One-loop corrections and all order factorization in deeply virtual Compton scattering

Abstract

We calculate the one-loop corrections to a general off-forward deeply virtual Compton process at leading twist for both parton helicity-dependent and independent cases. We show that the infrared divergences can be factorized entirely into off-forward parton distributions, even when one of the two photons is on shell. We argue that this property persists to all orders in perturbation theory. We obtain the next-to-leading order Wilson coefficients for the general leading-twist expansion of the product of two electromagnetic currents in the MS scheme. ͓S0556-2821͑98͒04521-4͔

Linking generalized parton distributions to constituent quark models

“…energy s = (P + q) 2 and the photon virtuality Q 2 are large while the invariant momentum square t = ∆ 2 = 2P · ∆ is small [1,4,5]. Under these conditions the factorization theorem [5,7,8] tells us that the amplitude factorizes in a hard scattering part (which is exactly calculable in perturbative QCD) and a soft, nonperturbative nucleon structure part. The contribution of the hard scattering part to leading order corresponds to the so called handbag diagram with photon scattering on a single parton (quark or antiquark).…”

“…As such they contain information on parton correlations and the internal spin structure of the nucleon. But the main interest to study GPD's comes from the fact that, due to the factorization theorem [5,7,8], they are candidate to provide us with a unifying theoretical background suitable to describe a variety of inclusive and exclusive processes in the deep inelastic scattering (DIS) regime. In particular, they enter the cross section for exclusive photon production, i.e.…”

Nucleon electromagnetic form factors

“…The all-order factorization theorem for the DVCS process on the nucleon has been proven in [Ji98a,Col99,Rad98]. Qualitatively one can say that the hard reactions allow one to perform a "microsurgery" of a nucleon by removing in a controlled way a quark of one flavor and spin and implanting instead another quark in the final nucleon.…”

Resumming soft and collinear contributions in deeply virtual Compton scattering

“…From the theory side, the interest for hard exclusive processes started with the Leipzig group [10]. Several studies 1 then set the basis of a consistent framework, called collinear factorization, to separate the short distance dominated partonic subprocesses and long distance hadronic matrix elements, at leading and next-to-leading order for DVCS [15][16][17][18][19][20] and…”