Quark-diquark approximation of the three-quark structure of baryons in the quark confinement model

Octet (1/2⁺) and decuplet (3/2⁺) baryons as relativistic three-quark states are investigated using the quark confinement model (QCM), the relativistic quark model, based on some assumptions about hadronization and quark confinement. The quark-diquark approximation of the three-quark, structure of baryons is proposed. In the framework of this approach, the main low-energy characteristics of baryons, such as magnetic moments, electromagnetic radii and form factors, the ratio of axial and vector constants in semileptonic baryon decays, strong form factors and decay widths, are described. The obtained results agree with experimental data.     

Baryon properties in the relativistic quark model

Properties of heavy and strange baryons are investigated in the framework of the relativistic quark-diquark picture. It is based on the relativistic quark model of hadrons, which was previously successfully applied for the calculation of meson properties. It is assumed that two quarks in a baryon form a diquark and baryon is considered as the bound quark-diquark system. The relativistic effects and diquark internal structure are consistently taken into account. Calculations are performed up to rather high orbital and radial excitations of heavy and strange baryons. On this basis the Regge trajectories are constructed. The rates of semileptonic decays of heavy baryons are calculated. The obtained results agree well with available experimental data.     

Heavy to light baryon weak form factors in the lightcone constituent quark model

Heavy to light baryon weak form factors are investigated in a lightcone constituent quark model. In a SU(4) symmetry broken scheme, both charged and neutral weak current-induced form factors are calculated at theq ² = 0 point including the leading relativistic effects in the spin composition of baryons. The corresponding semileptonic decays are described by assuming dipole dependence of form factors onq ².     

Form factors for exotic baryons of isospin <Emphasis Type="Italic">I</Emphasis> = 5/2

Electric form factors for exotic baryons are calculated within the relativistic quark model in the region of low and intermediate momentum transfers, Q ² ≤ 1 GeV². The charge radii of E ⁺⁺⁺ baryons are determined.     

Spectroscopy of Baryons as Relativistic Three-Quark Systems

We present results from a study of baryon spectral properties within a relativistic constituent-quark model. In particular, we demonstrate the performance of a universal quark model for all light-, strange-, and heavy-flavor baryons with regard to their spectroscopy. Thereby we produce insights into the effective interaction between constituent quarks of the various flavors up, down, strange, charm, and bottom. The relativistically invariant mass spectra are obtained by two different methods for calculating the microscopic three-quark systems: a stochastic variational method, solving the eigenvalue problem of the invariant mass operator expressed by differential equations, and a Faddeev integral-equation method, adapted to treating long-range interactions, such as the quark confinement. The corresponding results agree very well, generally within a few percents. Taking into account relativistic effects through Poincaré invariance of the mass operator, or equivalently of the Hamiltonian, turns out to be of utmost importance.     

Predictions for semileptonic decay rates of charmed baryons in the quark confinement model

Baryons as relativistic three-quark states are investigated in the quark confinement model (QCM), a relativistic quark model based on some assumptions about hadronization and quark confinement. In the framework of the quark-diquark approximation of the three-quark structure of baryons, the main characteristics of light (noncharmed) baryons are calculated. The obtained results agree with experimental data. Predictions are also given for semileptonic decay of charmed baryons and differential production cross-sections in quasielastic neutrino scattering of charmed baryons.     

Electromagnetic and Axial Form Factors of Octet and Decuplet Baryons

We report from a study of the elastic electromagnetic and axial form factors of all lowest baryon states with flavors up, down, and strange along relativistic constituent-quark models. We consider the baryons as relativistic bound states of three constituent quarks and solve the eigenvalue problem of the invariant mass operator. The corresponding eigenstates are employed to calculate manifestly covariant form factors within the point form of Poincaré-invariant quantum mechanics. The electromagnetic and axial current operators are constructed along the spectator model in point-form relativistic dynamics. We have thus obtained covariant predictions for the electroweak form factors, for momentum transfers up to Q ² ~ 4 GeV², as well as the electric radii, magnetic moments, and axial charges. The theoretical results in general agree very well with existing phenomenological data. In cases, where no experimental information is yet available, the results are well compatible with data from lattice quantum chromodynamics.     

