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

We study the twist-3 fragmentation functions H and (H) over tilde, 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 D-1 and the Collins function H-1(perpendicular to). We find that our result for the favored fragmentation function is consistent with the recent extraction on H and (H) over tilde from pp data. We also check numerically the equation of motion relation for H, (H) over tilde and find that relation holds fairly well in the spectator model. (C) 2015 The Authors. Published by Elsevier B.V.