Diffractive vector mesons beyond the s-channel helicity conservation
  We derive a full set, and determine the twist, of helicity amplitudes for diffractive production of light to heavy vector mesons in deep inelastic scattering. For large $Q^{2}$ all helicity amplitudes but the double-flip are calculable in perturbative QCD and are proportional to the gluon structure function of the proton at a similar hard scale. We find a substantial breaking of the $s$-channel helicity conservation which must persist also in real photoproduction. 
E.V. Kuraev (LTP, JINR, Dubna), N.N. Nikolaev (IKP, FZ Juelich and   L.D.Landau Institute, Moscow) and B.G. Zakharov (L.D.La...