On the Subleading-Soft Behaviour of QCD Amplitudes
  We elaborate on the radiative behaviour of tree-level scattering amplitudes in the soft regime. We show that the sub-leading soft term in single-gluon emission of quark-gluon amplitudes in QCD is controlled by differential operators, whose universal form can be derived from both on-shell recursion relation and gauge invariance, as it was shown to hold for graviton- and gluon-scattering. 
Hui Luo, Pierpaolo Mastrolia and William J. Torres Bobadilla
hep-th hep-ph