Dynamical Quark Model Research Articles

Λ/Λ¯ polarization and splitting induced by rotation and magnetic field

The global polarization of $\Lambda/{\bar \Lambda}$ and the splitting of ${\bar \Lambda}-\Lambda$ polarization induced by rotation and magnetic field has been investigated in a dynamical quark model by taking into account the axial vector interaction and the anomalous magnetic moment of quarks. It is found that the rotation leads to the spin polarization of quarks and anti-quarks with the same sign, while the magnetic field to opposite sign, which corresponds to the ${\bar \Lambda}-\Lambda$ polarization splitting. The combination of the two effects leads to perfect agreement with experiment data. Quantitatively, the axial vector spin polarization contributes 30$\%$ of the global polarization and the anomalous magnetic moment of quarks contributes 40$\%$ to the splitting of ${\bar \Lambda}-\Lambda$ polarization. However, at $\sqrt{s_{NN}} \leq 7.7 \text{GeV}$, it still remains a challenge to reach enough magnitude of the magnetic field at freeze-out.

Confinement and Chiral-Symmetry Breaking in the Covariant Spectator Theory

We show that in the framework of the covariant spectator theory (CST), the equations for the quark anti-quark bound state and for the quark mass function satisfy the requirement of chiral symmetry, incorporating spontaneous chiral symmetry breaking. We then present the results for the pion electromagnetic form factor obtained within a dynamical quark model formulated in Minkowski space and based on the CST.

Minimal Ward—Takahashi Vertices and Light Cone Pion Distribution Amplitudes from the GND Quark Model

The gauge-invariant, nonlocal, dynamical quark model is shown to generate minimal vertices that satisfy the Ward—Takahashi identities and the flat-like form of the light-cone pion distribution amplitudes. Non-flat form amplitudes can be produced only if we take a finite momentum cutoff and include nonzero pion mass corrections or go beyond the minimal vertices. A by-product of our investigation shows that the variable u appearing in light-cone pion distribution amplitudes is just the standard Feynman parameter in the Feynman parameter integrals.

Dynamical heavy-quark recombination and the nonphotonic single-electron puzzle at energies available at the BNL Relativistic Heavy Ion Collider (RHIC)

We show that the single, nonphotonic electron nuclear modification factor ${R}_{\mathit{AA}}^{e}$ is affected by the thermal enhancement of the heavy-baryon-to-heavy-meson ratio in relativistic heavy-ion collisions with respect to proton-proton collisions. We make use of the dynamical quark recombination model to compute such a ratio and show that this produces a sizable suppression factor for ${R}_{\mathit{AA}}^{e}$ at intermediate transverse momenta. We argue that this suppression factor needs to be considered, in addition to the energy loss contribution, in calculations of ${R}_{\mathit{AA}}^{e}$.

The effect of dynamical parton recombination on event-by-event observables

Within a dynamical quark recombination model, we explore various proposed event-by-event observables sensitive to the microscopic structure of the QCD-matter created at RHIC energies. Charge ratio fluctuations, charge transfer fluctuations and baryon-strangeness correlations are computed from a sample of central Au + Au events at the highest RHIC energy available (sNN=200 GeV). We find that for all explored observables, the calculations yield the values predicted for a quark–gluon plasma only at early times of the evolution, whereas the final state approaches the values expected for a hadronic gas. We argue that the recombination-like hadronization process itself is responsible for the disappearance of the predicted deconfinement signals. This might explain why no fluctuation signatures for the transition between quark and hadronic matter was ever observed in the experimental data up to now.

Dynamical study ofQQ–u¯d¯mesons

It has been recently conjectured by Selem and Wilczek 1 the existence of a ss-[ud] meson due to strong correlations between the two light antiquarks. We make a detailed study of this system within a dynamical quark model which has proven to be successful in reproducing the most important features of low-energy hadron phenomenology. Our results, obtained within a parameter-free calculation, show that the antidiquark component of the ssud system indeed entails the stronger attraction, and drives its energy much lower than the N{xi} threshold, but still above the K{sup 0}K*{sup -} or K*{sup 0}K{sup -} thresholds. We have also studied the ccud and bbud systems. Exotic mesons are only expected to exist in the limit of large mass for the two-quark subsystem, bbud, since the calculated mass is below the B{sup 0}B*{sup -} or B*{sup 0}B{sup -} thresholds.

