共查询到20条相似文献,搜索用时 31 毫秒
1.
B.-Q. Ma I. Schmidt J.-J. Yang 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):353-359
We investigate the spin structure of the nucleon in an extended Jaffe-Lipkin quark model. In addition to the conventional
3q structure, different (3q)(Q
) admixtures in the nucleon wave function are also taken into account. The contributions to the nucleon spin from various
components of the nucleon wave function are discussed. The effect due to the Melosh-Wigner rotation is also studied. It is
shown that the Jaffe-Lipkin term is only important when antiquarks are negatively polarized. We arrive at a new “minimal”
quark model, which is close to the naive quark model, in order to understand the proton spin “puzzle”.
Received: 4 November 2000 / Accepted: 23 October 2001 相似文献
2.
W.M. Alberico F. Giacosa M. Nardi C. Ratti 《The European Physical Journal A - Hadrons and Nuclei》2003,16(2):221-228
We employ the Nambu-Jona-Lasinio model to determine the vacuum pressure on the quarks in a baryon and hence their density
inside. Then we estimate the baryonic masses by implementing the local density approximation for the mean-field quark energies
obtained in a uniform and isotropic system. We obtain a fair agreement with the experimental masses.
Received: 27 September 2002 / Accepted: 4 October 2002 / Published online: 4 February 2003
RID="a"
ID="a"e-mail: giacosa@tphys.physik.uni-tuebingen.de
Communicated by A. Molinari 相似文献
3.
M. De Sanctis E. Santopinto M.M. Giannini 《The European Physical Journal A - Hadrons and Nuclei》1998,2(4):403-409
Abstact: We perform a calculation of the relativistic transition form factors for the electromagnetic excitation of the nucleon resonances.
We use as input the 3-quark wave functions obtained in a Constituent Quark Model with three-body forces in the hypercentral
approach. With respect to the non relativistic calculations a significant contribution is obtained up to Q
2≃ 2 (GeV/c)2. However, the low Q
2-behaviour exhibits a lack of strength, which may be connected with the need of taking into account explicitly further degrees
of freedom beyond the three constituent quark ones.
Received: 16 April 1998 相似文献
4.
H. Weigel 《The European Physical Journal A - Hadrons and Nuclei》1998,2(4):391-402
Abstact: Within an extended Skyrme soliton model for baryons the interplay between the collective radial motion and the SU(3)–flavor–rotations
is investigated. The coupling between these modes is mediated by flavor symmetry breaking. Collective coordinates which describe
the corresponding large amplitude fluctuations are introduced and treated canonically. When diagonalizing the resulting Hamiltonian
flavor symmetry breaking is fully taken into consideration. As eigenstates not only the low–lying (1/2)+ and (3/2)+ baryons but also their radial excitations are obtained and compared to the empirical data. In particular the relevance of
radial excitations for the penta–quark baryon Z
+ (Y=2, I=0, J
π=(1/2)+) is discussed. In this approach its mass is predicted to be 1.58 GeV. Furthermore the widths for various hadronic decays
are estimated which, for example, yields Γ(Z
+→NK) ∼ 100 MeV for the only permissible decay process of the Z
+.
Received: 20 April 1998 / Revised version: 29 May 1998 相似文献
5.
Y.B. DongOn leave from Institute of High Energy Physics Academia Sinica Beijing P. R. China--> A. Faessler K. Shimizu 《The European Physical Journal A - Hadrons and Nuclei》1999,6(2):203-210
Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion
of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results
show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a
difference between the relativistic and the nonrelativistic treatments.
Received: 10 March 1999 / Revised version: 14 June 1999 相似文献
6.
D. Lehmann 《The European Physical Journal A - Hadrons and Nuclei》1999,4(4):327-328
In an effective theory containing only quark degrees of freedom, such as the extended Nambu–Jona–Lasinio model, the influence
of the axial anomaly can be incorporated by a self-interaction of the 't Hooft determinant type. I will show that despite
the threshold problem related to the η′ meson this leads to a significant suppression of the η′ coupling g
η′qˉq to dynamical quarks which suggests a suppression of the η′NN vertex as compared to the ηNN vertex.
Received: 8 January 1999 相似文献
7.
C. Albertus E. Hernández J. Nieves J. M. Verde-Velasco 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):691-694
Working in the framework of a nonrelativistic quark model we evaluate the spectra and semileptonic decay widths for the ground
state of doubly heavy Ξ and Ω baryons. We solve the three-body problem using a variational ansatz made possible by the constraints imposed by heavy-quark
spin symmetry. In order to check the dependence of our results on the inter-quark interaction, we have used five different
quark-quark potentials which include Coulomb and hyperfine terms coming from one-gluon exchange, plus a confining term. Our
results for the spectra are in good agreement with a previous calculation done using a Faddeev approach. For the semileptonic
decay our results for the total decay widths are in good agreement with the ones obtained within a relativistic quark model
in the quark-diquark approximation. 相似文献
8.
