核子(强子)结构和性质的QCD研究

核子 (强子 )是夸克、胶子的束缚态 ,由量子色动力学 QCD描述。由于 QCD的基本特性(高能标度下的渐近自由、低能标度下色禁闭及动力学手征对称性破缺 ) ,对核子 (强子 )结构和性质的 QCD图象是标度相关的 .在高能标度下描述强子的是与探测强子结构的硬过程相联系的QCD部分子模型 .强子的夸克、胶子结构信息通过 QCD部分子求和规则得到 .QCD微扰论是适用的理论 .在低能标度时 ,必须发展 QCD非微扰途径来描述核子 (强子 )物理 .这里简要地讨论各种非微扰途径 (格点 QCD、Dyson- Schwinger方程、有效场论、QCD求和规则 )的某些结果和进展 ,并指出 QCD真空结构在描述低能标度下强子物理中担任重要角色 . The nucleon (hadron) is the bound state of guarks and gluons, which is described by the quantum chromodynamics (QCD). Due to the basic properties of QCD (the asymptotic freedom at the high energy scale, the color confinement and the dynamical chiral symmetry breaking at the low energy scale), the QCD picture for the nucleon’s (hadron’s) structure and property is scale dependent. At high energy scale, the QCD parton model, which is relative to the hard process for testing the...     

Quantum chromodynamics

Quantum Chromodynamics (QCD) is a quantum field theory of the strong interaction with non-abelian gauge fields mediating the interactions between quarks. The experimentally observed strong interactions are to be epiphenomena of these fundamental interactions. The experimental successes of QCD form the basis for our present optimism that a theory of the strong force has been found. However, QCD is still very vulnerable to default on both experimental and theoretical grounds. In this article we offer the reader a review of the properties and attempted solutions of QCD. Each section of this review can be read independently of the others. In the introduction we describe the properties of QCD and the hoped for confinement and PCAC phase transitions. This is followed by a section on the renormalization of non-abelian gauge field theories: the functional methods and the path integral, the BPHZ program, the BRS transformation and proof of renormalizability, the Slavnov-Taylor identities and Schwinger-Dyson equations. The renormalization group equations are derived and applied to physical processes. Two dimensional prototypes of QCD, the abelian Schwinger model and 2-D QCD, are reviewed. An extensive review of the perturbative development of QCD is given with emphasis on infrared divergences, exponentiation of leading logarithms, the Cornwall-Tiktopoulos equation and a non-perturbative approach to QCD. A self contained section on topological solitons follows with discussions of homotopy theory, vortices, monopoles and especially instantons, and the periodic vacuum. Recent results, the attempt to study phase transitions in QCD using the dilute gas approximation and Borel resummations in QCD, are examined. Most of the major areas of interest in QCD are covered in this review; the prime exceptions are lattice gauge theories and phenomenological QCD like the parton and potential models.     

AdS/QCD at finite density and temperature

We review some basics of AdS/QCD following a non-standard path and list a few results from AdS/QCD or holographic QCD. The non-standard path here is to use the analogy of the way one obtains an effective model of QCD like linear sigma model and the procedure to construct an AdS/QCD model based on the AdS/CFT dictionary.     

Lattice QCD

Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.     

Extraction of the x-dependence of the non-perturbative QCD b-quark fragmentation distribution component

Using recent measurements of the b-quark fragmentation distribution obtained in events, registered at the Z pole, the non-perturbative QCD component of the distribution has been extracted independently of any hadronic physics modelling. This distribution depends only on the way the perturbative QCD component has been denned. When the perturbative QCD component is taken from a parton shower Monte Carlo, the non-perturbative QCD component is rather similar with those obtained from the Lund or Bowler models. When the perturbative QCD component is the result of an analytic NLL computation, the non-perturbative QCD component has to be extended in a non-physical region and thus cannot be described by any hadronic modelling. In the two examples, used to characterize these two situations, which are studied at present, it happens that the extracted non-perturbative QCD distribution has the same shape, being simply translated to higher-x values in the second approach, illustrating the ability of the analytic perturbative QCD approach to account for softer gluon radiation than with a parton shower generator.     

The AdS/CFT Correspondence and Holographic QCD

Holographic QCD is an extra-dimensional approach to modeling QCD resonances and their interactions. Holographic models encode information about chiral symmetry breaking, Weinberg sum rules, vector meson dominance, and other phenomenological features of QCD. There are two complementary approaches to holographic model building: a top–down approach which begins with string-theory brane configurations, and a bottom–up approach which is more phenomenological. In this talk I will describe the AdS/CFT correspondence, which motivates Holographic QCD, and the techniques used to build holographic models of QCD and to calculate observables in those models. I will also discuss an intriguing lightcone approach to Holographic QCD discovered by Brodsky and De Teramond.     

