Deeply virtual Compton scattering and skewed parton distribution

The study of the structure of the nucleon is one of the most important frontiers in strong interaction physics. There are still many unanswered questions largely due to the non-perturbative nature of the bound state problem in QCD. Two traditional types of observables have been studied extensively, both theoretically and experimentally, for the last forty years: the parton (quark and gluon) distribution functions (PDF's) (via deeply inelastic scattering (DIS) or Drell-Yan processes), and elastic form factors of the nucleon. In the past few years, studies of a new type of nucleon observable, the skewed parton distributions (SPD's), have flourished(eg, [1]). The SPD's generalize and interpolate between the ordinary PDF's and elastic form factors and therefore contain rich structural information, They can be measured in (exclusive) diffractive processes in which the nucleon recoils elastically after receiving a non-zero momentum transfer in the so-called deeply virtual limit(2).