2+1维格点QCD真空波函数的计算

用改进的格点哈密顿量和截断本征方程法计算2+1维QCD真空波函数,结果显示出良好的标度行为.     

用改进的格点哈密顿量计算2+1维QCD0++胶球质量

用改进的格点哈密顿量和截断本征方程法计算2+1维QCD 0⁺⁺胶球质量,结果显示较好的标度行为.     

格点QCD中有限体积下形状因子的内插计算

在格点QCD的框架下,讨论了计算强子的形状因子的过程中,有限体积效应对所得结果的影响,并且给出了计算连续动量空间上形状因子数值的内插算法。本文以π介子的形状因子为例,介绍了从格点QCD中得到的三点关联函数出发计算π介子的形状因子的方法,并说明有限体积效应使得计算结果只能在分立动量上给出。本文探讨了一种保持旋转对称性的内插算法和一种对于傅立叶变换进行连续化的内插算法,基于分立的形状因子取值给出了连续动量空间上的形状因子,并且提供了模型模拟的结果与真实格点系统上的数值结果。本文提出的内插算法及数值模拟的结论不依赖于特定的格点系综,具有一定程度的普适性,能够推广到对于其他格点系统的有限体积效应的处理,同时为格点系统尺度的选取提供了有价值的参考。     

带费米子2+1维SU(20)群格点规范理论中的真空和手征对称性自发破缺

本文把纯规范场的严格基态和费米场的变分真空态结合起来,研究格点QCD中2+1维SU(20)群带费米子的真空结构,计算费米子真空凝聚<ψψ>,其结果有较好的标度行为.     

用改进的哈密顿量计算1+1维格点QCD中矢量介子质量谱

用变分法计算1+1维格点QCD中矢量介子的质量谱Mv.验证了理论的预言:对带Wilson夸克的格点哈密顿量的改进能使有限格距所引起的误差明显减小.     

用改进的格点哈密顿量计算2+1维QCD 0++胶球质量

用改进的格点哈密顿量和截断本征方程法计算2＋1维QCD 0^ 胶球质量,结果显示较好的标度行为。     

格点QCD的最新进展

格点QCD是量子场论中最可靠的非微扰方法,是粒子物理最前沿课题之一,被应用到多个交叉领域,对物理学和其它科学的发展产生深远影响.本报告综述该领域突破性新进展、并具有重大理论和实验意义的几个方面的成果.     

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.     

格点(1 1)维QCD中<ψ>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     

1+1维QCD中格点哈密顿量的一种改进形式

给出1+1维QCD中格点哈密顿量的一种简单有效的改进形式,并用它对矢量介子质量谱M_v在手征极限下的大N_c行为进行格点研究,数值计算的结果与强耦合分析的结果相一致.     

Coupled Channel Approach to S-Wave Hyperonic Interactions from Lattice QCD

We studied hyperonic interactions by lattice QCD simulation throuth coupled channel formalism. Our approach to baryon-baryon interactions is deriving a potential from inverting Schrödinger equation using Nambu-Bethe-Salpeter (NBS) wave function simulated on the lattice. The quark mass dependences and flavor SU(3) breaking effects of the potential matrix are also discussed by comparing with results of gauge configurations with different quark masses. Our numerical results are obtained from three ensembles of 2+1 flavor QCD gauge configurations, which corresponds to m _π ~ 700, 570 and 410 MeV, provided by the PACS-CS Collaboration.     

Meron pairs and fermion zero modes

Merons, conjectured as a semiclassical mechanism for color confinement in QCD, have been described analytically by either infinite action configurations or an Ansatz with discontinuous action. We construct a smooth, finite action, stationary lattice solution corresponding to a meron pair. We also derive an analytical solution for the zero mode of the meron pair Ansatz, show that it has the qualitative behavior of the exact zero mode of the lattice solution, and propose the use of zero modes to identify meron gauge field configurations in stochastic evaluations of the lattice QCD path integral.     

