MHV amplitudes MHV amplitudes In theoretical particle physics, maximally helicity violating amplitudes are amplitudes with n external gauge bosons, where n–2 gauge bosons have a particular helicity and the other two have the opposite helicity. These amplitudes are called MHV amplitudes, because at tree level, they violate helicity conservation to the maximum extent possible. The tree amplitudes in which all gauge bosons have the same helicity or all but one have the same helicity vanish. MHV amplitudes may be calculated very efficiently by means of the Parke–Taylor formula. Although developed for pure gluon scattering, extensions exist for massive particles, scalars (the Higgs)
Gauge fixing well to non-abelian gauge groups such as the SU(3) of QCD. The couplings between physical and unphysical perturbation axes do not entirely disappear under the corresponding change of variables; to obtain correct results, one must account for the non-trivial Jacobian of the embedding of gauge freedom axes within the space of detailed configurations. This leads to the explicit appearance of forward and backward polarized gauge bosons in Feynman diagrams, along with Faddeev–Popov ghosts, which are even more "unphysical" in that they violate the spin-statistics theorem. The relationship between these entities, and the reasons why they do not appear as particles