QCD sum rules and models for generalized parton distributions

Abstract

Dedicated to Klaus Goeke on occasion of his 60th birthdayI use QCD sum rule ideas to construct models for generalized parton distributions. To this end, the perturbative parts of QCD sum rules for the pion and nucleon electromagnetic form factors are interpreted in terms of GPDs and two models are discussed. One of them takes the double Borel transform at adjusted value of the Borel parameter as a model for nonforward parton densities, and another is based on the local duality relation. Possible ways of improving these Ansätze are briefly discussed.

Nucleon form factors from generalized parton distributions

“…In our parametrization R2, the good description found for the ratio F p 2 =F p 1 can be directly assigned to the extra suppressing factor of 1 ÿ x contained in the GPD Ex; t. The question, how this suppression is related to the quark orbital angular momentum, deserves further investigation. It is interesting to note that the extra 1 ÿ x factor for E u x function compared to H u x appears in the starting term of the QCD sum rule calculation of these functions [39]. Also, the dominant x !…”

Nucleon form factors of the energy-momentum tensor in the chiral quark-soliton model

“…The Pauli-Villars regularization is applicable only for mπ = 0 [73]. One popular assumption in literature in the context of modelling GPDs is to assume a generic factorized Ansatz of the type H(x, ξ, t) = H(x, ξ)G(t) where G(t) denotes the respective form factor (other approaches are discussed in [16,76,77,78,79,80]). This assumption implies that the form factors of the EMT should have approximately the same t-dependence as the electromagnetic form factors.…”

Holographic wave functions, meromorphization and counting rules

“…The spectral densities ρ(s 1 , s 2 , Q 2 ) can be calculated [21,25] using the Cutkosky rules and light-cone variables in the frame where the initial momentum p 1 has no transverse components p 1 = {p…”

“…The spectral densities ρ(s 1 , s 2 , Q 2 ) can be calculated [21,25] using the Cutkosky rules and light-cone variables in the frame where the initial momentum p 1 has no transverse components p 1 = {p + 1 = P, p − 1 = s 1 /P, 0 ⊥ }, while the momentum transfer q ≡ p 2 − p 1 has no "plus" component, p 2 = {P, (s 2 + q 2 ⊥ )/P, q ⊥ }:…”