Large-scale structure of the proton and quark distributions

The current d-quark distribution function (DF) inside a proton falls to zero at x → 1 (where x is the Bjorken variable) faster than the u-quark function. This is explained in the two-level QCD model due to a cluster which consists of u and d dressed (constituent) quarks. Predictions of the model are in good agreement with the experiment. Differences in DF of u- and d-quarks obtained in the present paper is really conditioned by coherent non-perturbative effects. But a relationship between these effects and the highest twist operators and 1/Q2 corrections at present remans unsolved