TViolation and the Off-Mass-Shell Corrections to Proton Compton Scattering

Although it is well known that a left-right asymmetry in the angular distribution of low-energy photons Compton-scattered from polarized protons may appear only if $T$ is violated in the electromagnetic interactions, the order of magnitude of this asymmetry can be determined only on the basis of a specific model. We consider a model in which all $T$ violation is contained in the off-mass-shell behavior of a model proton-photon vertex function, and we use dimensional arguments to determine the magnitude of the asymmetry in this case. On the basis of the model, we predict an asymmetry of ∼10%, and hence conclude that proton Compton scattering is a good test for the $T$ invariance of hadron electrodynamics.