Abstract
A part of the two-loop Lamb shift called the perturbed orbital term is evaluated with exact Dirac-Coulomb propagators. It is shown to be the most nonperturbative function of yet encountered in QED, so much so that even at the leading term in its expansion is of the opposite sign from the complete answer. The higher order contributions are to the ground state Lamb shift in hydrogen and and to the Lamb shift in hydrogen and , respectively.
- Received 13 February 1998
DOI:https://doi.org/10.1103/PhysRevLett.80.5297
©1998 American Physical Society