Nucleon structure functions in a chiral soliton model

The computation of nucleon structure functions within the Nambu-Jona-Lasinio chiral soliton model is outlined. After some technical remarks on the issue of regularization numerical results for the both unpolarized and polarized structure functions are presented. The generalization to flavor SU(3) is sketched.     

Nucleon form factors in a covariant diquark-quark model

In a model where constituent quarks and diquarks interact through quark exchange the Bethe-Salpeter equation in ladder approximation for the nucleon is solved. Quark and diquark confinement is effectively parametrized by choosing appropriately modified propagators. The coupling to external currents is implemented via non-trivial vertex functions for quarks and diquarks to ensure gauge invariance at the constituent level. Nucleon matrix elements are evaluated in a generalized impulse approximation, and electromagnetic, pionic and axial form factors are calculated.     

Nucleon form factors in a relativistic quark model

Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a difference between the relativistic and the nonrelativistic treatments. Received: 10 March 1999 / Revised version: 14 June 1999     

Nucleon charge form factors and chiral quark models

Calculations of the proton and neutron charge form factors G_E^p,n(q²) are presented, based on chiral bag as well as confining Dirac potential models with chiral pion-quark coupling. Special emphasis is placed on a detailed treatment of the charged pion cloud contribution to the nucleon current. The role of a finite extension of the pion-quark vertex in truncating the summation over intermediate quark bag states is studied. Quark core radii (including recoil corrections) are constrained by a simultaneous calculation of the nucleon axial form factor. The proton charge form factor is well reproduced for $\text{|q}{}^2\text{|}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? 0.7}\text{GeV}$ with quark core rms radii between 0.5–0.6 fm. About $\text{1}\text{3}$ of the proton charge is carried by the pion cloud in this model. The neutron charge form factor is obtained with the correct sign and overall q² dependence but needs further refinements, probably at the level of the isoscalar form factor.     

Nucleon form factors in a simple three-body quark model

We construct a simple 3-body quark model for the non strange nucleon resonances and we give results for the spectrum, the helicity amplitudes and the transition form factors. All the observables, in particular the transition form factors, are evaluated analytically and the results are compared with those of other models. Received: 15 November 1997     

Pion-nucleon vertex form factor in a chiral soliton model with vector mesons

We investigate the pion-nucleon vertex from factor in an extended Skyrme soliton model with explicit inclusion of ϱ and ω mesons. We find a pion-nucleon coupling constant quite close to the empirical value and a cutoff mass ⋮ ⋍ 0.9 MeV in a monopole approximation to the πNN form factor at low q². This value of ⋮ is considerably larger than the prediction of the original Skyrme model (⋮⋍0.6 GeV). We also investigate the ϱ-meson-nucleon form factor and present results for the NN isovector tensor potential in comparison with empirical data.     

Nucleon magnetic form factors in the cloudy bag model

The nucleon magnetic moments and magnetic form factors have been calculated in the cloudy bag model. The πNN, πNΔ, γπ form factors and the CM corrections have been taken into account. We obtained very good results for these quantities.     

Form factors in the projected linear chiral sigma model

Several nucleon form factors are computed within the framework of the linear chiral soliton model. To this end variational means and projection techniques applied to generalized hedgehog quark-boson Fock states are used. In this procedure the Goldberger-Treiman relation and a virial theorem for the pion-nucleon form factor are well fulfilled demonstrating the consistency of the treatment. Both proton and neutron charge form factors are correctly reproduced, as well as the proton magnetic one. The shapes of the neutron magnetic and of the axial form factors are good but their absolute values at the origin are too large. The slopes of all the form factors at zero momentum transfer are in good agreement with the experimental data. The pion-nucleon form factor exhibits to great extent a monopole shape with a cut-off mass ofΛ=690 MeV. Electromagnetic form factors for the vertexγNΔ and the nucleon spin distribution are also evaluated and discussed.     

Nucleon elastic form factors

The nucleon form factors are still the subject of active investigation even after an experimental effort spanning 50 years. This is because they are of critical importance to our understanding of the electromagnetic properties of nuclei and provide a unique testing ground for QCD motivated models of nucleon structure. Progress in polarized beams, polarized targets and recoil polarimetry have allowed an important and precise set of data to be collected over the last decade. I will review the experimental status of elastic electron scattering from the nucleon along with an outlook for future progress.     

Nucleon electromagentic form factors in the modified vector dominance model

For nucleon electromagnetic form factors, two-parameter expressions which reproduce quite well the experimental data in the spacelike region of the 4-momentum transfer squared are obtained.     

Nucleon form factors in dispersion theory

In the initial stage of the bottom-up picture of thermalization in heavy-ion collisions, the gluon distribution is highly anisotropic which can give rise to plasma instability. This has not been taken into account in our original paper (Phys. Lett. B 632, 257 (2006) hep-ph/0505164). It is shown that in the presence of instability there are scaling solutions, which depend on one parameter, that match smoothly onto the late stage of bottom-up when thermalization takes place.-1     

Covariant electroweak nucleon form factors in a chiral constituent-quark model

Results for the proton and neutron electric and magnetic form factors as well as the 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. Received: 28 February 2002 / Accepted: 14 March 2002     

Facets of confinement and dynamical chiral symmetry breaking

The gap equation is a cornerstone in understanding dynamical chiral symmetry breaking and may also provide clues to confinement. A symmetry-preserving truncation of its kernel enables proofs of important results and the development of an efficacious phenomenology. We describe a model of the kernel that yields: a momentum-dependent dressed-quark propagator in fair agreement with quenched lattice-QCD results; and chiral limit values, MeV and . It is compared with models inferred from studies of the gauge sector.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.38.Aw General properties of QCD (dynamics, confinement, etc.) - 11.30.Rd Chiral symmetries     

Nucleon structures functionsin the three-flavor NJL soliton model

We study the relevance of strange degrees of freedom for nucleon structure functions. For this purpose we employ the three-flavor generalization of the collective quantization approach to the chiral soliton of the bosonized Nambu-Jona-Lasinio model. Contrary to many other soliton models the hadronic tensor is tractable in this model. By applying the Bjorken limit to the hadronic tensor we extract the leading twist contributions to the nucleon structure functions at the low energy scale at which the model is assumed to approximate QCD. After transforming to the infinite momentum frame and performing the DGLAP evolution program to these structure functions we compare with available data for deep inelastic electron-nucleon scattering.     

Nucleon structure in the perturbative chiral quark model

We give an overview of recent applications of the perturbative chiral quark model (PCQM) in the analysis of the structure of the nucleon. The PCQM is based on an effective Lagrangian, where baryons are described by relativistic valence quarks and a perturbative cloud of Goldstone bosons as required by chiral symmetry. We discuss applications to the electromagnetic properties of the nucleon, to σ-term physics, to πN scattering including radiative corrections and to the strange form factors of the nucleon.