Effect of the excited and fourth generation leptons in lepton flavor   violating \mu^{-} \to e^{-}2\gamma decay
  We study the lepton flavor violating $\mu^- \to e^{-}2\gamma $ decay induced by the mediation of heavy leptons such as the excited and fourth generation leptons. We have examined the effects of these leptons in the $\mu^- \to e^{-}2\gamma $ decay. We have found that branching ratio of this decay is very sensitive to excited and fourth generation leptons. Furthermore, we have obtained the bounds on model parameters by using the current experimental limit of this decay. 
S. C. Inan
hep-ph