Electromagnetic corrections toγπ±→π0π±

The amplitude for the anomalous transitions $\gamma {\pi }^{\pm }\to {\pi }^0{\pi }^{\pm }$ is analyzed within chiral perturbation theory including electromagnetic interactions. The presence of a t-channel one-photon exchange contribution induces sizable $\mathcal{O}{(e}^2)$ corrections which enhance the cross section in the threshold region and bring the theoretical prediction into agreement with available data. In the case of the crossed reaction $\gamma {\pi }^0\to {\pi }^{+}{\pi }^{-},$ the same contribution appears in the s channel and its effects are small.