Pseudoscalar Decays into Two Photons in Chiral Perturbation Theory

We study the one-loop corrections in chiral perturbation theory to the $\gamma \gamma$ and $\gamma {\gamma }^{*}$ decays of the pseudoscalar mesons. The latter are divergent, thus requiring the existence of dimension-six terms contributing to the anomalous Lagrangian. Some examples of such terms are given. We also discuss the experimental consequences of the next-to-leading terms.