Radiative Four--Meson Amplitudes in Chiral Perturbation Theory

Abstract

We present a general discussion of radiative four--meson processes to $O(p^4)$ in chiral perturbation theory. We propose a definition of ``generalized bremsstrahlung'' that takes full advantage of experimental information on the corresponding non--radiative process. We also derive general formulae for one--loop amplitudes which can be applied, for instance, to $η\ra 3πγ$, $ππ\ra ππγ$ and $K \ra 3πγ$.