Gauge invariance of relativistic two-particle bound-state energies (I) |
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Authors: | G Feldman T Fulton DL Heckathorn |
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Institution: | Department of Physics, The Johns Hopkins University, Baltimore, Maryland 21218, USA |
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Abstract: | The gauge invariance of relativistic two-particle energy levels in quantum electrodynamics is demonstrated for both covariant and non-covariant gauges, by considering infinitesimal gauge transformations from a fixed gauge. The proof is carried out by expressing the bound-state energies in terms of ratios of contour integrals involving four-point Green functions in the neighborhood of their poles in the energy plane. The generalized Ward-Takahashi identities are then used to help reduce the Green functions which appear into forms which make the singularity structure of the four-point function apparent. The formalism is illustrated for the special cases of one- and two-photon exchange in perturbation theory. |
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