1998/03/02 by S. I. Nagorny, Nagorny, S. I., A. E. L. Dieperink +1
Physics and Astronomy · #FOS: Physical sciences #Nuclear Theory (nucl-th) #nucl-th
paper · pdf · doi:10.48550/arxiv.nucl-th/9803007
27 pages, 1 figure
arxiv created 1998/03/02 · arxiv updated 2009/12/01
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 F1+(q2) in a gauge invariant way for the unphysical time-like region, 4me2<q2, 4MN2.