Learning from Dispersive Effects in the Nucleon Polarisabilities

Abstract

A cartoon is drawn how and why to define and extract the energy dependence of the nucleon polarisabilities from low energy Compton scattering on the nucleon. The information dynamical polarisabilities contain about the low energy degrees of freedom inside the nucleon is extracted by comparing the chiral effective field theory calculation with dispersion theory results. Dynamical polarisabilities do not contain more or less information than the corresponding Compton scattering amplitudes, but as with any multipole decomposition, the facts are more readily accessible and easier to interpret. Stringent constraints for models and model-independent power countings of a low energy effective field theory of the nucleon follow from their analysis.