Study of lattice QCD by large scale numerical simulations including dynamical quark effects

在晶格QCD模拟中加入动态夸克环效应是定量研究强相互作用和获得在现象学上重要的强子矩阵元的重要问题之一。事实上，在忽略动力学夸克环效应的猝灭近似中，计算得到的强子质量谱与实验值相差约5-10%。最近还表明，在包含了u和d夸克的动力学环效应后，在淬灭近似中观察到的强子质量谱偏差约有一半消失。然而，在现实世界中，有三种轻夸克，u，d和s夸克，验证剩余偏差是否通过包含s夸克环效应而消失是很重要的。为此，我们使用O(a)改进的Wilson费米子进行了逼真的（2+1）风味QCD模拟，其中晶格QCD模拟的离散化误差已知为O(a^2)，晶格间距为a。我们计算了两个格间距为0.1fm和0.12fm的格上的强子质谱。假设在a有限的晶格上强子质量的依赖关系为^2，我们将强子质量外推到a=0，并发现外推强子质量的初步值与实验值一致。在现象学上重要的各种强子矩阵元素，如衰变常数的评估也已经完成，包括u和d夸克的动力环效应。

Including dynamical quark loop effects in lattice QCD simulations is one of the most important problem to make quantitative study of strong interaction and to obtain phenomenologically important hadronic matrix elements. In fact, in the quenched approximation where the dynamical quark loop effect is neglected, it has been shown that the evaluated hadron mass spectra deviate from experimental values by about 5-10%. It has also been shown recently that about half part of the deviation in hadron mass spectra observed in the quenched approximation disappears with the inclusion of the dynamical loop effect of u and d quarks. In the real world, however, there are three light quarks, u,d and s quarks, and it is important to verify if the remaining deviation disappears by the inclusion of the s quark loop effect. For this purpose we have made realistic (2+1) flavor QCD simulation with O(a) improved Wilson fermions in which the discretization error of lattice QCD simulation is known to be O(a^2) with a the lattice spacing. We have calculated hadron mass spectra on two lattices having lattice spacing a【approximately equal】 0.1fm and 0.12fm. We have extrapolated hadron masses to a=0 assuming a^2 dependence of hadron masses evaluated on lattices with finite a, and found that preliminary values of extrapolated hadron masses are consistent with experimental values. Evaluation of phenomenologically important various hadronic matrix elements such as decay constants have also been done including the dynamical loop effect of u and d quarks.