The Nucleon-Nucleon Interaction in a Chiral Constituent Quark Model

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.Comment: 31 pages, LaTe

Short--range impurity in the vicinity of a saddle point and the levitation of the 2D delocalized states in a magnetic field

The effect of a short--range impurity on the transmission through a saddle--point potential for an electron, moving in a strong magnetic field, is studied. It is demonstrated that for a random position of an impurity and random sign of its potential the impurity--induced mixing of the Landau levels diminishes {\em on average} the transmission coefficient. This results in an upward shift (levitation) of the energy position of the delocalized state in a smooth potential. The magnitude of the shift is estimated. It increases with decreasing magnetic field $B$ as $B^{-4}$.Comment: LaTeX, 20 page

The baryonic Y-shape confining potential energy and its approximants

We discuss the validity of replacing the complicated three-body confinement operator of the Y string junction type by three kinds of approximation which are numerically much simpler to handle: a one-body operator with the junction point at the centre of mass, a two-body operator corresponding to half the perimeter of the triangle formed by the three particles, and the average of both. Two different approaches for testing the quality of the approximations are proposed: a geometrical treatment based on the comparison of the potential energy strengths for the various inter quark distances, and a dynamical treatment based on the comparison of the corresponding effective string tensions using a hyperspherical approach. Both procedures give very similar results. It is shown how to simulate the genuine string junction operator by the approximations proposed above. Exact three-body calculations are presented in order to compare quantitatively the various approximations and to confirm our analysis.Comment: 28 pages, 5 figures, submitted to EPJ

Diquark Masses from Lattice QCD

We present first results for diquark correlation functions calculated in Landau gauge on the lattice. Masses have been extracted from the long distance behaviour of these correlation functions. We find that the ordering of diquark masses with spin 0 and 1 states in colour anti-triplet and sextet channels is in accordance with instanton motivated interaction models. Although we find evidence for an attractive interaction in colour anti-triplet states with a splitting between spin 0 and spin 1 diquarks that can account for the mass splitting between the nucleon and the delta, there is no evidence for a deeply bound diquark state.Comment: 12 pages, LaTeX2e uses revtex, 3 EPS-figures, small corrections, references update

Relativistic quark model and pentaquark spectroscopy

The relativistic five-quark equations are found in the framework of the dispersion relation technique. The solutions of these equations using the method based on the extraction of leading singularities of the amplitudes are obtained. The five-quark amplitudes for the low-lying pentaquarks are calculated under the condition that flavor SU(3) symmetry holds. The poles of five-quark amplitudes determine the masses of the lowest pentaquarks. The mass spectra of pentaquarks which contain only light quarks are calculated. The calculation of pentaquark amplitudes estimates the contributions of three subamplitudes. The main contributions to the pentaquark amplitude are determined by the subamplitudes, which include the meson states.Comment: 22 pages, pd

Effects of perturbative exchanges in a QCD-string model

The QCD-string model for baryons derived by Simonov and used for the calculation of baryon magnetic moments in a previous paper is extended to include also perturbative gluon and meson exchanges. The mass spectrum of the baryon multiplet is studied. For the meson interaction either the pseudoscalar or pseudovector coupling is used. Predictions are compared with the experimental data. Besides these exchanges the influence of excited quark orbitals on the baryon ground state are considered by performing a multichannel calculation. The nucleon-Delta splitting increases due to the mixing of higher quark states while the baryon magnetic momenta decrease. The multichannel calculation with perturbative exchanges is shown to yield reasonable magnetic moments while the mass spectrum is close to experiment.Comment: 37 pages Revtex with 2 figures, to be published in Phys. Atom. Nucl. dedicated to the 70th Birthday of Yu. A. Simono

Phenomenological study of hadron interaction models

We present a phenomenological study of three models with different effective degrees of freedom: a Goldstone Boson Exchange (GBE) model which is based on quark-meson couplings, the quark delocalization, color screening model (QDCSM) which is based on quark-gluon couplings with delocalized quark wavefunctions, and the Fujiwara-Nijmegen (FN) mixed model which includes both quark-meson and quark-gluon couplings. We find that for roughly two-thirds of 64 states consisting of pairs of octet and decuplet baryons, the three models predict similar effective baryon-baryon interactions. This suggests that the three very different models, based on different effective degrees of freedom, are nonetheless all compatible with respect to baryon spectra and baryon-baryon interactions. We also discuss the differences between the three models and their separate characteristics.Comment: 30 pages latex, 7 tables, 12 figs; submitted to Phys. Rev.

Baryon Structure and the Chiral Symmetry of QCD

Beyond the spontaneous chiral symmetry breaking scale light and strange baryons should be considered as systems of three constituent quarks with an effective confining interaction and a chiral interaction that is mediated by the octet of Goldstone bosons (pseudoscalar mesons) between the constituent quarks.Comment: Lecture given at the 35. Universit\"atswochen f\"ur Kern- und Teilchenphysik, Schladming, Austria, March 1996 (Perturbative and Nonperturbative Aspects of Quantum Field Theory, ed. by H. Latal and W. Schweiger, Springer 1996). Paper (23 pages) with 2 figures and the required macro lamuphy

Magneto-optical evidence of the percolation nature of the metal-insulator transition in the 2D electron system

We compare the results of the transport and time-resolved magneto-luminescence measurements in disordered 2D electron systems in GaAs-AlGaAs heterostructures in the extreme quantum limit, in particular, in the vicinity of the metal-insulator transition (MIT). At filling factors $\nu <1$, the optical signal has two components: the single-rate exponentially decaying part attributed to a uniform liquid and a power-law long-living tail specific to a microscopically inhomogeneous state of electrons. We interprete this result as a separation of the 2D electron system into a liquid and localized phases, especially because the MIT occurs strikingly close to those filling factors where the liquid occupies ${1\over 2}$ of the sample area (the percollation threshold condition in two-component media).Comment: 5 pages RevTex + 4 fig., to appear in PRB, Rapid Com