πNN and ΔπN Couplings in a Relativistic Quark Model Approach

Based on a relativistic quark model approach,the decay of Δ^ →π^ p,and the coupling constants of gΔπN and gπNN are studied.Our results are compared with data and empirical values.     

Nucleon Form Factors and N-△ Transitions in a Hypercentral Constituent Quark Model with Meson Cloud

We study the nucleon form factors and the nucleon-△（1232） transitions in a framework of hypercentral constituent quark model. The pion meson cloud effect is taken into account explicitly. Our results show that the pion cloud contributes substantially to the nucleon form factors as well as to the helicity amplitudes of △（1232）, and it gives an improved agreement compared to the experimental.     

Pion Cloud Effects on △-N Mass Splitting from Quark Models

Pion cloud effects on △-N mass splitting are studied based on quark models. Pseudo-scalar pion-quarkcoupling is discussed in the relativistic and nonrelativistic frameworks. We separately calculate the pion cloud effects bythe one-pion exchange potential and by another method which is consistent with the baryon chiral perturbation theory.Remark able discrepancy in the mass splitting between the two methods is shown.     

A study of transverse charge density of pions in relativistic quantum mechanics

The transverse charge density of pions is calculated based on relativistic quantum mechanics, where the pion is regarded as a quark-antiquark bound state. Corrections from the two spin-1/2 constituents and from the wave function of a quark and antiquark inside the bound system are discussed. The calculated results are compared to the results with a realistic effective Lagrangian approach as well as to that with a simple covariant model where the pion is regarded as a composite system with two scalar particles.     

In-Medium Nucleon Electromagnetic Form Factors in Vector Meson Dominance Model

We study medium modifications of the nucleon electromagnetic form factors in the vector meson dominance model. The in-medium vector meson masses are taken from a chiral SU(3) model. We find that the electric and magnetic form factors of the bound nucleon deviate considerably from those of the free nucleon. Our results are comparable to the results from the quark meson coupling model approach and are consistent with present experimental limits.     

Proton sea quark flavour asymmetry and Roper resonance

We study the proton and the Roper resonance together with the meson cloud model, by constructing a Hamiltonian matrix and solving the eigenvalue equation. The proton sea quark flavour asymmetry and some properties of the Roper resonance are thus reproduced in one scheme.     

△△ Dibaryon Structure in Extended Chiral SU（3） Quark Model

The structure of △△ dibaryon is studied in the extended chiral SU（3） quark model in which vector meson exchanges are included. The effect of the vector meson fields is very similar to that of the one-gluon exchange （OGE） interaction. Both in the chiral SU（3） quark model and in the extended chiral SU（3） quark model, the resultant mass of the △△ dibaryon is lower than the threshold of the △△ channel but higher than that of the △ Nπ channel.     

Glueball spectrum from N_f=2 lattice QCD study on anisotropic lattices

The lowest-lying glueballs are investigated in lattice QCD using N_f = 2 clover Wilson fermions on anisotropic lattices. We simulate at two different and relatively heavy quark masses, corresponding to physical pion masses of mπ～938 MeV and 650 MeV. The quark mass dependence of the glueball masses has not been investigated in the present study. Only the gluonic operators built from Wilson loops are utilized in calculating the corresponding correlation functions. In the tensor channel, we obtain the ground state mass to be 2.363(39) GeV and 2.384(67)GeV at mπ～938 MeV and 650 MeV, respectively. In the pseudoscalar channel, when using the gluonic operator whose continuum limit has the form of ∈_ijkTrB_iD_jB_k, we obtain the ground state mass to be 2.573(55) GeV and 2.585(65) GeV at the two pion masses. These results are compatible with the corresponding results in the quenched approximation. In contrast, if we use the topological charge density as field operators for the pseudoscalar, the masses of the lowest state are much lighter(around 1 GeV) and compatible with the expected masses of the flavor singlet qq meson. This indicates that the operator ∈ijk TrBiDjBk and the topological charge density couple rather differently to the glueball states and qq mesons. The observation of the light flavor singlet pseudoscalar meson can be viewed as the manifestation of effects of dynamical quarks. In the scalar channel, the ground state masses extracted from the correlation functions of gluonic operators are determined to be around 1.4-1.5 GeV, which is close to the ground state masses from the correlation functions of the quark bilinear operators. In all cases, the mixing between glueballs and conventional mesons remains to be further clarified in the future.     

Quenched Charmed Meson Spectra Using Tadpole Improved Quark Action on Anisotropic Lattices

Charmed meson charmonium spectra are studied with improved quark actions on anisotropic lattices. We measured the pseudo-scalar and vector meson dispersion relations for four lowest lattice momentum modes with quark mass values ranging from the strange quark to charm quark with three different values of gauge coupling β and four different values of bare speed of light v. With the bare speed of light parameter v tuned in a mass-dependent way, we study the mass spectra of D, Ds, ηc, D^＊, D^＊s and J/ψ mesons. The results extrapolated to the continuum limit are compared with the experiment, and a qualitative agreement is found.     

