Twist-3 fragmentation functions in a spectator model with gluon rescattering

We study the twist-3 fragmentation functions H and H˜, by applying a spectator model. In the calculation we consider the effect of the gluon rescattering at one loop level. We find that in this case the hard-vertex diagram, which gives zero contribution to the Collins function, does contribute to the fragmentation function H. The calculation shows that the twist-3 T-odd fragmentation functions are free of light-cone divergences. The parameters of the model are fitted from the known parametrization of the unpolarized fragmentation D1 and the Collins function H1⊥. We find that our result for the favored fragmentation function is consistent with the recent extraction on H and H˜ from pp data. We also check numerically the equation of motion relation for H, H˜ and find that relation holds fairly well in the spectator model.