Minimal lepton flavor violating realizations of minimal seesaw models

TL;DR

This paper explores how a global U(1)R symmetry in minimal lepton flavor violating seesaw models affects neutrino masses and charged lepton flavor violation, highlighting two model classes with distinct phenomenological implications.

Contribution

It classifies minimal type I seesaw models with a broken U(1)R symmetry into two classes and analyzes their impact on charged lepton flavor violation and baryon asymmetry.

Findings

Suppressed charged lepton flavor violation in models with decoupled right-handed neutrino masses.

Significant charged lepton flavor violation at TeV-scale right-handed neutrino masses.

Incompatibility of sizable flavor violation with baryon asymmetry preservation.

Abstract

We study the implications of the global U(1)R symmetry present in minimal lepton flavor violating implementations of the seesaw mechanism for neutrino masses. In the context of minimal type I seesaw scenarios with a slightly broken U(1)R, we show that, depending on the R-charge assignments, two classes of generic models can be identified. Models where the right-handed neutrino masses and the lepton number breaking scale are decoupled, and models where the parameters that slightly break the U(1)R induce a suppression in the light neutrino mass matrix. We show that within the first class of models, contributions of right-handed neutrinos to charged lepton flavor violating processes are severely suppressed. Within the second class of models we study the charged lepton flavor violating phenomenology in detail, focusing on mu to e gamma, mu to 3e and mu to e conversion in nuclei. We show that sizable contributions to these processes are naturally obtained for right-handed neutrino masses at the TeV scale. We then discuss the interplay with the effects of the right-handed neutrino interactions on primordial B - L asymmetries, finding that sizable right-handed neutrino contributions to charged lepton flavor violating processes are incompatible with the requirement of generating (or even preserving preexisting) B - L asymmetries consistent with the observed baryon asymmetry of the Universe.