Study of Lattice QCD by numerical simulations including dynamical quark effects

在格子QCD模拟中考虑动力学夸克圈效应是定量研究强相互作用和获得具有唯象意义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下，强子质量谱的计算值与实验值的偏差约为10%。对于N_f=2QCD，考虑了动力学u夸克和d夸克效应，我们用精确的混合蒙特卡罗(HMC)模拟算法进行了大规模模拟。结果表明，在淬灭近似下观察到的强子质量谱的很大一部分偏差随着N_f=2动力学夸克效应的加入而消失。然而，在现实世界中，有三个轻夸克，因此进行包括S夸克环效应在内的模拟是很重要的。为此，我们对奇数个O(A)改进的威尔逊费米子发展了有效的精确模拟算法。我们首次用O(A)改进的威尔逊费米子进行了N_f=3的QCD模拟，并估算了各种强子的质量谱，由此确定了基本的晶格QCD参数，如晶格间距和夸克质量。

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 hadron matrix elements. In fact it has been shown that in the quenched approximation where the dynamical quark loop effect is neglected the evaluated hadron mass spectrums deviate from experimental values by about 10%. For N_f = 2 QCD where the dynamical u and d quark effects are taken into account we have made large scale simulations with the exact hybrid Monte Carlo (HMC) simulation algorithm. It has been shown that a large part of the deviation in hadron mass spectrum observed in the quenched approximation disappears with the inclusion of N_f = 2 dynamical quark effect. In the real world, however, there are three light quarks and it is important to make simulations including the s quark loop effect. For this purpose we have developed efficient exact simulation algorithm for odd number of O(a) improved Wilson fermions. We have made first realistic N_f = 3 QCD simulation with O(a) improved Wilson fermions and estimated mass spectrum for various hadrons, from which fundamental lattice QCD parameters such as lattice spacing and quark masses are determined.