Wed·Oct 17, 2007Wednesday·October 17, 2007

1. 01*

   Individual complex Dirac eigenvalue distributions from random matrix theory and comparison to quenched lattice QCD with a quark chemical potential

   G. Akemann🇬🇧 · J. Bloch🇩🇪 · L. Shifrin🇬🇧 · T. Wettig🇩🇪

   We analyze how individual eigenvalues of the QCD Dirac operator at nonzero quark chemical potential are distributed in the complex plane. Exact and approximate analytical results for both quenched and unquenched distributions are derived from non-Hermitian random matrix theory. When comparing these to quenched lattice QCD spectra close to the origin, excellent agreement is found for zero and nonzero topology at several values of the quark chemical potential. Our analytical results are also applicable to other physical systems in the same symmetry class.

   hep-latPRL(2008)·21 citations
2. 02*

   Phase structure of twisted Eguchi-Kawai model

   Tomomi Ishikawa🇺🇸 · Tatsuo Azeyanagi🇯🇵 · Masanori Hanada🇯🇵 · Tomoyoshi Hirata🇯🇵

   We study the phase structure of the four-dimensional twisted Eguchi-Kawai model using numerical simulations. This model is an effective tool for studying SU(N) gauge theory in the large-N limit and provides a nonperturbative formulation of the gauge theory on noncommutative spaces. Recently it was found that its Z_N^4 symmetry, which is crucial for the validity of this model, can break spontaneously in the intermediate coupling region. We investigate in detail the symmetry breaking point from the weak coupling side. Our simulation results show that the continuum limit of this model cannot be taken.

   hep-lathep-thPoS(2007)·2 citations
3. 03*

   Spectral Properties of Quarks in the Quark-Gluon Plasma

   Frithjof Karsch🇺🇸 · Masakiyo Kitazawa🇯🇵

   We analyze the spectral properties of the quark propagator above the critical temperature for the deconfinement phase transition in quenched lattice QCD using clover improved Wilson fermions. The bare quark mass dependence of the quark spectral function is analyzed by varying the hopping parameter \kappa in Landau gauge. We assume a two-pole structure for the quark spectral function, which is numerically found to work quite well for any value of \kappa. It is shown that in the chiral limit the quark spectral function has two collective modes that correspond to the normal and plasmino excitations, while it is dominated by a single-pole structure when the bare quark mass becomes large.

   hep-lathep-phPoS(2007)·1 citation
4. 04*

   Centre Vortices in SU(3)

   Alan Ó Cais🇦🇺 · Waseem Kamleh🇦🇺 · Kurt Langfeld🇬🇧 · Ben Lasscock🇦🇺 · Derek Leinweber🇦🇺 · Lorenz von Smekal🇦🇺

   We investigate the effectiveness of using smearing as a means to generate a preconditioning transformation for gauge fields prior to fixing to Maximal Centre Gauge. This still leaves the gauge-fixed field in the original gauge orbit. As expected, we find that this preconditioning leads to higher maxima of the gauge-fixing condition, resulting in lower numbers of P-vortices. We also find that removing vortices appears to give a loss of confinement for all cases but that the string tension as measured from vortex-only configurations drops from about 65% to as low as 26% when using the preconditioning method.

   hep-latPoS(2007)·6 citations
5. 05*

   Running alpha(s) from Landau-gauge gluon and ghost correlations

   A. Sternbeck🇦🇺 · E.-M. Ilgenfritz🇩🇪 · K. Maltman🇦🇺 · M. Müller-Preussker🇩🇪 · L. von Smekal🇦🇺 · A. G. Williams🇦🇺

   We estimate the running coupling constant of the strong interactions within the nonperturbative framework of lattice QCD in Landau gauge. Our calculation is based on the ghost-gluon vertex which in the particular case of Landau gauge allows for a definition of alpha(s) in a MOM scheme solely in terms of the gluon and ghost dressing functions. As a first step we investigate the zero and two-flavour case and report here on preliminary results.

   hep-latPoS(2007)·48 citations
6. 06*

   Finite ma Errors of the Overlap Fermion

   S. J. Dong🇺🇸 · K. F. Liu🇺🇸

   In this talk, we shall assess the finite ma errors from the overlap fermion. We shall present results on the speed of light from the dispersion relation and hyperfine splitting between the vector and pseudoscalar mesons as a function to ma to reveal the m\Lambda_{QCD}a^2 and m^2a^2 errors. We conclude from this study that one should be limited to using ma less than 0.5 in order to keep the systematic ma errors below a few percent level.

