On Minimal realization of Topological Lorentz Structures with one-loop Seesaw extensions in A$_4$ Modular Symmetry

Abstract

The topological classification of one-loop Weinberg operator at dimension-5 leads to systematic categorization of one-loop neutrino mass models. All one-loop neutrino mass models must fall in one of these categories. Among these topological categories, loop extension of canonical seesaw scenarios is interesting in light of the current LHC run. Apart from one-loop contribution, these extensions result in dominant tree-level contribution to neutrino masses. The immediate remedy to obtain dominant one-loop contribution requires combination of flavor symmetries and enlarged field content. Alternatively, in this work, we propose a minimal way of realizing the topological structures with dominant one-loop contribution using modular variant of the permutation symmetries. In such a realization, no new fields are needed apart from those permitted by the topology itself. For the first time, we have realized one such topological Lorentz structure(T4-2-$i$) pertaining to one-loop extension of Type-II seesaw using modular A$_4$ symmetry. Here, modular weights play an important role in suppressing tree-level terms and stabilizing the particles running in the loop($N_i$, $\rho$ and $\phi$), thus, making them suitable dark matter candidates. In this work, we have explored the possibility of fermionic dark matter candidate where right-handed neutrino ($N_1$) is assumed to be lightest. We have, also, analyzed the compatibility of the model with neutrino oscillation data and obtained model predictions for effective Majorana mass $M_{ee}$ and $CP$ violation. Furthermore, the predictions on relic density of dark matter and its direct detection considering bound on lepton flavor violating process, $\mu\rightarrow e\gamma$ have, also, been investigated.