Nucleon magnetic moments in an extended chiral constituent quark model

We present results for the nucleon magnetic moments in the context of an extended chiral constituent quark model based on the mechanism of the Goldstone boson exchange, as suggested by the spontaneous breaking of chiral symmetry in QCD. The electromagnetic charge-current operator is consistently deduced from the model Hamiltonian, which includes all force components for the pseudoscalar, vector and scalar meson exchanges. Thus, the continuity equation is satisfied for each piece of the interaction, avoiding the introduction of any further parameter. A good agreement with experimental values is found. The role of isoscalar two-body operators, not constrained by the continuity equation, is also investigated.Comment: 7 pages, 1 table, submitted for publication to Phys. Lett. B, elsart.sty/elsart12.sty include

On the NN-final-state-interaction in the 16O(e,e′pp)^{16}{O}(e,e' pp) reaction

The influence of the mutual interaction between the two outgoing nucleons (NN-FSI) in the $^{16}{O}(e,e' pp)$ reaction has been investigated. Results for various kinematics are discussed. In general, the effect of NN-FSI depends on kinematics and the chosen final state in the excitation spectrum of $^{14}{C}$.Comment: 12 pages Revtex including 4 postscript figure

On the treatment of the Δ\Delta-contribution in electromagnetic pppp-knockout reactions

The treatment of the $\Delta$-current and its contribution in the exclusive $^{16}$O$(e,e'pp)^{14}$C and $^{16}$O$(\gamma,pp)^{14}$C knockout reactions are investigated in combination with the effects of correlations. Different parametrizations of the effective $\Delta$-current and different treatments of correlations in the two-nucleon overlap function are considered. The results are presented and discussed for a suitable choice of kinematics. It is found that the investigation of different mutually supplementing kinematics is necessary to resolve the uncertainties in the theoretical ingredients and extract clear and unambiguous information on correlations.Comment: 15 pages, 9 figures, EPJA styl

NN correlations and final-state interactions in (e,e'NN) reactions

After a brief overview of relevant studies on one-nucleon knockout showing the importance of quantitatively understanding the origin of the quenched spectroscopic factors extracted from data, attention is focussed on two-nucleon emission as a suitable tool to investigate nucleon-nucleon correlations inside complex nuclei. In particular, direct (e,e$'$pp) and (e,e$'$pn) reactions are discussed, and the role of final-state interactions is studied. The influence of the mutual interaction between the two outgoing nucleons is shown to depend on the kinematics and on the type of the considered reaction.Comment: 13 pages, 4 figures. Proceedings of 2nd Int. Conf. on Nuclear and Particle Physics with CEBAF at Jefferson Lab, Dubrovnik, 26-31 May 2003, to be published on Fyzika

The NN-final-state-interaction in two-nucleon-knockout reactions

The influence of the mutual interaction between the two outgoing nucleons (NN-FSI) in electro- and photoinduced two-nucleon knockout from $^{16}O$ has been investigated perturbatively. It turns out that the effect of NN-FSI depends on the kinematics and on the type of reaction considered. In the kinematics studied so far, the effect is larger in pp- than in pn-knockout and in electron induced than in photoinduced reactions.Comment: 10 pages including 9 postscript figures, contribution to the 6th workshop on "Electromagnetically Induced Two-Hadron Emission", Pavia, September 24-27, 200

Electroweak properties of baryons in a covariant chiral quark model

The proton and neutron electromagnetic form factors and the nucleon axial form factor have been calculated in the Goldstone-boson exchange constituent-quark model within the point-form approach to relativistic quantum mechanics. The results, obtained without any adjustable parameter nor quark form factors, are, due to the dramatic effects of the boost required by the covariant treatment, in striking agreement with the data.Comment: Proceedings of the Conference N*2001, Mainz; 4 pages, 3 figures included in eps format; World Scientific style file include

Electromagnetic proton-neutron knockout off 16O: new achievements in theory

Results for the cross sections of the exclusive 16O(e,e'pn)14N and 16O(gamma,pn)14N knockout reactions are presented and discussed in different kinematics. In comparison with earlier work, a complete treatment of the center-of-mass (CM) effects in the nuclear one-body current is considered in connection with the problem of the lack of orthogonality between initial bound and final scattering states. The effects due to CM and orthogonalization are investigated in combination with different treatments of correlations in the two-nucleon overlap function and for different parametrizations of the two-body currents. The CM effects lead in super-parallel kinematics to a dramatic increase of the 16O(e,e'pn) cross section to the 1_2^+ excited state (3.95 MeV) of 14N. In all the situations considered the results are very sensitive to the treatment of correlations. A crucial role is played by tensor correlations, but also the contribution of long-range correlations is important.Comment: 13 pages, 10 figure

Nucleon electromagnetic and axial form factors in point-form relativistic quantum mechanics

Results for the proton and neutron electric and magnetic form factors as well as the nucleon axial form factor are presented for constituent quark models, based on either one-gluon-exchange and Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The only input to the calculations is the nucleon wave function of the corresponding constituent quark model. A comparison is given to results of the instanton-induced constituent quark model treated with the Bethe-Salpeter equation.Comment: 4 pages, 6 figures, contribution to XVIII European Conference on Few-Body Problems in Physics, September 2002, Bled, Sloveni

Covariant electroweak nucleon form factors in a chiral constituent quark model

Results for the proton and neutron electric and magnetic form factors as well asthe nucleon axial and induced pseudoscalar form factors are presented for the chiral constituent quark model based on Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The direct predictions of the model yield a remarkably consistent picture of the electroweak nucleon structure.Comment: 4 pages, 3 figures revte