7 research outputs found
Strange quark mass and Lambda parameter by the ALPHA collaboration
We determine f_K for lattice QCD in the two flavor approximation with
non-perturbatively improved Wilson fermions. The result is used to set the
scale for dimensionful quantities in CLS/ALPHA simulations. To control its
dependence on the light quark mass, two different strategies for the chiral
extrapolation are applied. Combining f_K and the bare strange quark mass with
non-perturbative renormalization factors and step scaling functions computed in
the Schroedinger Functional, we determine the RGI strange quark mass and the
Lambda parameter in units of f_K.Comment: 7 pages, 4 figures; talk given at LATTICE 2011, XXIX International
Symposium on Lattice Field Theory, July 11-16 2011, Squaw Valley, Lake Tahoe,
Californi
The revelation principle and regularity conditions
The revelation principle asserts that every outcome brought by a mechanism
is realized by a truthful direct mechanism. The present paper investigates the regularity
conditions of these two mechanisms in the continuous space of the agentâs
type. It questions what regularity condition a general mechanism confers upon a
direct mechanism through the revelation principle. By so doing, we elucidate the
limit of the revelation principle
Critical slowing down and error analysis of lattice QCD simulations
In dieser Arbeit untersuchen wir das Critical Slowing down der Gitter-QCD Simulationen. Wir fĂŒhren eine Vorstudie in der quenched Approximation durch, in der wir feststellen, dass unsere SchĂ€tzung der exponentiellen Autokorrelation wie \tauexp(a) \sim a^{-5} skaliert, wobei der Gitterabstand ist. In unquenched Simulationen mit O(a)-verbesserten Wilson-Fermionen finden wir ein Ă€hnliches Skalierungsgesetz. Die Diskussion wird von einem gro\ss{}en Satz an Ensembles sowohl in reiner Eichtheorie als auch in der Theorie mit zwei entarteten Seequarks unterstĂŒtzt. Wir haben darĂŒber hinaus die Wirkung von langsamen algorithmischen Modi in der Fehleranalyse des Erwartungswertes von typischen Gitter-QCD-Observablen (hadronische Matrixelemente und Massen) untersucht. Im Kontext der Simulationen, die durch langsame Modi betroffen sind, schlagen wir vor und testen eine Methode, um zuverlĂ€ssige SchĂ€tzungen der statistischen Fehler zu bekommen. Diese Methode soll in dem typischen Simulationsbereich der Gitter-QCD helfen, nĂ€mlich dann, wenn die gesamte erfasste Statistik O(10)\tauexp ist. Dies ist der typische Fall bei Simulationen in der NĂ€he des Kontinuumslimes, wo der Rechenaufwand fĂŒr die Erzeugung von zwei unabhĂ€ngigen Datenpunkten sehr gro\ss{} sein kann. Schlie\ss{}lich diskutieren wir die Skalenbestimmung in N_f=2-Simulationen mit der Kaon Zerfallskonstante f_K als experimentellem Input. Die Methode wird zusammen mit einer grĂŒndlichen Diskussion der angewandten Fehleranalyse erklĂ€rt. Eine Beschreibung der öffentlich zugĂ€nglichen Software, die fĂŒr die Fehleranalyse genutzt wurde, ist eingeschlossen.In this work we investigate the critical slowing down of lattice QCD simulations. We perform a preliminary study in the quenched approximation where we find that our estimate of the exponential auto-correlation time scales as \tauexp(a)\sim a^{-5}, where is the lattice spacing. In unquenched simulations with O(a) improved Wilson fermions we do not obtain a scaling law but find results compatible with the behavior that we find in the pure gauge theory. The discussion is supported by a large set of ensembles both in pure gauge and in the theory with two degenerate sea quarks. We have moreover investigated the effect of slow algorithmic modes in the error analysis of the expectation value of typical lattice QCD observables (hadronic matrix elements and masses). In the context of simulations affected by slow modes we propose and test a method to obtain reliable estimates of statistical errors. The method is supposed to help in the typical algorithmic setup of lattice QCD, namely when the total statistics collected is of O(10)\tauexp. This is the typical case when simulating close to the continuum limit where the computational costs for producing two independent data points can be extremely large. We finally discuss the scale setting in Nf=2 simulations using the Kaon decay constant f_K as physical input. The method is explained together with a thorough discussion of the error analysis employed. A description of the publicly available code used for the error analysis is included
Charm quark mass and D-meson decay constants from two-flavour lattice QCD
We present a computation of the charm quark's mass and the leptonic D-meson decay constants f_D and f_{D_s} in two-flavour lattice QCD with non-perturbatively O(a) improved Wilson quarks. Our analysis is based on the CLS configurations at two lattice spacings (a=0.065 and 0.048 fm, where the lattice scale is set by f_K) and pion masses ranging down to ~ 190 MeV at L*m_pi > 4, in order to perform controlled continuum and chiral extrapolations with small systematic uncertainties
Charm quark mass and D-meson decay constants from two-flavour lattice QCD
We present a computation of the charm quark's mass and the leptonic D-meson decay constants f_D and f_{D_s} in two-flavour lattice QCD with non-perturbatively O(a) improved Wilson quarks. Our analysis is based on the CLS configurations at two lattice spacings (a=0.065 and 0.048 fm, where the lattice scale is set by f_K) and pion masses ranging down to ~ 190 MeV at L*m_pi > 4, in order to perform controlled continuum and chiral extrapolations with small systematic uncertainties
Critical slowing down and error analysis in lattice QCD simulations
We study the critical slowing down towards the continuum limit of lattice QCD
simulations with Hybrid Monte Carlo type algorithms. In particular for the
squared topological charge we find it to be very severe with an effective
dynamical critical exponent of about 5 in pure gauge theory. We also consider
Wilson loops which we can demonstrate to decouple from the modes which slow
down the topological charge. Quenched observables are studied and a comparison
to simulations of full QCD is made. In order to deal with the slow modes in the
simulation, we propose a method to incorporate the information from slow
observables into the error analysis of physical observables and arrive at safer
error estimates.Comment: 33 pages including 15 figures and 4 table
The strange quark mass and Lambda parameter of two flavor QCD
We complete the non-perturbative calculations of the strange quark mass and
the Lambda parameter in two flavor QCD by the ALPHA collaboration. The missing
lattice scale is determined via the kaon decay constant, for whose chiral
extrapolation complementary strategies are compared. We also give a value for
the scale r_0 in physical units as well as an improved determination of the
renormalization constant Z_A.Comment: 46 pages, 11 figures, v2: minor corrections, results unchange