Deeply virtual Compton scattering beyond next-to-leading order: the flavor singlet case

Abstract

We study radiative corrections to deeply virtual Compton scattering in the kinematics of HERA collider experiments to next--to--leading and next--to--next--to--leading order. In the latter case the radiative corrections are evaluated in a special scheme that allows us to employ the predictive power of conformal symmetry. As observed before, the size of next--to--leading order corrections strongly depends on the gluonic input, as gluons start to contribute at this order. Beyond next--to--leading order we find, in contrast, that the corrections for an input scale of few GeV^2 are small enough to justify the uses of perturbation theory. For $\xi > 5 10^{-3}$ the modification of the scale dependence is also small. However, with decreasing $\xi$ it becomes moderate or even large, in particular for the phase.