Paper detail

A simple form for the low-x generalized parton distributions in the skewed regime

We show that the generalized parton distributions (GPDFs) in the 'skewed' $x \approx ξ<< 1$ regime can be related in a particularly simple way to the usual diagonal distributions. This follows directly from the Shuvaev transform, but bypasses a direct evaluation of the poorly convergent double integral which this relation contains, thus allowing for a more transparent understanding of the physics involved; it avoids the necessity for any further low-x approximations for the diagonal partons, as well as permitting a clearer application to cases when the GPDFs unintegrated over the parton transverse momentum are required. We consider for illustration the specific examples of the central exclusive production of a Standard Model Higgs boson, and the photoproduction of a Upsilon meson at the LHC, and show how a careful evaluation of the GPDFs, which our simple results allow, is required to correctly calculate the predicted cross sections.