Electromagnetic properties of off-shell particles and gauge invariance
Abstract
Electromagnetic properties of off-shell particles are discussed on the basis of a purely electromagnetic reaction: virtual Compton scattering off a proton. It is shown that the definition of off-shell electromagnetic form factors is not gauge invariant and that these cannot be investigated in practice. Using only fundamental requirements of gauge invariance it is demonstrated that off-shell effects are cancelled in the longitudinal components of the total conserved current by the minimal contact current, while the off-shellness appears only in the the transverse (gauge invariant) non-pole part. This provides the possibility to introduce an on-shell extrapolated form factor F_1^+(q^2) in a gauge invariant way for the unphysical time-like region, 4m_e^2<q^2, 4M_N^2.
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Cite
@article{arxiv.nucl-th/9803007,
title = {Electromagnetic properties of off-shell particles and gauge invariance},
author = {S. I. Nagorny and A. E. L. Dieperink},
journal= {arXiv preprint arXiv:nucl-th/9803007},
year = {2007}
}
Comments
27 pages, 1 figure