Phenomenology of inverse seesaw using S3 modular symmetry

Abstract

Describing neutrino masses using the inverse seesaw mechanism with discrete flavor symmetry imposed through modular forms provides a testable framework at TeV scales with fewer parameters. S3, the smallest finite modular group—naturally requiring only two new sets of heavy neutrinos—offers a unique yet largely unexplored setting for constructing minimal neutrino mass models. In this work, we construct the minimal supersymmetric inverse seesaw model based on the modular S3 flavor symmetry. In our model, the light neutrino mass matrix depends on 6 real parameters: the complex modulus, an overall scale for light neutrino mass, a real ratio and a complex ratio of Yukawa coupling. Thanks to its minimality, our model offers various definite predictions: the lightest neutrino is massless, the neutrino masses are inverted ordering, the sum of the three light neutrino masses (∑imi) is 100 meV, the effective mass for the end point of the beta decay spectrum is 50 meV, the effective mass for neutrinoless double beta decay (mee) is in the range 38-58 meV. In particular, the predicted values for ∑imi and mee from our model are within reach of the next generation experiments. Our model also predicts radiative lepton flavor violating decays ℓ→ℓ′γ which are compatible with experimental constraints.