Exploring the feasibility of the charged lepton flavor violating decay $\mu \to e+\gamma$ in inverse and linear seesaw mechanisms with $A_4$ flavour symmetry

Abstract

One of the possible ways to explain the observed flavour structure of fundamental particles is to include flavor symmetries in the theories. In this work, we investigate the rare charged lepton flavour violating (cLFV) decay process ($\mu \to e\gamma$) in two of the low scale ($\sim$TeV) seesaw models: (i) the Inverse seesaw (ISS) and (ii) Linear seesaw (LSS) models within the framework of $A_4$ flavour symmetry. Apart from the $A_4$ flavour symmetry, some other symmetries like $U(1{)}_X$, $Z_4$ and $Z_5$ are included to construct the Lagrangian. We use results from our previous work \cite{Devi:2021ujp,Devi:2021aaz} where we computed unknown neutrino oscillation parameters within $3\sigma$ limits of their global best fit values, and apply those results to compute the branching ratio (BR) of the muon decay for both the seesaw models. Next we compare our results with the current experimental bounds and sensitivity limits of BR($\mu \to e\gamma$) as projected by various experiments, and present a comparative analysis that which of the two models is more likely to be tested by which current/future experiment. This is done for various values of currently allowed non-unitarity parameter. This comparative study will help us to pinpoint that which of the low scale seesaw models and triplet flavon VEV alignments will be more viable and favourable for testing under a common flavour symmetry ($A_4$ here), and hence can help discriminate between the two models.

Comments: 30 pages, 7 figures, 6 tables