The nuclear Coulomb sum rule in a relativistic model

The nuclear Coulomb sum rule is investigated in a relativistic quantum field theory of the nucleus based on baryons and mesons. First an effective, local, covariant, conserved electromagnetic current operator is constructed for the many-baryon system. It describes the electromagnetic structure of an isolated nucleon; the lowest-mass two-pion contribution to the spectral weight functions of the form factors is contained in it. The sum rule is then evaluated in a model based on baryons and neutral scalar and vector mesons. In the mean-field approximation (MFT) this model correctly describes the saturation properties of nuclear matter. The “one-body” term in the sum rule can be evaluated exactly through the use of the canonical anticommutation relations for the baryon field and the identification of conserved quantities. The remaining relativistic two-body contribution is evaluated in the MFT. Meson contributions to the sum rule at large momentum transfers $\text{q}\text{2k}{}_{\mathrm{<mtext>F</mtext>}}\text{? 1}$ completely dominate anticipated static, short-range, two-nucleon correlation contributions to the non-relativistic Coulomb sum rule. One possible implication is that the nucleus must (at least) be considered as a dynamic system of mesons and baryons.     

Kaon production at finite temperature and baryon density in an effective relativistic mean field model

We investigate the kaon production at finite temperature and baryon density by means of an effective relativistic mean-field model with the inclusion of the full octet of baryons. Kaons are considered taking into account of an effective chemical potential depending on the self-consistent interaction between baryons. The obtained results are compared with a minimal coupling scheme, calculated for different values of the anti-kaon optical potential.     

Calculations of electromagnetic nucleon form factors and electroexcitation amplitudes of isobars

In this paper, we present numerical results for electroproduction amplitudes of proton resonances and electromagnetic nucleon form factors calculated in a relativized quark model. Interactions with both transversely and longitudinally polarized virtual photons were considered. Contributions of the different effects included in our approach have been analysed through a sample comparison with the available data. We also discuss the validity of the usual single-quark transition ansatz and possible parametrizations of the potential acting between the constituent quarks of the baryon. Impressive agreement is obtained with the nucleon form factor data up to squared momentum transfers of 2.5 GeV², but still some problems remain with the Δ(1232) and higher resonances.     

Relativistic effects in the processes of heavy-quark fragmentation to double-heavy baryons

In the framework based on the quasipotential method and relativistic quark model, we investigate the heavy-quark fragmentation into double-heavy baryons with spin J = 1/2, 3/2. Adopting a two-step scenario for the fragmentation, we take into account relativistic corrections to the fragmentation probabilities at both stages of the production process for the double-heavy diquark and double-heavy baryon, correspondingly. We take into account all possible relativistic corrections including the terms connected with the transformation law of the bound-state wave function to the reference frame of the moving bound state. The text was submitted by the author in English.     

Nucleon structure in the perturbative chiral quark model

We give an overview of recent applications of the perturbative chiral quark model (PCQM) in the analysis of the structure of the nucleon. The PCQM is based on an effective Lagrangian, where baryons are described by relativistic valence quarks and a perturbative cloud of Goldstone bosons as required by chiral symmetry. We discuss applications to the electromagnetic properties of the nucleon, to σ-term physics, to πN scattering including radiative corrections and to the strange form factors of the nucleon.     

Relativistic Faddeev description of baryons and nucleon structure function in the NJL model

In this work we use the Nambu-Jona-Lasinio (NJL) model as an effective quark theory based on QCD to describe the structure of baryons. Based on the solutions of the relativistic 3-quark Faddeev equation in the ladder approximation, we discuss the masses of the nucleon and the delta, the static properties of the nucleon, and the quark light cone momentum distributions in the nucleon.     

A (p/E) calculation of strong pionic decays of baryons

Strong pionic decays of baryons are studied in a non—relativistic quark model framework via a convergent (p/E) expansion of the transition operator. Results are compared to the ones obtained within a more conventional (p/m) expansion.     

Equilibration in intermediate-energy heavy-ion collisions within a relativistic mean-field two-fluid model

A two-fluid model with meanσ- andω-fields is formulated for the treatment of heavy-ion collisions at incident energies around 1 GeV/u. In this energy range Fermi and Bose statistics for baryons and pions, respectively, cannot be replaced by Boltzmann statistics. The collisional coupling between the two fluids is formulated in terms of the effective nucleon-nucleon cross-sections in nuclear medium taking Pauli blocking into account. For two counterstreaming nuclear fluids the comparison of results obtained from our relativistic mean-field two-fluid model (RMF-TFM) and the relativistic Landau-Vlasov equation shows good agreement in the gross properties of the equilibration process.