Rare muon decays, heavy leptons, andCPviolation

We generalize and elaborate a model recently proposed by Cheng and Li. It is characterized by the breakdown of separate conservation laws for $e$ and $\mu$ lepton types and allows for such processes as $\mu \to e+\gamma$, $\mu \to 3e$. Our generalization incorporates the singly charged heavy lepton discovered in $e^{+}{e}^{-}$ colliding-beam experiments, and it opens up the possibility of introducing $\mathrm{CP}$-violating effects in lepton reactions. We analyze the $\mu \to 3e$ decay process, both with respect to rate (relative to $\mu \to e+\gamma$ and spectrum, including $\mathrm{CP}$-violating correlations. Other physically interesting features are also discussed for the generalized scheme: neutrino "sharing" and off-diagonal neutral-current effects.