共查询到20条相似文献,搜索用时 15 毫秒
1.
D. Ebert T. Feldmann C. Kettner H. Reinhardt 《The European Physical Journal C - Particles and Fields》2011,71(1):329-335
We present a phenomenological ansatz for coupling a heavy quark with two light quarks to form a heavy baryon. The heavy quark is treated in the heavy mass limit, and the light quark dynamics is approximated by propagating scalar and axial vector ??diquarks??. The resulting effective lagrangian, which incorporates heavy quark and chiral symmetry, describes interactions of heavy baryons with Goldstone bosons in the low energy region. As an application, the Isgur-Wise form factors are estimated. 相似文献
2.
D. Ebert T. Feldmann C. Kettner H. Reinhardt 《Zeitschrift fur Physik C Particles and Fields》1996,71(1):329-335
We present a phenomenological ansatz for coupling a heavy quark with two light quarks to form a heavy baryon. The heavy quark is treated in the heavy mass limit, and the light quark dynamics is approximated by propagating scalar and axial vector ‘diquarks’. The resulting effective lagrangian, which incorporates heavy quark and chiral symmetry, describes interactions of heavy baryons with Goldstone bosons in the low energy region. As an application, the Isgur-Wise form factors are estimated. 相似文献
3.
4.
简要介绍核物质中核子的质量、 半径及夸克凝聚的密度依赖关系基于QCD模型和QCD有效场论研究的现状, 并具体介绍整体色对称模型(GCM)的研究结果. GCM研究表明, 在小于临界密度的情况下, 核物质中核子的质量随核物质密度的增大而减小, 核子的半径和夸克凝聚随核物质密度的增大而增大. 当达到临界密度时, 核子质量减小为零, 核子半径变为无限大, 夸克凝聚突变为零, 进而提出一个核物质中手征对称性恢复的新机制. The status of the investigations on the nucleon mass, nucleon radius and quark condensate in the framework of QCD inspired models and QCD effective field theories is briefly reviewed. The results in the global color symmetry model (GCM) are described a little detailedly. The calculated results indicate that, before the maximal density is reached, the mass of a nucleon in nuclear matter decreases, the radius of a nucleon and the quark condensate increase very slowly, with the increase of the nuclear matter density. As the maximal nuclear matter density is reached, the mass of the nucleon vanishes gradually. The radius becomes infinite and the quark condensate vanishes suddenly. A new mechanism for the chiral symmetry restoration in nuclear matter is proposed. 相似文献
5.
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
6.
M. Jamin J.A. Oller A. Pich 《The European Physical Journal C - Particles and Fields》2002,24(2):237-243
In this work, the mass of the strange quark is calculated from QCD sum rules for the divergence of the strangeness-changing
vector current. The phenomenological scalar spectral function which enters the sum rule is determined from our previous work
on strangeness-changing scalar form factors [1]. For the running strange mass in the scheme, we find . Making use of this result and the light quark mass ratios obtained from chiral perturbation theory, we are also able to
extract the masses of the lighter quarks and . We then obtain and . In addition, we present an updated value for the light quark condensate.
Received: 18 October 2001 / Revised version: 22 January 2002 / Published online: 12 April 2002 相似文献
7.
We classify the parity- and time-reversal-violating operators involving quark and gluon fields that have effective dimension six: the quark electric dipole moment, the quark and gluon chromo-electric dipole moments, and four four-quark operators. We construct the effective chiral Lagrangian with hadronic and electromagnetic interactions that originate from them, which serves as the basis for calculations of low-energy observables. The form of the effective interactions depends on the chiral properties of these operators. We develop a power-counting scheme and calculate within this scheme, as an example, the parity- and time-reversal-violating pion–nucleon form factor. We also discuss the electric dipole moments of the nucleon and light nuclei. 相似文献
8.
