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arXiv · 2608.06157

Infrared singularities and the collinear limits of multi-leg scattering amplitudes

Sebastian Jaskiewicz
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Abstract

Scattering amplitudes admit a factorised structure in special kinematic limits, such as the soft and collinear limits. In this work, we investigate the multi-particle collinear limits of massless amplitudes at high perturbative orders, focusing on the exploration of the mechanisms via which strict collinear factorisation of $n$-particle scattering amplitudes is realised when $m$ particles become collinear. We show through four loops that the requirements on the structure of the massless soft anomalous dimension that are imposed by strict collinear factorisation in all two-particle collinear limits are enough to guarantee factorisation also in any multi-particle collinear limit. Demanding that strict collinear factorisation of massless partons is satisfied also for amplitudes that contain a massive coloured particle, we derive new constraints on the soft anomalous dimension by considering the collinear limit of three massless particles.

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Sebastian Jaskiewicz. 2026-08-06. Infrared singularities and the collinear limits of multi-leg scattering amplitudes. https://arxiv.org/abs/2608.06157

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