Abstract
Using local gauge invariance in the form of the Ward-Takahashi identity and the fact that properly constructed current operators must be free of kinematic singularities, it is shown that the magnetic moment and the quadrupole moment of an elementary spin-1 particle with mass and charge are related by , thus constraining the normalizations of the Sachs form factors. This relation holds true as a matter of course at the tree level in the standard model, but we prove that it remains true in general for dressed spin-1 states derived from elementary fields. General expressions for spin-1 propagators and currents with arbitrary hadronic dressing are given, which show that the result is independent of any dressing effect or model approach.
- Received 16 May 2019
DOI:https://doi.org/10.1103/PhysRevD.100.036008
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