Relativistic corrections to the nucleon charge radius in the constituent-quark model

1996 ◽  
Vol 109 (4) ◽  
pp. 425-433 ◽  
Author(s):  
M. De Sanctis
Keyword(s):  
Quark Model ◽  
Charge Radius ◽  
Constituent Quark ◽  
Constituent Quark Model ◽  
Relativistic Corrections

Exchange Currents in Baryons

1997 ◽  
Vol 52 (12) ◽  
pp. 877-940 ◽  
Author(s):  
Alfons J Buchmann
Keyword(s):  
Quark Model ◽  
Quadrupole Moment ◽  
Charge Radius ◽  
Constituent Quark ◽  
Magnetic Moments ◽  
Impulse Approximation ◽  
Constituent Quark Model ◽  
Pion Exchange ◽  
Electromagnetic Current ◽  
Gluon Exchange

This paper reviews calculations of the electromagnetic properties of baryons using the constituent quark model. We start with a short discussion of spontaneous chiral symmetry breaking, which is essential in understanding the transition from QCD to the constituent quark model. We then discuss a chiral version of the constituent quark model, which simulates the symmetries and dynamical content of the underlying field theory in terms of gluon, pion and sigma exchange between constituent quarks. We show that the electromagnetic current charge and current operators, usually approximated by one-body operators (impulse approximation), must be supplemented by appropriate two-body terms (exchange currents). The latter represent the gluon and pion exchange degrees of freedom in the electromagnetic current operator. These exchange currents must be included for reasons of completeness and consistency. Most importantly, however, they are needed in order for the electromagnetic current to be conserved. We also study the effect of scalar exchange currents connected with the confinement and sigma exchange potentials. By including these twobody exchange currents we go beyond the single-quark impulse approximation, which has mainly been used up to now. The inclusion of gluon- pion-, and scalar-exchange currents in the quark potential model is the new point of the present work. We show that for some observables, such as the magnetic moments, charge, and magnetic radii of the proton and charged Δ (1232) states, exchange currents contribute at the level of some 10%. The same holds true for the magnetic moments of the entire baryon octet, with the exception of the Ξ- magnetic moment. On the other hand, the neutron charge radius, the quadrupole moments of the Δ, and the N → Δ transition quadrupole moment, are dominated by pion and gluon exchange contributions to the charge density operator. The inclusion of the pion and gluon exchange currents leads to a neutron charge radius of the correct size and sign. Based on the gluon and pion exchange current diagrams, we derive parameter-free relations between the neutron charge radius, the quadrupole moment of the Δ, and the N → Δ transition quadrupole moment. Neglecting configuration mixing, we find that the neutron charge radius and the N → Δ transition quadrupole moment are simply related as QN→Δ = r2n√2. The implications of Siegert's theorem for the calculation of the E2 form factor in the N → Δ transition are studied. Finally, we discuss the axial coupling constant of the nucleon. We show that the inclusion of axial pair exchange currents does not significantly alter the NRQM prediction.

scholarly journals Low-lying configurations in a non-relativistic constituent quark model

2007 ◽  
Vol 34 (7) ◽  
pp. 1771-1782 ◽  
Author(s):  
W L Wang ◽  
F Huang ◽  
Z Y Zhang ◽  
Y W Yu ◽  
F Liu
Keyword(s):  
Quark Model ◽  
Constituent Quark ◽  
Constituent Quark Model

THE NLO QCD CALCULATION OF SEA QUARK DISTRIBUTIONS IN THE CORGI APPROACH, BASED ON THE CONSTITUENT QUARK MODEL

2007 ◽  
Vol 22 (24) ◽  
pp. 4519-4535 ◽  
Author(s):  
A. MIRJALILI ◽  
K. KESHAVARZIAN
Keyword(s):  
Quark Model ◽  
Mellin Transform ◽  
Constituent Quark ◽  
Constituent Quark Model ◽  
Standard Approach ◽  
Unknown Parameters ◽  
Electron Positron Annihilation ◽  
Electron Positron ◽  
Physical Scale ◽  
Good Agreement

Sea quark distributions in the NLO approximation, based on the phenomenological valon model or constituent quark model are analyzed. We use the parametrized inverse Mellin transform technique to perform a direct fit with available experimental data and obtain the unknown parameters of the distributions. We try to extend the calculation to the NLO approximation for the singlet and nonsinglet cases in DIS phenomena. We do also the same calculation for electron–positron annihilation. The resulting sea distributions are effectively independent of the process used. The approach of complete RG improvement (CORGI) is employed and the results are compared with the standard approach of perturbative QCD in the [Formula: see text] scheme with a physical scale. The comparisons with data are in good agreement. As is expected, the results in the CORGI approach indicate a better agreement to the data than the NLO calculation in the standard approach.

scholarly journals An overview of the hypercentral constituent quark model

2003 ◽  
Vol 50 (2) ◽  
pp. 263-272 ◽  
Author(s):  
M.M Giannini ◽  
E Santopinto ◽  
A Vassallo
Keyword(s):  
Quark Model ◽  
Constituent Quark ◽  
Constituent Quark Model

scholarly journals Electromagnetic form factors and the hypercentral constituent quark model

2007 ◽  
Vol 76 (6) ◽  
Author(s):  
M. De Sanctis ◽  
M. M. Giannini ◽  
E. Santopinto ◽  
A. Vassallo
Keyword(s):  
Quark Model ◽  
Constituent Quark ◽  
Form Factors ◽  
Constituent Quark Model ◽  
Electromagnetic Form Factors

scholarly journals STRUCTURE OF LIGHT AND HEAVY PENTAQUARKS

2005 ◽  
Vol 20 (08n09) ◽  
pp. 1797-1802 ◽  
Author(s):  
FL. STANCU
Keyword(s):  
Variational Method ◽  
Hyperfine Interaction ◽  
Quark Model ◽  
Constituent Quark ◽  
Constituent Quark Model ◽  
Positive Parity ◽  
Model Based ◽  
Quantum Numbers ◽  
The Masses

Light and heavy pentaquarks are described within a constituent quark model based on a spin-flavor hyperfine interaction. In this model the lowest state acquires positive parity. The masses of the light antidecuplet members are calculated dynamically using a variational method. It is shown that the octet and antidecuplet states with the same quantum numbers mix ideally due to SU (3)F breaking. Masses of the charmed antisextet pentaquarks are predicted within the same model.

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