Nucleon Polarizabilities: from Compton Scattering to Hydrogen Atom

TL;DR

This review summarizes the current understanding of nucleon polarizabilities, their measurement, theoretical calculations, and implications for hydrogen spectroscopy, highlighting recent advances and ongoing experimental efforts.

Contribution

It provides a comprehensive overview of nucleon polarizabilities, integrating recent lattice QCD, chiral effective-field theory, and experimental data, with emphasis on model-independent constraints and implications for the proton-radius puzzle.

Findings

Proton polarizability significantly affects muonic hydrogen measurements.

Recent lattice QCD and chiral EFT calculations have improved polarizability estimates.

Experimental programs are advancing measurements of nucleon polarizabilities.

Abstract

We review the current state of knowledge of the nucleon polarizabilities and of their role in nucleon Compton scattering and in hydrogen spectrum. We discuss the basic concepts, the recent lattice QCD calculations and advances in chiral effective-field theory. On the experimental side, we review the ongoing programs aimed to measure the nucleon (scalar and spin) polarizabilities via the Compton scattering processes, with real and virtual photons. A great part of the review is devoted to the general constraints based on unitarity, causality, discrete and continuous symmetries, which result in model-independent relations involving nucleon polarizabilities. We (re-)derive a variety of such relations and discuss their empirical value. The proton polarizability effects are presently the major sources of uncertainty in the assessment of the muonic hydrogen Lamb shift and hyperfine structure. Recent calculations of these effects are reviewed here in the context of the "proton-radius puzzle". We conclude with summary plots of the recent results and prospects for the near-future work.