The non-perturbative O(a)-improved action for dynamical Wilson fermions

We compute the improvement coefficient $c_{sw}$ that multiplies the Sheikholeslami-Wohlert term as a function of the bare gauge coupling for two flavour QCD. We discuss several aspects concerning simulations with improved dynamical Wilson fermions.Comment: Latex file, 2 figures, 6 pages, talk given by K.J. at the International Symposium on Lattice Field Theory, 21-27 July 1997, Edinburgh, Scotlan

Branchenanalyse Abfallwirtschaft: Entwicklungstendenzen und strukturelle Herausforderungen unter besonderer Berücksichtigung der kommunalen Dienstleistungen

Die Abfallwirtschaft ist eine Branche im Wandel. Allgemeine Entwicklungen wie der demographische Wandel oder die zunehmende Technologisierung treffen die Branche mit ihren etwa 160.000 Beschäftigten in ca. 3.000 Unternehmen auf besondere Art und Weise. Hinzu kommen sich stetig wandelnde Rechtsverordnungen wie das Kreislaufwirtschaftsgesetz oder das stark diskutierte Wertstoffgesetz. Auch das Abfallaufkommen, das sich durch eine zunehmende Fraktionierung sowie ein verändertes Konsumentenverhalten stetig verändert, beeinflusst die Arbeit in der Branche. Die vorliegende Studie analysiert die Auswirkungen die beschriebenen Umstrukturierungen und deckt Handlungsbedarf in Bezug auf zukünftige Branchentrends auf. Sie soll Anstöße für die Sicherung guter Arbeit geben und einen Beitrag zur Analyse und Bewertung Leistungspotentiale der Branche und deren Beschäftigten leisten

Relativistic Heavy Quarks on the Lattice

Lattice QCD should allow quantitative predictions for the heavy quark physics from first principles. Up to now, however, most approaches have based on the nonrelativistic effective theory, with which the continuum limit can not be taken in principle. In this paper we investigate feasibility of relativistic approaches to the heavy quark physics in lattice QCD. We first examine validity of the idea that the use of the anisotropic lattice could be advantageous to control the $m_Q a$ corrections. Our perturbative calculation, however, reveals that this is not true. We instead propose a new relativistic approach to handle heavy quarks on the isotropic lattice. We explain how power corrections of $m_Q a$ can be avoided and remaining uncertainties are reduced to be of order $(a\Lambda_{QCD})^2$.Comment: 39 pages, 8 figure as eps-fil

A Study of PCAC for the Nonperturbative Improvement of the Wilson Action

We present an exploratory study for the nonperturbative determination of the coefficient of the ${\cal O}(a)$ improvement term to the Wilson action, $c_{SW}$. Following the work by L\"{u}scher et al., we impose the PCAC relation as a nonperturbative improvement condition on $c_{SW}$, without, however, using the Schr\"{o}dinger functional in our calculation.Comment: 3 pages, LaTeX (uses espcrc2.sty), 4 postscript figures, to be published in the proceedings of Lattice'9

The continuum limit of the quark mass step scaling function in quenched lattice QCD

The renormalisation group running of the quark mass is determined non-perturbatively for a large range of scales, by computing the step scaling function in the Schroedinger Functional formalism of quenched lattice QCD both with and without O(a) improvement. A one-loop perturbative calculation of the discretisation effects has been carried out for both the Wilson and the Clover-improved actions and for a large number of lattice resolutions. The non-perturbative computation yields continuum results which are regularisation independent, thus providing convincing evidence for the uniqueness of the continuum limit. As a byproduct, the ratio of the renormalisation group invariant quark mass to the quark mass, renormalised at a hadronic scale, is obtained with very high accuracy.Comment: 23 pages, 3 figures; minor changes, references adde

The Light Hadron Mass Spectrum with Non-Perturbatively O(a) Improved Wilson Fermions

We compute the light hadron mass spectrum in quenched lattice QCD at $\beta = 6.0$ using the Sheikholeslami-Wohlert fermionic action. The calculation is done for several choices of the coefficient $c_{SW}$, including $c_{SW} = 0$ and the recently proposed optimal value $c_{SW} = 1.769$. We find that the individual masses change by up to 30\% under $O(a)$ improvement. The spectrum calculation suggests $c_{SW} \approx 1.4$ for the optimal value of the coefficient.Comment: 15 pages, uuencoded Z-compressed postscript file. Also available from http://www.desy.de/pub/preprints/desy/199

Computation of the improvement coefficient cswc_{sw} to 1-loop with improved gluon actions

The clover coefficient \csw is computed at one loop order of perturbation theory for improved gluon actions including six-link loops. The O(a) improvement coefficients for the dimension three isovector composite operators bilinear in the quark fields are also calculated.Comment: LATTICE98(improvement), 3 pages, Latex(espcrc2,epsf), 2 figure

Two-loop relation between the bare lattice coupling and the MSbar coupling in pure SU(N) gauge theories

We report the result of a computation of the relation between the renormalized coupling in the MSbar scheme of dimensional regularization and the bare coupling in the standard lattice formulation of the SU(N) Yang-Mills theory to two-loop order of perturbation theory and discuss some of its implications.Comment: 10 pages, postscript fil

Acceleration of Coarse Grain Molecular Dynamics on GPU Architectures

Coarse grain (CG) molecular models have been proposed to simulate complex sys- tems with lower computational overheads and longer timescales with respect to atom- istic level models. However, their acceleration on parallel architectures such as Graphic Processing Units (GPU) presents original challenges that must be carefully evaluated. The objective of this work is to characterize the impact of CG model features on parallel simulation performance. To achieve this, we implemented a GPU-accelerated version of a CG molecular dynamics simulator, to which we applied specic optimizations for CG models, such as dedicated data structures to handle dierent bead type interac- tions, obtaining a maximum speed-up of 14 on the NVIDIA GTX480 GPU with Fermi architecture. We provide a complete characterization and evaluation of algorithmic and simulated system features of CG models impacting the achievable speed-up and accuracy of results, using three dierent GPU architectures as case studie

Two Loop Computation of the Schroedinger Functional in Lattice QCD

We compute the Schroedinger functional (SF) for the case of lattice QCD with Wilson fermions (with and without SW improvement) at two-loop order in lattice perturbation theory. This allows us to extract the three-loop beta-function in the SF-scheme. These results are required to compute the running coupling, the Lambda-parameter and quark masses by finite size techniques with negligible systematic errors. In addition our results enable the implementation of two-loop O(a) improvement in SF-simulations.Comment: 30 pages, numerical changes in eqs.(A.9), (A.10), (5.6), (5.9), (5.12) due to the revision of hep-lat/9801007v2 (Christou et al.