《Nuclear Physics B》1986,271(1):188-226
By bosonization of an extended Nambu-Jona-Lasinio type of quark model with explicit breaking of chiral U(n) × U(n) symmetry we derive a effective low-energy lagrangian of composite scalar, pseudoscalar, vector and axial-vector mesons. This lagrangian contains the gauged Wess-Zumino term as well as higher order derivative terms of the Skyrme type, the coefficients of which agree with recent phenomenological estimates. In particular, the value predicted for the strength of the standard fourth-order Skyrme term is in satisfactory agreement with the results obtained by fitting the nucleon and delta masses. Our effective chiral lagrangian reproduces the wealth of the results of successful phenomenological lagrangians as, e.g. soft-pion theorems, Goldberger-Treiman relations, PCAC, the KSFR relation, the (approximate) Weinberg relation, etc. Moreover, the predicted mass spectra and decay constants of composite mesons are in qualitative agreement with the experimental findings. Furthermore, when electroweak interactions are included the lagrangian contains vector (axial-vector) dominance based on field-current identities. 相似文献
9.
C.A.Z. Vasconcellos H.T. Coelho F.G. Pilotto B.E.J. Bodmann M. Dillig M. Razeira 《The European Physical Journal C - Particles and Fields》1998,4(1):115-127
In the present work we propose a new bag model for hadrons, called the modified fuzzy bag model (MFBM). The distinguishing
feature of this model is the suppression of the pion field, as it enters the bag, by means of a scalar potential for the pions,
while still preserving chiral symmetry. The mechanism of pion suppression in the MFBM is similar to the mechanism of quark
suppression in the fuzzy bag model (FBM). The standard chiral transformation for the pion field suffers a natural alteration
in the MFBM, and as a result the model is chiral invariant. We present also a discussion of the FBM and study, in the quark
sector, the implications of the soft surface of the bag on the expectation value of the mass operator. In the pion-quark sector,
we study the effects of the suppression of the pion field on the form factor for the pion-nucleon interaction, on the pion-nucleon
coupling constant and on the nucleon axial charge . Calculations of the pion-nucleon form factor exhibit, in particular, an improvement over previous results. The pionic axial
current induces, in the MFBM, a nonvanishing and orientation dependent contribution to axial charge. An analysis of the asymptotic
behaviour of the axial charge shows that the role of the surface is to increase the difference of the contributions associated
to different orientations.
Received: 10 March 1997 / Revised version: 14 October 1997 相似文献
10.
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
11.
Hee-Jung Lee Chang Ho Hyun Chang-Hwan Lee Hyun-Chul Kim 《The European Physical Journal C - Particles and Fields》2006,45(2):451-457
We investigate the ΔS = 0 effective chiral Lagrangian from the instanton vacuum. Based on the ΔS = 0 effective weak Hamiltonian from the operator product expansion and renormalization group equations, we derive the strangeness-conserving
effective weak chiral Lagrangian from the instanton vacuum to order
and the next-to-leading order in the 1/Nc expansion at the quark level. We find that the quark condensate and a dynamical term which arise from the QCD and electroweak
penguin operators appear in the next-to-leading order in the 1/Nc expansion for the ΔS = 0 effective weak chiral Lagrangian, while they are in the leading order terms in the ΔS = 1 case. Three different types of form factors are employed and we find that the dependence on the different choices of
the form factor is rather insensitive. The low-energy constants of the Gasser-Leutwyler type are determined and discussed
in the chiral limit.
Arrival of the final proofs: 2 December 2005
PACS:
12.40.-y, 14.20.Dh 相似文献
12.
The phase structure of hadronic matter at high density relevant to the physics of compact stars and relativistic heavy-ion collisions is studied in a low-energy effective quark theory. The relevant phases that figure are (1) chiral condensation, (2) diquark color condensation (color superconductivity) and (3) induced Lorentz-symmetry breaking (“ISB”). For a reasonable strength for the effective four-Fermi current–current interaction implied by the low-energy effective quark theory for systems with a Fermi surface we find that the “ISB” phase sets in together with chiral symmetry restoration (with the vanishing quark condensate) at a moderate density while color superconductivity associated with scalar diquark condensation is pushed up to an asymptotic density. Consequently, color superconductivity seems rather unlikely in heavy-ion collisions although it may play a role in compact stars. Lack of confinement in the model makes the result of this analysis only qualitative but the hierarchy of the transitions we find seems to be quite robust. 相似文献
13.
