Improving Colour Computations in MadGraph5_aMC@NLO and Exploring a 1/Nc Expansion

TL;DR

This paper enhances MadGraph5_aMC@NLO to evaluate more complex QCD processes with improved speed by implementing recursive calculations and a novel colour expansion method, enabling efficient high-multiplicity computations.

Contribution

It introduces a recursive approach and a 1/Nc colour expansion in MadGraph5_aMC@NLO, allowing for faster and more flexible high-multiplicity QCD matrix-element evaluations.

Findings

Speed gains in high multiplicity samples without colour truncation

Extension to evaluate up to 2→6 particle processes

Implementation of Berends-Giele-like recursion

Abstract

In this paper, we present an extension of MadGraph5_aMC@NLO which is able to evaluate tree-level QCD matrix-elements up to $2\to 6$ (one more particle than before). To achieve this, we implemented Berends-Giele-like recursion, and re-implemented the way colour is computed such that we can now expand the colour matrix in powers of 1/Nc and truncate this expansion to a chosen order. For high multiplicity samples, even without truncating the colour matrix, the new implementation offers a speed gain compared to the previous MadGraph5_aMC@NLO code.