Off-diagonal quark distributions in pions in the effective single-instanton approximation

Nonperturbative functions that parametrize off-diagonal hadronic matrix ele ments of the light-cone leading-twist quark operators are considered. These functions are calculated within the proposed relativistic quark model allo wing for the nontrivial structure of the QCD vacuum, special attention bein g given to gauge invariance. Hadrons are treated as bound states of quarks; strong-interaction quark-pion vertices are described by effective interact ion Lagrangians generated by instantons. The parameters of the instanton va cuum, such as the effective radius of the instanton and the quark mass, are related to the vacuum expectation values of the quark-gluon operators of t he lowest dimension and to low-energy pion observables. (C) 2000 MAIK "Nauk a/Interperiodica".