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We present results for the static inter-quark potential, lightest glueballs, light hadron spectrum and topological susceptibility using a non-perturbatively improved action on a $16^3\times 32$ lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units ($\sim 1.7$ fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavours of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied ($M_{PS}/M_{V}\ge0.58$). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities., Comment: 53 pages, LaTeX/RevTeX, 16 eps figures; corrected clover action expression and various typos, no results changed

We investigate solidification in metal systems ranging in size from 64,000 to 524,288,000 atoms on the IBM BlueGene/L computer at LLNL. Using the newly developed ddcMD code, we achieve performance rates as high as 103 TFlops, with a performance of 101.7 TFlop sustained over a 7 hour run on 131,072 cpus. We demonstrate superb strong and weak scaling. Our calculations are significant as they represent the first atomic-scale model of metal solidification to proceed, without finite size effects, from spontaneous nucleation and growth of solid out of the liquid, through the coalescence phase, and into the onset of coarsening. Thus, our simulations represent the first step towards an atomistic model of nucleation and growth that can directly link atomistic to mesoscopic length scales.

The purpose of this research was to further investigate the hydrodynamics of the United States Pharmacopeia (USP) paddle dissolution apparatus using a previously generated computational fluid dynamics (CFD) model. The influence of paddle rotational speed on the hydrodynamics in the dissolution vessel was simulated. The maximum velocity magnitude for axial and tangential velocities at different locations in the vessel was found to increase linearly with the paddle rotational speed. Path-lines of fluid mixing, which were examined from a central region at the base of the vessel, did not reveal a region of poor mixing between the upper cylindrical and lower hemispherical volumes, as previously speculated. Considerable differences in the resulting flow patterns were observed for paddle rotational speeds between 25 and 150 rpm. The approximate time required to achieve complete mixing varied between 2 to 5 seconds at 150 rpm and 40 to 60 seconds at 25 rpm, although complete mixing was achievable for each speed examined. An analysis of CFD-generated velocities above the top surface of a cylindrical compact positioned at the base of the vessel, below the center of the rotating paddle, revealed that the fluid in this region was undergoing solid body rotation. An examination of the velocity boundary layers adjacent to the curved surface of the compact revealed large peaks in the shear rates for a region within ~3 mm from the base of the compact, consistent with a "grooving" effect, which had been previously seen on the surface of compacts following dissolution, associated with a higher dissolution rate in this region.

We describe a systematic approach to generating approximate actions for the lattice simulation of QCD. Three different tuning conditions are defined to match approximate with true actions, and it is shown that these three conditions become equivalent when the approximate and true actions are sufficiently close. We present a detailed study of approximate actions in the lattice Schwinger model together with an exploratory study of full QCD at unphysical parameter values. We find that the technicalities of the approximate action approach work quite well. However, very delicate tuning is necessary to find an approximate action which gives good predictions for all physical observables. Our best view of the immediate applicability of the methods we describe is to allow high statistics studies of particular physical observables after a low statistics full fermion simulation has been used to prepare the stage., Comment: 34 pages, 5 postscript figures, uses revtex and psfig

In June 2004 QCD was simulated for the first time at sustained speed exceeding 1 TeraFlops in the BlueGene/L supercomputer at the IBM T.J. Watson Research Lab. The implementation and performance of QCD in the BlueGene/L is presented., Talk presented at Lattice2004(machines), Fermilab, 21-26 June 2004, 3 pages, 5 figures

We study the quenched and unquenched lattice Schwinger model with Wilson fermions. The lowest non-trivial order of the systematic expansion recently proposed by Sexton and Weingarten is shown to allow good estimates of long distance physics from quenched configurations. Results for the static potential and the lowest bound state mass are presented.

