On the Evolution of Sum Rules for T-Odd Distribution and Fragmentation   Functions
  We test stability against probabilistic evolution of sum rules for transverse-momentum-dependent distribution and fragmentation functions. We find that preservation of the Burkardt sum rule for Sivers distribution functions is similar to the conservation of longitudinal momentum related to spin-averaged parton distributions. At the same time, preservation of the Schaefer-Teryaev sum rule for Collins functions is similar to preservation of the Burkhardt-Cottingham sum rule for the spin-dependent g_2 structure function. 
Philip G. Ratcliffe and Oleg V. Teryaev
hep-ph