Exploring asymmetries in three-body cLFV lepton decays: probing CP violation in HNL extensions of the SM

TL;DR

This paper investigates how angular asymmetries in three-body charged lepton flavor violating decays can reveal CP violation and distinguish Majorana sterile fermion extensions of the Standard Model, providing new experimental probes.

Contribution

It introduces new angular observables and correlations in cLFV decays, offering novel ways to test CP violation in models with Majorana sterile fermions.

Findings

Sizeable asymmetries can be observed in angular distributions.

Patterns of observables can potentially falsify the model.

Correlations between asymmetries enhance CP violation detection.

Abstract

In the context of Standard Model extensions via Majorana sterile fermions, the presence of additional CP violating phases (Dirac and Majorana) has been shown to be at source of important effects in charged lepton flavour violating (cLFV) transitions and decays. Here we will consider further angular observables that can be studied for polarised $\tau$ and $\mu$ cLFV decays. These include, among others, parity asymmetries and time-reversal asymmetries for generic cLFV 3-body decays, $\ell_\alpha^+ \to \ell_\beta^+ \ell_\gamma^+ \ell_\delta^-$. We address relevant correlations between the different classes of observables, and show that one can have sizeable asymmetries, which can be used to further probe this interesting class of SM extensions. Our study leads to the prediction of particular patterns of angular observables, which would allow to potentially falsify the model, should a cLFV signal be observed.