SSOR preconditioning in simulations of the QCD Schr\"odinger functional

We report on a parallelized implementation of SSOR preconditioning for O(a) improved lattice QCD with Schr\"odinger functional boundary conditions. Numerical simulations in the quenched approximation at parameters in the light quark mass region demonstrate that a performance gain of a factor $\sim$ 1.5 over even-odd preconditioning can be achieved.Comment: 15 pages, latex2e, 4 Postscript figures, uses packages elsart and epsfi

A non-perturbative computation of the B-meson decay constant and the b-quark mass in HQET

A lattice computation of the B-meson decay constant and the mass of the b-quark to leading order in the heavy quark effective theory is presented. The involved renormalization problems are solved non-perturbatively, and the continuum limit is taken. In the quenched approximation the results reported here already offer an interesting numerical precision, which will be further improved in the near future.Comment: Invited talk at International Europhysics Conference on High Energy Physics, EPS-HEP2003, 17-23 July 2003, Aachen, Germany, 5 pages, 7 figures, latex2e, uses epsfig, svjour and svep

The functional role of contrast adaptation

Prolonged inspection of high contrast sinewave gratings increases the contrast required to detect gratings having a similar spatial frequency and orientation. The functional role of such adaptation has, however, in the past, eluded disclosure. We here show that 5 min adaptation to a 2 c/deg sinewave grating of 0.8 contrast changes the observer's ability to discriminate the contrast level of a subsequently presented grating of the same spatial frequency and orientation. Similar to the threshold elevation effect, the observers required more incremental contrast for background contrast levels between 0.1 and 0.4 following adaptation. However, for contrast levels above 0.5, the observers required less delta contrast, following adaptation, to correctly discriminate which of two gratings was incremented in contrast. A simple model for adaptation is proposed to account for the findings which is based on a shift in the semi-saturation constant of the detector's contrast-response function. According to this model, adaptation acts to linearize the underlying mechanism's response in the region near the prevailing contrast level

Non-perturbative improvement of quark mass renormalization in two-flavour lattice QCD

We non-perturbatively determine the renormalization constant and the improvement coefficients relating the renormalized current and subtracted quark mass in O(a) improved two-flavour lattice QCD. We employ the Schr\"odinger functional scheme and fix the physical extent of the box by working at a constant value of the renormalized coupling. Our calculation yields results which cover two regions of bare parameter space. One is the weak-coupling region suitable for volumes of about half a fermi. By making simulations in this region, quarks as heavy as the bottom can be propagated with the full relativistic QCD action and renormalization problems in HQET can be solved non-perturbatively by a matching to QCD in finite volume. The other region refers to the common parameter range in large-volume simulations of two-flavour lattice QCD, where our results have particular relevance for charm physics applications.Comment: 31 pages including figures and tables, latex2e, uses JHEP3.cls; revised version published in JHEP, clarifying remarks and references added; typo(s) corrected, especially in eq. (3.10

Perturbative and non-perturbative studies of the SU(2)-Higgs model on lattices with asymmetric lattice spacings

We present a calculation of the O(g^2,\lambda) perturbative corrections to the coupling anisotropies of the SU(2)-Higgs model on lattices with asymmetric lattice spacings. These corrections are obtained by a one-loop calculation requiring the rotational invariance of the gauge and Higgs boson propagators in the continuum limit. The coupling anisotropies are also determined from numerical simulations of the model on appropriate lattices. The one-loop perturbation theory and the simulation results agree with high accuracy. It is demonstrated that rotational invariance is also restored for the static potential determined from space-space and space-time Wilson loops.Comment: 27pages, Latex, 7 figures (7 eps, 3 ps files), correction of misprint

O(a)\mathcal{O}(a) improved quark mass renormalization for a non-perturbative matching of HQET to three-flavor QCD

The use of Heavy Quark Effective Theory (HQET) on the lattice as an approach to B-physics phenomenology is based on a non-perturbative matching of HQET to QCD in finite volume. As a first step to apply the underlying strategy in the three-flavor ($N_f = 2+1$) theory, we determine the renormalization constant and improvement coefficients relating the renormalized current and subtracted quark mass of (quenched) valence quarks in $\mathcal{O}(a)$ improved $N_f=3$ lattice QCD. We present our strategy and first results for the relevant parameter region towards weak couplings along a line of constant physics, which corresponds to lattice resolutions $a\leq 0.02\,$fm and fixes the physical extent of the matching volume to $L\approx 0.5\,$fm.Comment: 7 pages including 7 figures, latex2e; Proceedings of the 36th International Symposium on Lattice Field Theory (Lattice 2018), 22-28 July 2018, Michigan State University, East Lansing, Michigan, US

Signal at subleading order in lattice HQET

We discuss the correlators in lattice HQET that are needed to go beyond the static theory. Based on our implementation in the Schr\"odinger functional we focus on their signal-to-noise ratios and check that a reasonable statistical precision can be reached in quantities like $f_{B_s}$ and $M_{B^\star}-M_B$.Comment: 3 pages, Lattice2004(heavy), v2: corrected definition of X^{kin/spin