EW and QCD One-Loop Amplitudes with RECOLA

TL;DR

RECOLA provides an automated framework to compute SM amplitudes at NLO, addressing the need for general EW and QCD computations with many external legs. It extends Dyson–Schwinger recursion to one-loop amplitudes by representing them as linear combinations of tensor integrals with loop-specific currents and a novel color-flow recursion. The code integrates COLLIER for tensor integrals and supports full SM with counterterms, R2 terms, complex-mass scheme, and dipole subtraction preparation; its two-phase workflow makes it efficient in both generation and phase-space evaluation. The approach enables scalable, reusable computation of structure-dressed amplitudes, reducing memory usage and demonstrating practical performance on representative multi-leg processes.

Abstract

We present the computer code RECOLA for the computation of EW and QCD amplitudes in the Standard Model at next-to-leading order. One-loop amplitudes are represented as linear combinations of tensor integrals whose coefficients are calculated by means of recursive relations similar to Dyson-Schwinger equations. A novel treatment of colour enables us to recursively construct the colour structure of the amplitude efficiently. RECOLA is linked with the library COLLIER for the computation of the tensor integrals.