Axion-Exchange Contribution to the Energy of Lithium-Like Ions

TL;DR

This paper investigates how axion exchange affects the energy levels of lithium-like ions, developing a relativistic QED formalism and providing constraints on axion properties through high-precision spectroscopy.

Contribution

It introduces a formalism for axion-mediated interelectronic interactions in relativistic bound-state QED, considering finite nuclear size effects.

Findings

Axion-induced energy contributions increase with nuclear charge Z.

Constraints on axion-electron interactions are derived from lithium-like bismuth.

High-precision spectroscopy of highly charged ions can probe new physics related to pseudoscalar bosons.

Abstract

Axions and axion-like particles are among the most promising candidates for dark matter and for manifestations of new physics beyond the Standard Model. In the present work, the contribution of axion exchange to the energy of lithium-like ions is investigated within the framework of relativistic bound-state quantum electrodynamics. A formalism for the interelectronic interaction mediated by axion exchange is developed in the Furry picture with finite nuclear size taken into account. Energy shifts are calculated for a wide range of nuclear charge numbers \(Z\) and axion masses. The magnitude of the axion-induced contribution is shown to increase with increasing \(Z\) for all states considered. Based on the analysis of lithium-like bismuth, constraints on the axion-electron interaction parameters are obtained in the high-mass region. The results indicate that precision spectroscopy of highly charged ions is a promising tool for searches for new physics associated with the exchange of pseudoscalar bosons.