Interplay of quark and meson degrees of freedom in a near-threshold resonance

We investigate the interplay of quark and meson degrees of freedom in a physical state representing a near-threshold resonance for the case of a single continuum channel. We demonstrate that such a near-threshold resonance may possess quite peculiar properties if both quark and meson dynamics generate weakly coupled near-threshold poles in the S -matrix. In particular, the scattering t -matrix may possess zeros in this case. We also discuss possible implications for production reactions as well as studies within lattice QCD.     

Interplay of quark and meson degrees of freedom in a near-threshold resonance: Multi-channel case

We investigate the interplay of quark and meson degrees of freedom in a physical state representing a near-threshold resonance for the case of multiple continuum channels. The aim is to demonstrate the full complexity of possible near-threshold phenomena. It turns out that those are especially rich, if both quark and meson dynamics generate simultaneously weakly coupled near-threshold poles in the S-matrix. We study the properties of this scenario in detail, such as t-matrix and production amplitude zeros, as well as various effects of the continuum channels interplay.     

Chiral dynamics with quark degrees of freedom

The possibility to detect DCC fluctuations is discussed. It is shown that interactions with quark background and dissipative effects due to interactions in the chiral field may result in damping of fluctuations. Since the magnitude of fluctuations depends strongly on the initial state and speed of chiral phase transition an accurate evaluation of all modifying processes is required to predict the observability of DCCs.     

Nucleon-nucleon correlations with quark degrees of freedom

A dynamical equation of two nucleons in a nucleus is formulated in the nonrelativistic quark model including Pauli blocking due to the other nucleons. This equation is solved with a model wave function containing the possiblity of six-quark bags with different radii. It is shown that the Pauli blocking effect is emphasized by the non-nucleonic degrees of freedom represented by six-quark bags. The modification of the quark momentum distribution for correlated nucleons is calculated and probabilities of non-NN components in nuclei are estimated.     

Exchange currents arising from quark degrees of freedom

We investigate the effects of antisymmetrization with respect to valence quarks in nuclei introducing “quark exchange currents”. Their effects in ordinary nuclei are found to be small for lack of contribution from s-wave nucleon pairs owing to spin-isospin symmetry. For example, the Gamow-Teller type β-decay matrix elements for A = 15, 17, 39, 41 and ∞ nuclei are reduced from the single-particle values by 2–8% depending on the baryon size. The effects seem to be larger for Σ-hypernuclei. For example, the magnetic moment of Σ+4Li(1+) is reduced by more than 15%. For Λ-hypernuclei, however, the effects on the magnetic moments tend to cancel each other, and about 1% reduction is obtained for 4ΛHe(1+).     

The effect of quark degrees of freedom on nuclear properties

Employing a simplified non-relativistic quark cluster model for deuteron and α-particle, we investigate the effects of quark exchange and modification of nucleon size on nuclear form factors, quark momentum distributions and nucleon quasifree scattering. We find that the size modification affects all the above quantities and that the quark exchange has an appreciable influence on the quasifree scattering.     

Isobaric degrees of freedom in nuclei as determined from nonrelativistic quark model

Isobaric degrees of freedom δδ in nuclei are determined from the quark cluster model of a nucleus. These additional degrees of freedom are brought in by the coloured quark exchange between different nucleon clusters present in nuclei. They are found to be important in the region of momentum transfer near 3.5 fm⁻¹. The mass dependence of these isobaric degrees of freedom in nuclei turns out to beA ^5/6.     

Heavy quark 1/m Q expansion of meson weak decay form factors in the relativistic quark model

The method of systematical expansion in the inverse powers of the heavy quark masses of the weak current matrix elements between heavy meson states is developed in the framework of the relativistic quark model based on the quasipotential approach in quantum field theory. The comparison of the first and second order terms of this expansion with the structure predicted by the heavy quark effective theory imposes strong constraints on the form of the long-range confining potential of quark-antiquark interaction. It is found that the confinig $q\bar q$ potential is effectively vector, while scalar potential is anticonfining and helps to reproduce the correct nonrelativistic limit. At large distances quarks have nonperturbative anomalous chromomagnetic moments. The obtained values of the potential parameters are in accord with the ones found in our previous consideration of meson masses and decay rates. We calculate the Isgur-Wise function. The first and the second order form factors within 1/m _Q expansion.     

Axial quark number and the η meson

We show, in the framework of chiral Lagrangians, that a concept of axial quark number is conveniently used in formulating a departure from a naive quark model of pseudoscalar mesons. Problems of the η are investigated from this point of view.     

Structure functions of the deuteron and meson exchange currents

The deuteron structure functionsA(q ²)B(q ²) and polarization tensorT(q ²) are studied within the Bonn model with meson exchange currents taken into account. It is shown that it is necessary to take all these currents into consideration including the retardation effects. ForA(q ²) the contribution of retardation effects does not depend on the choice of vertex form factors; whereas forB(q ²) it essentially depends on the choice of strong vertices. The best agreement with experiment is achieved for the Bonn relativistic potential.Dedicated to the memory of M. Gmitro.     

Effective meson lagrangian with chiral and heavy quark symmetries from quark flavor dynamics

By bosonization of an extended NJL model we derive an effective meson theory which describes the interplay between chiral symmetry and heavy quark dynamics. This effective theory is worked out in the low-energy regime using the gradient expansion. The resulting effective lagrangian describes strong and weak interactions of heavy B and D mesons with pseudoscalar Goldstone bosons and light vector and axial-vector mesons. Heavy meson weak decay constants, coupling constants and the Isgur-Wise function are predicted in terms of the model parameters partially fixed from the light quark sector. Explicit SU(3)_F symmetry breaking effects are estimated and, if possible, confronted with experiment.     

Form factors and structure functions of hadrons in the non-local quark model

The form factor of dipole type and the structure function with the threshold behaviour (1?x′)³ are derived for the proton in the non-local quark theory where deeply bound quarks are assumed in the relative motion of characteristic harmonic oscillation.