On the gauge invariance of the DVCS amplitude
  We analyze in detail the problem of gauge invariance of the deeply vitual Compton scattering (DVCS) amplitude. Using twist 3 one-gluon exchange diagram contributions and the QCD equations of motion, we derive the general gauge invariant expression of the DVCS amplitude on a (pseudo)scalar particle (pion, $He^4$). Similarly to the case of deep inelastic scattering, the amplitude does not depend on the twist-3 quark-gluon correlations at the Born level. The contribution of the derived amplitude to the single-spin asymmetry with longitudinally polarized lepton is calculated. 
I.V. Anikin (JINR, Dubna), B. Pire (CPhT, Ecole Polytechnique,   Palaiseau), O.V. Teryaev(CPhT, Ecole Polytechnique, Palaise...