VIRTUAL COMPTON-SCATTERING OFF THE NUCLEON IN CHIRAL PERTURBATION-THEORY

We investigate the spin-independent part of the virtual Compton scatte ring (VCS) amplitude of the nucleon within the framework of chiral per turbation theory. We perform a consistent calculation to third order i n external momenta according to Weinberg's power counting. With this c alculation we can determine the second- and fourth-order structure-dep endent coefficients of the general low-energy expansion of the spin-av eraged VCS amplitude based on gauge invariance, crossing symmetry, and the discrete symmetries. We discuss the kinematical regime to which o ur calculation can be applied and compare our expansion with the multi pole expansion by Guichon, Liu, and Thomas. We establish the connectio n of our calculation with the generalized polarizabilities of the nucl eon where it is possible.