A New Approach for Single Transverse-Spin Asymmetries from Twist-3   Soft-Gluon Mechanism
  A dominant QCD mechanism for the single transverse-spin asymmetry in hard processes is induced by the twist-3 quark-gluon correlations inside nucleon, combined with the soft-gluonic poles to produce the interfering phase for the associated partonic hard scattering. It is shown that the corresponding interfering amplitude can be calculated entirely in terms of the partonic Born cross section which participates in the twist-2 cross section formula for the spin-averaged process. 
Yuji Koike (Niigata University), Kazuhiro Tanaka (Juntendo University)