Soft Rescattering in DIS: Effects of Helicity Flip
  Soft rescattering in hard QCD processes may involve non-perturbative, chiral symmetry breaking interactions. We find that rescattering which changes the helicity of the struck quark gives rise to a leading twist single spin asymmetry in semi-inclusive DIS, the angular dependence of which is the same as that usually ascribed to the Collins effect.   We argue that helicity-changing rescattering can contribute also to $k_\perp$-integrated parton distributions. 
Paul Hoyer and Matti Jarvinen