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.     

重离子碰撞中的矢量介子自旋排列

在非对心相对论重离子碰撞中,参与反应的系统具有巨大的轨道角动量,从而使产生的夸克胶子等离子体具有极强涡旋场,并通过自旋-轨道相互作用导致部分子的自旋极化,经过强子化导致重子的自旋极化以及矢量介子的自旋排列等可观测效应.矢量介子的自旋排列是指其自旋密度矩阵的00元素ρ00偏离1/3.在矢量介子衰变到两个赝标介子的过程中,衰变产物的极角分布只与ρ00有关,以此可以对自旋排列进行测量.理论研究表明,重离子碰撞过程中,重子的自旋极化反映了夸克自旋极化的时空平均效应,而矢量介子自旋排列则反映了夸克反夸克自旋极化的局域相空间关联.本文回顾了相对论重离子碰撞中矢量介子自旋排列的相关理论工作.重点以非相对论夸克融合模型为例,明确地计入夸克极化的相空间依赖性,展示了矢量介子自旋排列与夸克反夸克自旋极化特别是它们之间相空间关联的关系.本文还讨论了涡旋、电磁场、有效φ介子场以及它们的局域涨落对φ介子自旋排列的贡献,结果显示强作用场的时空关联效应是导致φ介子自旋排列的主要因素.矢量介子自旋排列为探索强相互作用物质和强相互作用场的性质提供了新途径.     

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.     

关于Reggeon的结构

从强子组分夸克具有结构的观点出发，根据高能强作用软过程中的最大非微扰强作用反应假定,提出了关于Reggeon(IR)的结构模型.高能时对撞强子中的一对组分夸克-反夸克在最大反应下有一定的几率先分解为非微扰胶子和旋量团(反旋量团).此旋量团对将进一步演化而放射出一系列的非微扰胶子(和夸克对)并最终湮没.将这种过程与其逆向(厄米共轭)过程并合,就可得出有关的IR的场论结构图象.它是以旋量团为竖线,胶子为横线的一系列切割梯形图之和所代表.本文在系统能量大而动量转移很小的多重Regge运动学区间和只保留Ins的领头阶近似下,计算了这组切割梯形图相应的散射振幅,求出了它们的总和,得出了与轻夸克介子对应的典型Regge极点轨迹的简洁表达式,对结果进行了简单的讨论.     

量子色动力学非微扰传播子

本文在链近似下计算了QCD非微扰夸克和胶子完全传播子.我们仅考虑最低维非微扰效应即夸克凝聚<Ω│ψψ│Ω>和胶子凝聚<Ω│G²│Ω>对传播子的贡献,胶子凝聚通过作为<Ω│Aαμ(x)Abv(y)│Ω>在洛伦兹规范下展开级数的系数而引入.与采用固定点规范相比,胶子凝聚的引入没有破坏平移不变性.因而,我们计算出了夸克完全传播.如采用固定点规范不能做到这一点.     

核子–核子散射过程的研究和矢量介子交换势

在推广的手征SU(3)夸克模型下讨论了核子–核子散射过程和矢量介子交换势.给出了赝标π介子和矢量ρ和ω介子的GCM中心力的交换势和NN散射14个分波的相移.研究表明,矢量介子交换势可以替代单胶子交换势以解释核力的短程排斥.     

动力学部分子模型在核子和冷核物质中的应用

本工作研究了自由核子和冷原子核物质的动力学产生的海夸克和胶子分布。在动力学部分子模型中,所有的海夸克和胶子纯粹来自DGLAP方程描述的QCD涨落过程,而较少的固有海夸克成分忽略不计。在$Q_0^2\sim 0.1$ GeV2标度,选择最大熵方法估计的三价夸克分布作为非微扰输入。使用了在低$Q^2$(本工作研究了自由核子和冷原子核物质的动力学产生的海夸克和胶子分布。在动力学部分子模型中,所有的海夸克和胶子纯粹来自DGLAP方程描述的QCD涨落过程,而较少的固有海夸克成分忽略不计。在$Q_0^2\sim 0.1$ GeV2标度,选择最大熵方法估计的三价夸克分布作为非微扰输入。使用了在低$Q^2$($<1$ GeV2)下饱和的跑动强耦合常数。关于原子核效应,考虑了核子变胖和部分子-部分子重组增强的影响。核子及冷核物质的动力学部分子分布均符合实验观测。应用预言的原子核部分子分布抽取得到部分子在穿过冷核物质时的能量损失。     

非奇异重子谱的非微扰效应

在组态混合下,通过解三夸克系统的薛定谔方程,研究了N和△的能谱.考虑的夸克-夸克相互作用位,除通常的微扰单胶子交换位外,还包括两个具有非微扰效应的位,即具有色屏蔽效应的禁闭位和由手征破缺产生的π和σ交换位.所得到的重子谱表明非微扰效应改进了理论与实验的符合程度,从而给出了N和△体系较好的描述.     

