Structure of Di-Ω Dibaryon

Previously, we extended our chiral SU（3） quark model to include the coupling between the quark and vector chiral fields [Nucl. Phys. A 727（2003）321]. Here we further study the structure of （ΩΩ）ST=oo dibaryon in the extended chiral SU（3） quark model by solving a resonating group method equation. The vector meson exchanges effect, hidden colour channel and colour screening effect are investigated, respectively. The results show that the （ΩΩ）ST=oo system is still the deeply bound state in the extended chiral SU（3） quark model in which the vector meson exchanges control the short-range quark-quark interaction, which is similar to the results obtained from the chiral SU（3） quark model. When the model space is enlarged by including the hidden colour channel, it is found that the energy of the hidden colour state ｜CC〉str=-6,ST=oo is much higher than that of the （ΩΩ）ST=oo state, thus the CC channel has little effect on the binding energy of （ΩΩ）ST=oo state. When the error function confinement potential is considered, the bound state property would not change largely. Fhrther, scalar meson mixing is considered. No matter whether θs= -18° or ideal mixing is taken, （ΩΩ）ST=oo state is still a bound state.     

夸克模型与ΛN系统

在Λ超子中考虑味SU(3)对称破缺,在夸克势模型基础上引进夸克与σ和π介子场的耦合,运用相对论性的两夸克集团理论,研究了ΛN作用势、³S₁道和¹S₀道的ΛN弹性散射相移.     

New Closed Expression of Interaction Kernel in Bethe-Salpeter Equation for Quark-Antiquark Bound States

The interaction kernel in the Bethe-Salpeter equation for quark-antiquark bound states is derived newly from QCD in the case where the quark and the antiquark are of different flavors. The technique of the derivation is the usage of the irreducible decomposition of the Green＇s functions involved in the Bethe-Salpeter equation satisfied by the quark-antiquark four-point Green＇s function. The interaction kernel derived is given a closed and explicit expression which shows a specific structure of the kernel since the kernel is represented in terms of the quark, antiquark and gluon propagators and some kinds of quark, antiquark and/or gluon three, four, five and six-point vertices. Therefore, the expression of the kernel is not only convenient for perturbative calculations, but also suitable for nonperturbative investigations.     

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.     

核力夸克模型中N△道耦合效应的研究

在核力的夸克-SU(3)手征场耦合模型基础上研究了N△道耦合效应对NN散射相移的影响. 结果表明N△的5D0分波与NN道的1S0分波间的耦合效应较大,NN的D､F分波与N△道之间的耦合效应较小.     

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.     

In-medium pion dispersion relation and medium correction of Nπ■Δ near the threshold energy of pion production

Transport models cannot simultaneously explain very recent data on pion multiplicities and pion charged ratios from central collision of Sn+Sn at 0.27 A GeV.This stimulates further investigations on the pion dispersion relation,in-medium Nπ→Δ cross sections,and Δ→Nπ decay widths near the threshold energy or at subthreshold energy of pion production in isospin asymmetric nuclear matter.In this study,the pion dispersion relation,in-medium Nπ→Δ cross section,and Δ→Nπ decay width near the threshold energy are investigated in isospin asymmetric nuclear matter by using the one-boson-exchange model.With the consideration of the energy conservation effect,the in-medium Nπ→Δ cross sections are enhanced at s1/2 <1.11 GeV in a nuclear medium.The prediction of pion multiplicity and π-/π+ ratios near the threshold energy could be modified if this effect is considered in transport model simulations.     

相对论夸克模型和N—△能量劈裂

基于相对论夸克模型，在夸克层次上研究了N-△的质量和二者的能量劈裂，通过引入了赝标量π介子云效应，得到了π和核子宰的耦合常数gxNN，以及单胶子交换势和单π介子交换势分别对N-△能量劈裂的贡献，计算结果较好地与实验值得到了吻合。另外我们还比较了相对论与非对论夸克模型在处理上的不同。     

Theoretical Analysis of Structures of Ga4N4 Clusters

The structures and energies of a Ga4N4 cluster have been calculated using a full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO MD) method. We obtained twenty-four structures for a Ga4N4 cluster. The most stable structure we obtained is a C8 three-dimensional structure, the energy of which is lower than that of the C2v symmetry structure proposed by Kandalam et al. [J. Phys. Chem. B106 (2002) 1945] The calculated results show that the isomer with an N3 subunit is preferred, supporting the previous result made by Kandalam et al,We found that the most stable structure of Ga4N4 clusters presented semiconductor-like properties through the calculation of the density of states.     

手征SU(3)夸克模型研究低能Nπ散射相移

在手征,SU(3),夸克模型中,通过求解共振群方程动力学地研究了同位旋,I=1/2,和,I=3/2,道,Nπ,的,S,波和,P,波低能弹性散射相移.所用的模型参数由基态八重态和十重态重子的能量定出, 并能给出不同分波的,KN,散射相移.除了有明显共振态的道以外, 计算得到的各个分波的,Nπ,散射相移和实验值定性一致.     

Tensor Polarization t20 of the Deuteron and the ρπγ Process

Tensor Polarization t20 of the deuteron is calculated on the basis of a hybrid quark-hadron model.A relativistic wavefunction of the deuteron is used to calculate the relativistic impulse approximation and the contribution of the ρπγ meson exchange process.A good agreement with experimental data is achieved when and only when the ρπγ coupling is taken as positive.     

