Standard Model Decays of Tau into Three Charged Leptons

Abstract

Analytic expressions are given for the $τ$ decays into three charged leptons, $τ\rta \ell\ell\overline \ellν_τ\overline ν_\ell$, where the $\ell$ are combinations of electrons and muons, and for the radiative decays $τ\rta γ\ellν_τ\overline ν_\ell$. The branching ratios are sensitive functions of whether the final state $\ell$ are muons or electrons.