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)
Technicolor (physics) "M", and the coupling of quarks and leptons to the new particles must be suppressed relative to their coupling to the gauge bosons. This is the case with technicolor, so long as the lightest technivector mesons, "ρ" and "a", are heavier than 200–300 GeV. The "S"-parameter is sensitive to all new physics at the TeV scale, while "T" is a measure of weak-isospin breaking effects. The "U"-parameter is generally not useful; most new-physics theories, including technicolor theories, give negligible contributions to it. The "S" and "T"-parameters are determined by global fit to experimental data including "Z"-pole data from LEP at