated by a slight deviation of the modulus from a symmetric point. We point out that this small parameter governing charged-lepton mass hierarchies may also be responsible for the breaking of lepton number in a symmetry-protected low-scale seesaw, sourcing active neutrino masses and the mass splitting of a pseudo-Dirac pair of heavy neutrinos. We discuss the phenomenological implications of this mechanism, including the possibility to test the considered models at future planned and proposed heavy neutral lepton searches.