共查询到20条相似文献,搜索用时 15 毫秒
1.
We estimate the couplings in the Heavy Hadron Chiral Theory (HHCT) lagrangian from the QCD sum rules in an external axial
field. We take into account the perturbative correction to the meson correlator in the infinite mass limit. With the perturbative
correction and three successive power corrections, the meson correlator in an axial field becomes one of the best known correlators.
In spite of this, the corresponding sum rule is not very stable. It yields the result , where is the central value of the heavy meson decay constant with the perturbative correction [14]. This result is surprisingly
low as compared with the constituent quark model estimate . The sum rules for following from nondiagonal and diagonal baryon correlators in an external axial field suggest , while diagonal and nondiagonal baryon sum rules have too large uncertainties.
Received: 19 June 1997 / Published online: 20 February 1998 相似文献
2.
We demonstrate that the two-body interaction effects involving spectator quark can account for the discrepancy between theory
and experiment for the baryon magnetic moments and meson radiative decays. 相似文献
3.
We extract the mass spectrum of the triply heavy baryon Ωccb using the hypercentral constituent quark model. The first order correction is also added to the potential term of the Hamiltonian. The radial and orbital excited state masses are determined, and the Regge trajectories and magnetic moments for this baryon are also given. 相似文献
4.
We apply the perturbative chiral quark model at one loop to analyze the electromagnetic form factors of the baryon octet. The analytic expressions for baryon form factors, which are given in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion decay constant, axial nucleon coupling, strong pion-nucleon form factor), and the numerical results for baryon magnetic moments, charge and magnetic radii are presented. Our results are in good agreement with experimental data.Received: 7 January 2003, Revised: 4 November 2003, Published online: 15 April 2004PACS:
12.39.Ki Relativistic quark model - 13.40.Gp Electromagnetic form factors - 14.20.Dh Protons and neutrons - 14.20.Jn Hyperons 相似文献
5.
《Nuclear Physics A》1999,646(2):211-230
In this paper we discuss the binding energy of the H-particle using a chiral quark model, where pion exchange plays an important role to reproduce the mass difference between the nucleon and Δ resonance. Since the main source for the bound H-particle is believed to be the color magnetic interaction, which gives the nucleon and Δ mass difference, it is very interesting to investigate whether the chiral quark model gives rise to the bound H-particle or not. We employ an extended resonating group method in order to take into account the possibility of a change of baryon wave functions when two baryons interact with each other. We found that a change of baryon size together with the Hamiltonian which consists of gluon, pseudoscalar meson and sigma meson exchange potentials gives rise to the bound H-particle. The binding energy is found to be about 25 MeV in a hybrid chiral quark model. Differences between the ordinary gluon dominant model and chiral quark models are also investigated. It is found that a pure chiral model has no bound state when the widely used sigma-quark coupling strength is employed. 相似文献
6.
7.
The modifications of the nucleon structure due to the presence of an external baryon medium are investigated in a chiral quark meson theory. To that end the Nambu-Jona-Lasinio (NJL) model is combined with the projected chiral soliton model. The medium effects are incorporated using the medium modified values of the pion decay constant and the pion and sigma masses at finite density. These values are evaluated within the NJL model. Using functional integral techniques the latter is solved in a quark continuum at finite density. The effective meson values serve to fix the parameters of the linear chiral sigma model which is solved in a variational projected mean field approach in order to obtain the nucleon properties. All nucleon properties show modifications in the medium except for the pion nucleon coupling constant. The proton radius shows an increase of 19% and the nucleon mass a decrease of 17% if the medium reaches nuclear matter density. The magnetic moments and axial vector coupling constant are less modified. All form factors show remarkable reduction at finite transfer momenta. 相似文献
8.
C.J. Hamer 《Nuclear Physics B》1982,195(3):503-521
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. 相似文献
9.
ZHU Yao-yin WANG Xiu-jiang ZHAO Xuan ZENG Fan-an HOU Ren-chang WU Guang-han TENG Li-jian YU Chao-fan HE Yin WANG Fan 《理论物理通讯》1987,7(2):149-164
In this paper, the baryon is regarded as a two-body system which consists of a diquark and a quark. The baryon spectrum is calculated by means of the composite particle represenEation based on the nonrelativistic potential model.The effectfve quark potential is determined by fitting the meson spectrum. Therefore, there is only one adjustable parameter in the calculations, and that is the harmonic oscillator frequency. ω in the single-quark basis. The theoretical results are reasonably consistent with the experimental data. 相似文献
10.
The quark model with orbital motion of the valence quarks is constructed to reproduce the spin structure of baryons. The relations between the spin-averaged sum rules and baryon magnetic moments found in the previous works do not remain, unless the small orbital magnetic moments are neglected. In particular, when the orbital motion of the valence quarks leads to the small contribution of quark orbit-spin to baryon magnetic moments, the sum rules for polarized nucleon are in agreement with the recent experiment. 相似文献
11.
