LOW-ENERGY COMPTON-SCATTERING OF POLARIZED PHOTONS ON POLARIZED NUCLEONS

The general structure of the cross section of gamma N scattering with polarized photon and/or nucleon in initial and/or final state is syste matically described and exposed through invariant amplitudes. A low-en ergy expansion of the cross section up to and including the order O(om ega(4)) is given that involves ten structure parameters of the nucleon (dipole, quadrupole, dispersion, and spin polarizabilities). Their ph ysical meaning is discussed in detail. Using fixed-t dispersion relati ons, predictions for these parameters are obtained and compared with r esults of chiral perturbation theory. It is emphasized that Compton sc attering experiments at large angles can fix the most uncertain of the se structure parameters. Predictions for the cross section and double- polarization asymmetries are given and the convergence of the expansio n is investigated. The feasibility of the experimental determination o f some of the structure parameters is discussed.