arXiv subjects
Publications and source records attributed to Mike Peardon.
We present preliminary results for the static-light meson and baryon spectra for $N_f=2$ QCD. The study is performed on an anisotropic lattice and uses a new all-to-all propagator method allowing us to determine particle masses to a high precision.
A new method for computing all elements of the lattice quark propagator is proposed. The method combines the spectral decomposition of the propagator, computing the lowest eigenmodes exactly, with noisy estimators which are 'diluted', i.e. taken to have support only on a subset of time, space, spin or colour. We find that the errors are dramatically reduced compared to traditional noisy estimator techniques.
Lattice fermion actions are constructed with path integrals which are equivalent to the free one-flavour staggered fermion determinant. The Dirac operators used are local and have an identical spectrum of states to the staggered theory. Operators obeying a generalised Ginsparg-Wilson relation are developed.
The static-light matrix element needed to determine $f_B$ is studied on an anisotropic lattice with $N_f=2$. The improvement in precision due to stout links and all-to-all propagators is investigated.
The parameters of a 3+1 anisotropic quark action with Symanzik-improved glue are determined at 1-loop in perturbation theory.
A quark action designed for highly anisotropic lattice simulations is discussed. The mass-dependence of the parameters in the action is studied and the results are presented. Applications of this action in studies of heavy quark quantities are described and results are presented from simulations at an anisotropy of six, for a range of quark masses from strange to bottom.
An analytic method of smearing link variables in lattice QCD is proposed and tested. The differentiability of the smearing scheme with respect to the link variables permits the use of modern Monte Carlo updating methods based on molecular dynamics evolution for gauge-field actions constructed using such smeared links. In examining the smeared mean plaquette and the static quark-antiquark potential, no degradation in effectiveness is observed as compared to link smearing methods currently in use, although an increased sensitivity to the smearing parameter is found.
We present preliminary results for a non perturbative determination of the parameters in the action required to restore Lorentz invariance in long distance correlators, using the static interquark potential. Comparison with analytical results is made and further applications are discussed.
Results from simulations of quarkonia and heavy-light mesons on an anisotropic lattice are presented. The improved quark action and action-parameter tuning used in this study are discussed.
Techniques for efficient computation of the scalar glueball mass on the lattice are described. Directions and physics goals of proposed future calculations will be outlined.
A generalization of anisotropic lattices to include a 2+2 discretization is discussed. As a part of this program, we determine the one-loop correction to the gluon self-energy and analyse the restoration of Lorentz invariance in on-shell states for both the 2+2 and 3+1 cases. A 2+2 Wilson-like fermion action is also considered.
The implementation of gauge theories on a four-dimensional anisotropic lattice with two distinct lattice spacings is discussed, with special attention to the case where two axes are finely and two axes are coarsely discretized. Feynman rules for the Wilson gauge action are derived and the renormalizability of the theory and the recovery of the continuum limit are analyzed. The calculation of the gluon propagator and the restoration of Lorentz invariance in on-shell states is presented to one-loop order in lattice perturbation theory for $SU(N_c)$ on both 2+2 and 3+1 lattices.
A scheme for separating the high- and low-frequency molecular dynamics modes in Hybrid Monte Carlo (HMC) simulations of gauge theories with dynamical fermions is presented. The algorithm is tested in the Schwinger model with Wilson fermions.
The development of Monte Carlo algorithms for generating gauge field configurations with dynamical fermions and methods for extracting the most information from ensembles are summarised.
The pseudofermion action of the Hybrid Monte Carlo (HMC) algorithm for dynamical fermions is modified to directly incorporate Incomplete LU (ILU) factorisation. This reduces the stochastic noise and allows a larger molecular dynamics step-size to be taken, cutting the computational cost. Numerical tests using the two-flavour Schwinger model are presented, where a two-step ILU preconditioning of the even-odd fermion matrix allows the step-size to be increased by a factor of two over the standard even-odd formulation.
Results for the inter-quark potential and low-lying SU(3) glueball spectrum from simulations using a new improved action are presented. The action, suitable for highly anisotropic lattices, contains a two-plaquette term coupling with a negative coefficient as well as incorporating Symanzik improvement.
The spectrum of glueballs below 4 GeV in the SU(3) pure-gauge theory is investigated using Monte Carlo simulations of gluons on several anisotropic lattices with spatial grid separations ranging from 0.1 to 0.4 fm. Systematic errors from discretization and finite volume are studied, and the continuum spin quantum numbers are identified. Care is taken to distinguish single glueball states from two-glueball and torelon-pair states. Our determination of the spectrum significantly improves upon previous Wilson action calculations.
Anisotropic lattices are an efficient means of studying the glueballs of QCD, however problems arise with simulations of the lightest, scalar state. The mass is strongly dependent on the lattice spacing, even when a mean-field improved gluon action is used. The nature and cause of these errors are discussed and the scaling properties of the scalar from different lattice actions are presented.