Structure of Radiative Decay Amplitudes

Abstract

It is shown that the matrix element for decay processes involving the emission of a single photon may be obtained from the matrix element for the corresponding nonradiative decay and the magnetic moments of the particles involved, up to terms that vanish as the photon frequency $K\to 0$. Detailed discussions are given for decays involving three and four spinless particles, as well as for four spin ½ particles. The results are similar to those obtained by Low for bremsstrahlung in scattering processes, but some novel features arise when the nonradiative decay is forbidden by selection rules.