RADIATIVE 4-MESON AMPLITUDES IN CHIRAL PERTURBATION-THEORY

We present a general discussion of radiative four-meson processes to O (p(4)) in chiral perturbation theory. We propose a definition of ''gen eralized bremsstrahlung'' that takes full advantage of experimental in formation on the corresponding non-radiative process, We also derive g eneral formulae for one-loop amplitudes which can be applied, for inst ance, to eta --> 3 pi gamma, pi pi --> pi pi gamma and K --> 3 pi gamm a.