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Register a new userA Baryon Model in Covariant Constraint Dynamics
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An important ingredient of parton or string cascade models for ultrarelativistic heavy-ion reactions is a parton description of the baryon. Whereas previous models needed the concept of a diquark in an essential way, we have developed a new model using Diracs approach of Poincare-covariant many-body dynamics with constraints. In our model, the baryon is described as a dynamical set of three valence quarks and a fourth particle, the junction, which carries the momentum fraction of the sea quarks as well as all of the glue. The models parameters are the quark current masses, and one interaction strength, determined by the proton radius. Thus the model has no adjustable free parameters. Nevertheless, we obtain a remarkably good fit to the valence quark structure functions of the baryon
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We present a calculation of the three-quark core contribution to the mass of the Delta-baryon in a Poincare-covariant Faddeev framework. A consistent setup for the dressed-quark propagator, the quark-quark and quark-diquark interactions is used, where all the ingredients are solutions of their respective Dyson-Schwinger or Bethe-Salpeter equations in rainbow-ladder truncation. We discuss the evolution of the Delta mass with the current-quark mass and compare to the previously obtained mass of the nucleon.
Charm spectroscopy has studied under a string model. Charmed baryons are composed of diquark and charm quark which are connected by a constant tension. In a diquark picture, the quantum numbers $J^P$ of confirmed baryons are well assigned. We give energy predictions for the first and second orbital excitations. We see some correspondences with the experimental data. Meanwhile, we have obtained diquark masses in the background of charm quark which satisfy a splitting relation based on spin-spin interaction.
We solve a nonlocal generalisation of the NJL model in the Hartree approximation. This model has a separable interaction, as suggested by instanton models of the QCD vacuum. The choice of form factor in this interaction is motivated by the confining nature of the vacuum. A conserved axial current is constructed in the chiral limit of the model and the pion properties are shown to satisfy the Gell-Mann--Oakes--Renner relation. For reasonable values of the parameters the model exhibits quark confinement.
The structure of the pion wave function in the relativistic constituent quark model is investigated in the explicitly covariant formulation of light-front dynamics. We calculate the two relativistic components of the pion wave function in a simple one-gluon exchange model and investigate various physical observables: decay constant, charge radius, electromagnetic and transition form factors. We discuss the influence of the full relativistic structure of the pion wave function for an overall good description of all these observables, including both low and high momentum scales.
The covariant spectator formalism is used to model the nucleon and the $Delta$(1232) as a system of three constituent quarks with their own electromagnetic structure. The definition of the ``fixed-axis polarization states for the diquark emitted from the initial state vertex and absorbed into the final state vertex is discussed. The helicity sum over those states is evaluated and seen to be covariant. Using this approach, all four electromagnetic form factors of the nucleon, together with the {it magnetic} form factor, $G_M^*$, for the $gamma N to Delta$ transition, can be described using manifestly covariant nucleon and $Delta$ wave functions with {it zero} orbital angular momentum $L$, but a successful description of $G_M^*$ near $Q^2=0$ requires the addition of a pion cloud term not included in the class of valence quark models considered here. We also show that the pure $S$-wave model gives electric, $G_E^*$, and coulomb, $G^*_C$, transition form factors that are identically zero, showing that these form factors are sensitive to wave function components with $L>0$.
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