QED procedure applied to the quasidegenerate fine-structure levels of He-like ions - art. no. 062505

A procedure for bound-state QED is presented, based upon a covariant form o f the time-evolution operator. In contrast to the standard S-matrix formali sm, our procedure is applicable also to state,, that are quasidegenerate. A ll (quasi)singularities, which appear when an intermediate state is (quasi) degenerate with the initial state, are eliminated. Our procedure is closely related to many-body perturbation theory (MBPT) and may open up possibilit ies to combine QED and MBPT in a more systematic fashion. The procedure is applied to the fine structure of the heliumlike neon and argon ions, and go od agreement is obtained with recent experimental data.