Exclusive photoproduction of hard dijets and magnetic susceptibility of   QCD vacuum
  We argue that coherent production of hard dijets by linearly polarized real photons can provide direct evidence for chirality violation in hard processes, the first measurement of the magnetic susceptibility of the quark condensate and the photon distribution amplitude. It can also serve as a sensitive probe of the generalized gluon parton distribution. Numerical calculations are presented for HERA kinematics. 
V.M. Braun, S. Gottwald, D.Yu. Ivanov, A. Sch\"afer, L. Szymanowski