MHV Vertices And Tree Amplitudes In Gauge Theory
  As an alternative to the usual Feynman graphs, tree amplitudes in Yang-Mills theory can be constructed from tree graphs in which the vertices are tree level MHV scattering amplitudes, continued off shell in a particular fashion. The formalism leads to new and relatively simple formulas for many amplitudes, and can be heuristically derived from twistor space. 
Freddy Cachazo, Peter Svrcek, and Edward Witten