Compton scattering and the polarizabilities of the nucleon

We consider Compton scattering off the nucleon in the framework of fixed-t subtracted dispersion relations. The subtracted dispersion integrals are mainly saturated by πN intermediate states in the s channel, γN → πN → γN, and ππ intermediate states in the t channel, γγ → ππ → NN-bar. In the present formalism the nucleon polarizabilities enter as subtraction constants to be determined by a fit to the Compton data. We show results for Compton scattering discussing in particular the sensitivity on the scalar polarizability difference α - β and the backward spin polarizability γπ. (author)