We investigate the spectral properties of quark-quark-gluon correlators and
use this to study gluonic pole matrix elements. Such matrix elements appear in
principle both for distribution functions such as the Sivers function and
fragmentation functions such as the Collins function. We find that for a large
class of spectator models, the contribution of the gluonic pole matrix element
for fragmentation functions vanishes. This result is important in the study of
universality for fragmentation functions.Comment: 6pages, 2 figures: To appear in the Proceedings of DIFFRACTION 2008,
International Workshop on Diffraction in High-Energy Physics, La
Londe-les-Maures, France, 9-14 Sept 200
