Recent developments in nuclear structure theory: an outlook on the muonic atom program

TL;DR

This paper reviews recent advances in nuclear structure theory related to muonic atoms, emphasizing calculations of nuclear corrections to atomic spectra crucial for resolving the proton-radius puzzle.

Contribution

It presents updated ab initio calculations of nuclear structure corrections in muonic atoms, especially focusing on the deuteron and the role of two-body currents.

Findings

Ab initio estimates of Lamb shift corrections in muonic atoms.

Preliminary results on magnetic sum rules with two-body currents.

Two-body currents are key for future hyperfine splitting calculations.

Abstract

The discovery of the proton-radius puzzle and the subsequent deuteron-radius puzzle is fueling an on-going debate on possible explanations for the difference in the observed radii obtained from muonic atoms and from electron-nucleus systems. Atomic nuclei have a complex internal structure that must be taken into account when analyzing experimental spectroscopic results. Ab initio nuclear structure theory provided the so far most precise estimates of important corrections to the Lamb shift in muonic atoms and is well poised to also investigate nuclear structure corrections to the hyperfine splitting in muonic atoms. Independently on whether the puzzle is due to beyond-the-standard-model physics or not, nuclear structure corrections are a necessary theoretical input to any experimental extraction of electric and magnetic radii from precise muonic atom measurements. Here, we review the status of the calculations performed by the TRIUMF-Hebrew University group, focusing on the deuteron, and discuss preliminary results on magnetic sum rules calculated with two-body currents at next-to-leading order. Two-body currents will be an important ingredient in future calculations of nuclear structure corrections to the hyperfine splitting in muonic atoms.