Radiative corrections to ${\mathrm{\pi }}_{\mathit{l}2}$ (l=e or μ) decays are examined. Higher order electroweak leading logarithms short-distance QCD corrections, and structure dependent effects are incorporated. The results are employed to (1) test e-μ universality in Γ(π→eν${\mathrm{¯}}_{\mathit{e}}$(γ))/Γ(π→μν${\mathrm{¯}}_{\mathrm{\mu }}$(γ)), (2) extract an ${\mathit{f}}_{\mathrm{\pi }}$ which is used to check the Goldberger-Treiman relation and PCAC-anomaly prediction for Γ(${\mathrm{\pi }}^0$→γγ), and (3) determine the tau partial decay rate Γ(τ→π${\nu }_{\mathrm{\tau }}$(γ)).

• Received 16 September 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.3629