Distribution of valence quarks and light-cone QCD sum rules

A method for calculating the pion structure function directly in terms of light-cone wave functions is suggested. Taking twist-two and twist-four pion light-cone wave functions into account, it is shown that the QCD sum rule prediction is in agreement with the quark distribution obtained from an analysis of the Drell-Yan process. Twist-four quark-gluon light-cone wave functions give a large positive contribution to the pion structure function for x(B) < 0.2. A new constraint on the twist-two pion light-cone wave function is obtained. We argue that the leading twist pion wave function phi(pi)(u) similar or equal to 1 for u = 0.3 with an accuracy of about 20-30 %.