夸克非定域的真空凝聚结构

基于Dyson Schwinger方程和彩虹近似 ,我们导出了完全穿衣服 (fullydressed)的夸克传播子。利用所得到的夸克传播子 ,研究了非定域的夸克真空凝聚的结构 ,成功地预言了定域的夸克真空凝聚值和夸克胶子的混合真空凝聚值。理论预言的凝聚值与文献中常用的经验值完全一致。     

非微扰QCD真空中夸克真空凝聚的结构(英文)

基于Dyson-Schwinger方程(DSEs)所确定的夸克传播子和算符成积展开(OPE),在彩虹近似下,预言了QCD真空中非定域夸克真空凝聚的结构。这种结构由夸克自能函数Af和Bf决定,通过数值求解DSEs就可以得到这些自能函数。但是,直接数值求解DSEs方程非常复杂,这里采用Roberts和Williams提出的参数化方法,用参数化的夸克传播函数σf v(p2)和σf s(p2)计算夸克自能函数。同时,也计算了定域的夸克真空凝聚值,夸克胶子混合的真空凝聚值,以及夸克的虚度。理论预言和计算结果均与标准QCD求和定则、格点QCD和瞬子模型的理论结果大致相符。和这些模型的结果相比,参数化方法得到的轻夸克(u,d,s)的定域真空凝聚偏大,这主要是由于模型依赖导致的。与u,d夸克相比,s夸克的真空凝聚比较大,这是因为s夸克自身质量较大的缘故。当然,Roberts-Williams参数化的夸克传播子只是一个经验公式,只能近似描述夸克的传播。     

QCD真空凝聚和参数化的夸克传播子

基于整体色对称模型,用完全穿衣服参数化的夸克传播子研究了量子色动力学(QCD)真空的性质,预言了各种表征QCD真空的凝聚值.其结果与其他唯象QCD理论模型的预言是一致的.结果清楚地表明了参数化的夸克传播子是成功和可靠的.讨论了计算QCD真空凝聚值时积分截断参数的问题,提出了一个避免计算的结果对截断参数强烈依赖的物理方法.     

非定域夸克真空的结构和Kisslinger函数

夸克的真空凝聚是量子色动力学(QCD)研究中一个非常重要的问题.用完全穿衣服的夸克传播子研究了QCD真空性质和夸克的真空结构.计算了定域夸克的真空凝聚值,预言了夸克的真空结构.其结果与文献中的经验值相符合,也与Dyson-Schwinger方程解一致.说明参数化的夸克传播子是成功和可靠的.     

红外区Dyson-Schwinger方程的两种重整化方案的比较

在胶子和鬼传播子所满足的耦合的Dyson-Schwinger方程中, 采用裸胶子－鬼顶点, 利用两种重整化方案: 解析延拓方法和减除方法, 得到了胶子和鬼传播子的红外行为. 计算表明两种重整化方案在红外区对胶子和鬼传播子得到一致的结果.     

关于夸克凝聚和混合凝聚平移不变性的讨论

讨论夸克凝聚和混合凝聚在Lorentz规范下的泰勒展开式,这两个展开式可用来计算算符乘积展开中非微扰修正项的Wilson系数.与目前在QCD求和规则方法中所应用的、在固定点规范下的相应展开式相比,新的展开式具有平移不变性的优点.     

夸克的真空凝聚值和张量感应率及参数化的夸克传播子

利用以前提出的参数化的夸克传播子， 计算了夸克的真空凝聚值和QCD真空的张量感应率。 结果表明， 张量感应率对不同味道的夸克的依赖是很明显的， 而几乎不依赖于夸克的真空凝聚值的变化。 但夸克凝聚值却明显地与积分的截断值有关， 即依赖于微扰区与非微扰区的分界线， 在常用的积分截断值1—2 GeV2之间计算得到的夸克凝聚值与文献中常用的值及其他理论的预言值是一致的。 理论预言的张量感应率也与其他理论结果相一致。     

洛伦兹规范条件下对单胶子夸克势的QCD非微扰修正形式

在洛伦兹规范条件下,导出了具有平移不变性的双胶子两点函数真空平均值.利用所获得的双胶子真空期待值,给出了对微扰单胶子交换夸克–夸克势、夸克–反夸克对湮没和夸克–反夸克对激发势的最低阶非微扰QCD修正形式.     

