Forward Compton Scattering

Abstract

An analysis of the recently measured photon-proton total cross sections is performed. Smooth fits to the cross sections are obtained and used to calculate, by means of the forward dispersion relation, the real part of the spin-averaged forward amplitude. The resulting predictions for the real part are given. At high energies, the fits to the present total cross-section data, together with the calculated real part, suggest the presence in the high-energy behavoir of an extra real constant in addition to what one would have predicted from Regge theory and the high-energy behavior of the imaginary part. This extra real constant, which is consistent in sign and magnitude with the Thomson limit, $-\frac{\alpha }{M_N}$, could correspond to a fixed pole at $J=0\mathrm{}$ in Regge-pole language. Possible ways to test the forward dispersion relation are discussed.