Momentum sum rules for fragmentation functions

Abstract

Momentum sum rules for fragmentation functions are considered. In particular, we give a general proof of the Schäfer-Teryaev sum rule for the transverse momentum dependent Collins function. We also argue that corresponding sum rules for related fragmentation functions do not exist. Our model-independent analysis is supplemented by calculations in a simple field-theoretical model.

Comments: 12 pages; v2: Eqs. (44,46) added, minor additional changes, to appear in Phys. Lett. B