Radiative corrections to the decay $H^+ \to W^+ A^0$

Full one-loop electroweak corrections to the on-shell decay $H^+ \to W^+A^0$ are computed in the framework of models with two Higgs doublets (THDM). Such a decay may be dominant for $H^{\pm}$ over a wide range of parameter space relevant at present and future colliders. We show that the corrections may approach 40% and in particular are sensitive to $\lambda_5$, which parametrizes the discrete symmetry breaking term. We suggest that a measurement of the branching ratio of $H^+ \to W^+A^0$ may offer a possibility of measuring the magnitude of $\lambda_5$.