We compute from lattice QCD in the valence (quenched) approximation the partial decay widths of the lightest scalar glueball to pairs of pseudoscalar quark-antiquark states. These predictions and values obtained earlier for the scalar glueball's mass are in good agreement with the observed properties of $f_J(1710)$ and inconsistent with all other observed meson resonances., Comment: 12 pages of Latex, 3 PostsScript figures as separate uufile

We evaluate $f_{\pi}/ m_{\rho}$, $f_K/ m_{\rho}$, $1/f_{\rho}$, and $ m_{\phi}/(f_{\phi} m_{\rho})$, extrapolated to physical quark mass, zero lattice spacing and infinite volume, for lattice QCD with Wilson quarks in the valence (quenched) approximation. The predicted ratios differ from experiment by amounts ranging from 12\% to 17\% equivalent to between 0.9 and 2.8 times the corresponding statistical uncertainties., Comment: uufiles encoded copy of 40 page Latex article, including 14 figures in Postscript. The long version of hep-lat/9302012, IBM/HET 93-3

We discuss a class of reversible, discrete approximations to Hamilton's equations for use in the hybrid Monte Carlo algorithm and derive an asymptotic formula for the step-size-dependent errors arising from this family of approximations. For lattice QCD with Wilson fermions, we construct several different updates in which the effect of fermion vacuum polarization is given a longer time step than the gauge field's self-interaction. On a 44 lattice, one of these algorithms with an optimal choice of step size is 30% to 40% faster than the standard leapfrog update with an optimal step size.

We evaluate the coupling constant for the lightest scalar glueball to decay to pseudoscalar meson pairs. The calculation is done in the valence approximation on a $16^3 \times 24$ lattice at $\beta = 5.70$ for two different values of pseudoscalar meson mass., Comment: 3 pages, Latex, 1 PostScript figure, requires espcrc2.tex, espcrc2.sty neither of which is included, talk at Lat94

PUBLISHED, 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., MP is grateful to Enterprise-Ireland for support under grant SC/01/306.

The nature of the phase transition in the lattice Gross-Neveu model with Wilson fermions is investigated using a new analytical technique. This involves a new type of weak coupling expansion which focuses on the partition function zeroes of the model. Its application to the single flavour Gross-Neveu model yields a phase diagram whose structure is consistent with that predicted from a saddle point approach. The existence of an Aoki phase is confirmed and its width in the weakly coupled region is determined. Parity, rather than chiral symmetry breaking naturally emerges as the driving mechanism for the phase transition., 15 pages including 1 figure

A new method to determine the phase diagram of certain lattice fermionic field theories in the weakly coupled regime is presented. This method involves a new type of weak coupling expansion which is multiplicative rather than additive in nature and allows perturbative calculation of partition function zeroes. Application of the method to the single flavour Gross-Neveu model gives a phase diagram consistent with the parity symmetry breaking scenario of Aoki and provides new quantitative information on the width of the Aoki phase in the weakly coupled sector., 9 pages, 1 figure (minor changes) To be published in Phys. Lett. B

We present hadron mass spectrum results for valence Wilson fermions obtained from simulations on the GF11. We performed high statistic runs on three physical volumes, 8 3 × 32, 16 3 × 32, and 24 3 × 32, all with the same coarse lattice spacing, β = 5.7. We see no systematic difference between our 8 3 and 16 3 results at the large quark masses we could simulate on 8 3 . Our 16 3 and 24 3 results also agree at the small quark masses we simulated on these larger volumes.

The asymptotic expansion of the massive scalar field propagator on a n-dimensional lattice is derived. The method used is based on the evaluation of the asymptotic expansion of the modified Bessel function $I_{\nu}(\nu^{2} \beta)$ as the order $\nu$ grows to infinity., Comment: 13 pages, 2 figures. Updated version (accepted for publication on Phys. Lett. B) includes evaluation of the one-loop mass renormalization in lattice lambda phi^4 theory

Recent developments and applications of approximate actions for full lattice QCD are described. We present first results based on the stochastic estimation of the fermion determinant on $12^3\times 24$ configurations at $\beta=5.2$., Comment: 3 pages, Latex, no figures, Contribution to Lattice 97, The XV International Symposium on Lattice Field Theory, Edinburgh 22-26 July 1997

