$\tau \to \mu \mu \mu$ at a rate of one out of $10^{14}$ tau decays?

Patrick Blackstone, Matteo Fael, Emilie Passemar

We present in a full analytic form the partial widths for the lepton flavour violating decays ${\mu }^{\pm }\to e^{\pm }{e}^{+}{e}^{-}$ and ${\tau }^{\pm }\to {\ell }^{\pm }{\ell }^{\prime +}{\ell }^{\prime -}$, with $\ell,\el…