QCD Processes at the Amplitude Level

TL;DR

This paper reviews the challenges of applying QCD at the amplitude level, focusing on the interface between perturbative and nonperturbative regimes, and discusses how exclusive processes inform hadron structure understanding.

Contribution

It provides an overview of leading-twist QCD predictions and highlights the difficulties in studying QCD at the amplitude level, especially for exclusive and diffractive processes.

Findings

Leading-twist QCD predictions align with some experimental data.

Challenges remain in modeling the transition between perturbative and nonperturbative regimes.

Exclusive processes offer insights into the light-cone wavefunctions of hadrons.

Abstract

Some of the most difficult theoretical challenges of QCD occur at the interface of the perturbative and nonperturbative regimes. Exclusive and semi-exclusive processes, the diffractive dissociation of hadrons into jets, and hard diffractive processes such as vector meson leptoproduction provide new testing grounds for QCD and essential information on the structure of light-cone wavefunctions of hadrons, particularly the pion distribution amplitude. I review the basic features of the leading-twist QCD predictions and the problems and challenges of studying QCD at the amplitude level.