Nonforward 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 $〈{p}^{\ensuremath{'}}|\mathcal{O}(0,z)|p〉$ 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 nonforward distribution functions ${\mathcal{F}}_{\ensuremath{\zeta}}(X;t),$ discuss their spectral properties, evolution equations which they satisfy, basic uses and general aspects of factorization for hard exclusive processes.

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