PaperPanorama

HEP Lattice·hep-lat

Mon·Oct 8, 2007

16 papers—15 primary·1 cross-listed·reconstructed*

All16Primary15Cross-lists1
  1. 01*

    Decays of mesons with charm quarks on the lattice

    A. Ali Khan🇩🇪 · V. Braun🇩🇪 · T. Burch🇩🇪 · M. Göckeler🇩🇪 · G. Lacagnina🇮🇹 · A. Schäfer🇩🇪 · G. Schierholz🇩🇪

    We investigate mesons containing charm quarks on fine lattices with a^{-1} \sim 5 GeV. The quenched approximation is employed using the Wilson gauge action at \beta = 6.6 and nonperturbatively O(a) improved Wilson quarks. We present results for decay constants using various interpolating fields and give preliminary results for form factors of semileptonic decays of D_s mesons to light pseudoscalar mesons.

    hep-latPoS(2007)·1 citation
  3. 03*

    The phase structure of a chirally invariant lattice Higgs-Yukawa model

    Philipp Gerhold🇩🇪 · Karl Jansen🇩🇪

    We consider a chirally invariant lattice Higgs-Yukawa model based on the Neuberger overlap operator. As a first step towards the eventual determination of Higgs mass bounds we present the phase structure of the model analytically in the large Nf-limit in the physically interesting region of the Yukawa coupling constant. We confront the analytically obtained phase diagram with corresponding HMC-simulations and find an excellent agreement at large values of Nf. In the opposite case the large Nf computation still gives a good qualitative description of the phase diagram. We also present first and very preliminary results on the Higgs upper bound at one selected cut-off of the theory.

    hep-latPoS(2007)·3 citations
  4. 04*

    B -> D* l nu with 2+1 flavors

    Jack Laiho🇺🇸

    We present a calculation of the form factor for B -> D* l nu using a 2+1 improved staggered action for the light quarks (on the MILC configurations), and the Fermilab action for the heavy quarks. The form factor is computed at zero recoil using a new double ratio method which yields the form factor more directly than previous approaches.

    hep-latPoS(2007)·19 citations
  5. 05*

    Status of the MILC light pseudoscalar meson project

    C. Bernard🇺🇸 · C. DeTar🇺🇸 · Steven Gottlieb🇺🇸 · U.M. Heller🇺🇸 · J.E. Hetrick🇺🇸 · L. Levkova🇺🇸 · J. Osborn🇺🇸 · D. Renner🇺🇸 · R. Sugar🇺🇸 · D. Toussaint🇺🇸

    We discuss the current status of our calculation of the physics of pi and K mesons using three dynamical flavors of improved staggered quarks. This year, we have a new ensemble with a lattice spacing of 0.06 fm and a light sea mass of 0.2 m_s, as well as significant increases in statistics at several coarser lattice spacings and/or heavier sea masses. Results for decay constants, quark masses, low energy constants, condensates, and V_{us} are presented.

    hep-latPoS(2007)·110 citations
  6. 06*

    The kaon B-parameter from unquenched mixed action lattice QCD

    Christopher Aubin🇺🇸 · Jack Laiho🇺🇸 · Ruth S. Van de Water🇺🇸

    We present a preliminary calculation of B_K using domain-wall valence quarks and 2+1 flavors of improved staggered sea quarks. Both the size of the residual quark mass, which measures the amount of chiral symmetry breaking, and of the mixed meson splitting Delta_mix, a measure of taste-symmetry breaking, show that discretization effects are under control in our mixed action lattice simulations. We show preliminary data for pseudoscalar meson masses, decay constants and B_K. We discuss general issues associated with the chiral extrapolation of lattice data, and, as an example, present a preliminary chiral and continuum extrapolation of f_pi. The quality of our data shows that the good chiral properties of domain-wall quarks, in combination with the light sea quark masses and multiple lattice spacings available with the MILC staggered configurations, will allow for a precise determination of B_K.

    hep-latPoS(2007)·15 citations
  7. 07*

    Topological susceptibility in two-flavor lattice QCD with exact chiral symmetry

    S. Aoki🇯🇵 · T.W. Chiu🇹🇼 · H. Fukaya🇯🇵 · S. Hashimoto🇯🇵 · T.H. Hsieh🇹🇼 · T. Kaneko🇯🇵 · H. Matsufuru🇯🇵 · J. Noaki🇯🇵 · K. Ogawa🇹🇼 · T. Onogi🇯🇵 · N. Yamada (JLQCD and TWQCD Collaborations)🇯🇵

