Soft gluon-quark-antiquark emission in QCD hard scattering

TL;DR

This paper analyzes the emission of soft gluons and quark-antiquark pairs in QCD scattering, deriving a universal soft current and exploring its implications for charge asymmetry and mixed QCD-QED corrections.

Contribution

It provides the first tree-level evaluation of the soft gqar{q} current for arbitrary multiparton processes, including non-abelian and abelian terms, and discusses charge asymmetry effects.

Findings

Derived the soft gqar{q} current at tree level for general processes.

Identified charge asymmetry contributions from colour tripole interactions.

Extended results to QED and mixed QCD-QED radiative corrections.

Abstract

We consider the radiation of a soft gluon ($g$) and a soft quark-antiquark ($q{\bar q}$) pair in QCD hard scattering. In the soft limit the scattering amplitude has a singular behaviour that is factorized and controlled by a soft current, which has a process-independent structure in colour space. We evaluate the soft $gq{\bar q}$ current at the tree level for an arbitrary multiparton scattering process. The irreducible correlation component of the current includes strictly non-abelian terms and also terms with an abelian character. Analogous abelian correlations appear for soft photon-lepton-antilepton emission in QED. The squared current for soft $gq{\bar q}$ emission produces colour dipole and colour tripole interactions between the hard-scattering partons. The colour tripole interactions are odd under charge conjugation and lead to charge asymmetry effects. We consider the specific applications to processes with two and three hard partons, and we discuss the structure of the corresponding charge asymmetry contributions. We also generalize our QCD results to the cases of QED and mixed QCD$\times$QED radiative corrections.