Numerical NLO QCD calculations

TL;DR

This paper introduces a novel numerical algorithm for calculating one-loop QCD amplitudes that efficiently handles divergences and deformation of integration contours without relying on Feynman diagrams.

Contribution

It presents a Feynman graph-independent method using subtraction terms and contour deformation for numerical one-loop QCD calculations.

Findings

Applicable to massless and massive partons

Efficient calculation via recurrence relations

Handles divergences through subtraction terms

Abstract

We present an algorithm for the numerical calculation of one-loop QCD amplitudes. The algorithm consists of subtraction terms, approximating the soft, collinear and ultraviolet divergences of one-loop amplitudes and a method to deform the integration contour for the loop integration into the complex space. The algorithm is formulated at the amplitude level and does not rely on Feynman graphs. Therefore all required ingredients can be calculated efficiently using recurrence relations. The algorithm applies to massless partons as well as to massive partons.