NUCLEON SPIN AND ITS GAUGE INVARIANCE AND CANONICAL COMMUTATION RELATION

The nucleon spin structure has been shown to be described by a dynamical constituent quark model with ~85% q3 and [Formula: see text] Fock components. As a QCD system there is no gauge invariance and canonical commutation relation simultaneously satisfied decomposition of the nucleon spin operator. To keep gauge invariance but give up the canonical commutation relation of the angular momentum operator will ruin the multiple moments expansion and the partial wave decomposition. A weak gauge invariant condition is proposed where the canonical commutation relation of angular momentum operator is intact and the gauge invariance is only true for special sets of matrix elements instead of the operators.

Do Nuclei Possess Crystal–Like Structure?

A dynamical quark model of hadron and nucleus structure is proposed. It is shown in the framework of the model, called the Strongly Correlated Quark Model, that quarks and nucleons inside nuclei are arranged in crystal–like structure.

Anomalous action in gauge invariant, nonlocal, dynamical quark model

Anomalous sector of chiral Lagrangian is calculated in a gauge invariant, nonlocal, dynamical quark model. The Wess–Zumino term is proved coming from two kinds of sources, one is independent of and another dependent on dynamical quark self energy Σ(k2). p6 and more higher order anomalous sectors come only from Σ(k2) dependent source. After some cancellation, standard Wess–Zumino action is obtained.

Chiral Lagrangian from gauge invariant, nonlocal, dynamical quark model

Parameters of Gasser–Leutwyler chiral Lagrangian are proved saturated by dynamical quark self energy Σ ( k 2 ) in a gauge invariant, nonlocal, dynamical quark model.

Heavy hybrids with constituent gluons

Hybrid meson energies are calculated in the static quark limit with the Dynamical Quark Model (DQM). In the DQM, transverse gluons are represented as effective constituents with a dynamically generated mass. Hybrid masses are determined within the Tamm-Dancoff approximation for the resulting relativistic Salpeter equation. Although the general features of the adiabatic potential surfaces correspond with lattice data, the results disagree on level orderings. Similar problems appear to exist in all constituent glue models of hybrids. We conclude that constituent gluons do not accurately represent soft gluonic degrees of freedom.

Heavy hybrids with constituent gluons

Hybrid meson energies are calculated in the static quark limit with the Dynamical Quark Model (DQM). In the DQM, transverse gluons are represented as effective constituents with a dynamically generated mass. Hybrid masses are determined within the Tamm-Dancoff approximation for the resulting relativistic Salpeter equation. Although the general features of the adiabatic potential surfaces correspond with lattice data, the results disagree on level orderings. Similar problems appear to exist in all constituent glue models of hybrids. We conclude that constituent gluons do not accurately represent soft gluonic degrees of freedom. The steps necessary to correct this deficiency are discussed.

ON THE POSSIBILITY OF LOW MASS QUARK DROPLET STARS

The possibility of stable quark-droplet stars is investigated using dynamical density dependent quark mass model of confinement. Some of its gross properties has also been studied.

POSSIBILITY OF STRANGELETS IN NEUTRON MATTER

Using dynamical density dependent quark mass model of confinement the possibility of a composite phase of strangelets embedded in neutron matter is investigated. This particular phase is shown to be the absolute ground state of matter at the low density regime.

A note on the quadrupole (N → Δ) transition amplitude in quark models

Due to the usual strong truncation of the basis in dynamical quark model calculations, the charge-current operator for the quadrupole (N→ Δ) transition violates gauge invariance. It is demonstrated explicitly for the nonrelativistic constituent quark model that, in the standard 2ℏ ω-basis, calculations of the quadrupole transition form factor differ by an order of magnitude, depending on whether one uses the charge or current for the evaluation. Since this effect is related to the behaviour of the two operators under hermitean conjugation and time reversal, it is expected to be of importance also for other wavefunctions as well as in relativistic models.