《Physics letters. [Part B]》1987,198(2):126-130
Effects of the explicit breaking of flavour symmetry on the quark condensates in the large-Nc limit are examined with the use of a QCD-motivated effective lagrangian. It is shown that, as the current mass increases, the non-perturbative quark condensate decreases in the absolute values, which agrees well with that obtained from QCD sum rules, not only qualitatively but also quantitatively. The condensatesat finite temperature are also investigated in relation to the chiral transition. 相似文献
14.
We analyse the baryon mass spectrum in a framework which combines the 1/N
c expansion with chiral perturbation theory. Meson loop contributions involving the full SU(3) octet of pseudoscalar Goldstone
bosons are evaluated, and the influence of explicit chiral and flavor symmetry breaking by non-zero and unequal quark masses
is investigated. We also discuss sigma terms and the strangeness contribution to the nucleon mass.
Received: 29 June 1998 / Revised version: 25 November 1998 相似文献
15.
M. M. Islam 《Foundations of Physics》1994,24(3):419-425
The nonlinear -model with vector mesons introduced as gauge bosons and an interacting chiral quark sector depicts the nucleon as a topological soliton embedded in a chiral condensate. High-energy elastic pp and ¯pp scattering data from CERN ISR and SPS Collider appear to provide strong evidence in favor of this nucleon structure.Dedicated to Fritz Rohrlich for his lifelong devotion to physics.This work was supported in part by the U.S. Department of Energy. 相似文献
16.
《Nuclear Physics A》1998,637(3):421-432
We derive the expressions of the vector and axial current from a chiral Lagrangian restricted to nucleons and pions. They display mixing terms between the axial and vector currents. We study the modifications in the nuclear medium of the coupling constants of the axial current, namely the pion decay constant and the nucleonic axial one due to the requirements of chiral symmetry. We express the renormalizations in terms of the local scalar pion density. The latter also governs the quark condensate evolution and we discuss the link between this evolution and the renormalizations. In the case of the nucleon axial coupling constant this renormalization corresponds to a new type of pion exchange currents, with two exchanged pions. We give an estimate for the resulting quenching. Although moderate it helps explaining the quenching experimentally observed. 相似文献
17.
Th. Gutsche V. Lyubovitskij A. Faessler 《Progress in Particle and Nuclear Physics》2003,50(2):235-245
We give an overview of recent applications of the perturbative chiral quark model (PCQM) in the analysis of the structure of the nucleon. The PCQM is based on an effective Lagrangian, where baryons are described by relativistic valence quarks and a perturbative cloud of Goldstone bosons as required by chiral symmetry. We discuss applications to the electromagnetic properties of the nucleon, to σ-term physics, to πN scattering including radiative corrections and to the strange form factors of the nucleon. 相似文献
18.
在核物质中从手征等效Lagrange量得到的π介子有效质量是单值的,并且与π介子场的离壳扩展无关,例如PCAC选择.同位旋对称核物质中的有效π介子质量随增加的核密度有些上升,因此有效类时π介子衰变常数和密度相关的夸克凝聚渐渐下降.另外研究了内介质Gell–Mann–Oakes–Renner关系和其它内介质同一性.最后讨论了同位旋对称、各向同性和均匀的核物质中关于介子传播的等效Lagrange量的几个限制. 相似文献
19.
S. Kagiyama A. Nakamura T. Otofuji 《The European Physical Journal C - Particles and Fields》1999,7(2):305-311
Compressible bag model is formulated on the basis of lagrangian field theory. A specific application is done in conjunction
with - model. The results are similar to Chin-Walecka model and almost reproduce our previous results. The effective nucleon mass
does not become so small owing to the compressibility, in contrast to Chin-Walecka model.
Received: 12 May 1998 / Revised version: 9 July 1998 / Published online: 8 September 1998 相似文献
20.
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