B. Friman W. Nörenberg V.D. Toneev 《The European Physical Journal A - Hadrons and Nuclei》1998,3(2):165-170
We compute the modification of the quark condensate <ˉq q> in relativistic nucleus-nucleus collisions and estimate the 4-volume,
where the quark condensate is small (<ˉqq>/<ˉqq>0≤ 0.1–0.3) using hadron phase-space distributions obtained with the quark-gluon string model. As a function of the beam energy
the 4-volume rises sharply at a beam energy Elab/A ≃ (2–5) GeV, remains roughly constant up to beam energies ≃ 20 GeV and rises at higher energies. At low energies the reduction
of the condensate is mainly due to baryons, while at higher energies the rise of the 4-volume is due to the abundant mesons
produced. Based on our results we expect that moderate beam energies on the order of 10 GeV per nucleon are favourable for
studying the restoration of chiral symmetry in a baryon-rich environment in nucleus-nucleus collisions.
Received: 4 December 1997 / Revised version: 31 July 1998 相似文献
9.
This paper is a sequel of a previous one (Scalar mesons in a chiral quark model with glueball, Eur. Phys. J. A 8, 567 (2000)) where an attempt to construct an effective U(3)×U(3)-symmetric meson Lagrangian with a scalar glueball was made. The glueball was introduced by using the dilaton model on
the base of scale invariance. The scale invariance breaking because of current quark masses and the scale anomaly of QCD,
reproduced by the dilaton potential, was taken into account. However, in the previous paper, the scale invariance breaking
because of the terms like h
φφ2 and h
σ
, where φ and are the pseudoscalar and scalar isosinglets, was not taken into account. These terms are produced by the part of the 't Hooft
interaction that is connected with gluon anomalies. Allowing for the scale invariance breaking by these terms has a decisive
effect on the quarkonium-glueball mixing and noticeably changes the widths of glueball strong decays. Taking account of this
additional source of the scale invariance breaking and its implications are the subject of the present work. It is also shown
that in the decay of a glueball into four pions, the channel with two ρ-resonances dominates.
Received: 11 January 2001 / Accepted: 25 January 2001 相似文献
10.
11.
We consider a chiral one-loop hedgehog soliton of the bosonized SU(2)f Nambu & Jona-Lasinio model which is embedded in a hot medium of constituent quarks. Energy and radius of the soliton are
determined in self-consistent mean-field approximation. Quasi-classical corrections to the soliton energy are derived by means
of the pushing and cranking approaches. The corresponding inertial parameters are evaluated. It is shown that the inertial
mass is equivalent to the total internal energy of the soliton. Corrected nucleon and δ isobar masses are calculated in dependence
on temperature and density of the medium. As a result of the self-consistently determined internal structure of the soliton
the scaling between constituent quark mass, soliton mass and radius is noticeably disturbed.
Received: 26 September 1997 相似文献
12.
D. Ebert M. Nagy M. K. Volkov V. L. Yudichev 《The European Physical Journal A - Hadrons and Nuclei》2000,8(4):567-576
Ground-state scalar isoscalar mesons and a scalar glueball are described in a U(3)×U(3) chiral quark model of the Nambu-Jona-Lasinio (NJL) type with 't Hooft interaction. The latter interaction produces singlet-octet
mixing in the scalar and pseudoscalar sectors. The glueball is introduced into the effective meson Lagrangian as a dilaton
on the base of scale invariance. The mixing of the glueball with scalar isoscalar quarkonia and amplitudes of their decays
into two pseudoscalar mesons are shown to be proportional to current quark masses, vanishing in the chiral limit. Mass spectra
of the scalar mesons and the glueball and their main modes of strong decay are described.
Received: 14 July 2000 / Accepted: 31 July 2000 相似文献
13.
A.N. Ivanov H. Oberhummer N.I. Troitskaya M. Faber 《The European Physical Journal A - Hadrons and Nuclei》2000,7(4):519-535
The Nambu–Jona–Lasinio model of the deuteron suggested by Nambu and Jona–Lasinio (Phys. Rev. 124 (1961) 246) is formulated
from the first principles of QCD. The deuteron appears as a neutron–proton collective excitation, i.e. a Cooper np–pair, induced
by a phenomenological local four–nucleon interaction in the nuclear phase of QCD. The model describes the deuteron coupled
to itself, nucleons and other particles through one–nucleon loop exchanges providing a minimal transfer of nucleon flavours
from initial to final nuclear states and accounting for contributions of nucleon–loop anomalies which are completely determined
by one–nucleon loop diagrams. The dominance of contributions of nucleon–loop anomalies to effective Lagrangians of low–energy
nuclear interactions is justified in the large N
C expansion, where N
C is the number of quark colours.
