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.     

A Lattice Study of the Glueball Spectrum

Glueball Spectrum is studied using an improved gluonic action on asymmetric lattices in the pure SU(3) gauge theory.The smallest spatial lattice spacing is about 0.08 fm which makes the extrapolation to the continuum limit more reliable.In particular.attention is paid to the scalar glueball mass which is known to have problems in the extrapolation.Converting our lattice results to physical units using the scale set by the static quark potential,we obtain the following results for the glueball masses:MG(0 )=1730(90)MeV for the scalar glueball mass and MG(2 )=2400(95)MeV for the tensor glueball.     

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.     

相对论性无自旋氢原子的散射态

研究获得了相对论性无自旋氢原子散射态的精确解,给出了精确的相移表达式和按"k/2π标度"归一化的散射态的径向波函数,讨论了散射振幅的解析性质 .     

在格点上构造计算胶球质量的新途径

发展了一种为了计算胶球质量而构造格点算符的新途径.基于所选用算符的连续极限与状态量子数JPC两者之间的联系,状态的自旋就可以在数值模拟中唯一和直接地被确定下来.进而,这一途径可以被应用于计算任意自旋J的胶球质量.在淬火近似下,给出在SU(3)纯规范场中0⁺⁺态和2⁺⁺态胶球质量的初步结果,它们分别是1754(85)(86)MeV和2417(56)(117)MeV.     

Lattice QCD predictions for shapes of event distributions along the freezeout curve in heavy-ion collisions

We present lattice QCD results along the freezeout curve of heavy-ion collisions. The variance, skew and kurtosis of the event distribution of baryon number are studied through Padé resummations. We predict smooth behaviour of three ratios of these quantities at current RHIC and future LHC energies. Deviations from this at lower energies signal the presence of a nearby critical point.     

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.     

镍晶格中的晶格格林函数

在含缺陷体系的模拟中，格林函数作为一种重要的多尺度耦合方法，可以将缺陷产生的局域应变场和长程应力场耦合起来.在镍基高温合金蠕变的初期阶段，位错主要分布在基体相中，通过格林函数的多尺度桥接模式，可得到基体相中位错芯的平衡构型，为位错-杂质复合体间相互作用提供计算基础.基于晶格动力学理论和声子谱计算中的力常数矩阵，通过第一布里渊区特殊k点取样以及傅里叶变换，计算完整镍晶格中晶格格林函数，可用于镍基材料的多尺度模拟计算.     

纳米晶体线的晶格动力学格林函数及晶格振动

通过求解差分方程,推导了纳米晶体线的晶格动力学格林函数,分析了其晶格振动,并推导了声子数表象中的原子位移及晶格振动哈密顿公式.研究结果表明,纳米晶体线的晶格振动能带分裂为一系列的子带,格波只能沿纳米晶体线的纵向传播,沿纳米晶体线的横截面只存在驻波.     

Resistance Calculation of Pentagonal Lattice Structure of Resistors

In this study, the effective resistance between any two lattice sites in a two-dimensional pentagonal lattice structure of identical resistors is determined by means of the lattice Green’s function method. Some numerical results of the resistance for small separations between lattice sites are presented.     

A Note on the Time Development of Quantum Lattice Systems

The time development of quantum lattice systems is studied without any restrictions on the growth condition of the potential . A thermodynamic limit of quantum Gibbs state, a *-algebra and an automorphism group _t for which is a KMS state are constructed.     

2+1维U(1)改进格点规范理论中0++胶球波函数的三阶结果

用改进的格点规范场哈密顿量和截断本征方程法计算2+1维U(1)规范场的0++胶球波函数，三阶结果比二阶结果的标度行为有了较大的改善.     

存在耦合情况下SYNCH和MAD程序计算结果的分析

用SYNCH和MAD程序计算了一些含有坐标旋转的束流系统.由于坐标旋转,粒子的垂直和水平方向的运动发生耦合. 对计算结果进行的分析表明,对有横向耦合的束流系统,SYNCH程序给出的四个色散函数(ηx,ηx＇,ηy及ηy＇)是错误的.这两个程序给出的Twiss参数(βx,αx,βy和αy)也有较大的分歧.本文通过对一个简单的有耦合系统的计算结果的分析,说明这两个程序计算结果有错误和分歧.使用这些程序计算有耦合的束流系统时,应格外小心,以免得出错误的结果.     

