Baryon masses in the SU(4) skyrme model

We consider the SU(4) Skyrme model with explicit chiral and flavour symmetry-breaking terms. Using the masses of the 15-plet pseudoscalar mesons as the input, we calculate the masses of the 20-plet baryons. The baryon masses predicted by this model agree with results based on quark model to about 15%. We find that the generalized Gell-Mann Okubo mass relation is very well satisfied.     

Strangeness, charm, and bottom in a chiral quark-meson model

In this paper, we investigate an SU(3) extension of the chiral quark-meson model. The spectra of baryons with strangeness, charm, and bottom are considered within a “rigid oscillator” version of this model. The similarity between the quark sector of the Lagrangian in the model and the Wess-Zumino term in the Skyrme model is noted. The binding energies of baryonic systems with baryon numbers B=2 and 3 possessing strangeness or heavy flavor are also estimated. The results are in good qualitative agreement with those obtained previously in the chiral soliton (Skyrme) model.     

Static properties of nucleons in the Skyrme model

We compute static properties of baryons in an SU(2) × SU(2) chiral theory (the Skyrme model) whose solitons can be interpreted as the baryons of QCD. Our results are generally within about 30% of experimental values. We also derive some relations that hold generally in soliton models of baryons, and therefore, serve as tests of the $\text{1}\text{N}$ expansion.     

Constant-cutoff approach to radiative decays of hyperons: E2/M1 transition ratios

We suggest a quantum stabilization method for theSU(2) σ-model, based on the constant-cutoff limit of the cutoff quantization method developed by Balakrishnaet al., which avoids the difficulties with the usual soliton boundary conditions pointed out by Iwasaki and Ohyama. We investigate the baryon numberB=1 sector of the model and show that after the collective coordinate quantization it admits a stable soliton solution which depends on a single dimensional arbitrary constant. We then study the radiative decays ofJ ^π=3/2⁺ baryons using the constant-cutoff approach to theSU(3) collective treatment of the Skyrme model for hyperons. Thus we evaluate the widths and E2/M1 ratios, showing that there is a general qualitative agreement with the results obtained using the complete Skyrme model, as well as the nonrelativistic quark model and quenched lattice model, for the total widths.     

The Skyrme model,the strong coupling theory and the static quark model

We show that to leading order in the quark number N, the Skyrme model, the strong coupling theory and the static quark model share a common underlying symmetry group.     

Semileptonic decays of baryons in a relativistic quark model

We calculate semileptonic decays of light and heavy baryons in a relativistically covariant constituent quark model. The model is based on the Bethe-Salpeter equation in instantaneous approximation. It generates satisfactory mass spectra for mesons and baryons up to the highest observable energies. Without introducing additional free parameters we compute on this basis helicity amplitudes of electronic and muonic semileptonic decays of baryons. We thus obtain form factor ratios and decay rates in good agreement with experiment.     

Hara's theorem, quark model, and \gamma _5-dependent renormalization constants

We discuss the applicability of -dependent field renormalization as a means of renormalizing away the apparent violation of Hara's theorem observed in the quark model. It is pointed out that a result totally analogous to the violation of Hara's theorem is predicted by the quark model also for neutral baryons. For neutral baryons, however, such a result cannot be renormalized away. This proves that -dependent renormalization does not provide a proper way for a hadron-level understanding of the violation of Hara's theorem observed in the quark model. Received: 12 November 1997 / Revised version: 17 February 1998 Published online: 9 April 1998     

The skyrmion-skyrmion interaction

Using the Skyrme effective lagrangian, baryons emerge as topological solitons. This effective lagrangian is used in adiabatic calculations aimed at providing an essentially parameter-free model of the interaction between such solitons. The resulting skyrmion-skyrmion interaction can be understood as terms simulating the exchange of π-, ρ-, and ω-mesons between the solitons. It is readily transformed (by essentially projective techniques) into a low-energy nucleon-nucleon potential. Comparisons of this potential with the best available semiphenomenological nucleon-nucleon interactions are found to be successful at the 30% level. Similarities between the Skyrme model and the quark chiral-bag model are discussed.     

SU(3) symmetry breaking for masses, magnetic moments and sizes of baryons

We use the SU(3) Skyrme model to investigate the effects of symmetry breaking imposed by different pseudoscalar meson masses on the structure of baryons. Specifically, we calculate their mass splittings, magnetic moments, charge radii, semileptonic decays as well as different strangeness contents of the proton. Since the Skyrme soliton is allowed to deform under the pressure of the symmetry breaking we find significant variations in baryon sizes with respect to strangeness.     

