Color-Kinematics Duality and the Regge Limit of Inelastic Amplitudes

TL;DR

The paper tests the BCJ color-kinematics duality in the Regge limit by analyzing tree-level five-point amplitudes in scalar QCD and constructing gravitational counterparts via the double-copy method. Using Sudakov variables and MRK, it shows that the part of the gravitational amplitude corresponding to the square of the gauge MRK vertex (ΩμΩν) is universally reproduced, while subleading NμNν contributions and Steinmann-related terms are not fully captured when external matter is present. The results validate a key aspect of the gauge–gravity correspondence in a nontrivial inelastic setup while clarifying the duality’s limitations with non-gluonic external states. The findings inform how far the double-copy construction can be trusted for inelastic processes and point to which diagram topologies control the leading MRK behavior.

Abstract

We investigate tree-level five-point amplitudes in scalar-QCD expressed in terms of Sudakov variables and find the equivalent "gravitational" counterparts using the color-kinematics duality proposed by Bern, Carrasco, and Johannson. Taking the multi-Regge limit in the gravitational amplitudes, we show that those pieces in the coupling of two reggeized gravitons to one on-shell graviton directly stemming from the double copy of the vertex for two reggeized gluons to one on-shell gluon are universal and properly reproduced by the duality.