Chiral Extrapolation of Lattice Data of Λ_b→Λ_c Form Factors

An extrapolation to the physical limit for the lattice data of Λ_b →Λ_c form factors computed in the nonphysical region is made in this work through a class of fitting functions proposed by us with nonlinear dependence on m2/π derived in the chiral perturbative theory(ChPT) and the heavy quark effective theory(HQET) framework. Then the results are applied to calculate the differential and integrated Λ_b →Λ_c semileptonic decay rates. Meanwhile, a comparison between our results and those obtained through the extrapolation functions with naive linear dependenceon m2/π is made.It is shown that the difference between the extrapolated central values of these two cases is about 5%.The total uncertainties(depending on the momentum transfer q~2) in the linear case are about 5% ～10%(caused by the uncertainties of lattice data) and those in the nonlinear case are about 10% ～ 20%(caused by the uncertainties of both lattice data and input parameters in Ch PT and HQET). More accurate lattice data and parameters in ChPT and HQET are needed to reduce the uncertainties of the extrapolated results.     

Lattice Dynamics Study of Magnesium Chalcogenides

First-principles calculations,which are based on the plane-wave pseudopotential approach to density functional perturbation theory within the local density approximation,have been performed to investigate the structural,lattice dynamical and thermodynamic properties of zinc blende(B3) structure magnesium chalcogenides:MgS,MgSe and MgTe.The results of ground state parameters and phonon dispersion are compared and agree well with the experimental data available and other calculations.We obtain the change of Born effective charge and LO-TO splitting under hydrostatic pressure.Finally,by the calculations of phonon frequencies,some thermodynamic properties such as the entropy,heat capacity,internal energy,and free energy are also successfully obtained.     

2+1维U(1)格点规范场论中真空态的研究

对2+1维U(1)格点规范场论真空态进行研究,仔细推导出连续极限下真空谈函数中参数μ₀和μ₂的普适表达式,并用截断本征方程法进行数值计算.     

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。     

Unconventional Energy Bands and Chirality of Ultracold Atoms in Trilayer Honeycomb Lattice

We investigate ultracold fermionic atoms in the trilayer honeycomb lattice. In the low energy approximation, we derive an effective Hamiltonian for pseudospins. The energy spectrum shows a cubic form of the wavevector and is gapless. The quasiparticles and quasiholes are ehiral and show Berry＇s phase π when the wavevector adiabatically evolves along a closed circle, Furthermore, the experimental detection of the energy spectrum is proposed with Bragg scattering techniques.     

Lattice Boltzmann simulation for the energy and entropy of excitable systems

The internal energy and the spatiotemporal entropy of excitable systems are investigated with the lattice Boltzmann method.The numerical results show that the breakup of spiral wave is attributed to the inadequate supply of energy,i.e.,the internal energy of system is smaller than the energy of self-sustained spiral wave.It is observed that the average internal energy of a regular wave state reduces with its spatiotemporal entropy decreasing.Interestingly,although the energy difference between two regular wave states is very small,the different states can be distinguished obviously due to the large difference between their spatiotemporal entropies.In addition,when the unstable spiral wave converts into the spatiotemporal chaos,the internal energy of system decreases,while the spatiotemporal entropy increases,which behaves as the thermodynamic entropy in an isolated system.     

Lattice energy and phase transition of alkaline earth chalcogenide

In this study, we have investigated the high-pressure structural phase transition of alkaline earth's chalcogenides within the framework of three-body potentials. We are considering short-range repulsive interactions up to the second nearest neighbors. The structural phase transition from the low-pressure NaCl (B1) to the high-pressure CsCl (B2) structure is estimated by Gibbs free energy calculations. The results are satisfactory and in agreement with the available experimental and other theoretical results.