Gluon-Exchange Contributions to Nonleptonic Hyperon Decays

Recently, it has been demonstrated by Itoh et al. 1) that the inequality of relative distances between quarks in a baryon plays a significant role in the electromagnetic mass differences (EMMD) of 1/2+ baryons and 0mesons. It has been argued that the effect of the spin-spin interactions in altering the relative spatial distribution of quarks in a baryon must be considered in a dynamical quark model. This produces a nice fit for the experimentally observed EMMD's and results in a negative value for neutron's charge-radius. In this paper, we extend the above considerations (i.e., consider a spatially dependent spin-spin interactions) to the nonleptonic hyperon decays and calculate one gluon-exchange effects. Since the spin-spin force is repulsive between quarks with parallel spins and attractive between quarks with anti-parallel spins, the quark pairs in a spin-1 state will be, on the average, farther apart than those in spin-O state. We assume that baryon-wavefunctions are gaussian and depend upon the different interquark distances. The basic interaction between quarks is taken to be of Fermi-Breit type.!),2) It is known 3 ) that in the current-current picture of weak Hamiltonian with (V ~ A) charged currents, the quark-quark scattering

The spectra and decays of radial excitations in a dynamical quark model

By re-identifying some of the vector meson states which have been recently observed coupling to e+e-, the authors show that in all flavour sectors the spectra of radial excitations can be well described by a Klein-Gordon-type wave equation employing a simple, linear qq potential. The wavefunctions obtained by solving the equation are coupled with quark-pair creation hypothesis to predict a number of hadronic branching ratios of the light-quark, radially excited states. The suppression of large phase-space decays of the excited states is understood.

Quark dynamics and strong meson decays

The strong decays of meson resonances are treated in a dynamical quark model. The model is formulated in the framework of general field theory and therefore all calculations are fully relativistic covariant. Spectrum and wave functions are derived from a Bethe-Salpeter equation describing the binding of heavy quarks by a smooth, very strong interaction. The mesonic vertices are calculated with help of these BS amplitudes in triangle graph approximation, thereby guaranteeing a symmetric treatment of all mesons involved in the process. A particular spin dependence of the interaction has the consequence that the super-strong quark binding forces lead to mesonic forces of moderate strength only (saturation of quark forces!). The applications refer to the decays of vector mesons, tensor mesons, scalar mesons into pseudoscalars and vectors and are extended to resonances in the R region. In particular, we include the decays into two pions of the radial excited ϱ′(1600). The helicity structure of the decays of the axial vector meson is discussed.

Dynamical Model of Hadrons with Fermion Quarks

A dynamical quark model of hadrons is constructed in terms of the usual triplet of fractionally charged spin-\textonehalf{} quarks ($q$). They have a light mass ($\ensuremath{\approx}300$ MeV) and obey Fermi-Dirac statistics. In approximate nonrelativistic terms, the quark interactions are assumed to be described by a long-range effective single-particle Hartree potential with infinitely rising walls and by a strong short-range Yukawa-type one between quark pairs. These combine to prevent single-quark emission from a hadron and to give the observed early scaling and the asymptotic electromagnetic form factors $\ensuremath{\sim}\frac{1}{{t}^{2}}$. The energy-momentum propagating in the field between the interacting quarks is idealized as a virtual particle (the "core" of the baryon) so that the center of mass of the three quarks in the baryon and of the $q\overline{q}$ in the meson is not constrained. Implications of this model are discussed---in particular, the baryon wave functions and energy spectrum, the form-factor behavior, the Adler anomaly for ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}2\ensuremath{\gamma}$ decay, and the hadronic interactions.

A quark model and soft-pion emission in leptonic decay of mesons

It is shown that a simple dynamical quark model based on the lowest order perturbation theory reproduces the results of the current algebra. PCAC-technique for the leptonic decays of mesons