Sum rules for the T-odd fragmentation functions - art. no. 077903

The conservation of the intrinsic transverse momentum during parton fragmen tation imposes nontrivial constraints on T-odd fragmentation functions. The se significantly enhance the differences between the favored and unfavored fragmentation functions, which could be relevant to understand the azimutha l asymmetries of charged pion production observed recently by the HERMES Co llaboration.