Jet quenching and gluon to hadron fragmentation function in non-equilibrium QCD at RHIC and LHC

Theoretical understanding of the observed jet quenching measurements at RHIC and LHC is challenging in QCD because it requires understanding of parton to hadron fragmentation function in non-equilibrium QCD. In this paper, by using closed-time path integral formalism, we derive the gauge invariant definition of the gluon to hadron fragmentation function in non-equilibrium QCD which is consistent with factorization theorem in non-equilibrium QCD from first principles.     

Light-like Wilson line in QCD without path ordering

Unlike the Wilson line in QED the Wilson line in QCD contains path ordering. In this paper we get rid of the path ordering in the light-like Wilson line in QCD by simplifying all the infinite number of noncommuting terms in the SU(3) pure gauge. We prove that the light-like Wilson line in QCD naturally emerges when path integral formulation of QCD is used to prove factorization of soft and collinear divergences at all order in coupling constant in QCD processes at high energy colliders.     

Progress in vacuum susceptibilities and their applications to the chiral phase transition of QCD

The QCD vacuum condensates and various vacuum susceptibilities are all important parameters which characterize the nonperturbative properties of the QCD vacuum. In the QCD sum rules external field formula, various QCD vacuum susceptibilities play important roles in determining the properties of hadrons. In this paper, we review the recent progress in studies of vacuum susceptibilities together with their applications to the chiral phase transition of QCD. The results of the tensor, the vector, the axial–vector, the scalar, and the pseudo-scalar vacuum susceptibilities are shown in detail in the framework of Dyson–Schwinger equations.     

Rho Meson Distribution Amplitudes from QCD Sum Rules with Nonlocal Condensates

The leading-twist distribution amplitude for the longitudinal rho-meson was studied using QCD Sum Rules with nonlocal condensates and a spectral density which includes next-to-leading order radiative corrections. The obtained profile is compared with results from standard QCD sum rules, lattice QCD, holographic QCD, a light-front quark model, and the instanton liquid model. Preliminary estimates for the first two moments of the transverse ρ-meson distribution amplitude are also given.     

Magnetic Symmetry,Regge Trajectories,and the Linear Confinement in Dual QCD

Using the magnetic symmetry structure of non-Abelian gauge theories, we analyze the flux tube formulation and its implications on the hadronic Regge trajectories and the confinement of color isocharges in magnetically condensed (with as well as without the electric excitations) QCD vacuum. Starting with the fiber bundle structure of QCD, the dual potentials are used to construct the QCD Lagrangian which has been shown to develop a unique flux tube configuration in its dynamically broken phase. The vector mass mode of the condensed vacuum has been shown to play a leading role in flux tube energy and other confinement parameters. Using the flux tube energy and the angular momentum, the Regge trajectories for hadrons have been obtained and the linear confining properties of dual QCD have been established. The dyonic flux tube structure of the condensed QCD vacuum has been obtained by inducing the electric excitation of QCD monopoles and the confining nature along with the linearity of Regge trajectories in dyonically condensed QCD vacuum are shown to remain intact. Implications of the modification in Regge slope parameter, on improving the confining properties of dual QCD vacuum are also discussed. PACS: 12.38.Aw; 11.30.-j; 14.80.Hv; 12.39.Mk An erratum to this article is available at .     

规范场和夸克动力学模型--关于QCD和层子模型的议论

文章讨论了夸克QCD模型和层子模型的关系，说明夸克动力学模型的基础是非亚贝尔规范场理论．层子模型是半唯象理论，没有动力学互作用的机制．QCD由于以非亚贝尔规范场为动力学互作用机制，在高能行为有渐近自由的重要性质．层子模型是低能束缚态的唯象性质的模型，与渐近自由是完全无关．强调“渐近自由”是一个独立于夸克模型的物理概念，它的理论基础是非亚贝尔规范场理论；当把非亚贝尔规范场作为夸克相互作用建立了夸克的动力学模型——量子色动力学（quantum chromodynamics，QCD）；层子模型是想把静态夸克模型发展为动力学模型，但它走的路线与QCD完全不同，层子的互作用不涉及非亚贝尔规范场，与渐近自由是不同概念和不同思想和不同考察区域；文章还指出夸克动力学的QCD模型同层子模型是哲学思想不同，物理思想也不相同的路线，层子模型没有接纳非亚贝尔规范场而未能达成创新的成果．文章也强调三十多年前层子模型研究的创新意识和团队精神是我们值得推崇的优秀传统．     

