Radiative Corrections to pi_{l2} and K_{l2} Decays

We report on our reexamination of the radiative corrections to $π_{l2}$ and $K_{l2}$ decays. We perform a matching calculation, using a specific model with vector meson dominance in the long distance part and the parton model in the short 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 $f_π= (92.1 \pm 0.3)\,\mbox{MeV}$ and $f_K = (112.4 \pm 0.9) \, \mbox{MeV}$. For the ratios $R_π$ and $R_K$ of the electronic and muonic decay modes, we predict $R_π= (1.2354 \pm 0.0002) \cdot 10^{-4}$ and $R_K = (2.472 \pm 0.001) \cdot 10^{-5}$.

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