Abstract
In extensions of the standard model by Majorana fermions, the presence of additional CP violating phases has been shown to play a crucial role in lepton number violating processes. In this work we show that (Dirac and Majorana) CP violating phases can also lead to important effects in charged lepton flavour violating (cLFV) transitions and decays, in some cases with a significant impact for the predicted rates of cLFV observables. We conduct a thorough exploration of these effects in several cLFV observables, and discuss the implications for future observation. We emphasise how the presence of leptonic CP violating phases might lead to modified cLFV rates, and to a possible loss of correlation between cLFV observables.
Highlights
Neutrino oscillations signal the presence of physics beyond the Standard Model (SM)
In this work we have thoroughly addressed the impact of leptonic CP violating phases on the predictions of the rates of several charged lepton flavour violating (cLFV) observables, focusing on minimal SM extensions by heavy Majorana sterile fermions
Despite their minimality and simplicity, these extensions can be interpreted as representative of more complete constructions calling upon the addition of heavy neutral fermions
Summary
Neutrino oscillations signal the presence of physics beyond the Standard Model (SM). leptonic mixings and massive neutrinos open the door to the violation of charged lepton flavour. The role of heavy neutral leptons in what concerns charged lepton flavour violation (cLFV) (see for instance [7,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]) and lepton number violation (LNV) – see for instance [31,32,33,34,35,36,37,38,39,40,41,42] - has been extensively explored in recent years, be it in the context of mechanisms of neutrino mass generation, or in the framework of the above mentioned minimal adhoc extensions by one or more heavy states Several of these studies revealed a promising potential of SM extensions via HNL in what concerns cLFV: depending on the mass regime and mixings with the active states, one could expect significant contributions to several observables, well within the future experimental sensitivity (with interesting prospects in the μ − e sector).
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