Investigating the universality of five-point QCD scattering amplitudes at high energy

TL;DR

This paper explores the universal behavior of five-point QCD scattering amplitudes at high energy, demonstrating their factorization properties and predicting them at NNLL order within the Balitsky/JIMWLK framework.

Contribution

It provides the first NNLL predictions for these amplitudes and identifies a universal vertex for central-rapidity gluon emission in QCD and N=4 SYM.

Findings

Amplitudes exhibit universal factorization properties.

Predictions match full QCD scattering amplitudes.

Universal vertex for gluon emission is extracted.

Abstract

We investigate $2 \to 3$ QCD scattering amplitudes in multi-Regge kinematics, i.e. where the final partons are strongly ordered in rapidity. In this regime amplitudes exhibit intriguing factorisation properties which can be understood in terms of effective degrees of freedom called \emph{reggeons}. Working within the Balitsky/JIMWLK framework, we predict these amplitudes for the first time to next-to-next-to-leading logarithmic order, and compare against the limit of QCD scattering amplitudes in full colour and kinematics. We find that the latter can be described in terms of universal objects, and that the apparent non-universality arising at NNLL comes from well-defined and under-control contributions that we can predict. Thanks to this observation, we extract for the first time the universal vertex that controls the emission of the central-rapidity gluon, both in QCD and $N = 4$ super Yang-Mills.