Double spin asymmetry A_{LT} in direct photon production
  We study the longitudinal-transverse double spin asymmetry $A_{LT}$ for direct photon production in nucleon-nucleon scattering by using the collinear twist-3 approach. This asymmetry, which, for instance, could be measured at RHIC, contains a complete set of collinear twist-3 correlation functions in a transversely polarized nucleon. 
Zuo-Tang Liang, Andreas Metz, Daniel Pitonyak, Andreas Sch\"afer,   Yu-Kun Song, Jian Zhou
hep-ph