通过基矢光前量子化方法对π介子的研究

为研究介子的性质,通过基矢光前量子化方法获得介子的光前波函数。基失光前量子化是一种在哈密顿量体系下基于量子场论的非微扰方法。在哈密顿量中我们考虑了动能项、基于全息色动力学的横向禁闭势、与横向禁闭势互补的纵向禁闭势和基于QCD的夸克-胶子相互作用。我们的基矢空间包括最低阶的两个Fock空间,即领头阶■与次领头阶■。根据所得的光前波函数我们计算了介子衰变常数以及(基于领头Fock空间的)电磁半径,这些结果与粒子数据手册(PDG)上的结果相近。此外,我们计算了(基于领头Fock空间的)介子部分子分布,QCD演化后,与原先的结果相近(蓝江山等,Phys Rev Lett,2 019,122:172 001.),能够很好地描述费米国家实验室(FNAL)与欧洲核子中心(CERN)的实验数据。     

通过基矢光前量子化方法对π介子的研究

为研究介子的性质,通过基矢光前量子化方法获得介子的光前波函数。基失光前量子化是一种在哈密顿量体系下基于量子场论的非微扰方法。在哈密顿量中我们考虑了动能项、基于全息色动力学的横向禁闭势、与横向禁闭势互补的纵向禁闭势和基于QCD的夸克-胶子相互作用。我们的基矢空间包括最低阶的两个Fock空间,即领头阶■与次领头阶■。根据所得的光前波函数我们计算了介子衰变常数以及(基于领头Fock空间的)电磁半径,这些结果与粒子数据手册(PDG)上的结果相近。此外,我们计算了(基于领头Fock空间的)介子部分子分布,QCD演化后,与原先的结果相近(蓝江山等,Phys Rev Lett,2 019,122:172 001.),能够很好地描述费米国家实验室(FNAL)与欧洲核子中心(CERN)的实验数据。     

利用光前量子化方法计算电子的广义横向动量分布函数

强子和轻子是目前实验所能观测到的最小微观结构,但根据量子色动力学（QCD）,强子内还存在着部分子结构。在理论计算中,从Wigner函数出发可以得到多种分布函数,如横向动量分布函数（TMD）、广义部分子分布函数（GPD）以及广义横向动量分布函数（GTMD）。其中GTMD包含粒子内部部分子的三维动量和位置信息,从GTMD出发通过对横向动量积分和取横向转移动量为零分别得到GPD和TMD。本工作通过引入电子的光前波函数计算出物理电子的GTMD,并以此为出发点得到物理电子的TMD和GPD。一方面通过与微扰论的TMD和GPD的结果对比可以证明我们的计算结果是合理的,同时讨论了GPD中P波和S波的贡献。另一方面给出物理电子的内部部分子分布随横向转移动量、部分子横向动量以及纵向动量分数的变化关系。In anlogous to hadron, electron has similar structure because of dressing. So we can define the Transverse Momentum Distribution functions (TMD), the General Parton Distribution functions (GPD) and General Transverse Momentum Distribution functions (GTMD) of electron which come from the Wigner distribution function. The GTMD contain the information of momentum and position of parton in one particle, and the GPD or TMD can be calculated by integration of transverse momentum or setting the transverse transfer momentum which equal to zero. We introduce the light-front wave function of electron to calculate the GTMD of dressed electron, and then get the TMD and GPD. Our results are verified by comparing to calculations in literature and the contribution of GPD of P-wave and S-wave. And we show that the distribution functions at different transverse momentum transfer, transverse momentum of parton and the fraction of longitudinal momentum.     

K介子的光生和相应的辐射俘获过程的研究

分析了由交叉对称性相联系的K介子光生过程(γP→K+)和相应的辐射俘获过程(K-P→γA).即从低能QCD拉氏量出发,在手征夸克模型中,统一地描述了K介子的光生过程,进而又利用交叉对称性对相关的K-介子的辐射俘获过程做了深入的研究,得到了与实验结果符合得相当好的辐射俘获过程的分支比.     

发展中的K介子工厂

 一座工厂,总要有它的产品,“K介子工厂”的产品就是K介子束流,并用这束流与各种靶粒子或靶核相碰撞来完成预定的物理实验.通常,能够按照所需要的能量和流强提供介子束流的装置加上其他配套设备(如靶室、探测器等)一起就叫作“介子工厂”.早在70年代就诞生了π分子工厂,并使π核物理学的研究蓬勃开展起来,取得了不少研究成果.近年来,国际上许多大型核物理实验中心又相继提出了建立K介子工厂的计划,以便深入地进行K核物理学的研究.     

B→Kη′中双胶子聚合机制的进一步研究

双胶子聚合机制可能解释B→Kη′反常大的分支比.然而由于我们对η′犂犂有效顶点知之甚少,微扰QCD的理论计算存在很大的不确定性.本文尝试了几种不同的η′犂犂形状因子,并将数值结果和实验相比较.我们发现,虽然我们对η′犂犂形状因子了解得很少,但是如果B→Kη′衰变中双胶子聚合机制确实很重要的话,B→K^*η′的分支比将为10^－5量级,这可以被将来的实验检验.     

