On-shell Higgsing for EFTs

A bstract We study the on-shell version of Higgs mechanism in effective theories (EFTs) containing particles different spins, focusing on contact terms as a simple starting point. derive massive and their coefficients from massless amplitudes EFT above symmetry breaking scale, by covariantizing under little group. In little-group-covariant massive-spinor formalism, this notationally amounts to bolding spinor labels. Mass-suppressed contributions contact-term arise higher-point with additional soft legs. apply procedure obtain four-point featuring scalars, spin 1/2 fermions vectors, standard-model EFT. The subleading helicity-flipped components each term, which are dictated little-group covariance, associated residues factorizable amplitudes. Extra “frozen” Higgses emitted leg term supply light-like momentum component, needed form same polarization. As another application, we various three-point up three Higgses, standard-model-like toy model.