Perturbative QCD calculation of real and virtual Compton scattering

Abstract

We present the predictions of perturbative QCD for Compton scattering as a function of photon virtuality. Individual helicity amplitudes are given, along with formulas to permit calculation of the $\mathrm{eN}\ensuremath{\rightarrow}{e}^{\ensuremath{'}}{N}^{\ensuremath{'}}\ensuremath{\gamma}$ amplitudes. We discover remarkable structure in some of the amplitudes as a function of photon virtuality. Since $\mathrm{eN}\ensuremath{\rightarrow}{e}^{\ensuremath{'}}{N}^{\ensuremath{'}}\ensuremath{\gamma}$ contains a contribution from Bethe-Heitler scattering, whose magnitude and phase are known, the phases of the virtual Compton amplitudes can in principle be measured by interference with it. It has been shown that the leading-twist behavior of high-energy, large-angle Compton scattering is not affected by soft physics; thus at sufficiently high energies these predictions provide a stringent test of QCD.