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The simplest form of the Hyperfine Interaction (HFI) of quarks is a color-spin interaction, sometimes called Fermi-Breit (FB) HFI. For conventional hadrons, this HFI for quark-antiquark (qq̄) pairs is twice as strong as the same HFI for quark-quark (qq or q̄q̄) pairs, but this difference is absorbed into the different HFI constants for mesons and baryons, which are free parameters of the fits. For tetraquarks, however, qq̄ HFI is only half as strong as the qq/q̄q̄ HFI and both kinds of pairs coexist within the same state. Hence it is worth investigating a model with different fit constants for qq̄ and qq/q̄q̄ pairs. We have investigated 3 models of spin-color HFI for light scalar tetraquarks: 2 models with single constants for both kinds of pairs and one model with different fit constants. The light scalar nonet is chosen because of a lack of other experimentally observed multiplets interpretable as pure exotic states. Since even the nonet contains only 3 particles with distinct masses (i. e. 3 fit points), the constituent quark masses had to be taken from conventional hadron fits obtained in our previous work. The two-constant model did not prove to be a viable alternative to the one-constant models. [ABSTRACT FROM AUTHOR]

A Dyson-Schwinger equation calculation of the light hadron spectrum, which correlates the masses of meson and baryon ground- and excited-states within a single framework, produces a description of the Roper resonance that corresponds closely with conclusions drawn recently by EBAC. Namely, the Roper is a particular type of radial excitation of the nucleon's dressed-quark core augmented by a material meson cloud component. There are, in addition, some surprises. [ABSTRACT FROM AUTHOR]

We evaluate the pseudoscalar-meson coupling constants and the strangeness-conserving and the strangeness-changing axial charges of octet baryons in lattice QCD with two flavors of dynamical quarks. We find that the coupling constants and the axial charges have rather weak quark-mass dependence and the breaking in SU(3)-flavor symmetry is small at each quark-mass point we consider. [ABSTRACT FROM AUTHOR]

We discuss the recent progress in calculating the properties of ‘hybrid stars’ (stellar objects similar to neutron stars, classified by the incorporation of non-nucleonic degrees of freedom, including but not limited to hyperons and/or a quark-matter core) using the octet-baryon Quark-Meson Coupling (QMC) model. The version of QMC used is a recent improvement which includes the in-medium modification of the quark-quark hyperfine interaction. [ABSTRACT FROM AUTHOR]

The process of secondary baryon production in π±p collisions at high energies in the central and forward fragmentation regions is considered in the framework of the Quark-Gluon String Model. The contribution of the string-junction mechanism to the baryon production is analysed. The results of numerical calculations are in reasonable agreement with the experimental data on the Λ/A and p/p asymmetries. [ABSTRACT FROM AUTHOR]

In this work, the strong coupling constants of the octet baryons to the K and π mesons are studied within the Light Cone QCD sum rule method. It is well known that in the SU(3)f limit, these couplings can be expressed in terms of only 2 constants, so called F and D constants. In this work, the SU(3)f symmetry violating effects are also studied and it is shown that all the coupling constants can be expressed in terms of four analytical functions of the quark parameters. [ABSTRACT FROM AUTHOR]

We study the mass spectrum of baryons with two and three charmed quarks. For double charm baryons the spin splitting is found to be smaller than standard quark-model potential predictions. This splitting is not influenced either by the particular form of the confining potential or by the regularization taken for the contact term of the spin-spin potential. We consistently predict the spectra for triply charmed baryons. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

After referring to some basic features of chiral models for baryons, with quarks and mesons, we describe how to construct model states representing physical baryons. We consider soliton models such as the Linear Sigma Model or the Chromodielectric Model, and bag models such as the Cloudy Bag Model. These models are solved approximately using variational approaches whose starting point is a mean-field description. We go beyond the mean-field description by introducing quantum fluctuations in the mesonic degrees of freedom. This is achieved, in a first step, by using a quantum state to represent meson clouds and, secondly, by performing an angular momentum and isospin projection from the mean-field state (actually a coherent state). Model states for baryons (nucleon, Delta, Roper) constructed in this way are used to determine several physical properties. I this seminar we paid a particular attention to the nucleon-delta electromagnetic and weak transition, presenting the model predictions for the electromagnetic and axial amplitudes. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

By comparing SU (3)-breaking scales of linear mass formulae, it is shown that the lowest vector, axial-vector, and scalar mesons all have a qq configuration, while the ground-state octet and decuplet baryons are qqq. Also, the quark-level linear σ model is employed to predict similar qq and qqq states. Finally, the approximate mass degeneracy of the scalar a0(980) and f0(980) mesons is demonstrated to be accidental. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

We compute magnetic moments of baryons with a heavy quark in the bound state approach for heavy baryons. In this approach the heavy baryon is considered as a heavy meson bound to a light baryon. The latter is represented as a soliton excitation of light meson fields. We obtain the magnetic moments by sandwiching pertinent components of the electromagnetic current operator between the bound state wave-functions. We extract this current operator from the coupling to the photon field after extending the action to be gauge invariant. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

The I=1 and I=0 kaon-nucleon s, p, d, f, g-waves phase shifts have been calculated in a non relativistic quark potential model using the resonating group method (RGM). The interquark potential includes gluon exchanges with a spin-orbit interaction. This force was determined to reproduce as well as possible the meson and baryon spectra. The same force is employed for the cluster and intercluster dynamics and the relative KN wave function is calculated without any approximation. While some channels are correctly described, the theory is still unable to explain others. [ABSTRACT FROM AUTHOR]

Progress in computing the spectrum of excited baryons and mesons in lattice QCD is described. Large sets of spatially-extended hadron operators are used. The need for multi-hadron operators in addition to single-hadron operators is emphasized, necessitating the use of a new stochastic treatment of the low-lying modes of quark propagation which exploits Laplacian Heaviside quark-field smearing. A new glueball operator is tested and computing the mixing of this glueball operator with a quark-antiquark operator and multiple two-pion operators is shown to be feasible. [ABSTRACT FROM AUTHOR]