Hadron structure and gauge invariance in photo- and electroproduction of pions

Bos, J.W.; Scherer, Stefan; Koch, J.H.

doi:10.1016/0375-9474(92)90035-i

Cited by 22 publications

(28 citation statements)

References 24 publications

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“…The WTI requires q"l'"(p', p) = eQ q"PI"A(p', p; q ) = eQ-[D. '(p') -D. '(J' )] well established and several phenomenological models exist that take it into account [16,17]. For electromagnetic form factors Naus and Koch [13], Tiemeijer and Tjon [14] or Bos et aL [25] performed detailed calculations based on a meson-baryon interaction picture, all giving essentially the same results for the shape and the off-shell dependence of the form factors, but diR'ering somewhat in their predictions for the anomalous magnetic moments.…”

Section: B Form Factor Of Pionsmentioning

confidence: 99%

Microscopic model of the timelike electromagnetic form factor of the nucleon

1995

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A microscopic model of the electromagnetic form factor of the nucleon is developed in a hadronic framework, including pions, nucleons, and the E resonance explicitly. The spacelike on-shell form factors are reproduced and predictions for the half off-shell dependence are made. The impact of this off-shell dependence in the timelike sector (q ( 1 GeV, thus including the region of vector meson dominance) is of main interest in this investigation.PACS number(s): 13.40. Gp, 14.20.Dh

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Section: B Form Factor Of Pionsmentioning

confidence: 99%

Microscopic model of the timelike electromagnetic form factor of the nucleon

1995

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“…The importance of a consistent treatment of off-shell functions, in particular in the context of gauge invariance, has been realized and emphasized by many authors [6,[13][14][15][16][17]. In this context the most important constraint is provided by the Ward-Takahashi identity [18,19].…”

Section: Introductionmentioning

confidence: 99%

Compton scattering by a pion and off-shell effects

Scherer

Fearing²

1995

Phys. Rev. C

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We consider Compton scattering by a pion in the framework of chiral perturbation theory. We investigate off-shell effects in the s-and u-channel pole diagrams. For that purpose we perform a field transformation which, in comparison with the standard Gasser and Leutwyler Lagrangian, generates additional terms at order p 4 proportional to the lowest-order equation of motion. As a result of the equivalence theorem the two Lagrangians predict the same Compton scattering S-matrix even though they generate different off-shell form factors. We conclude that off-shell effects are not only modeldependent but also representation-dependent.

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“…For a similar discussion of the second point within the framework of a quantum field theoretical model see ref. [26].…”

Section: Resultsmentioning

confidence: 99%

Low-energy Compton scattering by a proton: Comparison of effective hamiltonians with relativistic corrections

1994

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We discuss two different methods of obtaining "effective 2 × 2 Hamiltonians" of the electromagnetic interaction which include relativistic corrections. One is the standard Foldy-Wouthuysen transformation which we compare with the Hamiltonian obtained from a direct reduction of the matrix element of the interaction Hamiltonian between positive-energy solutions of the free Dirac equation. The two approaches are applied to Compton scattering by a proton for which a low-energy theorem exists. It is found that the Foldy-Wouthuysen Hamiltonian yields the same result as a covariant calculation. This is not true for the direct reduction method which will in general lead to incorrect results even after restoring the gauge invariance property of the Hamiltonian. Furthermore, it is shown that an identification of the Z-diagrams of the usual Dirac representation with the contact graphs of the Foldy-Wouthuysen representation is incorrect beyond the order of the low-energy theorem.

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Hadron structure and gauge invariance in photo- and electroproduction of pions

Cited by 22 publications

References 24 publications

Microscopic model of the timelike electromagnetic form factor of the nucleon

Microscopic model of the timelike electromagnetic form factor of the nucleon

Compton scattering by a pion and off-shell effects

Low-energy Compton scattering by a proton: Comparison of effective hamiltonians with relativistic corrections

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