非微扰夸克传播子与核子结构函数的非平庸Q2依赖性研究

考虑最低维非微扰效应即夸克凝聚和胶子凝聚对夸克传播子的贡献,在链近似下,计算了QCD非微扰夸克传播子; 基于所获得的非微扰夸克传播子,对核子结构函数中的非微扰效应进行了分析,给出了核子结构函数的非平庸Q²依赖性.     

利用SLEGS开展夸克和胶子层次上的核物理研究

通过对国际上中能核物理的发展,特别是前沿领域中的现状的回顾,阐述了利用在上海原子核所计划建造的第三代同步辐射加速器(SSRF)上建立新一代的激光 电子康普顿背散射γ射线源(SLEGS)从事夸克和胶子层次上的中能核物理研究的科学目标及研究内容. The proposed SLEGS (Shanghai Laser Electron backscattering Gamma Source) will be a circular and linear polarization, new generation, high quality γ ray source with Eγ=0.2-0.87 GeV. The major scientific focus of nuclear physics research at SLEGS will be investigations of the microscopic quark gluon aspects of nucleons , nucleon resonance states and nuclei to test and develop non perturbative QCD. Using polarized photon induced reactions on unpolarized and polarized nucleon target such as γN→γ N, ...     

Susceptibilities of QCD Vacuum from Renormalized Dyson-Schwinger Equations

The pion and tensor vacuum susceptibilities are calculated in the framework of the renormalizable Dyson-Schwinger equations. A comparison with the results of other nonperturbative QCD approaches is given.     

Vacuum condensates of QCD

We study the properties of QCD vacuum state in this paper. The     

Dynamically Running Mass of Light Quark and QCD Vacuum Condensates

Based on Dyson-Schwinger equations (DSEs) in “rainbow“ approximation, the dynamically running mass of light quark and QCD vacuum condensate are investigated. The structure of non-local quark vacuum condensate, the values of local vacuum condensate of quarks and quark-gluon mixture, and dynamical transition of quark mass from current quark to constituent quark are illustrated. At the same time, according to the knowledge and experience learned from an extensive study of the solutions of DSEs, a parameterized form of confining quark propagator is suggested for a practical use. The new parameterized form of quark propagator is analytic everywhere in the finite complex p2-plane and has no Lehmann representation. The predictions for p2-dependence of effective quark masses, Mf(p2), defined by the self-energy functions Af(p2) and Bf(p2), both from the numerical solutions of DSEs and from its parameterized form, are shown dynamically. Our conclusion is that all numerical results are consistent with empirical values used in QCD sum rules and lattice QCD calculations. For a qualitative study, the parameterized form is a sufficiently good approximation to confining quark propagator.     

Dynamical Model of QCD Vacuum and Quark Confinement

The phase transition of a simple local gauge model is investigated in terms of the Nambu-Jona-Lasinio mechanism and it is pointed out that the physical vacuum of QCD is bound state of quark-antiquark pairs which can be viewed, generally, as a nearly perfect color dia-electric medium. An important relation between the vacuum expectation value of gauge fields and scalar fields is also derived by solving the Euler equation for the gauge fields. Based on this relation the SU_C(3) gauge potential is given which can be used to explain the asymptotic behavior and confinement of quarks in a hadron, and at the same time the Yukawa potential of strong interaction can be given too.     

Mixed Quark-Gluon Condensate Beyond Chiral Limit

Using the Dyson-Schwinger equation and perturbation theory, we calculate the mixed quark-gluon condensates in the chiral limit and in the case of nonzero quark current mass for the light quark u/d and strange quark s. The results show that the mixed quark-gluon condensate will decrease when the quark mass increases. For the quark with zero mass, we obtain mo2 = g（qσuvGuvq）/（qq） 0.68 GeV2, which is in good agreement with the QCD sum rules estimate mo2=（0.8± 0.2） GeV2.     

Vacuum condensates of QCD

We study the properties of QCD vacuum state in this paper. The values of various local quark vacuum condensates, quark-gluon mixed vacuum condensates, and the structure of non-local quark vacuum condensate are predicted by the solution of Dyson-Schwinger Equations in "rainbow" approximation with three sets of different parameters for effective gluon propagator. The light quark virtuality is also obtained in a consistent way. Our all theoretical results here are in good agreement with the empirical values used widely in literature and many other theoretical calculations.