Accurate determinations of alpha(s) from realistic lattice QCD

We obtain a new value for the QCD coupling constant by combining lattice QCD simulations with experimental data for hadron masses. Our lattice analysis is the first to (1) include vacuum polarization effects from all three light-quark flavors (using MILC configurations), (2) include third-order terms in perturbation theory, (3) systematically estimate fourth and higher-order terms, (4) use an unambiguous lattice spacing, and (5) use an [symbol: see text](a2)-accurate QCD action. We use 28 different (but related) short-distance quantities to obtain alpha((5)/(MS))(M(Z)) = 0.1170(12).     

Nucleon-nucleon scattering from fully dynamical lattice QCD

We present results of the first fully dynamical lattice QCD determination of nucleon-nucleon scattering lengths in the 1S0 channel and 3S1 - 3D1 coupled channels. The calculations are performed with domain-wall valence quarks on the MILC staggered configurations with a lattice spacing of b = 0.125 fm in the isospin-symmetric limit, and in the absence of electromagnetic interactions.     

Monopoles, instantons and chiral condensate in lattice QCD

We analyze the interplay of topological objects in four-dimensional QCD at finite temperature on the lattice. The distributions of color magnetic monopoles in the maximum abelian gauge are computed around instantons. Studies are performed in both pure and full QCD and in both the confinement and deconfinement phase. We find an enhanced probability for monopoles inside the core of an instanton on gauge field average. This is independent of the topological charge definition used. For specific gauge field configurations we visualize the situation graphically. Moreover the correlation of monopole loops and instantons with the chiral condensate is investigated. Strong evidence is found that clusters of the quark condensate and topological objects coexist locally on individual configurations.     

Topology of dynamical lattice configurations including results from dynamical overlap fermions

We investigate how the topological charge density in lattice QCD simulations is affected by violations of chiral symmetry caused by the fermion action. To this end we compare lattice configurations generated with a number of different actions including first configurations generated with exact dynamical overlap quarks. We visualize the topological profiles after mild smearing. In the topological charge correlator we measure the size of the positive core, which is known to shrink to zero extension in the continuum limit. To leading order we find the core size to scale linearly with the lattice spacing with the same coefficient for all actions, even including quenched simulations. In the subleading term the different actions vary over a range of about 10%. Our findings suggest that non-chiral lattice actions at current lattice spacings do not differ much for observables related to topology, both among themselves and compared to overlap fermions.     

Few-Baryon Interactions from Lattice QCD

We report the recent progress on the determination of three-nucleon forces (3NF) in lattice Quantum Chromodynamics (QCD). We utilize the Nambu–Bethe–Salpeter wave function to define the potential in quantum field theory, and extract two-nucleon forces and 3NF on equal footing. The enormous computational cost for calculating multi-baryon correlators on the lattice is drastically reduced by developing a novel contraction algorithm (the unified contraction algorithm). Quantum numbers of the three-nucleon system are chosen to be (I, J ^P ) = (1/2, 1/2⁺) (the triton channel), and we extract 3NF in which three nucleons are aligned linearly with an equal spacing. Lattice QCD simulations are performed using N _f = 2 dynamical clover fermion configurations at the lattice spacing of a = 0.156fm on a 16³ × 32 lattice with a large quark mass corresponding to m _π = 1.13 GeV. Repulsive 3NF is found at short distance.     

Lattice QCD Calculation of ππ Scattering Length

We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV.In the "Asqtad" improved staggered fermion formulation,we measure full ππ four-point correlators for isospin I = 0 and 2 channels,and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results.Extrapolating to the physical pion mass yields scattering lengths as mπaI=2 0 = 0.041 6(2) and m π a I =0 0 = 0.186(2) for isospin I = 2 and 0 channels,respectively.Our lattice simulation for ππ scattering length in I = 0 channel is an exploratory study,where we include the disconnected contribution,and our preliminary result is near to its experimental value.These simulations are carried out with MILC 2 + 1 flavor gauge configurations at lattice spacing a ≈ 0.15 fm.