Quark confinement potential and the quark-diquark model for nucleons (original) (raw)

Nucleon properties in the covariant quark-diquark model

The European Physical Journal A, 2000

In the covariant quark-diquark model the effective Bethe-Salpeter (BS) equations for the nucleon and the ∆ are solved including scalar and axialvector diquark correlations. Their quark substructure is effectively taken into account in both, the interaction kernel of the BS equations and the currents employed to calculate nucleon observables. Electromagnetic current conservation is maintained. The electric form factors of proton and neutron match the data. Their magnetic moments improve considerably by including axialvector diquarks and photon induced scalar-axialvector transitions. The isoscalar magnetic moment can be reproduced, the isovector contribution is about 15% too small. The ratio µ GE/GM and the axial and strong couplings gA, gπNN , provide an upper bound on the relative importance of axialvector diquarks confirming that scalar diquarks nevertheless describe the dominant 2-quark correlations inside nucleons. PACS. 11.10.St (Bound states; Bethe-Salpeter equations) -12.39.Ki (Relativistic quark model) -12.40.Yx (Hadron mass models and calculations) -13.40.Em (Electric and magnetic moments) -13.40.Gp (Electromagnetic form factors) -13.75.Gx (Pion-baryon interactions) -14.20.Dh (Protons and neutrons)

A comparison between relativistic and semi-relativistic treatment in the diquark–quark model

Physics Letters B, 2000

In the diquark-quark model of the nucleon including scalar and axialvector diquarks we compare solutions of the ladder Bethe-Salpeter equation in the instantaneous Salpeter approximation and in the fully covariant (i.e. four-dimensional) treatment. We obtain that the binding energy is severely underestimated in the Salpeter approximation. For the electromagnetic form factors of the nucleon we find that in both approaches the overall shapes of the respective form factors are reasonably similar up to Q 2 ≈ 0.4 GeV 2 . However, the magnetic moments differ substantially as well as results for the pion-nucleon and the axial coupling of the nucleon.

Nucleon form factors in a covariant diquark-quark model

Nuclear Physics A, 1997

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 nontrivial vertex functions for quarks and diquarks to ensure gauge invariance at the constituent level. Nucleon matrix elements are evaluated in a generalised impulse approximation, and electromagnetic, pionic and axial form factors are calculated.

An introduction to the quark model

arXiv: High Energy Physics - Phenomenology, 2012

This document contains a review on the quark model, prepared for lectures at the Niccolo Cabeo School at Ferrara in May 2012. It includes some historical aspects, the spectral properties of the 2-body and 3-body Schrodinger operators applied to mesons and baryons, the link between meson and baryon spectra, the role of flavour independence, and the speculations about stable or metastable multiquarks. The analogies between few-charge systems and few-quark bound states will be underlined.

A quark-meson coupling model based on Bogoliubov's model of the nucleon

The quark-meson coupling model due to Guichon is formulated on the basis of the independent quark model of the nucleon proposed by Bogoliubov and is applied to a phenomenological description of symmetric nuclear matter. The model predicts, at saturation density, the compressibility K = 249 MeV and the quark effective mass m * q = 249.1 MeV, the effective nucleon mass being M * = 747.3 MeV. The predicted nucleon mass radius is r = 0.93 fm.

Quark models of nuclear matter:(I). Basic models and ground-state properties

1992

Nuclear matter is moüeled directly in the constituent quark coordinates . A many-body string flip potential is used which confines quarks, allows hadrons to separate and is symmetric in all quark coordinates . Variational Monte Carlo results are presented for the energy, wave function and quark correlation function of nuclear and quark matter for various densities. These show how quark clustering decreases with density. A percolation phase transition from nuclear to quark matter is observed which is characterized by a dramatic rearrangement of strings.

Long- and medium-range components of the nuclear force in quark-model based calculations

Physical Review C, 2001

Quark-model descriptions of the nucleon-nucleon interaction contain two main ingredients, a quark-exchange mechanism for the short-range repulsion and meson-exchanges for the medium-and long-range parts of the interaction. We point out the special role played by higher partial waves, and in particular the 1 F 3 , as a very sensitive probe for the meson-exchange part employed in these interaction models. In particular, we show that the presently available models fail to provide a reasonable description of higher partial waves and indicate the reasons for this shortcoming.

A higher-dimensional model of the nucleon-nucleon central potential

Frontiers of Physics, 2013

Based on a theory of extra dimensional confinement of quantum particles [E. R. Hedin, Physics Essays 25, 2 (2012)], a simple model of a nucleon-nucleon (NN) central potential is derived which quantitatively reproduces the radial profile of other models, without adjusting any free parameters. It is postulated that a higher-dimensional simple harmonic oscillator confining potential localizes particles into 3-d space, but allows for an evanescent penetration of the particles into two higher spatial dimensions. Producing an effect identical with the relativistic quantum phenomenon of zitterbewegung, the higher-dimensional oscillations of amplitude mc /  can be alternatively viewed as a localized curvature of 3-d space back and forth into the higher dimensions. The overall spatial curvature is proportional to the particle's extradimensional ground state wave function in the higher-dimensional harmonic confining potential well. Minimizing the overlapping curvature (proportional to the energy) of two particles in proximity to each other, subject to the constraint that for the two particles to occupy the same spatial location one of them must be excited into the 1 st excited state of the harmonic potential well, gives the desired NN potential. Specifying only the nucleon masses, the resulting potential well and repulsive core reproduces the radial profile of several published NN central potential models. In addition, the predicted height of the repulsive core, when used to estimate the maximum neutron star mass, matches well with the best estimates from relativistic theory incorporating standard nuclear matter equations of state. Nucleon spin, Coulomb interactions, and internal nucleon structure are not considered in the theory as presented in this article.

Modern theory of nuclear forces

Nuclear Physics A, 2005

Nuclear forces can be systematically derived using effective chiral Lagrangians consistent with the symmetries of QCD. I review the status of the calculations for two-and three-nucleon forces and their applications in few-nucleon systems. I also address issues like the quark mass dependence of the nuclear forces and resonance saturation for fournucleon operators.