Abstract
A class of approximate photon-particle-particle vertex functions including higher-order corrections for particles with spin \ensuremath{\le}1 is shown to saturate the relevant Ward-Takahashi identities and to possess the Poincar\'e substructure of the point vertex in certain gauges that is reflective of gauge-covariant photon attachments. This leads to an approximate, higher-spin generalization of the exact scalar-bubble theorem for the persistence of radiation amplitude zeros in the presence of self-energy graphs. This also leads to further insight into the structural features of a spectral-weight ansatz frequently employed in implementing the gauge technique for solving the Schwinger-Dyson equations. The Poincar\'e substructure of the vertex for the axial-vector coupling of a photon to a spin-1/2 particle is determined and some possible applications of this result are discussed.
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