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

Non-perturbative tests of continuum HQET through small-volume two-flavour QCD

We study the heavy quark mass dependence of selected observables constructed from heavy-light meson correlation functions in small-volume two-flavour lattice QCD after taking the continuum limit. The light quark mass is tuned to zero, whereas the range of available heavy quark masses $m_h$ covers a region extending from around the charm to beyond the bottom quark mass scale. This allows entering the asymptotic mass-scaling regime as $1/m_h \to 0$ and performing well-controlled extrapolations to the infinite-mass limit. Our results are then compared to predictions obtained in the static limit of continuum Heavy Quark Effective Theory (HQET), in order to verify non-perturbatively that HQET is an effective theory of QCD. While in general we observe a nice agreement at the few-% level, we find it to be less convincing for the small-volume pseudoscalar decay constant when perturbative matching is involved.Comment: 42 pages, 10 figures, 12 tables; JHEP styl

Static quarks with improved statistical precision

We present a numerical study for different discretisations of the static action, concerning cut-off effects and the growth of statistical errors with Euclidean time. An error reduction by an order of magnitude can be obtained with respect to the Eichten-Hill action, for time separations beyond 1.3 fm, keeping discretization errors small. The best actions lead to a big improvement on the precision of the quark mass Mb and F_Bs in the static approximation.Comment: 3 pages, 4 figures, Lattice2003(heavy

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

Effective heavy-light meson energies in small-volume quenched QCD

We study effective energies of heavy-light meson correlation functions in lattice QCD and a small volume of (0.2 fm)^4 to non-perturbatively calculate their dependence on the heavy quark mass in the continuum limit. Our quenched results obtained here constitute an essential intermediate step of a first fully non-perturbative computation of the b-quark's mass in the static approximation that has recently been presented as an application of a new proposal to non-perturbatively renormalize the Heavy Quark Effective Theory. The renormalization constant and the improvement coefficients relating the renormalized current and subtracted quark mass are determined in the relevant parameter region at weak couplings, which allows to perform the numerical simulations at several, precisely fixed values of the renormalization group invariant heavy quark mass in a range from 3 GeV to 15 GeV.Comment: 24 pages including figures and tables, latex2e; version published in JHEP, small additions, results unchange

Non-perturbative scaling tests of twisted mass QCD

We present a scaling study of lattice QCD with O(a) improved Wilson fermions and a chirally twisted mass term. In order to get precise results with a moderate computational effort, we have considered a system of physical size of 0.75^3 * 1.5 fm^4 with Schroedinger functional boundary conditions in the quenched approximation. Looking at meson observables in the pseudoscalar and vector channels, we find that O(a) improvement is effective and residual cutoff effects are fairly small.Comment: 5 pages, 4 figures, Lattice 2000 (Improvement and Renormalization), two misprints correcte

Cutoff effects in twisted mass lattice QCD

We present a first numerical study of lattice QCD with O(a) improved Wilson quarks and a chirally twisted mass term. Renormalized correlation functions are derived from the Schroedinger functional and evaluated in an intermediate space-time volume of size 0.75^3 x 1.5 fm^4. In the quenched approximation precise results are then obtained with a moderate computational effort, allowing for a detailed study of the continuum approach. The latter is discussed in terms of observables which converge to meson masses and decay constants in the limit of large space-time volume. In the O(a) improved theory we find residual cutoff effects to be at the level of a few percent for lattice spacings of about 0.1 fm.Comment: 20 pages, 5 figures. Comments about the uncertainties on improvement coefficients adde