Lepton Flavor Violating tau and muon decays
  In this work the following lepton flavor violating $\tau$ and $\mu$ decays are studied: $\tau^- \to \mu^- \mu^- \mu^+$, $\tau^- \to e^- e^- e^+$, $\mu^- \to e^- e^- e^+$, $\tau^- \to \mu^- \gamma$, $\tau^- \to e^- \gamma$ and $\mu^- \to e^- \gamma$. We work in a constrained supersymmetric scenario with universal soft breaking terms and where the MSSM particle content is extended by the addition of three heavy right handed Majorana neutrinos and their supersymmetric partners. The generation of neutrino masses is done via the seesaw mechanism. We analize all these lepton flavor violating decays in terms of the relevant input parameters, which are the usual mSUGRA parameters and the seesaw parameters. In the numerical analysis compatibility with the most recent experimental upper bounds on all these $\tau$ and $\mu$ decays, with the neutrino data, and with the present lower bounds on the supersymmetric particle masses are required. Two typical scenarios with degenerate and hierarchical heavy neutrinos are considered. We will show here that the minimal supergravity and seesaw parameters do get important restrictions from these $\tau$ and $\mu$ decays in the hierarchical neutrino case. 
E. Arganda, M.J. Herrero