All-Order Collinear Behavior in Gauge Theories
D. A. Kosower
TL;DR
The paper addresses collinear factorization in gauge-theory amplitudes, proving all-order factorization for the leading-color contribution using a unitarity-based method and providing an explicit formula for the associated splitting amplitudes. It connects the squared tree-level splitting amplitudes, summed over helicities, to Altarelli–Parisi kernels, reinforcing the universality of infrared behavior in gauge theories. The results yield a practical framework for computing collinear limits in high-energy processes and inform precision QCD predictions. This work thus advances both the theoretical understanding and computational tools for gauge-theory amplitudes in collinear regimes.
Abstract
I give a proof, using the unitarity-based method, of the collinear factorization of the leading-color contribution to gauge-theory amplitudes. The proof also provides a concrete formula which can be used to compute the associated splitting amplitudes.