   hep-latPoS(2007)·8 citations
7. 07*

   Moving NRQCD and B to K* gamma

   Stefan Meinel🇬🇧 · Ronald Horgan🇬🇧 · Lew Khomskii🇬🇧 · Laurent C. Storoni🇬🇧 · Matthew Wingate🇬🇧

   The formulation of NRQCD discretized in a reference frame boosted relative to the B rest frame will enable calculation of B form factors over a larger range of momentum transfer. We have initiated a program to calculate form factors describing the rare decay B to K* gamma. We discuss the strategy and challenges of the project. As a first step in the numerical calculations, we present first results for bottomonium quantities using the O(Lambda_{QCD}^2/m^2, v_{NR}^4) moving NRQCD action.

   hep-latPoS(2007)·7 citations
8. 08*

   The High Density Region of QCD from an Effective Model

   R. De Pietri🇮🇹 · A. Feo🇮🇹 · E. Seiler🇩🇪 · I.-O. Stamatescu🇩🇪

   We study the high density region of QCD within an effective model obtained in the frame of the hopping parameter expansion and choosing Polyakov-type loops as the main dynamical variables representing the fermionic matter. This model still shows the so-called sign problem, a difficulty peculiar to non-zero chemical potential, but it permits the development of algorithms which ensure a good overlap of the simulated Monte Carlo ensemble with the true one. We review the main features of the model and present results concerning the dependence of various observables on the chemical potential and on the temperature, in particular of the charge density and the Polykov loop susceptibility, which may be used to characterize the various phases expected at high baryonic density. In this way, we obtain information about the phase structure of the model and the corresponding phase transitions and cross over regions, which can be considered as hints about the behaviour of non-zero density QCD.

   hep-lathep-phhep-thPoS(2007)·0 citations
9. 09*

   The 2+1 flavor topological susceptibility from the asqtad action at 0.06 fm

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

   We report new data for the topological susceptibility computed on 2+1 flavor dynamical configurations with lattice spacing 0.06 fm, generated with the asqtad action. The topological susceptibility is computed by HYP smearing and compared with rooted staggered chiral perturbation theory as the pion mass goes to zero. At 0.06 fm, the raw data is already quite close to the continuum extrapolated values obtained from coarser lattices. These results provide a further test of the asqtad action with rooted staggered flavors.

   hep-latPoS(2007)·17 citations
10. 10*

    Chiral Random Two-Matrix Theory and QCD with imaginary chemical potential

    G. Akemann🇬🇧

    We summarise recent results for the chiral Random Two-Matrix Theory constructed to describe QCD in the epsilon-regime with imaginary chemical potential. The virtue of this theory is that unquenched Lattice simulations can be used to determine both low energy constants Sigma and F in the leading order chiral Lagrangian, due to their respective coupling to quark mass and chemical potential. We briefly recall the analytic formulas for all density and individual eigenvalue correlations and then illustrate them in detail in the simplest, quenched case with imaginary isospin chemical potential. Some peculiarities are pointed out for this example: i) the factorisation of density and individual eigenvalue correlation functions for large chemical potential and ii) the factorisation of the non-Gaussian weight function of bi-orthogonal polynomials into Gaussian weights with ordinary orthogonal polynomials.

    ↳ hep-thhep-latActa Phys.Polon.B(2007)·4 citations
11. 11*

    Theoretical progress on pi pi scattering lengths and phases

    Gilberto Colangelo🇨🇭

    pi pi scattering at low energy is sensitive to the structure of the QCD vacuum. I review the calculations of the pi pi scattering lengths and phases, and group them in three cathegories: 1. those based on very general theoretical constraints (like dispersion relations and crossing symmetry) and phenomenology, 2. those which in addition make explicit use of chiral symmetry, 3. the first-principle ones, done with lattice QCD. I then compare these to the experimental results. Thanks to recent progress in all these and in the experimental determination of the scattering lengths we are improving substantially our knowledge of the QCD vacuum.

    ↳ hep-phhep-latPoS(2008)·15 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.