Triply heavy baryons in the constituent quark model

The constituent quark model is used to compute the ground and excited state masses of QQQ baryons containing either c or b quarks.The quark model parameters previously used to describe the properties of charmonium and bottomonium states were used in this analysis.The non-relativistic three-body bound state problem is solved by means of the Gaussian expansion method which provides sufficient accuracy and simplifies the subsequent evaluation of the matrix elements.Several low-lying states with quantum numbers J^P=1/2^±,3/2^±,5/2^±and 7/2^+are reported.We compare the results with those obtained by the other theoretical formalisms.There is a general agreement for the mass of the ground state in each sector of triply heavy baryons.However,the situation is more puzzling for the excited states,and appropriate comments about the most relevant features of our comparison are given.     

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.     

Magnetic moments of the strange baryons in the bag model

We break SU(3) symmetry in the bag model by giving the singlet quark a mass m. The magnetic moment ratios of the strange baryons are calculated and compared with exact SU(6) predictions and with experiment.     

Heavy baryons in the relativistic quark model

In the framework of the relativistic quasipotential quark model the mass spectrum of baryons with two heavy quarks is calculated. The quasipotentials for interactions of two quarks and of a quark with a scalar and axial vector diquark are evaluated. The bound state masses of baryons with are computed.     

Extraction of the pion-nucleon sigma-term from the spectrum of exotic baryons

The pion-nucleon sigma-term is extracted on the basis of the soliton picture of the nucleon from the mass spectrum of usual and the recently observed exotic baryons, assuming that they have positive parity. The value found is consistent with that inferred by means of conventional methods from pion-nucleon scattering data. The study can also be considered as a phenomenological consistency check of the soliton picture of baryons.Received: 6 February 2004, Revised: 3 May 2004, Published online: 12 October 2004PACS: 12.39.Ki Relativistic quark model - 12.38.Lg Other nonperturbative calculations - 14.20.-c Baryons (including antiparticles)     

Pentaquarks: Facts and puzzles

On the occasion of the celebration of the 70th birthday of Prof. Yu.A. Simonov, we contribute a brief review of the status of exotic baryons, which are most likely pentaquark states. We summarize the experimental status of exotic baryons, discuss the baryon antidecuplet to which exotic baryons possibly belong, and review theoretical expectations for the masses and widths of recently discovered Θ and Ξ_3/2 baryons which have come from studies of QCD sum rules, lattice QCD, and quark models. We also pay special attention to the dynamical calculation of pentaquark masses in a framework of the QCD string approach originally elaborated by Simonov for baryons and using the Jaffe-Wilczek \([ud]^2 \bar q\) approximation for the pentaquark states.     

Bound-state approach to strangeness in the Skyrme model

We show that baryons carrying heavy flavors, such as strangeness and charm, can be described by bound states of the corresponding heavy mesons in the background field of the basic SU(2) skyrmion. This method is quantitatively successful to O(N_c⁰), in the sense of the large-N_c expansion, but at O(1/N_c) it experiences problems associated with our lack of knowledge of higher-derivative terms in the Skyrme action. We derive a model-independent mass relation for strange baryons which is in excellent agreement with experiment.     

Static baryon properties in a relativistic quark model with centre-of-mass correction

The static properties such as magnetic moments, charge radii and axial vector coupling constant ratios of the quark core of baryons in the nucleon octet have been calculated in an independent-quark model based on the Dirac equation with equally mixed scalar-vector potential in linear form in the current quark mass limit. The results obtained with appropriate corrections due to centre-of-mass motion are in reasonable agreement with experimental data. The magnetic moments of the quark core of baryons in the charmed andb-flavoured sectors have also been calculated with this model and the overall predictions so obtained compare very well with other model predictions.     

Hyperons Analogous to the Λ(1405)

The low mass of the Λ(1405) hyperon with j ^P =  1/2^?, which is higher than the ground state Λ(1116) mass by 290 MeV, is difficult to understand in quark models. We analyze the hyperon spectrum in the bound state approach of the Skyrme model that successfully describes both the Λ(1116) and the Λ(1405). This model predicts that several hyperon resonances of the same spin but with opposite parity form parity doublets that have a mass difference of around 300 MeV, which is indeed realized in the observed hyperon spectrum. Furthermore, the existence of the ${\Xi(1620)}$ and the ${\Xi(1690)}$ of j ^P  = 1/2^? is predicted by this model. Comments on the Ω baryons and heavy quark baryons are made as well.     

Charmed baryons in a relativistic quark model

We calculate mass spectra of charmed baryons within a relativistically covariant quark model based on the Bethe-Salpeter equation in instantaneous approximation. Interactions are given by a linearly rising three-body confinement potential and a flavor-dependent two-body force derived from QCD instanton effects. This model has already been successfully applied to the calculation of light flavor baryon spectra and is now extended to heavy baryons. Within the same framework we compare the results to those obtained with the more conventional one-gluon exchange potential.