规范场和夸克动力学模型——关于QCD和层子模型的议论

文章讨论了夸克QCD模型和层子模型的关系,说明夸克动力学模型的基础是非亚贝尔规范场理论.层子模型是半唯象理论,没有动力学互作用的机制.QCD由于以非亚贝尔规范场为动力学互作用机制,在高能行为有渐近自由的重要性质.层子模型是低能束缚态的唯象性质的模型,与渐近自由是完全无关.强调“渐近自由”是一个独立于夸克模型的物理概念,它的理论基础是非亚贝尔规范场理论;当把非亚贝尔规范场作为夸克相互作用建立了夸克的动力学模型——量子色动力学（quantum chromodynamics,QCD）;层子模型是想把静态夸克模型发展为动力学模型,但它走的路线与QCD完全不同,层子的互作用不涉及非亚贝尔规范场,与渐近自由是不同概念和不同思想和不同考察区域;文章还指出夸克动力学的QCD模型同层子模型是哲学思想不同,物理思想也不相同的路线,层子模型没有接纳非亚贝尔规范场而未能达成创新的成果.文章也强调三十多年前层子模型研究的创新意识和团队精神是我们值得推崇的优秀传统.     

QUANTUM CHROMODYNAMICS AS THE TRORY OF INTERACTIONS

Recent developmeht of testing QCD as the theory of strong interactions is reviewed. Emphasis is put on the success of perturbative QCD and the determination of the fundamental scale parameter scale parameter A. Recent development of heavy quarkonium physics is also reviewed from the point of view of QCD and the possibility that future heavy quarkonium experiments can provide further quantitative QCD tests is discussed.     

QCD dirac operator at nonzero chemical potential: lattice data and matrix model

Recently, a non-Hermitian chiral random matrix model was proposed to describe the eigenvalues of the QCD Dirac operator at nonzero chemical potential. This matrix model can be constructed from QCD by mapping it to an equivalent matrix model which has the same symmetries as QCD with chemical potential. Its microscopic spectral correlations are conjectured to be identical to those of the QCD Dirac operator. We investigate this conjecture by comparing large ensembles of Dirac eigenvalues in quenched SU(3) lattice QCD at a nonzero chemical potential to the analytical predictions of the matrix model. Excellent agreement is found in the two regimes of weak and strong non-Hermiticity, for several different lattice volumes.     

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.     

Finite-size scaling behavior in the <Emphasis Type="Italic">O</Emphasis>(4) model

The exact nature of the QCD phase transition has still not been determined conclusively, and there are contradictory results from lattice QCD simulations about the scaling behavior for two quark flavors. Ultimately, this issue can be resolved only by a careful scaling and finite-size scaling analysis of the lattice results. We use a renormalization group approach to obtain finite-size scaling functions for the O(4) model, which are relevant for this analysis. Our results are applicable to lattice QCD studies of the QCD phase boundary.     

Decoupling of heavy quarks in mass-independent momentum subtraction schemes

Heavy quark decoupling in Quantum Chromodynamics (QCD) defined by mass-independent momentum subtraction (MOM) is investigated. The coefficients of the functions which allow for twoloop matching of the QCD parameters below and above a heavy quark threshold are calculated for some MOM schemes. The resulting numerical relations between the QCD scales and between the renormalization group invariant light-quark mass parameters off andf?1 flavour QCD are given.     

Thermo-field dynamics and quark–hadron phase transition in QCD

Based on the topological structure of gauge theory, an effective dual version of QCD has been reviewed and analyzed for the phase structure and color confining properties of QCD by invoking the dynamical magnetic symmetry breaking. The multi-flux-tube configuration of condensed QCD vacuum has been explored and associated glueball masses and inter-quark potential have been derived. Thermal response of QCD vacuum has been analyzed using path-integral formalism alongwith the mean-field approach and associated thermodynamical potential is used to derive thermal form of glueball masses, monopole condensate, inter-quark potential and monopole density which then lead to an estimate of the critical temperature of QCD phase transition. During its thermal evolution, a smooth transition of hadronic system via a weakly bound QGP phase to the fully deconfined phase is established and the thermal evolution profiles of various parameters are shown to indicate a second-order deconfinement phase transition and the restoration of magnetic symmetry. Monopole density calculations have been shown to lead to gradual evaporation of magnetic condensate into thermal monopoles during QCD phase transition.