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Local gauge invariance implies Siegert's hypothesis

H. W. L. Naus
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Abstract

The nonrelativistic Ward-Takahashi identity, a consequence of local gauge invariance in quantum mechanics, shows the necessity of exchange current contributions in case of nonlocal and/or isospin-dependent potentials. It also implies Siegert's hypothesis: in the nonrelativistic limit, two-body charge densities identically vanish. Neither current conservation, which follows from global gauge invariance, nor the constraints of (lowest order) relativity are sufficient to arrive at this result. Furthermore, a low-energy theorem for exchange contributions is established.

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H. W. L. Naus. 1996-08-29. Local gauge invariance implies Siegert's hypothesis. https://doi.org/10.1103/physrevc.55.1580

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