Gauge invariant unitary theory for pion photoproduction

Antwerpen, C. H. M. van; Afnan, I. R.

doi:10.1103/physrevc.52.554

Cited by 25 publications

(43 citation statements)

References 48 publications

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“…We find that the data we have considered in this work can be described by the conserved currents J µ defined by Eqs. (16) and (17). We have briefly investigated the model dependence due to the freedom in choosing n. We have found that the choice n = (1, 0, 0, 0), which leads to J = J(SL) and J 0 = | q| ω J z (SL) gives very similar results at high Q 2 .…”

Section: The Sl Modelmentioning

confidence: 48%

“…We have not explored those possibilities, since they are also not related microscopically to the substructure of the hadrons involved, and are as phenomenological as the prescription defined by Eqs. (16)- (17). We will return to this problem when our model is further developed, as discussed in section V.…”

Section: The Sl Modelmentioning

confidence: 99%

“…All results presented in this paper are from using the choice Eqs. (16)- (17). We emphasize that this choice is a phenomenological part of our model, simply because we have not implemented any substructure dynamics of hadrons into our formulation.…”

Section: The Sl Modelmentioning

confidence: 99%

“…The SL model is one of the dynamical models developed [7,[13][14][15][16][17][18][19][20][21] in recent years. Compared with other approaches based on the tree-diagrams of effective Lagrangians [22][23][24] or dispersion-relations [25][26][27], the main objective of a dynamical approach is to separate the reaction mechanisms from the excitation of the internal structure of the hadrons involved.…”

Section: Introductionmentioning

confidence: 99%

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Dynamical study of theΔexcitation inN(e,e′π)reactions

2001

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The dynamical model developed in [Phys. Rev. C 54, 2660] has been applied to investigate the pion electroproduction reactions on the nucleon. It is found that the model can describe to a very large extent the recent data of p(e, e ′ π 0 ) reaction from Jefferson Laboratory and MIT-Bates. The extracted magnetic dipole(M1), electric dipole(E2), and Coulomb(C2) strengths of the γN → ∆ transition are presented. It is found that the C2/M1 ratio drops significantly with Q 2 and reaches about -13% at Q 2 =4 (GeV/c) 2 , while the E2/M1 ratio remains close to the value ∼ −3% at the Q 2 = 0 photon point.The determined M1 transition form factor drops faster than the usual dipole form factor of the proton. We also find that the non-resonant interactions can dress the γN → ∆ vertex to enhance strongly its strength at low Q 2 , but much less at high Q 2 . Predictions are presented for future experimental tests.Possible developments of the model are discussed. PACS number(s): 13.75. Gx,21.45.+v,25.20.Lj

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Section: The Sl Modelmentioning

confidence: 48%

Section: The Sl Modelmentioning

confidence: 99%

Section: The Sl Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dynamical study of theΔexcitation inN(e,e′π)reactions

2001

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“…On the two-particle level the problem was first solved by Gross and Riska [13] who showed that the one-body current combined with the gauged interaction kernel of the two-body Bethe-Salpeter equation gives a gauge invariant two-body current. Similar progress was made by van Antwerpen and Afnan [14] who showed how to construct a gauge invariant current for the relativistic πN system where pion absorption can take place. More recently, we have introduced a general method where any system described by integral equation can be gauged [10].…”

Section: B Gauging the Spectator Equationmentioning

confidence: 71%

Gauging the three-nucleon spectator equation

Kvinikhidze

Blankleider

1997

Phys. Rev. C

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We derive relativistic three-dimensional integral equations describing the interaction of the three-nucleon system with an external electromagnetic field. Our equations are unitary, gauge invariant, and they conserve charge. This has been achieved by applying the recently introduced gauging of equations method to the three-nucleon spectator equations where spectator nucleons are always on mass shell. As a result, the external photon is attached to all possible places in the strong interaction model, so that current and charge conservation are implemented in the theoretically correct fashion. Explicit expressions are given for the three-nucleon bound state electromagnetic current, as well as the transition currents for the scattering processes γ 3 He→ NNN , N d → γN d, and γ 3 He→ N d. As a result, a unified covariant three-dimensional description of the NNN -γNNN system is achieved.

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A Gauge Invariant Unitary Theory for Pion Photoproduction

Antwerpen

Afnan

1994

Few-Body Problems in Physics ’93

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A covariant, unitary and gauge invariant theory for pion photoproduction on a single nucleon is presented. To achieve gauge invariance at the operator level one needs to include both the πN and γπN thresholds. The final amplitude can be written in terms of a distorted wave in the final πN channel provided one includes additional diagrams to the standard Born term in which the photon is coupled to the final state pion and nucleon. These additional diagrams are required in order to satisfy gauge invariance.Most calculations to date for pion photoproduction on a single nucleon have included two ingredients: (i) A Born term which is taken to be gauge invariant. (ii) A final state interaction or distortion that is needed to satisfy the Watson theorem or unitarity.However, the inclusion of the pionic degrees of freedom into the problem changes the current and charge distribution and thus the coupling of the photon to the nucleon.Hence any consistent theory of pion photoproduction has to include the effect of the pionic degrees of freedom on the charge and current distribution. In other words one needs to satisfy unitarity and gauge invariance at the same time. Clearly, the inclusion of both of these symmetries to all orders requires a full solution to the field theory. Here, we

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Gauge invariant unitary theory for pion photoproduction

Cited by 25 publications

References 48 publications

Dynamical study of theΔexcitation inN(e,e′π)reactions

Dynamical study of theΔexcitation inN(e,e′π)reactions

Gauging the three-nucleon spectator equation

A Gauge Invariant Unitary Theory for Pion Photoproduction

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