Leading-color fully differential two-loop soft corrections to QCD dipole showers

TL;DR

This paper presents a novel method for calculating next-to-leading order soft-gluon corrections in QCD dipole showers, enabling more accurate Monte Carlo simulations of particle collisions.

Contribution

It introduces a new subtraction scheme for differential two-loop soft corrections, compatible with Monte Carlo integration, and implements it in Pythia and Sherpa.

Findings

The method accurately reproduces the two-loop cusp anomalous dimension.

The new algorithm improves the precision of QCD dipole shower simulations.

Comparisons show consistency with the CMW scheme.

Abstract

We compute the next-to-leading order corrections to soft-gluon radiation differentially in the one-emission phase space. We show that their contribution to the evolution of color dipoles can be obtained in a modified subtraction scheme, such that both one- and two-emission terms are amenable to Monte-Carlo integration. The two-loop cusp anomalous dimension is recovered naturally upon integration over the full phase space. We present two independent implementations of the new algorithm in the two event generators Pythia and Sherpa, and we compare the resulting fully differential simulation to the CMW scheme.