QCD collinear factorization, its extensions and the partonic distributions

TL;DR

This paper reviews the collinear factorization theorem in QCD, its extensions to exclusive processes involving GPDs, GDAs, and TDAs, and discusses the potential to explore partonic interactions and distributions inside hadrons.

Contribution

It provides a comprehensive overview of the extensions of collinear factorization to non-forward distributions and discusses implications for understanding partonic structures.

Findings

Factorization theorem applies to deep inelastic scattering and exclusive processes.

Extensions include GPDs, GDAs, and TDAs for probing non-forward distributions.

High-precision data combined with perturbative calculations can reveal detailed partonic structures.

Abstract

I review the basics of the collinear factorization theorem applied primarily to deep inelastic scattering (DIS) involving forward parton distributions (PDFs) and the extensions of this theorem for exclusive processes probing non-forward parton distributions (GPDs), the generalized distribution amplitudes (GDAs) and the transition distribution amplitudes (TDAs). These QCD factorization theorem is an important tool in the description of hard processes in QCD. Whenever valid, it permits to represent the cross section or the scattering amplitude for such a process as a convolution in partonic momenta of a perturbatively calculable part (the coefficient function, CF) which involves the hard scale of the process with non-perturbative (soft) distributions of active partons inside the hadrons involved in a process. The reliability of the perturbatively determined hard part together with high precision experimental data on relevant observables gives a hope for the possibility to uncover fine details of interpartonic interactions and spatial distributions of partons inside hadrons. I conclude with some remarks about QCD factorization with transverse momentum dependent PDFs