Nucleon Polarisabilities from Deuteron Compton Scattering, and Its Lessons for Chiral Power Counting

A brief review of Compton scattering off the deuteron in Chiral Effective Field Theory, including gauge invariance and the correct Thomson limit. We model-independently determine the iso-scalar, spin-independent dipole polarisabilities of the nucleon at zero energy from all Compton data below 100 MeV as \alpha_{E1}^s=11.3+-0.7_{stat}\+-0.6_{Baldin}+-1_{theory}, \beta_{M1}^s=3.2-+0.7_{stat}+-0.6_{Baldin}+-1_{theory}, each in 10^{-4} fm^3. Proton and neutron polarisabilities are therefore identical within (predominantly statistical) errors