2019 Impact factor 2.176
Hadrons and Nuclei
Eur. Phys. J. A 5, 417-428

Gauge constraints and electromagnetic properties of off-shell particles

S.I. Nagorny1,2 - A.E.L. Dieperink3

1 Nationaal Instituut voor Kernfysica en Hoge-Energiefysica, P.O. Box 41882, 1009, DB Amsterdam, The Netherlands
2 Free University of Amsterdam, Deptartment of Physics and Astronomy, de Boelelaan 1081, 1081, HV Amsterdam, The Netherlands
3 Kernfysisch Versneller Instituut, 9747, AA Groningen, The Netherlands

Received: 23 March 1999 Communicated by V.V. Anisovich

Abstract
The consequences of the gauge constraints for off-shellness in the electromagnetic (EM) vertices have been considered, using Compton scattering as an example. We have found that even if the gauge constraint for the 3-point EM Green function allows for off-shell effects in the charge (Dirac) form factor, they vanish in the total Compton scattering amplitude due to the gauge constraint for the 4-point EM Green function only. In addition, the representations of the Compton amplitude in terms of either reducible or irreducible vertices are equivalent for conserved currents.

PACS
13.40.Gp Electromagnetic form factors - 13.60.Fz Elastic and Compton Scattering - 14.70.Bh Photons


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