Received: 10 March 2000 相似文献
14.
L. Theußl R.F. Wagenbrunn B. Desplanques W. Plessas 《The European Physical Journal A - Hadrons and Nuclei》2001,12(1):91-101
π and η decay 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 3
P
0 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 π and η decay 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 parameterization of the meson wave function
entering the 3
P
0 model.
Received: 11 May 2001 / Accepted: 17 September 2001 相似文献
15.
16.
M. Koll R. Ricken D. Merten B.C. Metsch H.R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):73-94
We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation.
Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual
interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with
a natural solution of the U
A(1) problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this
paper, we will also discuss our results concerning numerous meson decay properties. For processes like π+/K
+↦e
+υeγ and 0-↦γγ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors
of the K
?3 decay and on the decay constants of the π, K and η mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged π
and K mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data.
Received: 28 August 2000 / Accepted: 12 September 2000 相似文献
17.
R. Bonnaz B. Silvestre-Brac C. Gignoux 《The European Physical Journal A - Hadrons and Nuclei》2002,13(3):363-376
In the framework of the non-relativistic quark model, an exhaustive study of radiative transitions in mesons is performed.
Emphasis is placed on several points. Some traditional approximations (long-wavelength limit, non-relativistic phase space,
dipole approximation for E1 transitions, Gaussian wave functions) are analyzed and their effects commented. A complete treatment using three different
types of realistic quark-antiquark potential is made. The overall agreement with experimental data is quite good, but some
improvements are suggested.
Received: 16 October 2001 / Accepted: 18 December 2001 相似文献
18.
Bo-Wen Xiao Xin Qian Bo-Qiang Ma 《The European Physical Journal A - Hadrons and Nuclei》2002,15(4):523-527
The electromagnetic form factor of the kaon meson is calculated in the light-cone formalism of the relativistic constituent
quark model. The calculated K+ form factor is consistent with almost all of the available experimental data at low-energy scale, while other properties
of the kaon could also be interrelated in this representation with reasonable parameters. Predictions of the form factors
for the charged and neutral kaons at a higher-energy scale are also given, and we find the non-zero K0 form factor at Q
2≠ 0 due to the mass difference between the strange and down quarks inside K0.
Received: 21 June 2002 / Accepted: 29 July 2002 / Published online: 3 December 2002
RID="a"
ID="a"e-mail: mabq@phy.pku.edu.cn
Communicated by A. Sch?fer 相似文献
19.
U. Löring B.Ch. Metsch H.R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2001,10(4):395-446
This is the second of a series of three papers treating light-baryon resonances up to 3 GeV within a relativistically covariant
quark model based on the three-fermion Bethe-Salpeter equation with instantaneous two- and three-body forces. In this paper
we apply the covariant Salpeter framework (which we developed in the first paper, U. L?ring, K. Kretzschmar, B.Ch. Metsch,
H.R. Petry, Eur. Phys. J. A 10, 309 (2001)) to specific quark model calculations. Quark confinement is realized by a linearly rising three-body string potential
with appropriate spinorial structures in Dirac space. To describe the hyperfine structure of the baryon spectrum we adopt
't Hooft's residual interaction based on QCD-instanton effects and demonstrate that the alternative one-gluon exchange is
disfavored on phenomenological grounds. Our fully relativistic framework allows to investigate the effects of the full Dirac
structures of residual and confinement forces on the structure of the mass spectrum. In the present paper we present a detailed
analysis of the complete non-strange-baryon spectrum and show that several prominent features of the nucleon spectrum such
as, e.g., the Roper resonance and approximate “parity doublets” can be uniformly explained due to a specific interplay of relativistic
effects, the confinement potential and 't Hooft's force. The results for the spectrum of strange baryons will be discussed
in a subsequent paper, see U. L?ring, B.Ch. Metsch, H.R. Petry, this issue, p. 447.
Received: 27 March 2001 / Accepted: 17 April 2001 相似文献
20.
We study the static scalar susceptibility of the nuclear medium, i.e., the change of the quark condensate for a small modification of the quark mass. In the linear sigma model it is linked to
the in-medium sigma propagator and its magnitude increases due to the mixing with the softer modes of the nucleon-hole excitations.
We show that the pseudoscalar susceptibility, which is large in the vacuum, owing to the smallness of the pion mass, follows
the density evolution of the quark condensate and thus decreases. At normal nuclear matter density the two susceptibilities
become much closer, a partial chiral symmetry restoration effect as they become equal when the full restoration is achieved.
Received: 20 July 2002 / Accepted: 14 September 2002 / Published online: 21 January 2003
RID="a"
ID="a"e-mail: chanfray@ipnl.in2p3.fr
Communicated by A. Molinari 相似文献