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

We show that the generalized parton distribution functions (GPDFs) in the skewed x approximate to xi << 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 permits 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 J/psi and Upsilon mesons 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.