    We determine the topological susceptibility in two-flavor QCD using the lattice simulations at a fixed topological sector. The topological charge density is unambiguously defined on the lattice using the overlap-Dirac operator which possesses exact chiral symmetry. Simulations are performed on a lattice at lattice spacing 0.12 fm at six sea quark masses ranging in -- with the physical strange quark mass. The is extracted from the constant behavior of the time-correlation of flavor-singlet pseudo-scalar meson two-point function at large distances, which arises from the finite size effect due to the fixed topology. In the small regime, our result of is proportional to as expected from chiral effective theory. Using the formula by Leutwyler-Smilga, we obtain the chiral condensate in QCD as , in good agreement with our previous result obtained in the -regime.

    hep-lathep-phhep-thPLB(2008)·83 citations
  8. 08*

    The running of the bare coupling in SU(N) gauge theories

    Chris Allton · Michael Teper · Aurora Trivini

    For N>4 there is a first order bulk transition that cleanly separates the strong and weak coupling regimes of SU(N) lattice gauge theories with the plaquette action. We find that in this case the calculated string tension can be readily fitted throughout the weak coupling region by a standard 3-loop perturbative expression modified by lattice spacing corrections of the expected form. While our fits demand the presence of the latter, they are not constraining enough to tell us which of the various bare coupling schemes is a `good' one, in the sense that terms in the beta-function beyond 3-loops are indeed negligible (in the relevant range of scales). To resolve this ambiguity we work in SU(3), using the Schrodinger Functional coupling scheme as a benchmark, and find that the Parisi mean-field improved coupling scheme matches it very well. Using the latter scheme, we have fitted the values of the string tension that have been calculated for SU(3) to SU(8), to obtain Lambda_MSbar/sqrt(sigma) = 0.503(2)(40) + 0.33(3)(3)/N**2, where the first error is statistical and the second is our estimate of the systematic error from all sources.

    hep-latPoS(2007)·5 citations
  9. 09*

    Finite Size Scaling for the O(N) universality class from Renormalization Group Methods

    Bertram Klein (1)🇩🇪 · Jens Braun (2) ((1) Technische Universität München, (2) TRIUMF)🇨🇦

    The QCD phase diagram at finite temperature and density is a topic of considerable interest. Although much progress has been made in recent years, some open questions remain. Even at zero density, the order of the transition for two light flavors of fermions has not yet been conclusively established. While considerable evidence exists in favor of a second-order transition for massless quarks and a crossover for massive quarks, some recent results with two flavors of staggered fermions suggest a transition of first order. Since lattice simulations are performed in finite simulation volumes, actual phase transitions cannot be observed directly. Thus, finite-size scaling is a very useful tool in the analysis of lattice data. By comparing the scaling behavior of observables to the expected scaling properties, values of critical exponents can be confirmed and the order as well as the universality class of a transition can be established. In the comparison to lattice QCD results, the critical exponents and the universal scaling functions have been obtained mainly by means of lattice simulations of O(N) spin models, and results are usually restricted to the critical temperature or the point at which the susceptibilities peak. We propose to use a non-perturbative Renormalization Group method for this purpose. We have calculated the critical finite-size scaling behavior and the universal scaling functions for the three-dimensional O(4)-model for a wide range of temperatures and values of the symmetry breaking parameter. Our results are suitable for a comparison to lattice QCD results for the chiral susceptibility and the order parameter and can be used to check the consistency of the finite-size scaling behavior with that of the O(N) universality class.

    hep-latPoS(2007)·2 citations
  11. 11*

    Baryon masses with dynamical twisted mass fermions

    ETM Collaboration: Constantia Alexandrou🇨🇾 · Tomasz Korzec🇨🇾 · Giannis Koutsou (Univ. of Cyprus)🇨🇾 · Remi Baron🇫🇷 · Pierre Guichon (Saclay)🇫🇷 · Mariane Brinet🇫🇷 · Jaume Carbonell🇫🇷 · Vincent Drach (Grenoble)🇫🇷 · Zhaofeng Liu🇫🇷 · Olivier Pène (Orsay)🇫🇷 · Carsten Urbach (Univ. of Liverpool)🇬🇧

