We present and discuss results for cutoff effects in the PCAC masses and the mass dependence of r0 for full QCD and various fermion actions. Our discussion of how one computes mass dependences – here of r0 – is also relevant for comparisons with chiral perturbation theory.
We present first results for the step scaling function σP of the renormalization factor ZP of the pseudoscalar density. The simulations are performed within the framework of the Schrödinger functional with two flavors of O(a) improved Wilson fermions. The knowledge of σP is required to compute the renormalization group invariant quark masses. We also study… (More)
We address the locality problem arising in simulations, which take the square root of the staggered fermion determinant as a Boltzmann weight to reduce the number of dynamical quark tastes from four to two. We study analytically and numerically the square root of the staggered fermion operator as a candidate to define a two taste theory from first… (More)
We present a computation of the decay constant FB s in quenched QCD. Our strategy is to combine new precise data from the static approximation with an interpolation of the decay constant around the charm quark mass region. This computation is the first step in demonstrating the feasability of a strategy for FB in full QCD. The continuum limits in the static… (More)
We present a numerical study for different discretisations of the static action, concerning cutoff 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… (More)
We report on the latest results on the running coupling of two flavour QCD in the Schrödinger functional scheme. Results for the step scaling function are obtained from simulations on lattices L/a = 8 and L/a = 16 which confirm the first results from lattices L/a = 4, 5, 6 presented one year ago by the ALPHA collaboration. We also discuss some algorithmic… (More)
We present a non-perturbative computation of the running of the coupling α s in QCD with two flavours of dynamical fermions in the Schrödinger functional scheme. We improve our previous results by a reliable continuum extrapolation. The Λ-parameter characterizing the high-energy running is related to the value of the coupling at low energy in the continuum… (More)
We present an algorithmic study for the simulation of two massless flavors of O(a) improved Wilson quarks with Schrödinger functional boundary conditions. The algorithm used is Hybrid Monte Carlo with two pseudo-fermion fields as proposed by M. Hasenbusch. A gain in CPU cost of a factor two is reached when compared to one pseudo-fermion field due to the… (More)