Semiclassical mechanism for single-spin asymmetry in \pi^0-production
  The chiral quark model combined with unitarity and impact parameter picture provides simple semiclassical mechanism for generation of the single-spin asymmetry $A_N$ in the $\pi^0$-production in the polarized proton collisions at RHIC. We derive its linear $x_F$-dependence in polarized proton fragmentation region along with the energy and transverse momentum independence at large $p_T$ values. 
S.M. Troshin, N.E. Tyurin