Evaluation of two-photon exchange graphs for highly charged heliumlike ions

Abstract
Contributions of one-loop ladder and crossed-ladder graphs to the ground-state energy of heliumlike ions are calculated in Furry representation QED. With the aid of a contour rotation, the graphs are evaluated to all orders in Zα in the range Z=10–110. Particular attention is given to the relation of this work to recent many-body perturbation theory and configuration-interaction calculations.