Ian Duck 《Zeitschrift für Physik A Hadrons and Nuclei》1994,350(1):71-88
The bag model of confined relativistic quarks in chiral-invariant interaction with scalar, pseudoscalar, vector, and pseudovector mesons, as well as gluons, is used to calculate the masses and wave functions of the spin-1/2 baryon octet and spin-3/2 decuplet, using selfconsistent Brillouin-Wigner bound state perturbation theory. Chiral symmetry breaking is invoked with the sigma model. SU (6) and SU (3) symmetries are broken by the experimental meson spectrum, and a strange quark mass. Mass corrections are calculated to one loop order, limited to the baryons of the octet and decuplet and the lowest lying mesons. Encouraging results are obtained, especially for theΔ — N and theΣ — Λ splittings. Convergence and stability have not been demonstrated, but are evidently improved by the self-consistency requirement. An initial parameter tuning gives a fit to all the octet and decuplet masses within ≦0.02 GeV, at the price of choosing the bag radius, the non-strange baryon input bag mass, and the strange quark mass. Even these small discrepancies can be dramatically reduced by fine-tuning the vector meson coupling and including an instanton contribution peculiar to theΛ. 相似文献
12.
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. 相似文献
13.
W. Delaney 《International Journal of Theoretical Physics》1974,10(4):239-251
A semiclassical model in which elementary particles are represented as systems of charged shells with associated quark-like quantum numbers is presented. Specifically the baryons are considered. Formulas are obtained which express baryon masses and magnetic moments in terms of model parameters which relate baryon and quark properties. Basically, the mass and moment formulas are expressions for mass ratios and magnetic moment ratios. Simple identifications for the model parameters lead to a prediction for the proton-electron mass ratio and to fairly accurate predictions for the baryon magnetic moments in units of the proton moment. The mass and moment formulas, which relate corresponding properties of different particles, are generalised such as to express relationships between the members of a sequence of particles, where such a sequence is conceived of as containing only one (normal) baryon. A specific sequence, containing the proton and electron, is proposed; various physical properties of the particles in the sequence are determined. In particular, a second prediction for the proton-electron mass ratio is obtained; the two predictions differ numerically but both agree with the measured value of the mass ratio within experimental error. 相似文献
14.
C. Haupt B. Metsch H. -R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2006,28(2):213-225
We show that static properties like the charge radius and the magnetic moment of relativistic three-fermion bound states with
instantaneous interactions can be formulated as expectation values with respect to intrinsically defined wave functions. The
resulting operators can be given a natural physical interpretation in accordance with relativistic covariance. We also indicate
how the formalism may be generalized to arbitrary moments. The method is applied to the computation of static baryon properties
with numerical results for the nucleon charge radii and the baryon octet magnetic moments. In addition, we make predictions
for the magnetic moments of some selected nucleon resonances and discuss the decomposition of the nucleon magnetic moments
in contributions of spin and angular momentum, as well as the evolution of these contributions with decreasing quark mass. 相似文献
15.
B. L. Ioffe 《Physics of Atomic Nuclei》2009,72(7):1214-1221
A short review is presented of the spontaneous violation of chiral symmetry in QCD vacuum. It is demonstrated that this phenomenon
is the origin of baryon masses in QCD. The value of nucleon mass is calculated, as well as the masses of hyperons and some
baryonic resonances, and expressed mainly through the values of quark condensates—, q = u, d, s,—the vacuum expectation values (v.e.v.) of quark field. The concept of v.e.v. induced by external fields is introduced. It
is demonstrated that such v.e.v. induced by static electromagnetic field results in quark condensate magnetic susceptibility,
which plays the main role in determination of baryon magnetic moments. The magnetic moments of proton, neutron, and hyperons
are calculated. The results of calculation of baryon octet β-decay constants are also presented.
The text was submitted by the author in English. 相似文献
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18.
We study the properties of neutron stars using the chiral quark–meson coupling model, in which the quark–quark hyperfine interaction due to the exchanges of gluon and pion based on chiral symmetry is considered. We also examine the effects of hyperons and Δ-isobars in a neutron star. Extending the SU(6) spin-flavor symmetry to more general SU(3) flavor symmetry in the vector–meson couplings to baryons, the maximum mass of neutron star can reach the recently observed massive pulsar mass, ${1.97 \pm 0.04 M_{\odot}}$ . In this calculation, Λ and Ξ are generated in a neutron star, while Σ and Δ-isobars do not appear. 相似文献
19.
Nils A. Törnqvist Piotr Żenczykowski 《Zeitschrift fur Physik C Particles and Fields》1986,30(1):83-97
In current QCD inspired analyses of the hadron spectrum nonperturbative quark loops are generally neglected. We study the validity of this assumption by estimating mass splittings and mixings induced by hadronic mass renormalization to the (70,1?) baryon multiplet. All intermediate states in the loop composed of a ground state meson (0?+, 1??) and a ground state baryon (1/2+, 3/2+) are included. We use a3 P 0 type model for the partial decay widths and spectral functions. Using unitarity and analyticity one finds a definite prediction for the masses and mixings, in good agreement with experiment, even when the perturbative one-gluon exchange is completely ignored. Our result thus allows for a smaller one-gluon exchange overall contribution, which would resolve the difficulty of the apparent smallness of the observed spin-orbit coupling. In particular if one adds the (nonperturbative) unitarity corrections to the one-gluon exchange contribution the gluon coupling constant can be reduced by a factor of 3 giving a reasonable value αs≈0.3. 相似文献
20.
The independent particle approximation is used to treat the bound state problems in the quark model. The solution for meson states obtained in this approximation is the same as that obtained from the Bethe-Salpeter equation. The solution for the baryon states is also obtained. The mass spectra of mesons and baryons determined from these equations are in agreement with the experiment. 相似文献