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.