GAUGE INVARIANCE AND REGGE-POLE THEORY IN COMPTON SCATTERING

The kinematics of Compton scattering by a boson target are studied. It is shown that a special interpretation of gauge invariance follows as a requirement of Lorentz invariance of S-matrix elements in the limit of zero photon mass. As a consequence, it is demonstrated that the Pomeranchuk trajectory can contribute to the forward-Compton-scattering amplitude without introducing a singular Regge residue function, in contrast with results obtained via the conventional formulation. The close correspondence with perturbation theory (not required a priori) is also discussed. It is found, however, that a similar treatment of gauge invariance for the Yang-Mills field cannot be given consistently. © 1969 The American Physical Society.