Improving colour computations in MadGraph5_aMC@NLO and exploring a expansion

Andrew Lifson; Olivier Mattelaer

doi:10.1140/epjc/s10052-022-11078-2

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2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2022) 82: 1144
https://doi.org/10.1140/epjc/s10052-022-11078-2

Special Article - Tools for Experiment and Theory

Improving colour computations in MadGraph5_aMC@NLO and exploring a $1 / N_{c}$ expansion

Andrew Lifson¹^,2^a and Olivier Mattelaer²

¹ Department of Astronomy and Theoretical Physics, Lund University, Sölvegatan 14A, 223 62, Lund, Sweden
² Centre for Cosmology, Particle Physics and Phenomenology (CP3), Université catholique de Louvain, Chemin du Cyclotron 2, 1348, Louvain-la-Neuve, Belgium

^a andrew.lifson@thep.lu.se

Received: 19 October 2022
Accepted: 24 November 2022
Published online: 19 December 2022

Abstract

In this paper, we present an extension of MadGraph5_aMC@NLO which is able to evaluate tree-level QCD matrix-elements up to $2 \to 6$ $2\rightarrow 6$ (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 $1 / N_{c}$ $$1/N_c$$ 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.

© The Author(s) 2022

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