Static hyperon properties in a linearizedSU(3)-Chiral Bag model

We use a linearized Chiral Bag model to describe the strange octet and decuplet baryons. The approach is canonically extended to spontaneously broken chiral SU(3)_L × SU(3)_R, and the corresponding Goldstone Bosons are identified with the pseudoscalar meson octet. We include explicit symmetry breaking corrections both for baryons and mesons. The linearized quark-meson intraction is applied in a self-consistent calculation of the masses and, for Δ, Σ^* and Ξ^*, of the decay widths. Our special interest is in the influence of theK- andη-cloud (in addition to theπ) on hyperon static properties. We show results for radii, masses, decay widths and renormalization constants as obtained by a fit to the experimental hyperon spectra. The effects of theK- andη-mesons are found to be non-negligible, although supressed by symmetry breaking effects. The effective gluon coupling α is reduced in comparison to the SU(2)_L × SU(2)_R case. In addition, we discuss the dependence on the bag constantB. It turns out that the lightest hyperon states, Λ and Σ are well described and stable for B^1/4 < 130 MeV. The heavier strange baryons have stable solutions also for larger values ofB. The bag radii determined at the minimal energies are R₀?1.15 fm for the octet and R₀?1.25 fm for the decuplet baryons.     

Vector and Tensor Coupling Constants of SU(3) Baryons in a Chiral Soliton Model

We report in the present talk a recent investigation on the vector properties of SU(3) baryons, based on a chiral soliton model. All relevant parameters from the model are adjusted to the experimental data of the masses and magnetic moments of the baryon octet. We compute the electromagnetic transitions for the baryon octet, the decuplet, and the antidecuplet. The numerical predictions for transition magnetic moments and radiative partial decay widths are in a very good agreement with all data of existing experiment and the vector meson dominance being used, the coupling constants for the vector mesons and antidecuplet baryon vertices are determined from the calculated transition magnetic moments.     

To the description of hadron mass spectrum in the nonrelativistic quark potential model

The comparison of different confinement models of hadrons in non-relativistic quark potential model with the use of hyperspherical functions is carried out in the present work. Numerical values of the masses of non-strange (the lightest) hadrons belonging to the meson octet and baryon decuplet are obtained in this model. The best values of masses are obtained with the potential which incorporates the quasi-relativistic one-gluon exchange and the confinement termAr ⁿ withn=2/3. The natural appearance of the Yukawa-type potential in this model is also discussed.     

Nuclear Matter in a Chiral SU(3) Quark Mean-Field Model

A quark meson coupling model based on SU(3)_L×SU(3)_R symmetry and scale invariance is proposed. The quarks and mesons get masses through symmetry broken. We apply this SU(3) chiral constituent quark model to investigating the nuclear matter at finite temperature and density. The effective baryon masses, compression modulus and hyperon potentials are all reasonable. The critical temperature of liquid-gas phase transition is also calculated in this model.     

SU(2) Yang-Mills theory in (1 + 1) dimensions: A finite-lattice approach

Finite-lattice methods are used to calculate the masses of the lowest-lying baryon and meson states in the two-dimensional SU(2) Yang-Mills theory. No sign of a phase transition is seen at non-zero quark mass m. Both the meson and baryon mass vanish at m = 0: this is presumably a “chiral protection” mechanism.     

Spinor strong interaction model for baryon spectra

The spinor strong interaction model recently proposed by the author to account for meson spectra is applied to baryons. Quark-quark strong interaction is of massless scalar type. Harmonic confinement arises as naturally as linear confinement for mesons. No approximation is needed in order to derive, from the proposed covariant spinor baryon equations, coupled nonlinear radial equations for the ground-state spin-1/2 and spin-3/2 baryons in the rest frame. These equations are effectively of sixth order and call for a particle classification other than the usual unrelativistic one. Simplified analytical solutions are given. Internal functions and mass operators are analogously introduced. With these and the above simplified space-time solution, baryon data yield bare quark masses that agree approximately with those analogously obtained earlier from meson data.     

