Electromagnetic properties of off-shell particles and gauge invariance

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

Keywords:

• Quantum electrodynamics
• Form factor (quantum field theory)
• Gauge theory
• Transverse plane
• Gauge (firearms)
• Compton scattering
• Invariant (mathematics)
• Physics
• Proton
• Conserved current

• Correction
• Source
• Cite
• Save
• Machine Reading By IdeaReader