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.     

夸克胶子混合真空凝聚和Dyson-Schwinger方程

基于夸克传播子的Dyson-Schwinger方程，计算了夸克胶子混合真空凝聚和夸克真空凝聚. 这些凝聚不仅联系着夸克在真空态中的虚度，而且也表征了真空中夸克分布的空间宽度. 真空凝聚的存在直接反映着QCD真空的非微扰结构. 计算表明：上夸克与下夸克的虚度为λ²_u,d=0.7GeV²，奇异夸克的虚度为λ²_s=1.6GeV². 这些结果与许多用完全不同的方法得到的结果一致.     

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。     

QCD真空凝聚效应对R比值的非微扰修正

本文讨论了QCD真空凝聚效应对强子结构函数中R比值(R≡σ_L/σ_I)的影响.利用背景场的基本思想,本文从有效拉氏量出发,计算了夸克凝聚对R比值的非微扰修正(Q^－2项).结果显示本文所给出的修正在小x区较敏感.     

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。     

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.     

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.     

格点(1+1)维QCD中<ψψ>的变分研究

改进的哈密顿量对格点(1+1)维QCD中Wilson费米子真空凝聚<ψψ>做变分研究.结果不但与连续理论的预言值一致,而且几乎不依赖于Wilson参数r.对于改进的哈密顿量而言,么正变换算符中的三链项对<ψψ>的贡献是很重要的.     

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.     

Tensor Susceptibilities of QCD Vacuum and Parameterized Quark Propagator

Based on the parameterized fully dressed quark propagator proposed by us, the tensor susceptibilities of QCD vacuum and quark vacuum condensates are investigated. Our predicted values of the tensor susceptibilities are in agreement with those predicted by many other theoretical models with QCD feature. The results also show that the tensor susceptibility of QCD vacuum strongly depends on flavor of quark but not sensitive to variation of quark vacuum condensates. However, the quark vacuum condensate is very sensitive to the change of cut-off-parameter μ^2 of the integration, that is, it depends on the separation point of perturbative and non-perturbative QCD region. The successful predictions clearly indicate the extensive validity of our parameterized fully dressed quark propagator used here.     

Non-perturbative Aspects of QCD and Parameterized Quark Propagator

Based on the Global Color Symmetry Model, the non-perturbative Q, CD vacuum is investigated in the parameterized fully dressed quark propagator. Our theoretical predictions for various quantities characterized the QCD vacuum are in agreement with those predicted by many other phenomenologieal QCD inspired models. The successful predictions clearly indicate the extensive validity of our parameterized quark propagator used here. A detailed discussion on the arbitrariness in determining the integration cut-off parameter ofμ in calculating QCD vacuum condensates and a good method, which avoided the dependence of calculating results on the cut-off parameter is also strongly recommended to readers.     

Quark Gluon Condensate,Virtuality and Susceptibility of QCD Vacuum

We study vacuum of QCD in this work. The structure of non-local quark vacuum condensate, values of various local quark and gluon vacuum condensates, quark-gluon mixed vacuum condensate, quark and gluon virtuality in QCD vacuum state, quark dynamical mass and susceptibility of QCD vacuum state to external field are predicted by use of the solutions of Dyson-Schwinger equations in “rainbow” approximation with a modeling gluon propagator and three different sets of quark-quark interaction parameters. Our theoretical predictions are in good agreement with the correspondent empirical values used widely in literature, and many other theoretical calculations. The quark propagator and self-energy functions are also obtained from the numerical solutions of Dyson-Schwinger equations. This work is centrally important for studying non-perturbative QCD, and has many important applications both in particle and nuclear physics.     

Vacuum condensates of QCD

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

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.     

Linear Chemical Potential Dependence of Two-Quark Condensate

By differentiating the inverse dressed quark propagator at finite chemical potential μ with respect to μ, the linear response of the dressed quark propagato r to the chemical potential can be obtained, From this we extract a modelindependent formula for the linear chemical potential dependence of the in-medium two-quark condensate and show by two independent methods （explicit calculation and Lorentz covariance arguments） that the first-order contribution in μ to the in-medium two-quark condensate vanishes identically. Therefore if one wants to study the in-medium two-quark condensate one should expand to at/east the second order in the chemical potential μ.     

Parametrization of Fully Dressed Quark Propagator

Based on an extensive study of the Dyson-Schwinger equations for a fully dressed quark propagator in the “rainbow” approximation, a parametrized form of the quark propagator is suggested. The corresponding quark self-energy Σ_f and the structure of non-local quark vacuum condensate <0|:\bar{q}(x)q(0):|0> are investigated. The algebraic form of the quark propagator proposed in this work describes a confining quark propagation, and is quite convenient to be used in any numerical calculations.     

Vacuum Condensates from the Modification of Global Color Symmetry Model

Based on the quark propagator in the instanton dilute liquid approximation, we have determined the quark condensate , the mixed quark gluon condensate g,μνσ^μνq) and the four-quark condensate at the mean-field level in the framework of global color symmetry model. The numerical calculation shows that our result is compatible with the range obtained within other nonperturbative approaches. In particular, we have found that even at the mean-field level the naive vacuum saturation approximation is not a good approximation when we consider nonlocal four-quark condensate.