Mass breaking in a relativistic quark model for mesons

We study symmetry breaking via quark mass differences in a relativistic quark model where mesons are built from heavy (m > 3 GeV) spin $\text{1}\text{2}$) quarks and antiquarks. The meson (squared-)mass differences are linearly related to the number of strange, charmed, etc. quarks in the mesons. We show that the previously assumed SU_n symmetry of the mesonic couplings holds, i.e., quark mass differences only show up in the masses of the external particles, not in the three meson vertex itself.     

Flavor mixing in the low energy hadron dynamics: Interplay of theSU f (3) breaking and theU A (1) anomaly

We extend our previous investigation about the flavor mixing or the OZI violating process in the light quark systems with the use of the generalized Nambu-Jona-Lasinio model incorporating theU _A (1) anomaly. The OZI breaking effects newly studied in the meson sector include the and meson decay constants, their couplings with nucleon as well as the masses and the mixing property of the scalar mesons. As for the baryon sector, we reexamine the strangeness content of the proton and the -N sigma term _N by taking into account the interactions between the constituent quarks. It is found that the short-range spin-spin interaction between the quarks gives anO(10 MeV)-enhancement for the theoretical value of the sigma term. Anomalous quark contents of other octet and decuplet baryons (hyperons) are also examined. It is shown that the axial anomaly induces the anomalous quark contents which are not expected in the naive quark model, while the short-range interaction between the quarks acts to suppress (enhance) the quark contents of the decuplet (octet) baryons. All the results indicate that the following picture holds systematically:m _s is so large that (i) the strangeness mixing induced by the anomaly is considerably suppressed and that (ii) the naive chiral perturbation does not work in the strange sector even in the tree level of the meson fields (largeN _c limit). The spin problem of nucleon, which is another subject related to the flavor mixing, is also examined with the use of our effective model.This paper is a modified version of the paper SUNY-NTG-89-49, RYU-THP-89-2 (August 1989)     

Spinor strong interaction model for meson spectra

A model for a bound quark-antiquark system is constructed from quark spinor equations and the associated pseudoscalar massless interaction potential equations in a way departing from conventional relativistic quantum mechanics. From the so-constructed covariant meson equations, linear confinement arises naturally. Nonlinear radial equations for the pseudoscalar and vector mesons in the rest frame are derived without approximation. An internal complex space is introduced for representation of the quark flavors. Quark masses are generalized to operators operating on functions in this space. A simple model is proposed for the meson internal functions and mass operators producing the squares of the average quark masses as eigenvalues. The present space-time model calls for a particle classification scheme different from the usual nonrelativistic one. When combined with the internal model, it may account for the gross structure of the meson spectra together with the form of an empirical relation. Upper limits of bare quark masses are estimated from simplified analytical solutions of the radial equations and agree approximately with the bare quark masses obtained from baryon data in a companion paper. The radial equations are solved numerically yielding estimates of the strong interaction radii of the ground state mesons.     

On the light meson mass formulae from quantum chromodynamics

We reconsider the Gell-Mann-Okubo light meson mass formulae using the moment sum rules ratios and taking into account non-leading quark masses and vacuum condensate effects. We also extract the strange quark mass value from the ?-ρ mass difference. The poorly known masses of the (I=0,J ^PC =0⁺⁺) scalar mesons are discussed.     

Meson cloud and SU(3) symmetry breaking in parton distributions

We apply the meson cloud model to the calculation of non-singlet parton distributions in the nucleon sea, including the octet and the decuplet cloud baryon contributions. We give special attention to the differences between non-strange and strange sea quarks, trying to identify possible sources of SU(3) flavor breaking. An analysis in terms of the parameter is presented, and we find that the existing SU(3) flavor asymmetry in the nucleon sea can be quantitatively explained by the meson cloud. We also consider the baryon, finding similar conclusions. Received: 28 July 2000 / Published online: 23 October 2000     