    We present results on the mass of the nucleon and the using two dynamical degenerate twisted mass quarks. The evaluation is performed at four quark masses corresponding to a pion mass in the range of 690-300 MeV on lattices of size 2.1 fm and 2.7 fm. We check for cutoff effects by evaluating these baryon masses on lattices of spatial size 2.1 fm with lattice spacings fm and fm, determined from the pion sector and find them to be within our statistical errors. Lattice results are extrapolated to the physical limit using continuum chiral perturbation theory. The nucleon mass at the physical point provides a determination of the lattice spacing. Using heavy baryon chiral perturbation theory at we find fm, with a systematic error due to the chiral extrapolation estimated to be about the same as the statistical error. This value of the lattice spacing is in good agreement with the value determined from the pion sector. We check for isospin breaking in the -system. We find that and are almost degenerate pointing to small flavor violating effects.

    hep-lathep-phnucl-thPoS(2007)·13 citations
  13. 13*

    Towards a non-perturbative matching of HQET and QCD with dynamical light quarks

    Michele Della Morte (CERN)🇨🇭 · Patrick Fritzsch (Muenster U.)🇩🇪 · Jochen Heitger (Muenster U.)🇩🇪 · Harvey B. Meyer (MIT)🇺🇸 · Hubert Simma (DESY)🇩🇪 · Rainer Sommer (DESY)🇩🇪

    We explain how the strategy of solving renormalization problems in HQET non-perturbatively by a matching to QCD in finite volume can be implemented to include dynamical fermions. As a primary application, some elements of an HQET computation of the mass of the b-quark beyond the leading order with N_f=2 are outlined. In particular, the matching of HQET and QCD requires relativistic QCD simulations in a volume with L ~ 0.5 fm, which will serve to quantitatively determine the heavy quark mass dependence of heavy-light meson observables in the continuum limit of finite-volume two-flavour lattice QCD. As a preparation for the latter, we report on our determination of the renormalization constants and improvement coefficients relating the renormalized current and subtracted bare quark mass in the relevant weak coupling region. The calculation of these coefficients employs a constant physics condition in the Schroedinger functional scheme, where the box size L is fixed by working at a prescribed value of the renormalized coupling.

    hep-latPoS(2007)·12 citations
  15. 15*

    Preparing for N_f=2 simulations at small lattice spacings

    M. Della Morte🇨🇭 · P. Fritzsch🇩🇪 · B. Leder🇩🇪 · S. Takeda🇩🇪 · O. Witzel🇩🇪 · U. Wolff🇩🇪 · H. Meyer🇺🇸 · H. Simma🇩🇪 · R. Sommer🇩🇪

    We discuss some large effects of dynamical fermions. One is a cutoff effect, others concern the contribution of multi-pion states to correlation functions and are expected to survive the continuum limit. We then turn to the preparation for simulations at small lattice spacings which we are planning down to around a=0.04fm in order to understand the size of O(a^2)-effects of the standard O(a)-improved theory. The dependence of the lattice spacing on the bare coupling is determined through the Schr"odinger functional renormalized coupling.

    hep-latPoS(2007)·11 citations
  16. 16*

    Dynamically induced scalar quark confinement: A link between chiral symmetry breaking and confinement

    Reinhard Alkofer🇦🇹 · Christian S. Fischer🇩🇪 · Felipe J. Llanes-Estrada🇪🇸 · Kai Schwenzer🇦🇹

    Employing functional approaches the infrared behaviour of Landau gauge QCD vertex functions is investigated. Results for the ghost-gluon, three-gluon and quark-gluon vertex functions are presented. As can be analytically shown a linear rising potential between heavy quarks is generated by infrared singularities in the dressed quark-gluon vertex. The selfconsistent mechanism that generates these singularities implies the existence of scalar Dirac amplitudes of the full vertex and the quark propagator. These amplitudes can only be present when chiral symmetry is broken, either explicitly or dynamically. The corresponding relations thus constitute a novel mechanism that directly links chiral symmetry breaking with confinement.

    ↳ hep-phhep-latPoS(2007)·6 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.