Showing papers by "Thomas DeGrand published in 2002"
TL;DR: In the case of light sea quarks as mentioned in this paper, the error due to the missing strange sea quark and to partial quenching, and an estimate of the effects of chiral logarithms at small quark mass was found.
Abstract: We present results for ${f}_{B},$ ${f}_{{B}_{s}},$ ${f}_{D},$ ${f}_{{D}_{s}}$ and their ratios in the presence of two flavors of light sea quarks ${(N}_{f}=2)$ We use Wilson light valence quarks and Wilson and static heavy valence quarks; the sea quarks are simulated with staggered fermions Additional quenched simulations with nonperturbatively improved clover fermions allow us to improve our control of the continuum extrapolation For our central values the masses of the sea quarks are not extrapolated to the physical u, d masses; that is, the central values are ``partially quenched'' A calculation using ``fat-link clover'' valence fermions is also discussed but is not included in our final results We find, for example, ${f}_{B}{=190(7)(}_{\ensuremath{-}17}^{+24}{)(}_{\ensuremath{-}2}^{+11}{)(}_{\ensuremath{-}0}^{+8})\mathrm{MeV},$ ${f}_{{B}_{s}}{/f}_{B}{=116(1)(2)(2)(}_{\ensuremath{-}0}^{+4}),$ ${f}_{{D}_{s}}{=241(5)(}_{\ensuremath{-}26}^{+27}{)(}_{\ensuremath{-}4}^{+9}{)(}_{\ensuremath{-}0}^{+5})\mathrm{MeV},$ and ${f}_{B}{/f}_{{D}_{s}}{=079(2)(}_{\ensuremath{-}4}^{+5}{)(3)(}_{\ensuremath{-}0}^{+5}),$ where in each case the first error is statistical and the remaining three are systematic: the error within the partially quenched ${N}_{f}=2$ approximation, the error due to the missing strange sea quark and to partial quenching, and an estimate of the effects of chiral logarithms at small quark mass The last error, though quite significant in decay constant ratios, appears to be smaller than has been recently suggested by Kronfeld and Ryan, and Yamada We emphasize, however, that as in other lattice computations to date, the lattice $u,d$ quark masses are not very light and chiral log effects may not be fully under control
77 citations
TL;DR: In this paper, the hairpin amplitude and the fermion zero-mode susceptibility were derived from a graph with disconnected quark lines and used to infer the mass of the eta-prime meson in full quenched QCD.
Abstract: The quarks in quenched QCD have an anomalous self-interaction in the flavor singlet Goldstone boson channel. This coupling is extracted from a graph with disconnected quark lines, and is used to infer the mass of the eta-prime meson in full QCD. When the fermions are described by an overlap action, the Witten-Veneziano relation is an exact relation between the topological susceptibility (as defined through fermionic zero modes) and the inferred value of the eta-prime mass. Using an overlap action we compute the hairpin amplitude and determine the fermion zero-mode susceptibility, the inferred eta-prime mass and other parameters characterizing the low energy chiral properties of quenched QCD.
44 citations
01 Mar 2002
TL;DR: In this paper, the authors present preliminary results for the heavy-light leptonic decay constants in the presence of three light dynamical flavors, and generate dynamical configurations with improved staggered and gauge actions and analyze them for heavy light physics with tadpole improved clover valence quarks.
Abstract: We present preliminary results for the heavy-light leptonic decay constants in the presence of three light dynamical flavors. We generate dynamical configurations with improved staggered and gauge actions and analyze them for heavy-light physics with tadpole improved clover valence quarks. When the scale is set by m ρ , we find an increase of ≈23% in f B with three dynamical flavors over the quenched case. Discretization errors appear to be small (≲3%) in the quenched case but have not yet been measured in the dynamical case.
7 citations
TL;DR: In this paper, preliminary results from simulations with 2+1 dynamical quark flavors at a lattice spacing of 0.09 fm are combined with earlier results at a=0.13 fm.
Abstract: Preliminary results from simulations with 2+1 dynamical quark flavors at a lattice spacing of 0.09 fm are combined with earlier results at a=0.13 fm. We examine the approach to the continuum limit and investigate the dependence of the pseudoscalar masses and decay constants as the sea and valence quark masses are separately varied.
3 citations
01 Mar 2002
TL;DR: In this paper, the phase diagram of finite temperature QCD with three degenerate flavors and with two light flavors and the mass of the third held approximately at the strange quark mass was explored.
Abstract: We present preliminary results [1] from exploring the phase diagram of finite temperature QCD with three degenerate flavors and with two light flavors and the mass of the third held approximately at the strange quark mass. We use an order α2sa2, a4 Symanzik improved gauge action and an order αsa2, a4 improved staggered quark action. The improved staggered action leads to a dispersion relation with diminished lattice artifacts, and hence better thermodynamic properties. It decreases the flavor symmetry breaking of staggered quarks substantially, and we estimate that at the transition temperature for an Nt = 8 to Nt = 10 lattice all pions will be lighter than the lightest kaon. Preliminary results on lattices with Nt = 4, 6 and 8 are presented.
3 citations
TL;DR: In this paper, an in-progress calculation of B_K in quenched approximation using overlap fermions is presented, using a kernel with nearest and next-nearest neighbor interactions and HYP-blocked gauge connections.
Abstract: I present first results from an in-progress calculation of B_K in quenched approximation using overlap fermions. My particular implementation of the overlap uses a kernel with nearest and next-nearest neighbor interactions and HYP-blocked gauge connections. Matching to the continuum NDR regularization is done perturbatively. I present preliminary results at beta=5.9 and 6.1 (lattice spacings 0.125 and 0.09 fm) for quark masses, pseudoscalar decay constants, and B-parameter -- B_K(NDR(mu=2 GeV) is 0.66(3-4).
3 citations
01 Mar 2002
TL;DR: In this paper, the authors describe how to compute with the overlap action (relatively) cheaply, and then turn to physics: low modes of the Dirac operator show a lumped chiral density which peaks at the locations of instantons and anti-instantons.
Abstract: A chiral fermion action allows one to do very clean studies of chiral symmetry breaking in QCD I will briefly describe how to compute with the overlap action (relatively) cheaply, and then turn to physics: Low modes of the Dirac operator show a “lumped” chiral density which peaks at the locations of instantons and anti-instantons These modes dominate correlation functions at small quark mass in many channels The picture qualitatively (and in some cases quantitatively) resembles an instanton liquid model