Predictions from scoto-seesaw with $A_4$ modular symmetry

Abstract

This paper's novelty lies in introducing a hybrid scoto-seesaw model rooted in $A_4$ discrete modular symmetry leading to several interesting phenomenological implications. The scoto-seesaw framework leads to generation of one mass square difference $(\Delta m_{\mathrm{atm}}^2$) using the type-I seesaw mechanism at the tree level. Additionally, the scotogenic contribution is vital in obtaining the other mass square difference ($\Delta m_{\mathrm{sol}}^2$) at the loop level, thus providing a clear interpretation of the two different mass square differences. The non-trivial transformation of Yukawa couplings under the $A_4$ modular symmetry helps to explore neutrino phenomenology with a specific flavor structure of the mass matrix. In addition to predictions for neutrino mass ordering, mixing angles and CP phases, this setup leads to precise predictions for $\sum m_i$ as well as $|m_{ee}|$. In particular, the model predicts $\sum m_i\in (0.073,0.097)$ eV and $\left|m_{ee}\right|\in (3.15,6.66)\times 10^{-3}$ eV range; within reach of upcoming experiments. Furthermore, our model is also promising for addressing lepton flavor violations, i.e., ${\ell }_{\alpha }\to {\ell }_{\beta }\gamma$, ${\ell }_{\alpha }\to 3{\ell }_{\beta }$ and $\mu -e$ conversion rates while staying within the realm of current experimental limits.

Comments: 38 pages, 4 tables, 15 figures, V3 minor correction, results unchanged, matches with published version in PLB