Influence of dynamical strange quark on finite-temperature QCD transition

通过一系列证据，夸克-胶子等离子体似乎是在RHIC相对论重离子碰撞的早期阶段产生的。为了定量地提取夸克-胶子等离子体的热力学性质，直接从QCD的第一原理出发进行有限温度QCD的晶格计算是必不可少的。由于QCD跃迁温度给出的典型能量标度是关于奇异夸克质量的，所以现实的模拟需要对奇异夸克(三味QCD)进行动力学处理，而不是对常规的上下夸克(双味QCD)进行动力学处理。然而，由于各种困难，大多数大规模的模拟都是在双味QCD中进行的。为了对夸克-胶子等离子体进行逼真的模拟，本项目旨在对三味QCD进行系统的研究。作为三味工程的第一步，我们对各种…进行了系统的比较最近针对奇数味道的QCD提出了更精确的算法。我们发现PHMC算法的一个版本对于系统研究三味QCD是足够有效的。从PHMC算法的预备模拟中，我们还发现规范作用和夸克作用的改进对于以目前计算机的能力进行连续统外推是必不可少的。最后，我们确定了改进参数c&lt；sw&gt；在相关耦合参数下的非微扰值。在此基础上，我们开始了零温下三味QCD的强子光谱的系统研究。我们分别在16^3×32，20^3×40和24^3×56晶格上研究了三种晶格间距，0.122，0.10和0.07fm。在前两个晶格上的模拟已经完成，在最精细的晶格上的模拟正在进行中。我们证实，与先前研究中观察到的猝灭光谱的差异相反，三味QCD正确地再现了实验的介子光谱。我们还发现，在淬灭的QCD中，轻u，d夸克质量和S夸克质量比以前估算的要小20-30%。我们还研究了有限温度QCD中物态方程和热力学参数的有效计算方法。在淬火模拟中，我们已经证明了各向异性晶格为我们提供了这样一种有效的方法。因此，我们首次利用三个晶格间距的数据进行了状态方程的受控连续外推。为了在具有动力学夸克的QCD中进行更真实的计算，我们估计了具有改进的夸克和胶子作用的双味QCD中各向异性系数的非微扰值。较少

Through a series of evidences, the quark-gluon plasma seems to be created in the early stage of relativistic heavy-ion collisions at RHIC. In order to extract thermodynamic properties of the quark-gluon plasma quantitatively, a lattice calculation of finite temperature QCD-directly from the first principles of QCD-is indispensable. Because the typical energy scale given by the QCD transition temperature is about the strange quark mass, a realistic simulation require a dynamical treatment of the strange quark (three-flavor QCD) besides conventional up and down quarks (two-flavor QCD). Due to various difficulties, however, most large-scale simulations have been done in two-flavor QCD.Toward a realistic simulation of the quark-gluon plasma, this project aims at a systematic study of three-flavor QCD. We also study efficient methods for thermodynamic quantities in finite-temperature lattice QCD.As the first step of the three-flavor project, we carried out a systematic comparison of various … More exact algorithms proposed recently for QCD with odd number of flavors. We found a version of the PHMC algorithm is efficient enough for a systematic study of three-flavor QCD. From a preparative simulation using the PHMC algorithm, we also find that improvement of both gauge and quark actions is indispensable for a continuum extrapolation with present power of computers. Finally we determined non-perturbative values of the improvement parameter c_<sw> at relevant coupling parameters.Based on these results, we started a systematic study of hadronic spectroscopy in three-flavor QCD at zero temperature. We studied at three lattice spacings, 0.122, 0.10, and 0.07 fm, on 16^3x32, 20^3x40, and 24^3x56 lattices, respectively. Simulations on the first two lattices have been completed, and that on the finest lattice on-going. We confirmed that, in contrast to the discrepancy of quenched spectrum observed in a previous study, three-flavor QCD reproduces experimental meson spectrum correctly. We also found that the light u,d quark mass and the s quark mass are about 20--30% smaller than those evaluated previously in the quenched QCD.We also studied efficient methods to calculate the equation of state and thermodynamic quantities in finite-temperature QCD. In a quenched simulation, we have shown that anisotropic lattices provide us with such an efficient way. Accordingly, we have carried out the first controlled continuum extrapolation of the equation of state using data at three lattice spacings. To carry out a more realistic calculation in QCD with dynamical quarks, we evaluated non-perturvative values of anisotropy coefficients in two-flavor QCD with improved quark and gluon actions. Less