J.E. Hetrick

Electromagnetic splittings of hadrons from improved staggered quarks in full QCD

S. Basak ,a† A. Bazavov, b C. Bernard, c C. DeTar,d W. Freeman,b Steven Gottlieb,a U.M. Heller,e J.E. Hetrick, f J. Laiho,c L. Levkova,d J. Osborn,g R. Sugar,h and D. Toussaintb (MILC Collaboration) a Department of Physics, Indiana University Bloomington, IN 47405, USA b Physics Department, University of Arizona Tucson, AZ 85721, USA c Physics Department, Washington University St. Louis, MO 63130, USA d Physics Department, University of Utah Salt Lake City, UT 84112, USA e American Physical Society One Research Road, Box 9000, Ridge, NY 11961-9000, USA f Physics Department, University of the Pacific Stockton, CA 95211, USA g Argonne Leadership Computing Facility, Argonne National Laboratory Argonne, IL 60439, USA h Physics Department, University of California Santa Barbara, CA 93106, USA E-mail: sbasak@indiana.edu

Gauge fixing on the lattice

Abstract The first numerical evidence of gauge-fixed vacuum copies on the lattice is presented for SU(2) and U(1) in 4 and 2 dimensions. Gauge transformations between these copies have non-trivial topological structure which is displayed. Photon propagators do not show the correct behavior if copies are not excluded.

Thermodynamics for two flavor QCD

Abstract We conclude our analysis of the Nt = 6 equation of state (EOS) for two flavor QCD, first described at last years conference. We have obtained new runs at amq = 0.025 and improved runs and amq = 0.0125. The results are extrapolated to mq = 0, and we extract the speed of sound as well. We also present evidence for a restoration of the SU(2)×SU(2) chiral symmetry just above the crossover, but not of the axial U(1) chiral symmetry.

Simulations with dynamical HISQ quarks

We report on the status of a program of generating and using configurations with four flavors of dynamical quarks, using the HISQ action. We study the lattice spacing dependence of physical quantities in these simulations, using runs at several lattice spacings, but with the light quark mass held fixed at two tenths of the strange quark mass. We find that the lattice artifacts in the HISQ simulations are much smaller than those in the asqtad simulations at the same lattice spacings and quark masses. We also discuss methods for setting the scale, or assigning a lattice spacing to ensembles run at unphysical parameters.

Predictions from Lattice QCD

In the past year, we calculated with lattice QCD three quantities that were unknown or poorly known. They are the q{sup 2} dependence of the form factor in semileptonic D {yields} K/{nu} decay, the decay constant of the D meson, and the mass of the B{sub c} meson. In this talk, we summarize these calculations, with emphasis on their (subsequent) confirmation by experiments.

Light hadron spectrum: MILC results with the Kogut-Susskind and Wilson actions

We present the current status of our ongoing calculations of the light hadron spectrum with both KogutSusskind (KS) and Wilson quarks in the valence or quenched approximation. We discuss KS quarks first and find that the chiral extrapolation is potentially the biggest source of systematic error. For the Wilson case, we focus on finite volume and source size effects at 6/g 2 = 5.7. We find no evidence to support the claim that there is a finite volume effect between Ns = 16 and 24 of approximately 5%.

The locality of the fourth root of the staggered fermion determinant in the interacting case.

The fourth root approximation in LQCD simulations with dynamical staggered fermions requires justification. We test its validity numerically in the interacting theory in a renormalization group framework.

Heavy light decay constants from Wilson and static quarks

Abstract MILC collaboration results for fB, fBs, fD, fDs and their ratios are presented. These results are still preliminary, but the analysis is close to being completed. Sources of systematic error, both within the quenched approximation and from quenching itself, are estimated. We find, for example, fB = 153±10−13 −0+36 +13MeV, and f B s f B = 1.10±0.02 −0.03 −0.02 +0.05 +0.03 , where the errors are statistical, systematic (within the quenched approximation), and systematic (of quenching), respectively. The extrapolation to the continuum and the chiral extrapolation are the largest sources of error. Present central values are based on linear chiral extrapolations; a shift to quadratic extrapolations would raise fB by 20 MeV and make the error within the quenched approximation more symmetric.

Exotic hybrid mesons with light quarks

Abstract Hybrid mesons, made from a quark, an antiquark and gluons, can have quantum numbers inaccessible to conventional quark-antiquark states. Confirmation of such states would give information on the role of “dynamical” color in low energy QCD. We present preliminary results for hybrid meson masses using light Wilson valence quarks.

Recent MILC spectrum results

Abstract We report on results from three spectrum calculations with staggered quarks: 1) a quenched calculation with the standard action for the gluons and quarks; 2) a quenched calculation with improved actions for both the gluons and quarks; and 3) a calculation with two flavors of dynamical quarks using the standard actions for the gluons and quarks.