Radiative corrections to πl2 and Kl2 decays

We reexamine radiative corrections to πl2 and Kl2 decays. We perform a matching calculation, including vector and axial vector resonances as explicit degrees of freedom in the long distance part. By considering the dependence on the matching scale and on the hadronic parameters, and by comparing with model independent estimates, we scrutinize the model dependence of the results. For the pseudoscalar meson decay constants, we extract the values fπ = (92.1 ± 0.3) MeV and fK = (112.4 ± 0.9) MeV. For the ratios Rπ and RK of the electronic and muonic decay modes, we predict Rπ = (1.2354 ± 0.0002) × 10−4 and RK = (2.472 ± 0.001) × 10−5.