Diagrammatic structures of the Nielsen identity

Abstract

The Γ-function, or the effective potential of a gauge field theory should comply with the Nielsen identity, which implies how the effective potential evolves as we shift the gauge-fixing term. In this paper, relying on an abelian toy model, we aim at proving this identity in a diagrammatic form with the R‾ξ gauge. The basic idea is to find out the ghost chain after partially differentiating the diagram by the ξ parameter, and shrink the waists of the diagram into points to separate the bulk-part and C-part of the diagrams. The calculations can be generalized to the models implemented with non-abelian groups, multiple Higgs and fermion multiplets, and to the finite temperature cases.