arXiv subjects

W. Plessas

Publications and source records attributed to W. Plessas.

At least 37 records · Page 2Linked to original sources

arXiv2004

Extended Goldstone-Boson-Exchange Constituent Quark Model

We present an extension of the Goldstone-boson-exchange constituent quark model including additional interactions beyond the ones used hitherto. For the hyperfine interaction between the constituent quarks we assume pseudoscalar, vector, and scalar meson exchanges and consider all relevant force components produced by these types of exchanges. The resulting model, which corresponds to a relativistic Poincare-invariant Hamiltonian (or equivalently mass operator), provides a unified framework for a covariant description of all light and strange baryons. The ground states and resonances up to an excitation energy of about 2 GeV are reproduced in fair agreement with phenomenology, with the exception of the first excitations above the Lambda and Xi ground states.

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arXiv2004

Strong Decays of Baryons

A Poincare-invariant description of mesonic baryon resonance decays is presented following the point form of relativistic quantum mechanics. In this contribution we focus on pionic decay modes. It is found that the theoretical results in general underestimate the experimental ones considerably. Furthermore, the problem of a nontrivial normalization factor appearing in the definition of the decay operator is investigated. The present results for decay widths suggest a normalization factor that is consistent with the choice adopted for the current operator in the studies of electroweak nucleon form factors.

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arXiv2004

Point-Form Approach to Baryon Structure

A critical discussion is given of the results for baryon electromagnetic and axial form factors obtained from relativistic constituent quark models in the framework of Poincaré-invariant quantum mechanics. The primary emphasis lies on the point-form approach. First we summarize the predictions of the Goldstone-boson-exchange constituent quark model for the electroweak nucleon structure when using a spectator-model current in point form. Then the influences of different dynamics inherent in various kinds of constituent quark models (Goldstone-boson-exchange, one-gluon-exchange, instanton-induced interactions) are discussed. Finally the point-form results are compared to analogous predictions calculated in instant form. Relativistic effects are always of sizeable magnitude. A nonrelativistic approach is ruled out. The instant-form results are afflicted with severe shortcomings. In the spectator-model approximation for the current, only the point-form results appear to be reasonable a-priori. In fact, the corresponding quark model predictions provide a surprisingly good description of all elastic electroweak observables in close agreement with existing experimental data, specifically for the Goldstone-boson-exchange constituent quark model.

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arXiv2004

Covariant baryon charge radii and magnetic moments in a chiral constituent quark model

The charge radii and magnetic moments of all the light and strange baryons are investigated within the framework of a constituent quark model based on Goldstone-boson-exchange dynamics. Following the point-form approach to relativistic quantum mechanics, the calculations are performed in a manifestly covariant manner. Relativistic (boost) effects have a sizeable influence on the results. The direct predictions of the constituent quark model are found to fall remarkably close to the available experimental data.

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arXiv2004

Strong Decays of N and Delta Resonances in the Point-Form Formalism

We present covariant predictions of relativistic constituent quark models for pi and eta decay widths of N and Delta resonances. The results are calculated for a model decay operator within the point-form spectator approximation. It is found that most theoretical values underestimate the experimental data considerably.

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arXiv2003

Baryons as Relativistic Three-Quark Systems

We discuss some recent developments in the description of baryons as three-quark systems within relativistic constituent quark models. In particular we address the issues of excitation spectra, electroweak structure, and mesonic resonance decays. The necessities of implementing simultaneously the symmetries of low-energy quantum chromodynamics and of relativistic invariance are emphasized.

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arXiv2002

Nucleon electromagnetic and axial form factors in point-form relativistic quantum mechanics

Results for the proton and neutron electric and magnetic form factors as well as the nucleon axial form factor are presented for constituent quark models, based on either one-gluon-exchange and Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The only input to the calculations is the nucleon wave function of the corresponding constituent quark model. A comparison is given to results of the instanton-induced constituent quark model treated with the Bethe-Salpeter equation.

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arXiv2002

Relativistic Study of Mesonic Baryon Resonance Decays

Mesonic baryon resonance decays are calculated from constituent quark models along a Poincaré-invariant generalization of the elementary emission model. Covariant results of pionic decay widths are presented for the Goldstone-boson-exchange constituent quark model.

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arXiv2002

Electroweak properties of the nucleon in a chiral constituent quark model

Results for all elastic electroweak nucleon form factors are presented for the chiral constituent quark model based on Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The direct predictions of the model yield a remarkably consistent picture of the electroweak nucleon structure.