对相干态在通过参量转换中的演化与量子化光涡态的实现

本文讨论了光学参量频率转换过程中对相干态的演化问题, 获得了对相干态时间演化的解析表达式及在位形空间的波函数, 发现通过适当调节系统元件及相互作用时间, 对相干态在位形空间中的波包能呈现出量子涡态特性, 并且与这样涡态相关的波函数具有修正Bessel-Gaussian形式的结构, 即非高斯型波函数. 在相干态表象下, 这一量子化涡态是两模湮没算符平方和的本征态. 这一讨论揭示了产生量子化涡态的另一可实现方案.     

标量介子f0(980)光生过程γp→pf0(980)的研究

轻标量介子性质研究是当今中高能核物理研究中的热点问题之一,特别是质量低于1 GeV的标量介子f₀（980）的内部结构一直存在争议,至今未达成共识。基于前人的研究结果,运用有效拉氏量方法,对f₀（980）粒子的光生过程γp→pf₀（980）进行了更深入的理论研究。探讨了两种传播子形式下得矢量介子ρ和ω交换的贡献,第一种是选择雷吉传播子,第二种是选择普通费曼传播子。第二种形式的微分散射截面理论结果与现有实验数据符合比第一种形式的结果好。基于此,计算了两种形式的总截面,两种形式给出的理论结果相差很大。另外,给出了γp→pf₀（980）→pπ+π-过程的π+π-不变质量分布的理论预言,发现π+π-不变质量分布对于f₀（980）于K-K的耦合常数（g_f0KK）有很强的依赖关系,不同的g_f0KK给出明显不同的π+π-不变质量分布。将来相关实验数据可以验证这些理论预言,并对矢量介子传播子形式和耦合常数g_f0KK做出限制,加深人们对f₀（980）粒子的认识。We study the scalar meson f0(980) in the γp→pf0(980) reaction within an effective Lagrangian approach. Based on previous studies, we calculate the differential cross sections of this reaction. We take two types of the propagators of vector mesons ρ and ω, one is the Regge form, the other one is the normal Feynman propagator. It is found that our theoretical results for the differential cross sections with the Feynman propagator are in agreement with the current experimental data. For the total cross sections, the results with the two types of propagator are much different. On the other hand, we predict the π+π- invariant mass distribution of the γp→pf0(980)→pπ+π- reaction. We find that the π+π- invariant mass distribution depends sensitively on the value of the coupling constant gf0KK. We hope that the future experiments can test our model calculation and give further constraints on the value of gf0KK and also the nature of f0(980).     

Electron Anomalous Magnetic Moment in Basis Light-Front Quantization Approach

We apply the Basis Light-Front Quantization approach to the Hamiltonian field theory of Quantum Electrodynamics in free space. We solve for the mass eigenstates corresponding to an electron interacting with a single photon in light-front gauge. Based on the resulting non-perturbative ground state light-front amplitude we evaluate the electron anomalous magnetic moment. The numerical results from extrapolating to the infinite basis limit reproduce the perturbative Schwinger result with relative deviation less than 0.6%. We report significant improvements over previous works including the development of analytic methods for evaluating the vertex matrix elements of QED.     

Light-Front Quantization of the Restricted Gauge Theory of QCD2

In this talk we study the light-front quantization of the restricted gauge theory of QCD₂à la Cho et al.     

Canonical Quantization of the Two-Gauge-Potential Light-Front Formulation of the Electric-Magnetic Interaction

The recently proposed two-gauge-potential Lagrangian describing the electric-magnetic interaction is studied within the light-front canonical quantization. Two choices of gauge-fixing conditions are discussed. The resulting propagators are compared with those obtained via the alternative field-strength approach.     

Light-Front BRST Quantization of the Vector Schwinger Model with a Photon Mass Term

Vector Schwinger model with a mass term for the photon, describing 2D electrodynamics with mass-less fermions, studied by us recently (UK, Mod. Phys. Lett A22, 2993 (2007), PoS LC2008, 008 (2008), UK and DSK, Int. J. Mod. Phys. A22, 6183 (2007), UK, Mod. Phys. Lett A27, 1250157 (2012)), represents a new class of models. This theory becomes gauge-invariant when studied on the light-front. This is in contrast to the instant-form theory which is gauge-non-invariant. The light-front Hamiltonian and path integral quantization of this theory has been studied recently by one of us (UK, Mod. Phys. Lett. A27 (No. 27) 1250157 (2012)). In the present work we study the light-front Becchi-Rouet-Stora and Tyutin (BRST) quantization of this theory under appropriate light-cone BRST gauge-fixing. Here the BRST (gauge) symmetry of the theory is maintained even under BRST-gauge-fixing which is in contrast to its Hamiltonian and path integral quantization where the gauge symmetry of the theory necessarily gets broken under gauge-fixing.     

Quantization of the Schwarzschild Black Hole: A Noether Symmetry Approach

We study the canonical formalism of a spherically symmetric space-time. In the context of the 3+1 decomposition with respect to the radial coordinate r, we set up an effective Lagrangian in which a couple of metric functions play the role of independent variables. We show that the resulting r-Hamiltonian yields the correct classical solutions which can be identified with the space-time of a Schwarzschild black hole. The Noether symmetry of the model is then investigated by utilizing the behavior of the corresponding Lagrangian under the infinitesimal generators of the desired symmetry. According to the Noether symmetry approach, we also quantize the model and show that the existence of a Noether symmetry yields a general solution to the Wheeler-DeWitt equation which exhibits a good correlation with the classical regime. We use the resulting wave function in order to (qualitatively) investigate the possibility of the avoidance of classical singularities.