The Electromagnetic Interaction in Chiral Perturbation Theory

We investigate electromagnetic effects in the framework of chiral perturbation theory. Using a completely independent method, we confirm Urech's results for the divergences of the one--loop functional in the electromagnetic sector. We perform a one--loop analysis of all $P_{\ell 2}$ ($P = \pi, K, \eta$) and the $K_{\ell 3}$ form factors $f_+^{K^+\pi^0}(0)$, $f_+^{K^0\pi^-}(0)$, including a systematic treatment of the $\cO(e^2p^2)$ contributions in the mesonic part. We illustrate our results by several numerical estimates.