arXiv subjects
Publications and source records attributed to Z. Sroczynski.
We consider the Rational Hybrid Monte Carlo algorithm for performing exact 2+1 flavour fermion simulations. The specific cases of ASQTAD and domain wall fermions are considered. We find that in both cases the naive performance is similar to conventional hybrid algorithms.
Many appplications in computational science are sufficiently compute-intensive that they depend on the power of parallel computing for viability. For all but the "embarrassingly parallel" problems, the performance depends upon the level of granularity that can be achieved on the computer platform. Our computational particle physics applications require machines that can support a wide range of granularities, but in general, compute-intensive state-of-the-art projects will require finely grained distributions. Of the different types of machines available for the task, we consider cluster computers. The use of clusters of commodity computers in high performance computing has many advantages including the raw price/performance ratio and the flexibility of machine configuration and upgrade. Here we focus on what is usually considered the weak point of cluster technology; the scaling behaviour when faced with a numerically intensive parallel computation. To this end we examine the scaling of our own applications from numerical quantum field theory on a cluster and infer conclusions about the more general case.
We present results for the performance of QCD code on ALiCE, the Alpha-Linux Cluster Engine at Wuppertal. We describe the techniques employed to optimise the code, including the metaprogramming of assembler kernels, the effects of data layout and an investigation into the overheads incurred by the communication.
We present results for the static inter-quark potential, lightest glueballs, light hadron spectrum and topological susceptibility using a non-perturbatively improved action on a $16^3\times 32$ lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units ($\sim 1.7$ fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavours of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied ($M_{PS}/M_{V}\ge0.58$). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities.
We compute $Λ_{\bar{MS}}$ for two flavors of light dynamical quarks using non-perturbatively $O(a)$ improved Wilson fermions. We improve on a recent calculation by employing Padé-improved two-loop and three-loop perturbation theory to convert the lattice numbers to the $\bar{MS}$ scheme.
We present a report on the status of the GRAL project (Going Realistic And Light), which aims at simulating full QCD with two dynamical Wilson quarks below the vector meson decay threshold, m_ps/m_v < 0.5, making use of finite-size-scaling techniques.
The scale parameter $Λ_{\overline{MS}}$ is computed on the lattice in the quenched approximation and for $N_f = 2$ flavors of light dynamical quarks. The dynamical calculation is done with non-perturbatively $O(a)$ improved Wilson fermions. In the continuum limit we obtain $Λ_{\overline{MS}}^{N_f=0} = 243(1)(10)$ MeV and $Λ_{\overline{MS}}^{N_f=2} = 217(16)(11)$ MeV, respectively.
We present first results from calculations using O(a) improved (FNAL) space-time asymmetric action on a 12^3 x 24 quenched lattice at β= 5.7 and c_SW = 1.57. The asymmetry parameter is determined non-perturbatively from the energy-momentum dispersion relation. This improvement scheme is mass dependent, and the calculations have been done in the charm and bottom quark mass sectors since it is at these heavier masses that the asymmetry is expected to be relevant.
We present the first results for the static quark potential and the light hadron spectrum using dynamical fermions at $β=5.2$ using an O(a) improved Wilson fermion action together with the standard Wilson plaquette action for the gauge part. Sea quark masses were chosen such that the pseudoscalar-vector mass ratio, m_PS/m_V$, varies from 0.86 to 0.67. Finite-size effects are studied by using three different volumes, 8^3\cdot 24, 12^3\cdot 24 and 16^3\cdot 24. Comparing our results to previous ones obtained using the quenched approximation, we find evidence for sea quark effects in quantities like the static quark potential and the vector-pseudoscalar hyperfine splitting.
UKQCD's dynamical fermion project uses the Generalised Hybrid Monte-Carlo (GHMC) algorithm to generate QCD gauge configurations for a non-perturbatively O(a) improved Wilson action with two degenerate sea-quark flavours. We describe our implementation of the algorithm on the Cray-T3E, concentrating on issues arising from code verification and performance optimisation, such as parameter tuning, reversibility, the effect of precision, the choice of matrix inverter and the behaviour of different molecular dynamics integration schemes.