A.Y. Korchin

Pion and photon induced reactions on the nucleon in a unitary model

O. Scholten, A.Y. Korchin, V. Pascalutsa, D. Van Neck

Physics Letters B

384 (1-4), 13-19

1996

A1

Published while none of the authors were employed at the CMM

Abstract

We present a relativistic calculation of pion scattering, pion photoproduction and Compton scattering on the nucleon in the energy region of the Δ-resonance (upto 450 MeV photon lab energy), in a unified framework which obeys the unitarity constraint. It is found that the recent data on the cross section for nucleon Compton scattering determine accurately the parameters of the electromagnetic nucleon-Δ coupling. The pion-photoproduction partial-wave amplitudes, calculated with parameters fitted to the pion-nucleon and Compton scattering, agree well with the recent Arndt analysis.

DOI

http://dx.doi.org/10.1016/0370-2693(96)00825-8

Low-energy theorems for virtual nucleon-nucleon bremssrahlung; formalism and results

A.Y. Korchin, O. Scholten, D. Van Neck

Nuclear Physics A

602 (3-4), 423-448

1996

A1

Published while none of the authors were employed at the CMM

Abstract

We present results for cross sections and response functions in virtual bremsstrahlung induced by nucleon-nucleon collisions NN → NN + e⁺e⁻, based on two different low-energy theorems. The first low-energy theorem is a generalization of Low's theorem for real-photon bremsstrahlung. The second low-energy theorem was derived by Liou et al. for real photons, and is generalized here to the case of virtual photons. The two low-energy theorems are compared by calculating the cross section and response functions in the kinematical region of possible future experiments. We find that for most observables the amplitude up to leading order only in the photon energy does not provide a reliable description, and that the next order term is very important. The differences between the two low-energy theorems turn out to be sizeable for pp, but quite small for pn virtual bremsstrahlung. We also pay attention to the correct implementation of the generalized Pauli principle and crossing symmetry which the reaction amplitude must obey.

DOI

http://dx.doi.org/10.1016/0375-9474(96)00095-4

Radiative proton-deuteron capture in a gauge invariant relativistic model

A.Y. Korchin, D. Van Neck, O. Scholten, M. Waroquier

Physical Review C

59 (4), 1890-1905

1999

A1

Published while none of the authors were employed at the CMM

DOI

http://dx.doi.org/10.1103/PhysRevC.59.1890

Production of e+ e− pairs in proton-deuteron capture to 3He

A.Y. Korchin, D. Van Neck, M. Waroquier, O. Scholten, A.E.L. Dieperink

Physics Letters B

441 (1-4), 17-26

1998

A1

Published while none of the authors were employed at the CMM

DOI

http://dx.doi.org/10.1016/S0370-2693(98)01197-6

Electromagnetic interaction in chiral quantum hadrodynamics and decay of vector and axial-vector mesons

A.Y. Korchin, D. Van Neck, M. Waroquier

Physical Review C

67 (1), 015207

2003

A1

Abstract

The chiral invariant quantum hadrodynamics (QHD) III model of Serot and Walecka is applied in the calculation of some meson properties. The electromagnetic interaction is included by extending the symmetry of the model to the local U(1)×SU(2)R×SU(2)L group. The minimal and nonminimal contributions to the electromagnetic Lagrangian are obtained in a new representation of QHD-III. Strong decays of the axial-vector meson, a1→πρ,a1→πσ, and the electromagnetic decays ρ⃗ππγ,a1→πγ, and ρ⃗πγ are calculated. The low-energy parameters for the π-π scattering are calculated in the tree-level approximation. The effect of the auxiliary Higgs bosons, introduced in QHD-III in order to generate masses of the vector and axial-vector mesons via the Higgs mechanism, is studied as well. This is done on the tree level for π-π scattering and on the level of one-loop diagrams for the a1→πγ decay. It is demonstrated that the model successfully describes some features of meson phenomenology in the nonstrange sector.

DOI

http://dx.doi.org/10.1103/PhysRevC.67.015207

Compton Scattering on the Proton and Light Nuclei in the \Delta-Resonance Region

L. Van Daele, D. Van Neck, M. Waroquier, A.Y. Korchin

Acta Physica Polonica B

33(3), 847-871

2002

A1

Abstract

Microscopic calculations of Compton scattering on the free proton and light nuclei are presented. For the description of Compton scattering on the proton the conventional K-matrix approach and the ``Dressed K-Matrix'' model are introduced. The latter approach can be used to calculate polarizabilities as well as Compton scattering for photon energies upto 1 GeV since it obeys the symmetry properties which are appropriate in the different energy regions. In particular, crossing symmetry, gauge invariance and unitarity are satisfied. The extent of violation of analyticity (causality) is used as an expansion parameter. Coherent Compton scattering on light nuclei at 200--300 MeV is studied in the impulse approximation and is shown to be a sensitive probe of the in-medium properties of the \Delta -resonance. Modifications of the properties of the \Delta-resonance due to the nuclear medium are accounted for through the self-energy operator of the \Delta. The dominant medium effects such as the Pauli blocking effects in the decay width, effective nucleon mass and particle--hole excitations in the pion propagator are consistently included in nuclear matter.

DOI

http://dx.doi.org/

Coherent Compton scattering on light nuclei in the Δ-resonance region

L. Van Daele, A.Y. Korchin, D. Van Neck, O. Scholten, M. Waroquier

Physical Review C

65 (1), 014613

2001

A1

Abstract

Coherent Compton scattering on light nuclei in the Δ-resonance region is studied in the impulse approximation and is shown to be a sensitive probe of the in-medium properties of the Δ resonance. The elementary amplitude on a single nucleon is calculated from the unitary K-matrix approach developed previously. Modifications of the properties of the Δ resonance due to the nuclear medium are accounted for through the self-energy operator of the Δ, calculated from the one-pion loop. The dominant medium effects such as the Pauli blocking, mean-field modification of the nucleon and Δ masses, and particle-hole excitations in the pion propagator are consistently included in nuclear matter.