A Non-perturbative Effect in Deep Inelastic Scattering
  The HERA data at large $Q^2$ and small-$x$ investigate large distances on the light-cone. At such large distances the scattered quarks can maintain their colour identity by polarizing the vacuum as they transfer energy to it. We calculate the probability for the creation of quark-antiquark pairs from the polarized QCD vacuum and their contribution to the structure function. 
E.A. Paschos