572 research outputs found

    Heavy-light decay constants using clover valence quarks and three flavors of dynamical improved staggered quarks

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    Starting in 2001, the MILC Collaboration began a large scale calculation of heavy-light meson decay constants using clover valence quarks on ensembles of three flavor configurations. For the coarse configurations, with a=0.12 fm, eight combinations of dynamical light and strange quarks have been analyzed. For the fine configurations, with a=0.09 fm, three combinations of quark masses are studied. Since we last reported on this calculation, statistics have been increased on the fine ensembles, and, more importantly, a preliminary value for the perturbative renormalization of the axial-vector current has become available. Thus, results for f_B, f_{B_s}, f_D and f_{D_s} can, in principle, be calculated in MeV, in addition to decay-constant ratios that were calculated previously.Comment: Talk presented at Lattice2004(heavy), Fermilab, June 21-26, 2004; 3 pages, 3 color figure

    Thermodynamics with 3 and 2+1 Flavors of Improved Staggered Quarks

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    We present preliminary results 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 αs2a2,a4\alpha_s^2 a^2, a^4 Symanzik improved gauge action and an order αsa2,a4\alpha_s a^2, a^4 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=8N_t=8 to Nt=10N_t=10 lattice {\em all} pions will be lighter than the lightest kaon. Preliminary results on lattices with Nt=4N_t=4, 6 and 8 are presented.Comment: 3 pages, 6 figures, contribution to Lattice2001(hightemp) August 19--24, 2001, Berlin, German

    High temperature QCD with three flavors of improved staggered quarks

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    We present an update of our study of high temperature QCD with three flavors of quarks, using a Symanzik improved gauge action and the Asqtad staggered quark action. Simulations are being carried out on lattices with Nt=4, 6 and 8 for the case of three degenerate quarks with masses less than or equal to the strange quark mass, msm_s, and on lattices with Nt=6 and 8 for degenerate up and down quarks with masses in the range 0.2 m_s \leq m_{u,d} \leq 0.6 m_s, and the strange quark fixed near its physical value. We also report on first computations of quark number susceptibilities with the Asqtad action. These susceptibilities are of interest because they can be related to event-by-event fluctuations in heavy ion collision experiments. Use of the improved quark action leads to a substantial reduction in lattice artifacts. This can be seen already for free fermions and carries over into our results for QCD.Comment: Lattice2002(Non-zero temperature and density

    Three Flavor QCD at High Temperatures

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    We have continued our study of the phase diagram of high temperature QCD with three flavors of improved staggered quarks. We are performing simulations with three degenerate quarks with masses less than or equal to the strange quark mass m_s and with degenerate up and down quarks with masses m_{u,d} less than the strange quark mass. For the quark masses studied to date, we find a crossover that strengthens as m_{u,d} decreases, rather than a bona fide phase transition. We present new results for the crossover temperature extrapolated to the physical value of m_{u,d}, and for quark number susceptibilities.Comment: Poster presented at Lattice 2004 (non-zero), Fermilab, June 21-26, 2004, 3 pages, 3 figure

    Static hybrid quarkonium potential with improved staggered quarks

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    We are studying the effects of light dynamical quarks on the excitation energies of a flux tube between a static quark and antiquark. We report preliminary results of an analysis of the ground state potential and the Σg+\Sigma^{\prime+}_g and Πu\Pi_u potentials. We have measured these potentials on closely matched ensembles of gauge configurations, generated in the quenched approximation and with 2+1 flavors of Asqtad improved staggered quarks.Comment: Lattice2002(heavyquark

    Momentum Dependent Vertices σγγ\sigma \gamma \gamma, σργ\sigma \rho \gamma and σρρ\sigma \rho \rho : The NJL Scalar Hidden by Chiral Symmetry

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    We calculate the momentum dependence of three particle vertices σγγ\sigma \gamma \gamma, σργ\sigma \rho \gamma and σρρ\sigma \rho \rho in the context of a Nambu Jona Lasinio type model. We show how they influence the processes γγσππ\gamma \gamma \rightarrow \sigma \rightarrow \pi \pi, ργσ\rho \rightarrow \gamma \sigma and γγρρ\gamma \gamma \rightarrow \rho \rho and how chiral symmetry shadows the presence of the σ\sigma.Comment: 9 pages (latex), 5 figures available from the authors, preprint Coimbra 940506, IJS-TP-94/10, accepted for publication in Zeit. f. Physik

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

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    We improve the calculation of the equation of state for two flavor QCD by simulating on Nt=6N_t=6 lattices at appropriate values of the couplings for the deconfinement/chiral symmetry restoration crossover. For amq=0.0125am_q=0.0125 the energy density rises rapidly to approximately 1 GeV/fm3{\rm GeV/fm^3} just after the crossover(mπ/mρ0.4m_\pi/m_\rho\approx 0.4 at this point). Comparing with our previous result for Nt=4N_t=4~\cite{eos}, we find large finite NtN_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

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    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 Nt=4N_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

    The effect of age and font size on reading text on handheld computers

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    Though there have been many studies of computer based text reading, only a few have considered the small screens of handheld computers. This paper presents an investigation into the effect of varying font size between 2 and 16 point on reading text on a handheld computer. By using both older and younger participants the possible effects of age were examined. Reading speed and accuracy were measured and subjective views of participants recorded. Objective results showed that there was little difference in reading performance above 6 point, but subjective comments from participants showed a preference for sizes in the middle range. We therefore suggest, for reading tasks, that designers of interfaces for mobile computers provide fonts in the range of 8-12 point to maximize readability for the widest range of users

    Recent MILC spectrum results

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    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.Comment: Poster presented at LATTICE96(spectrum);4 pages of LaTeX, uses espcrc2 and epsf, six postscript figures include
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