The quark‐level linear σ model

This review of the quark‐level linear σ model (QLLσM) is based upon the dynamical realization of the pseudoscalar and scalar mesons as a linear representation of SU(2)× SU(2) chiral symmetry, with the symmetry weakly broken by current quark masses. In its simplest SU(2) incarnation, with two non‐strange quark flavors and three colors, this nonperturbative theory, which can be selfconsistently bootstrapped in loop order, is shown to accurately reproduce a host of low‐energy observables with only one parameter, namely the pion decay constant f_π. Extending the scheme to SU(3) by including the strange quark, equally good results are obtained for many strong, electromagnetic, and weak processes just with two extra constants, viz. f_K and <π |H_weak|K>. Links are made with the vector‐meson‐dominance model, the BCS theory of superconductivity, and chiral‐symmetry restoration at high temperature. Finally, these ideas are cautiously generalized to the electroweak sector, including the W, Z, and Higgs bosons, and also to CP violation.     

Mass differences and vector currents

Hadron mass differences are related to the divergences of the weak hadronic vector currents. The nearly conservedSU(3)-charges are used to understand the approximate validity of mass formulae. We present a simple argument —involving the formal quark structure of the relevant operators —for octet dominance and predict equald/f-ratios for the strong mass differences and the leading part of the electromagnetic mass splitting. Furthermore, mass formulae connecting differentSU(3)-multiplets are derived. A remarkable universality property of the coupling of the various particles to the divergences is observed by which even baryon and meson mass differences are related.     

Sum rules for the pseudoscalar BBP couplings

In the ‘tadpole’ type mechanism of Coleman and Glashow, where all the summetry breaking effects are generated through symmetry breaking terms belonging to the same regular representation (octet in the case of SU(3) and15 in SU(4)), the strangeness changing (charm changing) effects generated through theS ₆(S ₉) tadpole must vanish. We exploit this null result to find relations between the BBP coupling constants and the baryon masses in the strange as well as charm sector.     

Magnetic moments of the nucleon octet calculated in the cloudy bag model

The formalism of the cloudy bag model is used to calculate the pion coupling to the strange members of the nucleon octet (and delta decuplet). We then calculate the magnetic moments of all members of the octet, including lowest-order pionic corrections. Results are presented as a function of the radius of the bag, R, which is the only true free parameter of the model. Excellent agreement is obtained with experiment for bag radii ranging from 0.8 to 1.1 fm.     

Hadron spectroscopy with instanton induced quark forces

It is shown that within the framework of a non-relativistic quark model with string-like confinement and an instanton induced residual quark-quark interaction it is possible to account simultaneously for the baryon and the meson spectra, including theπ- η- η′ splitting for pseudoscalar mesons, up to energies of roughly 2 GeV.     

Spectroscopy with high spin selective compound reactions induced by heavy ions

The constituent symmetry group U(6) is incorporated in the null plane quark model of mesons. We obtain the value m_u=5.4 MeV, and the estimate m_s=125?160 MeV for the masses of the non-strange and the strange quarks respectively. Some checks of the model in terms of meson mass formulas are given.     

Mass relations for heavy mesons

In a non-relativistic quark model, by parametrizing the quark-antiquark potentials, some mass relations have been obtained. Algebraic expressions for the masses of higher flavour meson isosinglets have been given in terms of the meson masses of lower symmetries. Hallock and Oneda’s contention of two types of sumrules for nonet mesons in SU(3) has been examined and the possibilities of such different sum-rules of this type in SU(4) and SU(5) have been explored.     

Effective meson lagrangian with chiral and heavy quark symmetries from quark flavor dynamics

By bosonization of an extended NJL model we derive an effective meson theory which describes the interplay between chiral symmetry and heavy quark dynamics. This effective theory is worked out in the low-energy regime using the gradient expansion. The resulting effective lagrangian describes strong and weak interactions of heavy B and D mesons with pseudoscalar Goldstone bosons and light vector and axial-vector mesons. Heavy meson weak decay constants, coupling constants and the Isgur-Wise function are predicted in terms of the model parameters partially fixed from the light quark sector. Explicit SU(3)_F symmetry breaking effects are estimated and, if possible, confronted with experiment.