Gregory W. Kilcup

QCD with dynamical Wilson fermions. II.

We present results for the QCD spectrum and the matrix elements of scalar and axial-vector densities at β=6/g2=5.4, 5.5, 5.6. The lattice update was done using the hybrid Monte Carlo algorithm to include two flavors of dynamical Wilson fermions. We have explored quark masses in the range ms≤mq≤3ms. The results for the spectrum are similar to quenched simulations and mass ratios are consistent with phenomenological heavy-quark models. The results for matrix elements of the scalar density show that the contribution of sea quarks is comparable to that of the valence quarks. This has important implications for the pion-nucleon σ term.

Theβ-function for pure gauge SU(3)

Abstract We present detailed results for the non-perturbative s-function of the SU(3) lattice gauge theory using theb = √3 renormalization group transformation (RGT). The results are compared to those obtained from theb = 2RGT, and from measurements of the deconfinement temperature, the string tension and the scalar glueball mass. Above6/g 2 ≈ 6.75our results are consistent with asymptotic scaling, while for6.0 2 g 2 , in the region where the s-function shows a dip, the glueball mass shows significant deviations from scaling.

COMPARISON OF UPDATE ALGORITHMS FOR PURE GAUGE SU(3)

We show that the overrelaxed algorithm of Creutz and of Brown and Woch is the optimal local update algorithm for simulation of pure gauge SU(3). Our comparison criterion includes computer efficiency and decorrelation times. We also investigate the rate of decorrelation for the Hybrid Monte Carlo algorithm.

On the finite-temperature transition of QCD

Abstract Using an exact algorithm to incorporate dynamical quarks, we present evidence from numerical simulations that the finite-temperature transition in QCD is first order for realistic quark masses. For two light flavors of quarks we see a two state signal, with flip-flops between these states. For four flavors we show that the first-order transition extends to quark masses heavier than T c .

Up quark mass in lattice QCD with three light dynamical quarks and implications for strong CP invariance.

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.

Sea quarks and the hadron spectrum

Abstract We present lattice Monte Carlo results demonstrating the effects of dynamical quarks on the hadron spectrum. We show that the sea quarks do not influence the nucleon and the rho in an identical manner, and the ratio M N M p decreases as the sea quark mass is decreased. We also find a large value for the sea quark contribution to the matrix element 〈N| u u+ d d|N〉 .

Status and prospects of the computational approach to high-energy physics

We review the status of lattice computer calculations in Quantum Chromo-dynamics (QCD) and mention a new field of computational high-energy physics—that of Strings or random surfaces. After outlining Monte Carlo Field Theory we explain in detail both QCD and Strings—describing how these theories are discretized on a lattice, what one can calculate, and how much computer time is required. We include a summary of the concurrent QCD machines which have been, and are being, built. We speculate on the prospects for such work, including a prediction for when QCD will besolved!

Weak interaction matrix elements with staggered fermions

Abstract We present a progress report on the calculation of weak interaction matrix element using staggered fermions. We are using several new techniques, including include Landau gauge operators and quark wall propagators. We give preliminary results for the kaon B parameter.

Testing improved staggered fermions withmsandBK

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.