Effects of external fields on the Lamb shift

Abstract

It is shown that an external radiation field interacting with an atom alters the value of the Lamb shift. The effect of various spectral profiles is calculated with particular reference to the existence of an electromagnetic mass shift and changes in the Bethe formula. Thermal corrections due to black body radiation are considered and are shown never to be important, in contrast with previous work. Mass renormalization due to external field interactions is shown not to be a useful concept. It is concluded that the only important modification is due to the interaction with excitation and decay photons, and that this is likely to be very small in most experiments.