Meson twist-4 parton distributions in terms of twist-2 distribution   amplitudes at large Nc
  We show that in the large N_c limit four-quark twist-4 distributions in the pion can be expressed in terms of twist-2 pion distribution amplitude. This allows us to compute the isospin-2 structure function of the pion F_2^{I=2}(x_B) in the large N_c limit. The method can be easily applied to other mesons as well. 
N.-Y. Lee, P.V. Pobylitsa, M.V. Polyakov, and K. Goeke