MHV Lagrangians for Yang--Mills and QCD

Understand

Over the past few decades, it has been realised that gauge theory scattering amplitudes have structures much simpler than the traditional Feynman graph driven approach would suggest.

• In particular, Parke and Taylor found a particularly simple expression for the tree-level amplitudes with two gluons of different helicity than the others (the so-called MHV amplitudes).
• Cachazo, Svrcek and Witten (CSW) devised rules for constructing tree-level amplitudes by sewing lower-valence MHV amplitudes together with scalar propagators.
• It was shown by Mansfield in 2005 that a canonical change of the field variables could be constructed that resulted in a lagrangian whose vertices were proportional to MHV amplitudes, continued off-shell by CSW's prescription, the so-called Canonical MHV Lagrangian.