Charged lepton flavor violation in supersymmetric low-scale seesaw models

Abstract

We study charged lepton flavor 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 flavor 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 flavor violation, soft and supersymmetric, and calculate a number of possible lepton-flavor-violating transitions, such as the photonic decays of muons and taus, $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$, $\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ and $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$, their neutrinoless three-body decays, $\ensuremath{\mu}\ensuremath{\rightarrow}eee$, $\ensuremath{\tau}\ensuremath{\rightarrow}eee$, $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\mu}\ensuremath{\mu}$, $\ensuremath{\tau}\ensuremath{\rightarrow}ee\ensuremath{\mu}$ and $\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\mu}\ensuremath{\mu}$, and the coherent $\ensuremath{\mu}\ensuremath{\rightarrow}e$ conversion in nuclei. After taking into account the exclusion bounds placed by present experiments of lepton flavor violation, we derive combined theoretical limits on the universal heavy Majorana mass scale ${m}_{N}$ and the light-to-heavy neutrino mixings. Supersymmetric low-scale seesaw models offer distinct correlated predictions for lepton-flavor-violating signatures, which might be discovered in current and projected experiments, such as MEG, COMET/PRISM, Mu2e, super-BELLE and LHCb.