Skewed Parton Distributions
  Applications of perturbative QCD to deeply virtual Compton scattering and hard exclusive electroproduction processes require a generalization of usual parton distributions for the case when long-distance information is accumulated in nonforward matrix elements of quark and gluon light-cone operators. We describe two types of nonperturbative functions parametrizing such matrix elements: double distributions F(x,y;t) and skewed distribution functions   F_\zeta(X;t), discuss their properties, and basic uses in the QCD description of hard exclusive processes. 
A.V. Radyushkin