G. Kilcup

Lattice calculation of I=2 pion scattering length

We present results for the I=2 pion scattering length calculated using staggered fermions in the quenched approximation. The calculation uses the finite volume dependence of the energy of a two pion state. We find good agreement with current algebra predictions for scattering of Goldstone pions, and reasonable agreement for the non-Goldstine pions.

Is strong CP invariance due to a massless up quark

A standing mystery in the Standard Model is the unnatural smallness of the strong CP violating phase. A massless up quark has long been proposed as one potential solution. A lattice calculation of the constants of the chiral Lagrangian essential for the determination of the up quark mass, 2 alpha_8 - alpha_5, is presented. We find 2 alpha_8 - alpha_5 = 0.29 +/- 0.18, which corresponds to m_u / m_d = 0.410 +/- 0.036. This is the first such calculation using a physical number of dynamical light quarks, N_f = 3.

On the Nf and a dependence of BK

Abstract We present results of a study of B K using tadpole improved gauge-invariant staggered operators. Using three ensembles of 16 3 × 32 configurations with varying numbers of dynamical flavors, we observe a small dependence on N f . Using 7 quenched ensembles at different values of β, we extrapolate to a = 0.

Testing improved staggered fermions with M(S) and B(K)

We study the improvement of staggered fermions using hypercubically smeared links. We calculate the strange quark mass and the kaon B parameter, B{sub K}, in quenched QCD on a 16{sup 3}x64 lattice at {beta}=6.0. We find m{sub s}(MS,2 GeV)=101.2{+-}1.3{+-}4 MeV and B{sub K}(MS,2 GeV)=0.578{+-}0.018{+-}0.042, where the first error is from statistics and fitting, and the second from using one-loop matching factors. The scale (1/a=1.95 GeV) is set by M{sub {rho}}, and m{sub s} is determined using the kaon mass. Comparing to quenched results obtained using unimproved staggered fermions and other discretizations, we argue that the size of discretization errors in B{sub K} is substantially reduced by improvement.

Electroweak matrix elements: 1990 update

Abstract I review some of the past years activity in the application of lattice QCD to hadronic matrix elements.

Matrix elements relevant for Δ I = 1 / 2 rule and ɛ ′ /ɛ from lattice QCD with staggered fermions

We perform a study of matrix elements relevant for the Delta I=1/2 rule and the direct CP-violation parameter epsilon-prime from first principles by computer simulation in Lattice QCD. We use staggered (Kogut-Susskind) fermions, and employ the chiral perturbation theory method for studying K to 2 Pi decays. Having obtained a reasonable statistical accuracy, we observe an enhancement of the Delta I=1/2 amplitude, consistent with experiment within our large systematic errors. Finite volume and quenching effects have been studied and were found small compared to noise. The estimates of epsilon-prime are hindered by large uncertainties associated with operator matching. In this paper we explain the simulation method, present the results and address the systematic uncertainties.

Status of the QCDSP project

Abstract We describe the completed 8,192-node, 0.4Tflops machine at Columbia as well as the 12,288-node, 0.6Tflops machine assembled at the RIKEN Brookhaven Research Center. Present performance as well as our experience in commissioning these large machines is presented. We outline our on-going physics program and explain how the configuration of the machine is varied to support a wide range of lattice QCD problems, requiring a variety of machine sizes. Finally a brief discussion is given of future prospects for large-scale lattice QCD machines.

Applications of the eigenmodes of the staggered Dirac operator

Abstract We have constructed the lowest few eigenvectors of the staggered Dirac operator on SU (3) gauge configurations, both quenched and dynamical. We use these modes to study the topological charge and to construct approximate hadronic correlators.

QCDSP — A status report

Abstract The QCDSP machine at Columbia University has grown to 2,048 nodes achieving a peak speed of 100 Gigaflops. Software for quenched and Hybrid Monte Carlo (HMC) evolution scheme has been developed for staggered fermions, with support for Wilson and clover fermions under development. We provide an overview of the runtime environment, the current status of the QCDSP construction program and preliminary results not presented elsewhere in these proceedings.

Calculating weak matrix elements using HYP staggered fermions

Abstract We present preliminary results of weak matrix elements relevant to CP violation calculated using the HYP (II) staggered fermions. Since the complete set of matching coefficients at the one-loop level became available recently, we have constructed lattice operators with all the g2 corrections included. The main results include both δI = 3 2 and δI = 1 2 contributions.We present preliminary results of weak matrix elements relevant to CP violation calculated using the HYP (II) staggered fermions. Since the complete set of matching coefficients at the one-loop level became available recently, we have constructed lattice operators with all the