We evaluate the partial decay widths of the lightest scalar glueball to pairs of pseudoscalar quark-antiquark states. The calculation is done in the valence (quenched) approximation on a $16^3 \time 24$ lattice at $\beta = 5.7$. These predictions and values obtained earlier for the infinite volume continuum limit of the scalar glueball's mass are in good agreement with the observed properties of $f_J(1710)$ and inconsistent with all other observed meson resonances., Comment: 8 pages of Latex, 12 PostScript figures, 2 macros included, plenary talk given by D. Weingarten at Lattice 95, to appear in conference proceedings

The first stage in the construction of the 0.8 Teraflops Supercomputer at Columbia, a working, two node parallel computer, has been successfully completed. The next stage, a 512 node, 26 Gigaflops prototype, is in its final construction phase. A general description and current status of the hardware and software is presented., 4 pages, uuencoded compressed Postscript file, contribution to Lattice 95

We describe a systematic expansion for full QCD. The leading term in the expansion gives the valence approximation. The expansion reproduces full QCD if an infinite number of higher terms are included., 3 pages, latex, no figures, requires espcrc2.sty (included at end) Contribution to Lattice 94 proceedings

We evaluate pseudoscalar, vector, spin 1/2 and spin 3/2 baryon masses predicted by lattice QCD with Wilson quarks in the valence (quenched) approximation for a range of different values of lattice spacing, lattice volume and quark mass. Extrapolating these results to physical quark mass, then to zero lattice spacing and infinite volume we obtain values for eight mass ratios. We also determine the zero lattice spacing, infinite volume limit of an alternate set of five quantities found without extrapolation in quark mass. Both sets of predictions differ from the corresponding observed values by amounts consistent with the predicted quantities' statistical uncertainties., Comment: 108 pages of Latex, including 50 PostScript figures, tarred, compressed and uuencoded. IBM-HET-94-3. (The first version of this posting exceeded the size limit. I squeezed the second version in by dropping out the figues. This version gets the figures in but has to be run through Latex and dvips.)

We evaluate the infinite volume, continuum limits of eight hadron mass ratios predicted by lattice QCD with Wilson quarks in the valence (quenched) approximation. Each predicted ratio differs from the corresponding observed value by less than 6\%., Comment: 13 pages of Latex + 2 PostScript files attached, IBM/HET 92-3

We obtain estimates of several hadron mass ratios, for Wilson quarks in the valence (quenched) approximation, extrapolated to physical quark mass, infinite volume and zero lattice spacing., 10 pages of Latex + 2 PostScript files attached

The GF11 project at IBM’s T. J. Watson Research Center is entering full production for QCD numerical calculations. This paper describes the GF11 hardware and system software, and discusses the first production program which has been developed to run on GF11. This program is a variation of the Cabbibo Marinari pure gauge Monte Carlo program for SU(3) and is currently sustaining almost 6 gigaflops on 360 processors in GF11.

We present the matrix elements squared for all (2 → 2) and (2 → 3) parton scattering subprocesses calculated at O(αs3). The matrix elements are presented in n dimensions to regulate singularities due to the emission of soft or collinear radiation. We use these results to discuss one-hadron inclusive scattering, considering only a limited number of parton subprocesses. A preliminary analysis is made of the implications of our results for gluon-gluon scattering in the absence of quarks.

Explicit formulae are given in QCD for the processes which contribute to the hadroproduction of heavy quarks Q. The processes considered are 1. (1) q + q → Q + Q , 2. (2) g + g → Q + Q , 3. (3) Q + Q → q + q + g , 4. (4) Q + Q → g + g + g . All mass effects are included. A comparison of the exact matrix elements with the results of the leading pole and soft gluon approximation is made.

A new method to analytically determine the partition function zeroes of weakly coupled theories on finite-size lattices is developed. Applied to the lattice Schwinger model, this reveals the possible absence of a phase transition at fixed weak coupling. We show how finite-size scaling techniques on small or moderate lattice sizes may mimic the presence of a spurious phase transition. Application of our method to the Gross-Neveu model yields a phase diagram consistent with that coming from a saddle point analysis., Talk at LATTICE99, 3 pages, 2 figures