Review of Rare and Forbidden $τ$ Decays

Abstract

This is a review of rare and forbidden decays of the $τ$ lepton. For the rare decays, this includes new results on the chiral anomaly decay $\taupietapio$, new upper limits on the second-class-current decay $\taupieta$, and the observations of the Cabibbo-suppressed decay $\tauketa$ and the internal conversion decay $\taueee$. For the forbidden decays, there are new upper limits on the radiative decays $\tauegamma$ and $\taumugamma$. Some forbidden decays which have not been previously searched for are also suggested.