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 S 3, 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 S 3 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 (ᵢ mᵢ ∑ i m i) 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 (m₄₄ m ee) is in the range 38-58 38 - 58 meV. In particular, the predicted values for ᵢ mᵢ ∑ i m i and m₄₄ m ee 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.