Single Transverse Spin Asymmetry for Semi-Inclusive Deep Inelastic   Scattering
  Establishing the twist-3 formalsim for the single transverse spin asymmetry, we present a complete single-spin-dependent cross section for SIDIS, $ep^\uparrow\to e\pi X$, associated with the twist-3 distribution for the transversely polarized nucleon. We emphasize that the consistency condition from the Ward identities for color gauge invariance is crucial to prove factorization property of the cross section. 
Hisato Eguchi, Yuji Koike (Niigata University) and Kazuhiro Tanaka   (Juntendo University)