Dynamic electron screening in nuclear and mesonic atom E1 transitions

Atomic electrons can influence the electromagnetic transition rates of nuclei and mesonic atoms. We examine this dynamic electron screening effect for E1 transitions. The screening factor is expressed in terms of the forward Rayleigh scattering amplitude, and, for easy computation, the photoelectric cross section. We find that the effect can be large for low-energy transitions, but such transitions are rare for nuclei. The effect on mesonic atom cascades is usually small, but can be quite significant for high-precision experiments and those which look at transitions from high initial n.