Simulationen der QCD mit dynamischen Overlap-Fermionen

在晶格强子现象学中，一些主要的系统不确定性是由于所使用的典型费米子作用量缺乏手征对称性而引起的。因此，对于我们的研究小组来说，继续进行例如动力学重叠费米子的模拟是至关重要的。到目前为止，只有淬火模拟是可行的，主要是由于纯粹的成本，以评估矩阵符号函数，以及由于算法的困难与稳定的混合蒙特卡罗（HMC）计划，处理零交叉的本征模式的威尔逊运营商。我们在伍珀塔尔/扎姆的QCD小组已经进行了十多年的动力学费米子模拟（SESAM项目，T（L项目）。就重叠费米子离散而言，我们已经引入了最佳Zolotarev计划的符号函数，这证明是非常适合的HMC算法。最近，我们已经取得了实质性的改进，嵌套反演与HMC和10传播计算的因子5。我们已经实现了一个2味HMC码的显式处理的零交叉的一个本征模式。在这个子项目中，我们的目标是产生和评估的动力学重叠配置与两个和三个轻海夸克。我们将开发一个新的单味手征投影HMC代码来加速非常轻的夸克制度的拓扑涨落。我们将HMC扩展到改进的规范作用和双模交叉问题。此外，我们将与其他子项目特别子项目协调，在尺寸为163 x32的晶格上进行一项旨在尽可能轻的海夸克的试点研究。1.我们将把截断的本征模近似推广到重叠费米子，计算的不连通图和弦断裂的全对全传播子。研究小组的其他成员也将使用生成的配置。然而，对它们进行评估的oberservables的精确集合将取决于我们将实现的算法的效率。

Some of the main systematic uncertainties in lattice hadron phenomenology are caused by the lack of chiral symmetry of typical fermion actions used. Thus, it is of central importance for our Forschergruppe to proceed towards simulations with e.g. dynamical Overlap fermions. So far only quenched simulations were feasible, primarily due to the sheer costs to evaluate the matrix sign function as well as due to algorithmic difficulties with the stability of the Hybrid Monte Carlo (HMC) scheme, handling zero-crossing of eigenmodes of the Wilson operator. Our QCD-group at Wuppertal/ZAM has carried out simulations with dynamical fermions over more than 10 years (SESAM project, T(L project). As far as the Overlap fermion discretization is concerned, we have introduced the optimal Zolotarev scheme for the sign function which turns out to be well suited for the HMC algorithm. Recently, we have achieved substantial improvements to the nested inversions with a factor 5 for HMC and 10 for propagator computations. We have already implemented a 2-flavor HMC-code with explicit treatment of zero crossing for one eigenmode. In this sub-project we aim at the generation and evaluation of dynamical Overlap configurations with two and three light sea quarks. We will develop a new one-flavor chirally projected HMC code to accelerate topological fluctuations in the very light quark regime. We will extend the HMC to improved gauge actions and the two-mode crossing problem. Furthermore, we will carry out a pilot study aiming for sea quarks as light as possible on lattices of size 163x32, in coordination with the other sub-projects, paricular sub-project. 1. We will extend the truncated eigenmode approximation to Overlap fermions, computing disconnected diagrams for ¿¿ and all-to-all propagators for string breaking. The generated configurations will also be used by the other members of the Forschergruppe. The precise set of oberservables evaluated on them will, however, depend on the efficiency of the algorithm we will achieve.