Disentangling the Regge cut and Regge pole in perturbative QCD

TL;DR

This paper develops a method to distinguish between Regge poles and Regge cuts in high-energy gauge-theory amplitudes, enabling the calculation of the Regge trajectory beyond two loops and linking it to infrared singularities.

Contribution

It introduces a technique to disentangle Regge cuts and poles in perturbative QCD, allowing for higher-loop calculations of the Regge trajectory and impact factors.

Findings

Regge cut is associated with nonplanar exchanges

Regge pole arises from planar exchanges

Regge trajectory linked to cusp anomalous dimension

Abstract

The high-energy limit of gauge-theory amplitudes features both a Regge pole and Regge cuts. We show how to disentangle these, and hence how to determine the Regge trajectory beyond two loops. While the nonplanar part of multiple Reggeon $t$-channel exchange forms a Regge cut, the planar part contributes to the pole along with the single Reggeon. With this, we find that the infrared singularities of the trajectory are given by the cusp anomalous dimension. By matching to recent QCD results, we determine the quark and gluon impact factors to two loops and the Regge trajectory to three loops.