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-2 and twist-4 pion light-cone wave functions into account, it is shown that the QCD sum rule prediction is in agreement with quark distribution obtained from analysis of the Drell-Yan process. Twist-4 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-2 pion light-cone wave function is obtained. We argue that the leading twist pion wave function \phi_\pi(u) \simeq 1 for u=0.3 with an accuracy of about 20-30%.