Unitarity cut
= Unitarity cut
A contribution to the <unitarity> relation for the <S-matrix> obtained by placing a set of intermediate lines <on shell> and summing their intermediate states. In a physical-state formulation only physical states enter the sum. When covariant <gauge boson> index sums include auxiliary polarizations, matching <Faddeev-Popov ghost field> contributions are needed to reproduce the physical result in a <Non-Abelian gauge theory>.