Heavy-Light Decay Constants: Conclusions from the Wilson Action

We report on the results of a MILC collaboration calculation of $f_B$, $f_{B_s}$, $f_D$, $f_{D_s}$ and their ratios. We discuss the most important errors in more detail than we have elsewhere.Comment: LATTICE98(heavyqk) 3 latex pages and 3 postscript figures. The perturbative correction calculated by Kuramashi has been adjusted to take into account the fact that we match to the continuum at the kinetic mass of the heavy meson, not the pole mass. This produces a 2 to 4 MeV change in final results for decay constants, and has negligible effect on decay constant ratio

Kink interactions in SU(N)×Z2SU(N)\times Z_2

There are $N-1$ classes of kink solutions in $SU(N)\times Z_2$. We show how interactions between various kinks depend on the classes of individual kinks as well as on their orientations with respect to each other in the internal space. In particular, we find that the attractive or repulsive nature of the interaction depends on the trace of the product of charges of the two kinks. We calculate the interaction potential for all combinations of kinks and antikinks in $SU(5)\times Z_2$ and study their collisions. The outcome of kink-antikink collisions, as expected from previous studies, is sensitive to their initial relative velocity. We find that heavier kinks tend to break up into lighter ones, while interactions between the lightest kinks and antikinks in this model can be repulsive as well as attractive.Comment: 11 pages, 9 figures. Two insignificant sign errors corrected in the revised versio

The Nt=6N_t=6 equation of state for two flavor QCD

We improve the calculation of the equation of state for two flavor QCD by simulating on $N_t=6$ lattices at appropriate values of the couplings for the deconfinement/chiral symmetry restoration crossover. For $am_q=0.0125$ the energy density rises rapidly to approximately 1 ${\rm GeV/fm^3}$ just after the crossover($m_\pi/m_\rho\approx 0.4$ at this point). Comparing with our previous result for $N_t=4$~\cite{eos}, we find large finite $N_t$ corrections as expected from free field theory on finite lattices. We also provide formulae for extracting the speed of sound from the measured quantities.Comment: Contribution to Lattice 95 proceedings (combines talks presented by T. Blum and L. Karkkainen). LaTeX, 8 pages, uses espcrc2.sty, postscript figures include

Critical Behavior at the Chiral Phase Transition

Quantum chromodynamics with two zero mass flavors is expected to exhibit a phase transition with O(4) critical behavior. Fixing the universality class is important for phenomenology and for facilitating the extrapolation of simulation data to physical quark mass values. At Lattice '96 the Tsukuba and Bielefeld groups reported results from new simulations with dynamical staggered quarks at $N_t = 4$, which suggested a departure from the expected critical behavior. We report observations of similar deviations and discuss efforts in progress to understand this phenomenon.Comment: 3 pp, LaTeX with 6 encapsulated Postscript figures. Lattice '97 proceeding

Properties of the a1 Meson from Lattice QCD

We determine the mass and decay constant of the $a_1$ meson using Monte Carlo simulation of lattice QCD. We find $M_{a_1} = 1250 \pm 80$ MeV and $f_{a_1} = 0.30 \pm 0.03 ~({\rm GeV})^2$, in good agreement with experiment.Comment: 9 page uu-encoded compressed postscript file. version appearing in Phys. Rev. Lett. 74 (1995) 459

High-Precision Lattice QCD Confronts Experiment

We argue that high-precision lattice QCD is now possible, for the first time, because of a new improved staggered quark discretization. We compare a wide variety of nonperturbative calculations in QCD with experiment, and find agreement to within statistical and systematic errors of 3% or less. We also present a new determination of alpha_msbar(Mz); we obtain 0.121(3). We discuss the implications of this breakthrough for phenomenology and, in particular, for heavy-quark physics.Comment: 2 figures, revte

Thermodynamics for two flavor QCD

We conclude our analysis of the N_t=6 equation of state for two flavor QCD, first described at last year's conference. We have obtained new runs at am_q=0.025 and improved runs at am_q=0.0125. The results are extrapolated to m_q=0, and we extract the speed of sound as well. We also present evidence for a restoration of the SU(2) X SU(2) chiral symmetry just above the crossover, but not of the axial U(1) chiral symmetry.Comment: Poster presented at LATTICE96(finite temperature). 4 pages, LaTeX plus 5 encapsulated Postscript figure

The continuum limit in the quenched approximation

Previous work at $6/g^2=5.7$ with quenched staggered quarks is extended with new calculations at 5.85 and 6.15 on lattices up to $32^3\times 64$. These calculations allow a more detailed study of extrapolation in quark mass, finite volume and lattice spacing than has heretofore been possible. We discuss how closely the quenched spectrum approaches that of the real world.Comment: 4 pages, uuencoded compressed PostScript, contribution to Lattice '9