Lepton flavor violation inZand lepton decays in supersymmetric models

Abstract

The observation of charged lepton flavor nonconservation would be a clear signature of physics beyond the standard model. In particular, supersymmetric (SUSY) models introduce mixings in the sneutrino and the charged slepton sectors which could imply flavor-changing processes at rates accessible to upcoming experiments. In this paper we analyze the possibility to observe $\stackrel{\ensuremath{\rightarrow}}{Z}{\mathcal{l}}_{I}{\mathcal{l}}_{J}$ in the GigaZ option of TESLA at DESY. We show that although models with SUSY masses above the current limits could predict a branching ratio $\mathrm{BR}(\stackrel{\ensuremath{\rightarrow}}{Z}\ensuremath{\mu}e)$ accessible to the experiment, they would imply an unobserved rate of $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e\ensuremath{\gamma}$ and thus are excluded. In models with a small mixing angle between the first and the third (or the second and the third) slepton families GigaZ could observe $\stackrel{\ensuremath{\rightarrow}}{Z}\ensuremath{\tau}\ensuremath{\mu}$ (or $\stackrel{\ensuremath{\rightarrow}}{Z}\ensuremath{\tau}e)$ consistently with present bounds on ${\mathcal{l}}_{J}\ensuremath{\rightarrow}{\mathcal{l}}_{I}\ensuremath{\gamma}.$ In contrast, if the mixing angles between the three slepton families are large the bounds from $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e\ensuremath{\gamma}$ push these processes below the reach of GigaZ. We show that in this case the masses of the three slepton families must be strongly degenerated (with mass differences of order ${10}^{\ensuremath{-}3}).$ We update the limits on the slepton mass insertions ${\ensuremath{\delta}}_{LL,RR,LR}$ and discuss the correlation between flavor changing and ${g}_{\ensuremath{\mu}}\ensuremath{-}2$ in SUSY models.