相对论夸克模型和N–Δ能量劈裂

基于相对论夸克模型,在夸克层次上研究了N-Δ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和核子之间的耦合常数g_πNN,以及单胶子交换势和单π介子交换势分别对N-Δ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相对论夸克模型在处理上的不同.     

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。     

The dilepton-production cross section in principal value resummation

Using a recent calculation of the perturbative hard part for dilepton production that sums large threshold corrections to all orders in perturbative QCD, we compute the corresponding cross sections. The hard part has been evaluated using principal value resummation and contains all singular momentum-dependent corrections. We also include a resummation of large Sudakov terms, which are independent of parton momenta. We give predictions for the dilepton-mass distribution, the rapidity distribution and the rapidity-integrated K-factor at fixed-target energies and compare with various experimental results in several kinematic regimes. We find that principal value resummation produces cross sections that are finite and well-behaved. For both protons and anti-protons on fixed targets, the resummed cross sections are, in general, in excellent agreement with the data.     

A unified description of the perturbative photon structure function inx space

We give here in detail the derivation of the various contributions to the photon structure function in the perturbative region. The lowx region problem is pointed out and the QCD corrections to the hadronic part are discussed, including the quasi perturbative region of higher twist effects. The transition from highQ ² to lowQ ² is examined and the basis for a realistic and consistent simulation of higher order QCD processes is given.     

The gluon propagator in temporal gauge

The implementation of Gauss's law in perturbative calculations in temporal gauge is achieved through ana explicit construction of the vacuum state. In this scheme the free gluon propagator is calculated. Terms in addition to the principal value part are found.     

Renormalization group analysis of the τ-lepton decay within QCD

A technique to sum up the regular corrections appearing under the analytical continuation from the space like momentum region to the time like one is proposed. A perturbative part of the inclusive semileptonic decay width of the τ-lepton in analyzed in detail.     

Quarkonium spectral functions with complex potential

We study quarkonium spectral functions at high temperatures using a potential model with complex potential. The real part of the potential is constrained by the lattice QCD data on static quark anti-quark correlation functions, while the imaginary part of the potential is taken from perturbative calculations. We find that the imaginary part of the potential has significant effect on quarkonium spectral functions, in particular, it leads to the dissolution of the 1S charmonium and excited bottomonium states at temperatures about 250 MeV and melting of the ground state bottomonium at temperatures slightly above 450 MeV.     

Nonperturbative contribution to the quark form factor within the instanton model

The nonperturbative effects in the quark form factor are considered in the Wilson loop formalism, within the framework of the instanton liquid model. For the integration path corresponding to this form factor, the explicit expression for the vacuum expectation value of the Wilson operator is found to the leading order. It is shown that the instantons produce the power-like corrections to the perturbative result, which are comparable in magnitude with the perturbative part at the scale of order of the inverse average instanton size. It is demonstrated that the instanton contributions to the quark form factor are exponentiated to high orders in the small instanton density parameter.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.38.-t Quantum chromodynamics - 11.15.Tk Other nonperturbative techniques     

Scalar trace anomaly and anti-gravitational interaction in a perturbative approach to self-consistent cosmologies

We present a perturbative approach to the equations controlling the behavior of the recently proposed self-consistent, causal, singularity-free cosmologies. This approach sheds a new light on the threshold mass which governs both the (in)stability of empty Minkowski space and the existence of these cosmologies. An unexpected fact arises at the lower order of this perturbative scheme: the mass of the massive (scalar) field coupled non-minimally to gravitation is completely absorbed in a rescaling of the gravitational constant. The latter becomes negative, thereby causing an effective anti-gravitational interaction when the corresponding mass exceeds the minkowskian instability threshold. Moreover, the source of this effective antigravitational interaction is the usual scalar trace anomaly associated with the residual massless part of the matter field.     

e-A深度非弹性散射中胶子辐射振幅的新计算方法

在e-A深度非弹性散射过程中, 喷注穿过冷核介质时, 多重散射诱导胶子辐射会导致对碎裂函数的修正及喷注的能量损失.前期研究中关于计算e-A深度非弹性散射中胶子辐射振幅的两种方法: 螺旋振幅近似和微扰QCD严格计算都异常繁杂. 本文发展了一种新的方法, 可以方便计算出多重散射导致胶子辐射的振幅, 得到的碎裂函数的修正以及能量损失与严格计算的结果一致.     

Mixing coefficients of the lattice weak hamiltonian with dimension five operators

We compute the mixing coefficients of the four fermion operators which appear in the non-leptonic ΔS=1, octet hamiltonian with operators of dimension five. The calculation completes the construction of the perturbative part of the weak hamiltonian, to be used in Monte Carlo simulations of lattice QCD with Wilson fermions.     

Diffractive scattering on the deuteron projectile in the NLO: triple interaction of reggeized gluons

High-mass diffractive production of protons on the deuteron target is studied in the next-to-leading order (NLO) of the perturbative QCD in the BFKL approach. The non-trivial part of the NLO contributions coming from the triple interactions of the exchanged reggeons is considered. Analytic formulas are presented and shown to be infrared free and so are ready for practical calculation.