Skewed and double distributions in the pion and the nucleon - art. no. 114017

We study the non-forward matrix elements of twist-2 QCD light-ray operators and their representations in terms of skewed and double distributions, con sidering the pion as well as the nucleon. We point out the importance of ex plicitly including all twist-2 structures in the double distribution repres entation, which naturally leads to a "two-component" structure of the skewe d distribution, with different contributions in the regions \X\ > xi/2 and \X\ < xi/2. We compute the skewed and double quark distributions in the pio n at a low normalization point in the effective chiral theory based on the instanton vacuum. Also, we derive the crossing relations expressing the ske wed quark distribution in the pion through the distribution amplitude for t wo-pion production. Measurement of the latter in two-pion production in gam ma*gamma and gamma*N reactions could provide direct information about the s kewed as well as the usual quark-antiquark distribution in the pion. [S0556 -2821(99)00423-3].