Colour connection structure of (supersymmetric) QCD ($2\to2$) processes

TL;DR

The paper addresses how colour connections govern soft-gluon radiation in QCD and supersymmetric QCD 2→2 processes, focusing on resolving ambiguities in colour decomposition for multi-flow amplitudes. It critiques the Marchesini–Webber procedure and introduces a proportional distribution method that yields positive-definite full terms while preserving the correct pole structure. The authors apply the approach to 2→2 sparton processes, providing explicit matrix elements and colour decompositions for SUSY QCD suitable for implementation in the HERWIG Monte Carlo generator. They conclude that the new method should have limited impact on soft radiation predictions but emphasize the need for further study of SUSY showering and hadronisation.

Abstract

The colour connection structure of QCD ($2\to2$) processes is discussed, with emphasis on its application to the supersymmetric 2 parton $\to$ 2 sparton processes, which are currently being implemented in the HERWIG Monte Carlo event generator. The procedure described by Marchesini and Webber is found to be inadequate, and a new method is proposed. However, this alteration is unlikely to significantly affect the theoretical predictions for soft gluon radiation. A complete list of supersymmetric QCD $2\to2$ matrix elements and their colour decompositions is presented.