Resonant leptogenesis in inverse see-saw framework with modular S4 symmetry

Abstract We introduce a lepton mass generation and flavor mixing model, realized through a (2,3) inverse seesaw structure based on modular $$ S_4 $$ S 4 symmetry. The model employs modular forms to construct the lepton Yukawa couplings, significantly simplifying the framework by reducing redundant parameters. A detailed numerical analysis demonstrates consistency with current neutrino oscillation data, yielding specific outputs for the mixing angles and CP-violating phases. The Dirac CP phase is predicted to lie near $$\delta _{\textrm{CP}} \approx \pm 90^\circ $$ δ CP ≈ ± 90 ∘ , corresponding to near-maximal leptonic CP violation. The total neutrino mass lies within $$\sum m_\nu \approx 0.0587\text {--}0.0924$$ ∑ m ν ≈ 0.0587 -- 0.0924 eV, and the effective Majorana mass $$|m_{ee}| \approx (0.002\text {--}0.02)$$ | m ee | ≈ ( 0.002 -- 0.02 ) eV, within reach of upcoming neutrinoless double beta decay experiments such as nEXO and AMoRE-II. The model also remains consistent with current bounds on charged lepton flavor violating processes from MEG and BaBar. We further explore resonant leptogenesis enabled by quasi-degenerate heavy neutrino states and show that the observed baryon asymmetry of the universe can be successfully generated in this scenario. The combined treatment of low-energy observables and high-scale baryogenesis demonstrates the predictivity and testability of the modular $$ S_4 $$ S 4 -based ISS(2,3) framework.