Soft sub-leading divergences in Yang-Mills amplitudes

TL;DR

The paper identifies a sub-leading 1/ε divergence in the soft limit of colour-ordered Yang-Mills tree amplitudes, analogous to recent gravity results. Using a BCFW-based analysis, it derives a universal sub-leading term S^{(1)} that acts as an angular-momentum generator on the n-point amplitude, with S^{(1)} explicitly given in spinor form. Unlike gravity, YM lacks a sub-sub-leading term at tree level, but the sub-leading piece remains gauge-invariant and potentially connected to asymptotic symmetries of Yang-Mills on flat spacetime. The results hint at deeper universal structures at tree level and invite exploration of loop corrections and boundary symmetry interpretations.

Abstract

In this short note I show that the soft limit for colour-ordered tree-level Yang-Mills amplitudes contains a sub-leading divergent term analogous to terms found recently by Cachazo and Strominger for tree-level gravity amplitudes.