Hard exclusive reactions and hadron structure

According to a now well established framework [1], the Bjorken limit of exclusive reactions with a hard probe allows factorization of the amplitudes into a perturbatively calculable subprocess at quark and gluon level on the one hand and hadronic matrix elements of light cone non local operators expressed through hadron (eventually generalized [2]) distribution amplitudes and generalized parton distribution (GPD) (resp. a transition distribution amplitude [3]) describing the transition from the baryon target to a baryon (resp. another hadron or photon) on the other hand. As demonstrated in the presentations at this workshop, experimental data from DESY and JLab are now confirming this framework, and they seem to show that its applicability is quite precocious in terms of Q. Important in that respect is the analysis of spin asymmetries which are particularly sensitive to the interference between the dVCS and Bethe-Heitler processes [4].