Jet-like QED processes : on general properties of impact factors
  In this article, general properties of impact factors involved in jet-like QED processes are explored. In particular, a general link is established between their helicity properties and their order of magnitude as defined by jet-like kinematics. Exact results are given for some processes in the strict forward direction and a general method is proposed to track orders in the calculation of multi-bremsstrahlung processes. 
Christian Carimalo
hep-ph