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arXiv2001

Covariant electroweak nucleon form factors in a chiral constituent quark model

Results for the proton and neutron electric and magnetic form factors as well asthe nucleon axial and induced pseudoscalar form factors are presented for the chiral constituent quark model based on Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The direct predictions of the model yield a remarkably consistent picture of the electroweak nucleon structure.

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arXiv2001

Covariant axial form factor of the nucleon in a chiral constituent quark model

The axial form factor G_A of the nucleon is investigated for the Goldstone-boson-exchange constituent quark model using the point-form approach to relativistic quantum mechanics. The results, being covariant, show large contributions from relativistic boost effects. The predictions are obtained directly from the quark-model wave functions, without any further input such as vertex or constituent-quark form factors, and fall remarkably close to the available experimental data.

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arXiv2001

Electroweak properties of baryons in a covariant chiral quark model

The proton and neutron electromagnetic form factors and the nucleon axial form factor have been calculated in the Goldstone-boson exchange constituent-quark model within the point-form approach to relativistic quantum mechanics. The results, obtained without any adjustable parameter nor quark form factors, are, due to the dramatic effects of the boost required by the covariant treatment, in striking agreement with the data.

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arXiv2000

Hadronic Decays of N and ΔResonances in a Chiral Quark Model

πand ηdecay modes of light baryon resonances are investigated within a chiral quark model whose hyperfine interaction is based on Goldstone-boson exchange. For the decay mechanism a modified version of the 3P0 model is employed. Our primary aim is to provide a further test of the recently proposed Goldstone-boson-exchange constituent quark model. We compare the predictions for πand ηdecay widths with experiment and also with results from a traditional one-gluon-exchange constituent quark model. The differences between nonrelativistic and semirelativistic versions of the constituent quark models are outlined. We also discuss the sensitivity of the results on the parametrization of the meson wave function entering the 3P0 model.

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arXiv2000

Covariant nucleon electromagnetic form factors from the Goldstone-boson-exchange quark model

We present a study of proton and neutron electromagnetic form factors for the recently proposed Goldstone-boson-exchange constituent quark model. Results for charge radii, magnetic moments, and electric as well as magnetic form factors are reported. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. All the predictions by the Goldstone-boson-exchange constituent quark model are found in remarkably good agreement with existing experimental data.

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arXiv2000

Faddeev approach to confined three-quark problems

We propose a method that allows for the efficient solution of the three-body Faddeev equations in the presence of infinitely rising confinement interactions. Such a method is useful in calculations of nonrelativistic and especially semirelativistic constituent quark models. The convergence of the partial wave series is accelerated and possible spurious contributions in the Faddeev components are avoided. We demonstrate how the method works with the example of the Goldstone-boson-exchange chiral quark model for baryons.

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arXiv1997

Unified description of light- and strange-baryon spectra

We present a chiral constituent quark model for light and strange baryons providing a unified description of their ground states and excitation spectra. The model relies on constituent quarks and Goldstone bosons arising as effective degrees of freedom of low-energy QCD from the spontaneous breaking of chiral symmetry. The spectra of the three-quark systems are obtained from a precise variational solution of the Schrödinger equation with a semirelativistic Hamiltonian. The theoretical predictions are found in close agreement with experiment.

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arXiv1997

Effective Q-Q Interactions in Constituent Quark Models

We study the performance of some recent potential models suggested as effective interactions between constituent quarks. In particular, we address constituent quark models for baryons with hybrid Q-Q interactions stemming from one-gluon plus meson exchanges. Upon recalculating two of such models we find them to fail in describing the N and Δspectra. Our calculations are based on accurate solutions of the three-quark systems in both a variational Schrödinger and a rigorous Faddeev approach. It is argued that hybrid {Q-Q} interactions encounter difficulties in describing baryon spectra due to the specific contributions from one-gluon and pion exchanges together. In contrast, a chiral constituent quark model with a Q-Q interaction solely derived from Goldstone-boson exchange is capable of providing a unified description of both the N and Δspectra in good agreement with phenomenology.

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arXiv1996

Coulomb-Sturmian separable expansion approach: Three-body Faddeev calculations for Coulomb-like interactions

We demonstrate the feasibility and efficiency of the Coulomb-Sturmian separable expansion method for generating accurate solutions of the Faddeev equations. Results obtained with this method are reported for several benchmark cases of bosonic and fermionic three-body systems. Correct bound-state results in agreement with the ones established in the literature are achieved for short-range interactions. We outline the formalism for the treatment of three-body Coulomb systems and present a bound-state calculation for a three-boson system interacting via Coulomb plus short-range forces. The corresponding result is in good agreement with the answer from a recent stochastic-variational-method calculation.

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