Nucleon-Nucleon Interaction and the Mixing of Scalar Meson

Whether the mixing of scalar meson exists or not is an interesting question. We consider the mixing of scalar meson and further study the nucleon-nucleon interaction in the chiral SU（3） quark model by solving the resonating group method equation. The results are analyzed and compared with no mixing, ideal mixing and general mixing. It seems that the nucleon-nucleon interaction and binding energy of deuteron can be reasonably described with the different mixing of scalar meson.     

Recent results from the HERMES experiment

Results are presented from the Hermes experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon.Data have been accumulated for pion and kaon double spin asymmetries,single-spin azimuthal asymmetries for meson electroproduction,deep virtual Compton scattering （DVCS）,and meson multiplicities.These results provide information on the properties of the strange sea in the proton,constraints on transverse momentum dependent quark parton distributions,and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton.     

The density-and isospin-dependent ?-formation cross section and its decay width

The energy-, density-, and isospin-dependent ?-formation cross section σ_(Nπ→?)~* and ?-decay width are calculated based on the relativistic BUU approach in which the effective mass splitting of nucleon and ? baryons in isospin-asymmetric matter is considered by the inclusion of the δ meson exchange in the effective Lagrangian density and the density-dependent coupling constants of Hofmann et al. The results show that the σ_(Nπ→?)~* is decreased(increased) moderately with increasing density with(without)the consideration of medium modifications on pion mass. Meanwhile, if the invariant mass of the system is not far from the ?pole mass, the ?-decay width is also weakly dependent on density. The mass splitting effect of differently charged nucleon and ?baryons on σ_(Nπ→?)~* is found to be more obvious than that of pion mesons but much weaker than the mass splitting in the hard ?production channel NN → N?. Further, the largest mass-splitting influence is seen in the π~-p → ?~0 and π~+n → ?~+ channels but not in the production of ?~- and ?~(++) isobars.     

The mass of the isodoublet of the 2^1S0 meson nonet revisited

In the qq quark model, the states π（1300）, η（1295） and η（1475） are assigned as the 2^1S0 meson nonet. The mass of the isodoublet remains interesting and needs further confirmation in experiments. This paper employs the phenomenological trajectory on the （N, M^2）-plot and meson meson mixing methods to calculate the mass of this state, the calculated results are 1341 MeV and 1311.58 ± 59 MeV respectively. These predictions can be compared with experiments in the future.[第一段]     

Heavy meson spectra for heavy quark potential in quantum chromodynamics with dilaton

For heavy meson systems, we study the heavy quark potential, which emerges from the effective dilaton－gluon coupling inspired from the superstring theory. We put emphasis on the new confinement generating mechanism of this potential through the investigation of the spin-averaged energy levels of the heavy meson systems. By using a unified approach to the solutions of the Schr?dinger and the spinless Salpeter equations, we can examine in a realistic way the effects of using a relativistic kinetic energy. The obtained results agree favourably with other predictions, and the relativistic equation can better account for the observed energy levels.     

Antikaon condensation in neutron star matter with strong magnetic fields

We study the influence of strong magnetic fields on antikaon condensation in neutron star matter using the quark-meson coupling (QMC) model. The QMC model describes a nuclear many-body system as nonoverlapping MIT bags interacting through the self-consistent exchange of scalar and vector meson mean fields. It is found that the presence of strong magnetic fields alters the threshold density of antikaon condensation significantly. The results of the QMC model are compared with those obtained in a relativistic mean-field (RMF) model.     

△-Resonance Effective Mass in Medium

Based on the relativistic chiral effective field theory, we study the effective mass of the △-resonance in medium by investigating the self-energy of the △-resonance related to the πN decay channel in symmetric nuclear matter. We find that the effective mass of △-resonance decreases evidently with increasing nuclear density p. In our calculation, we also consider the influence of the shifts of the nucleon mass, pion mass and its decay constant due to the restoration of chiral symmetry in medium. The results are roughly consistent with the data given by Lawrence Berkeley National Laboratory.     

夸克和弦模型中非奇异轻介子的类雷吉谱(英文)

本工作重新考察了相对论弦模型和准相对论夸克模型中轻介子的类雷吉谱。基于辅助场技术,提出了非奇异轻介子的一个解析质量公式,由此推导出了一个准线性的Regge-Chew-Frautschi轨迹关系,并将此关系用相应介子的实验数据（PDG）进行了检验。检验结果表明,和实验观测数据比较,夸克模型对介子质量的预言与弦模型的相符,但在角动量较大时,夸克模型的预言稍微优于弦模型。We revisit the Regge-like spectra of light mesons in the relativistic string model and the simirelativistic quark model. An analytical mass formula is proposed for light mesons based on the auxiliary field technique, and a quasi-linear Regge-Chew-Frautschi plot with flavor dependence is derived and verified with the experimental data(PDG) for light mesons.The results show that the quark model predictions for meson masses agree with those of the string model, but are slightly better when the angular momentum is relatively large as compared with the observed data.