Charged Lepton Flavour Violation in Supersymmetric Low-Scale Seesaw Models

TL;DR

This paper investigates charged lepton flavor violation in supersymmetric low-scale seesaw models, analyzing both soft and supersymmetric sources, and predicts observable signatures in upcoming experiments.

Contribution

It provides a comprehensive calculation of lepton-flavor-violating processes in minimal supergravity models with low-scale seesaw mechanisms, including new supersymmetric contributions.

Findings

Derived limits on heavy Majorana mass scale and neutrino mixings.

Predicted correlated lepton-flavor-violating signatures detectable in future experiments.

Identified distinct signatures for supersymmetric low-scale seesaw models.

Abstract

We study charged lepton flavour violation in low-scale seesaw models of minimal supergravity, which realize large neutrino Yukawa couplings thanks to approximate lepton-number symmetries. There are two dominant sources of lepton flavour violation in such models. The first source originates from the usual soft supersymmetry-breaking sector, whilst the second one is entirely supersymmetric and comes from the supersymmetric neutrino Yukawa sector. Within the framework of minimal supergravity, we consider both sources of lepton flavour violation, soft and supersymmetric, and calculate a number of possible lepton-flavour-violating transitions, such as the photonic decays of muons and taus, mu -> e gamma, tau -> e gamma and tau -> mu gamma, their neutrinoless three-body decays, mu -> e e e, tau -> e e e, tau -> mu mu mu, tau -> e e mu and tau -> e mu mu, and the coherent mu -> e conversion in nuclei. After taking into account the exclusion bounds placed by present experiments of lepton flavour violation, we derive combined theoretical limits on the universal heavy Majorana mass scale mN and the light-to-heavy neutrino mixings. Supersymmetric low-scale seesaw models offer distinct correlated predictions for lepton-flavour-violating signatures, which might be discovered in current and projected experiments, such as MEG, COMET/PRISM, Mu2e, super-BELLE and LHCb.