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Quadrupole moment of the nucleon in chiral constituent quark model  [PDF]
Harleen Dahiya,Neetika Sharma
Physics , 2010,
Abstract: The electromagnetic form factors are the most fundamental quantities to describe the internal structure of the nucleon and the shape of a spatially extended particle is determined by its {\it intrinsic} quadrupole moment which is first order moment of the charge density operator. With some experimental indications of a deformed nucleon, we have calculated the {\it intrinsic} quadrupole moment of the octet and decuplet baryons in the framework of chiral constituent quark model \chiCQM which is quite successful in explaining some of the important baryon properties in the nonperturbative regime.
Nucleon-nucleon scattering in a chiral constituent quark model  [PDF]
D. Bartz,Fl. Stancu
Physics , 2000, DOI: 10.1103/PhysRevC.63.034001
Abstract: We study the nucleon-nucleon interaction in a chiral constituent quark model by using the resonating group method, convenient for treating the interaction between composite particles. The calculated phase shifts for the 3S1 and 1S0 channels show the presence of a strong repulsive core due to the combined effect of the quark interchange and the spin-flavour structure of the effective quark-quark interaction. Such a symmetry structure stems from the pseudoscalar meson exchange between the quarks and is a consequence of the spontaneous breaking of the chiral symmetry. We perform single and coupled channel calculations and show the role of coupling of the $\Delta\Delta$ and hidden color CC channels on the behaviour of the phase shifts.
The Nucleon-Nucleon Interaction in a Chiral Constituent Quark Model  [PDF]
Fl. Stancu,S. Pepin,L. Ya. Glozman
Physics , 1997, DOI: 10.1103/PhysRevC.56.2779
Abstract: We study the short-range nucleon-nucleon interaction in a chiral constituent quark model by diagonalizing a Hamiltonian comprising a linear confinement and a Goldstone boson exchange interaction between quarks. The six-quark harmonic oscillator basis contains up to two excitation quanta. We show that the highly dominant configuration is $\mid s^4p^2[42]_O [51]_{FS}>$ due to its specific flavour-spin symmetry. Using the Born-Oppenheimer approximation we find a strong effective repulsion at zero separation between nucleons in both $^3S_1$ and $^1S_0$ channels. The symmetry structure of the highly dominant configuration implies the existence of a node in the S-wave relative motion wave function at short distances. The amplitude of the oscillation of the wave function at short range will be however strongly suppressed. We discuss the mechanism leading to the effective short-range repulsion within the chiral constituent quark model as compared to that related with the one-gluon exchange interaction.
Nucleon Electromagnetic Form Factors in a chiral constituent-quark model  [PDF]
P. Demetriou,S. Boffi,M. Radici,R. F. Wagenbrunn
Physics , 1999,
Abstract: The electromagnetic form factors of the nucleon are calculated in an extended chiral constituent-quark model where the effective interaction is described by the exchange of pseudoscalar, vector, and scalar mesons. Two-body current-density operators, constructed consistently with the extended model Hamiltonian in order to preserve gauge invariance and current conservation, are found to give a significant contribution to the nucleon magnetic form factors and improve the estimates of the nucleon magnetic moments.
Covariant electroweak nucleon form factors in a chiral constituent quark model  [PDF]
S. Boffi,L. Ya. Glozman,W. Klink,W. Plessas,M. Radici,R. F. Wagenbrunn
Physics , 2001,
Abstract: 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.
Nucleon form factors in a chiral constituent-quark model  [PDF]
S. Boffi,P. Demetriou,M. Radici,R. F. Wagenbrunn
Physics , 1998, DOI: 10.1103/PhysRevC.60.025206
Abstract: The electromagnetic form factors of the nucleon have been calculated in a chiral constituent-quark model. The nucleon wave functions are obtained by solving a Schr\"odinger-type equation for a semi-relativistic Hamiltonian with an effective interaction derived from the exchange of mesons belonging to the pseudoscalar octet and singlet and a linear confinement potential. The charge-density current operator has been constructed consistently with the model Hamiltonian in order to preserve gauge invariance and to satisfy the continuity equation.
Nucleon-Nucleon interaction in a chiral constituent quark model  [PDF]
D. Bartz,Fl. Stancu
Physics , 1999, DOI: 10.1063/1.1303013
Abstract: We study the nucleon-nucleon (NN) problem as a six-quark system in a nonrelativistic chiral constituent quark model where the Hamiltonian contains a linear confinement and a pseudoscalar meson (Goldstone boson) exchange interaction between the quarks. This interaction has a long range Yukawa-type part, depending on the mass of the exchanged meson and a short range part, mainly responsible for the good description of the baryon spectra. We calculate the NN potential in the adiabatic approximation as a function of Z, the separation distance between the centres of the two three-quark clusters. The orbital part of the six-quark states is constructed either from the usual cluster model states or from molecular orbital single particle states. The latter are more realistic, having proper axially and reflectionally symmetries. In both cases the potential presents an important hard core at short distances, explained through the dominance of the [51]{FS} configuration. However in the molecular orbital basis the core is less repulsive, as a consequence of the fact that this basis gives a better upper bound for the energy of the six-quark system. We calculate the potential for the 3S1 and 3S0 channels with two different parametrizations. We find a small (few MeV) attractive pocket for one of these parametrizations. A middle range attraction is simulated by the addition of a sigma-meson exchange interaction between quarks, of a form similar to that of the pseudoscalar meson exchange. The present study is an intermediate, useful step towards dynamical calculations based on the resonating group method.
Nucleon magnetic moments in an extended chiral constituent quark model  [PDF]
R. F. Wagenbrunn,M. Radici,S. Boffi,P. Demetriou
Physics , 2000, DOI: 10.1007/s10050-000-5075-8
Abstract: 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.
Chiral Constituent quarks and their role in quark distribution functions of nucleon and pion  [PDF]
K. Suzuki,W. Weise
Physics , 1997, DOI: 10.1016/S0375-9474(98)00132-8
Abstract: We investigate the structure of constituent quarks and study implications for quark distribution functions of hadrons. Constituent quarks are constructed by dressing bare quarks with Goldstone bosons using the chiral quark model. We calculate resulting corrections to the twist-2 structure functions $f_1(x)$, $g_1(x)$ and $h_1(x)$. The Goldstone boson fluctuations produce a flavor asymmetry of the quark distribution in the nucleon in agreement with experimental data. They also generate significant depolarization effects which reduce the fraction of the nucleon spin carried by quarks. Corrections to the transversity spin structure function $h_1(x)$ differ from those to $g_1(x)$, and in particular we find a large reduction (40%) of the $d$-quark tensor charge, which is consistent with recent lattice calculations. We also study the pion structure function and find the momentum fraction carried by the sea quarks in the pion to be considerably larger than that in the nucleon.
Chiral Symmetry: Pion-Nucleon Interactions in Constituent Quark Models  [PDF]
C. M. Maekawa,M. R. Robilotta
Physics , 1996, DOI: 10.1103/PhysRevC.55.2675
Abstract: We study the interactions of an elementary pion with a nucleon made of constituent quarks and show that the enforcement of chiral symmetry requires the use of a two-body operator, whose form does not depend on the choice of the pion-quark coupling. The coordinate space NN effective potential in the pion exchange channel is given as a sum of terms involving two gradients, that operate on both the usual Yukawa function and the confining potential. We also consider an application to the case of quarks bound by a harmonic potential and show that corrections due to the symmetry are important.
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