Abstract
We present a derivation of the last unknown part of the contribution to the Lamb shift of a two-electron atom, induced by the radiative QED effects beyond the Bethe logarithm. This derivation is performed in the framework of nonrelativistic quantum electrodynamics and is valid for the triplet (spin ) atomic states. The obtained formulas are free from any divergences and are suitable for a numerical evaluation. This opens a way for a complete numerical calculation of the QED effects in helium, which will allow an accurate determination of the nuclear charge radius from measurements of helium transition frequencies.
- Received 1 December 2020
- Accepted 15 December 2020
DOI:https://doi.org/10.1103/PhysRevA.103.012803
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