Contributions of qqqqq Components to Axial Charges of Proton and N（1440）

The axial charges of the proton and N（1440） are studied in the framework of an extended constituent quark model （CQM） including qqqqq components. The cancellation between the contributions of qqq components and qqqqq components gives a natural explanation to the experimental value of the proton axial charge, which can not be well reproduced in the traditional CQM even after the SU（6） × O（3） symmetry breaking is taken into account. The experimental value of axial charge pins down the proportion of the qqqqq component in the proton to about 20%, which is consistent with the ones given by the strong decay widths and helicity amplitudes. Besides, an axial charge for N（1440） about 1 is predicted with 30% qqqqq component, which is obtained by the strong and electromagnetic decays.     

Axial charges of N（1535） and N（1650） in two-flavor lattice QCD

We show the lattice QCD results on the axial charge gAN＊-N＊ of negative parity nucleon resonances, N＊（1535） and N＊（1650）, which are key clues to the chiral structure in baryon sector. The measurements are performed with up and down dynamical quarks employing the renormalization-group improved gauge action at β=1.95 and the O（a） improved clover quark action with the hopping parameters, κ=0.1375, 0.1390 and 0.1400. In order to properly separate signals of N＊ （1535） and N＊ （1650）, we construct 2 × 2 correlation matrices and diagonalize them. Wraparound contributions in the correlator, which can be another source of signal contaminations, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of N＊ （1535） takes small values as gAN＊N＊-O（0.1）, whereas that of N＊ （1650） is about 0.5, which is found independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model.     

Electronic Structures of Wurtzite GaN with Ga and N Vacancies

The electronic band structures of wurtzite GaN with Ga and N vacancy defects are investigated by means of the first-principles total energy calculations in the neutral charge state. Our results show that the band structures can be significantly modified by the Ga and N vacancies in the GaN samples. Generally, the width of the valence band is reduced and the band gap is enlarged. The defect-induced bands can be introduced in the band gap of GMV due to the Ga and N vacancies. Moreover, the GaN with high density of N vacancies becomes an indirect gap semiconductor. Three defect bands due to Ga vacancy defects are created within the band gap and near the top of the valence band. In contrast, the N vacancies introduce four defect bands within the band gap. One is in the vicinity of the top of the valence band, and the others are near the bottom of the conduction band. The physical origin of the defect bands and modification of the band structures due to the Ga and N vacancies are analysed in depth.     

Subtraction of Spurious Centre-of-Mass Motion in Quark Delocalization and Colour Screening Model

The quark delocalization colour screening model provides an alternative approach for the NN intermediate range attraction, which is attributed to the σ meson exchange in the meson exchange and chiral quark model. However the quark delocalization induces the spurious centre-of-mass motion （CMM）. A method for subtracting the spurious CMM proposed before is applied to the new scattering calculation. The subtraction of the spurious CMM results in an additional NN attraction. The NN scattering data are refitted by a fine tune of the colour screening constant.     

Structures of（ΩΩ）0＋and（[1]Ω）1＋in Extended Chiral SU（3） Quark Model

The structures of (ΩΩ)0 and ([1]Ω)1 are studied in the extended chiral SU(3) quark model in which vector meson exchanges are included. The effect from the vector meson fields is very similar to that from the one-gluon exchange (OGE) interaction. Both in the chiral SU(3) quark model and in the extended chiral SU(3) quark model,di-omega (ΩΩ)0 is always deeply bound, with over one hundred MeV binding energy, and ([1]Ω)1 ‘s binding energy is around 20 MeV. An analysis shows that the quark exchange effect plays a very important role for making di-omega (ΩΩ)0 deeply bound.     

Quantization of the O（N） Nonlinear Sigma Model

The Hamilton-Jacobi method of quantizing singular systems is discussed.The equations of motion are obtained as total differential equations in many variables.It is shown that if the system is integrable,one can obtain the canonical phase space coordinates and set of canonical Hamilton-Jacobi partial differential equations without any need to introduce unphysical auxiliary fields.As an example we quantize the O(2) nonlinear sigma model using two different approaches:the functional Schrodinger method to obtain the wave functionals for the ground and the exited state and then we quantize the same model using the canonical path integral quantization as an integration over the canonical phase-space coordinates.     

Structures and Electronic Properties of CuN （N≤13） Clusters

A systematic study on the structures and electronic properties of copper clusters has been performed using the density functional theory. In the calculation, there are many isomers near the ground state for small copper clusters. Our results show that the three-dimensional isomers of copper clusters start from Cu7 cluster and then show a tendency to form more compact structures. The results of the formation energy and the second derivative of binding energy with duster size show that besides N = 8, N =11 is also a magic number. Furthermore, it is the first time to find that the ground state of 11-atom clusters is a biplanar structure as same as the 13-atom cluster. The clear odd-even alternation as cluster size for the formation energy indicates the stability of electronic close shell existed in the range studied.     

Generation of NIulticomponent NIotional Coherent and Squeezed Coherent States of N Trapped Ions by a Dispersive Interaction

Following the recent proposal by Solano E et al. [Phys. Rev. Left. 87 (2001) 060402] a procedure is proposed to generate arbitrary discrete multicomponent motional coherent and squeezed coherent states of N trapped ions by additionally using a dispersive bichromatic interaction in a long-living and fast way. In this procedure, two lasers in the Raman configuration are tuned quasiresonant and resonant with N two-level ions under different conditions, respectively. Furthermore, we show how the idea can be used for the generation of two-mode SU(2) Schrdinger cat states for the vibrational motion of a single ion trapped in a two-dimensional harmonic potential.     

Ab Initio Study of Structural and Electronic Properties of Hexagonal BC2N

We investigate hexagonal BC2N in graphite unit cells using the first-principles method and calculate the total energies, lattice parameters, and electronic band structures after full relaxation. It is shown that stable hexagonal BC2N should be stacked sequentially with one graphite layer and one h-BN layer. The density of states indicates that this structure should have metallicity.