# QED theory of the specific mass shift in atoms

## TL;DR

This paper develops a quantum electrodynamics approach to accurately calculate the nuclear recoil effect on atomic energy levels, including relativistic corrections, for ions with atomic numbers 5 to 100.

## Contribution

It introduces a nonperturbative QED formalism for the interelectronic interaction correction to the nuclear recoil effect in atoms and ions, extending beyond lowest-order relativistic approximations.

## Key findings

- Calculated recoil corrections for He-like and Li-like ions across Z=5-100.
- Analyzed the behavior of the two-electron recoil effect beyond lowest-order relativistic approximation.
- Provided insights into relativistic effects on nuclear recoil in high-Z ions.

## Abstract

The quantum electrodynamics formalism to treat the interelectronic-interaction correction of first order in $1/Z$ to the two-electron part of the nuclear recoil effect on binding energies in atoms and ions is developed. The nonperturbative in $\alpha Z$ calculations of the corresponding contribution to the energies of the $1s^2$ state in He-like and the $1s^2 2s$ and $1s^2 2p_{1/2}$ states in Li-like ions are performed in the range $Z=5-100$. The behavior of the two-electron part of the nuclear recoil effect beyond the lowest-order relativistic approximation as $Z$ grows is studied.