Nucleon Polarizabilities: from Compton Scattering to Hydrogen Atom

Understand

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.