QCD factorization of exclusive processes beyond leading twist: gamma*T -> rhoT impact factor with twist three accuracy

TL;DR

This paper develops a consistent factorization approach for exclusive scattering amplitudes beyond leading twist, incorporating higher Fock states and twist-3 accuracy, and demonstrates its equivalence with covariant methods through explicit impact factor calculations.

Contribution

It introduces a novel method for factorization beyond leading twist using Taylor expansion and light-cone invariance, and proves its equivalence with covariant operator product expansion techniques.

Findings

Derived impact factor for gamma* -> rhoT transition at twist 3

Established equivalence between light-cone and covariant parametrizations

Validated the method through explicit impact factor calculations

Abstract

We describe a consistent approach to factorization of scattering amplitudes for exclusive processes beyond the leading twist approximation. The method involves the Taylor expansion of the scattering amplitude in the momentum space around the dominant light-cone direction and thus naturally introduces an appropriate set of non-perturbative correlators which encode effects not only of the lowest but also of the higher Fock states of the produced particle. The reduction of original set of correlators to a set of independent ones is achieved with the help of equations of motion and invariance of the scattering amplitude under rotation on the light-cone. We compare the proposed method with the covariant method formulated in the coordinate space, based on the operator product expansion. We prove the equivalence of two proposed parametrizations of the rhoT distribution amplitudes. As a concrete application, we compute the expressions of the impact factor for the transition of virtual photon to transversally polarised rho-meson up to the twist 3 accuracy within these two quite differents methods and show that they are identical.