Fri·Oct 12, 2001Friday·October 12, 2001

1. 01*

   Gribov Copies and Gauge Fixing in Lattice Gauge Theories

   O. Oliveira🇵🇹 · P. J. Silva🇵🇹

   We address the problem of the gauge fixing versus Gribov copies in lattice gauge theories. For the Landau gauge, results show that a suitable combination of evolutionary algorithms with traditional steepest descent methods identifies the global maximum of the optimisation function. We discuss the performance of the combined algorithm on small cubic lattices for SU(2) and SU(3).

   hep-latNucl.Phys.B Proc.Suppl.(2002)·8 citations
2. 02*

   The $U_A(1)$ Problem on the Lattice

   L. Giusti🇺🇸 · G.C. Rossi🇨🇭 · M. Testa🇮🇹 · G. Veneziano🇨🇭

   If the expression of the topological charge density operator, suggested by fermions obeying the Ginsparg--Wilson relation, is employed, it is possible to prove on the lattice the validity of the Witten--Veneziano formula for the ${\eta }^{\prime }$ mass. Recent numerical results from simulations with overlap fermions in 2 (abelian Schwinger model) and 4 (QCD) dimensions give values for the mass of the lightest pseudo-scalar flavour-singlet state that agree with theoretical expectations and/or experimental data.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·5 citations
3. 03*

   Topological Charge Fluctuations and Low-Lying Dirac Eigenmodes

   S.J. Dong🇺🇸 · T. Draper🇺🇸 · I. Horvath🇺🇸 · N. Isgur🇺🇸 · F.X. Lee🇺🇸 · J. McCune🇺🇸 · J.B.Zhang🇦🇺 · H.B. Thacker🇺🇸

   We discuss the utility of low-lying Dirac eigenmodes for studying the nature of topological charge fluctuations in QCD. The implications of previous results using the local chirality histogram method are discussed, and the new results using the overlap Dirac operator in Wilson gauge backgrounds at lattice spacings ranging from a~0.04 fm to a~0.12 fm are reported. While the degree of local chirality does not change appreciably closer to the continuum limit, we find that the size and density of local structures responsible for chiral peaking do change significantly. The resulting values are in disagreement with the assumptions of the Instanton Liquid Model. We conclude that the fluctuations of topological charge in the QCD vacuum are not locally quantized.

   hep-lathep-phnucl-thNucl.Phys.B Proc.Suppl.(2002)·8 citations
4. 04*

   Monopoles, confinement and deconfinement in lattice compact QED in (2+1)D with external fields

   M.N. Chernodub🇷🇺 · E.-M. Ilgenfritz🇯🇵 · A. Schiller🇩🇪

   Finite temperature compact electrodynamics in (2+1) dimensions is studied in the presence of external electromagnetic fields. The deconfinement temperature is found to be insensitive to the external fields. This result corroborates our observation that external fields create additional small--size magnetic dipoles from the vacuum which do not spoil the confining properties of the model at low temperature. However, the Polyakov loop is not an order parameter of confinement. It can vanish in deconfinement in the presence of external field. This does not mean the restoration of confinement for certain external field fluxes. As a next step in the study of (2+1)D QED, the influence of monopoles on the photon propagator is studied. First results are presented showing this connection in the confining phase (without external field).

   hep-lathep-phNucl.Phys.B Proc.Suppl.(2002)·3 citations
5. 05*

   The Chiral Critical Point in 3-Flavour QCD

   Ch. Schmidt🇩🇪 · K. Karsch🇩🇪 · E. Laermann🇩🇪

   We determine the second order endpoint of the line of first order phase transitions, which occur in the light quark mass regime of 3-flavour QCD at finite temperature, and analyze universal properties of this chiral critical point. A detailed analysis of Binder cumulants and the joint probability distributions of energy like and ordering-field like observables confirms that the chiral critical point belongs to the universality class of the 3d Ising model. From a calculation with improved gauge and staggered fermion actions we estimate that the transition is first order for pseudo-scalar meson masses less than about 200 MeV.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·8 citations
6. 06*

   Quark and Gluon Propagators in Covariant Gauges

   L. Giusti🇫🇷 · M.L. Paciello🇮🇹 · S. Petrarca🇮🇹 · B. Taglienti🇮🇹 · N. Tantalo🇮🇹

   We present data for the gluon and quark propagators computed in the standard lattice Landau's gauge and for three values of the covariant gauge-fixing parameter lambda=0,8,16. Our results are obtained using the SU(3) Wilson action in the quenched approximation at beta=6.0 and volume=16^3x32.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·13 citations
7. 07*

   A new method for Monte Carlo simulation of theories with Grassmann variables

   T. Bakeyev🇷🇺

   A new algorithm for simulation of theories with dynamical fermions is presented. The algorithm is based on obtaining the new configuration U' from the old one U by solving the equation M(U')\eta= \omega M(U)\eta, where M is fermionic operator, \eta is random Gaussian vector, and \omega is random real number close to unity. This algorithm can be used for acceleration of current simulations in theories with fermions.

   hep-latcond-matNucl.Phys.B Proc.Suppl.(2002)·0 citations
8. 08*

   Clear Evidence of a Continuum Theory of 4D Euclidean Simplicial Quantum Gravity

   H.S.Egawa🇯🇵 · S.Horata🇯🇵 · T.Yukawa🇯🇵

   Four-dimensional (4D) simplicial quantum gravity coupled to both scalar fields (N_X) and gauge fields (N_A) has been studied using Monte-Carlo simulations. The matter dependence of the string susceptibility exponent gamma^{(4)} is estimated. Furthermore, we compare our numerical results with Background-Metric-Independent (BMI) formulation conjectured to describe the quantum field theory of gravity in 4D. The numerical results suggest that the 4D simplicial quantum gravity is related to the conformal gravity in 4D. Therefore, we propose a phase structure in detail with adding both scalar and gauge fields and discuss the possibility and the property of a continuum theory of 4D Euclidean simplicial quantum gravity.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·10 citations
9. 09*

   Investigation of gauge-fixed pure U(1) theory at strong coupling

   S. Basak🇮🇳 · Asit K. De (SINP, Calcutta)🇮🇳

   We numerically investigate the phase diagram of pure U(1) gauge theory with gauge fixing at strong gauge coupling. The FM-FMD phase transition, which proved useful in defining Abelian lattice chiral gauge theory, persists also at strong gauge coupling. However, there the transition seems no to be longer continuous. At large gauge couplings we find evidences for confinement.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·1 citation
10. 10*

    Quenched Chiral Behavior of Hadrons with Overlap Fermions

    Shao-Jing Dong🇺🇸 · Terrence Draper🇺🇸 · Ivan Horvath🇺🇸 · Frank Lee🇺🇸 · Jianbo Zhang🇦🇺

    We study the quenched chiral behavior of hadrons with the pseudoscalar mass as low as $\approx 280$ MeV. We look for quenched chiral logs in the pion mass, determine the renormalized quark mass, and observe quenched artifacts in the $a_0$ and $N^{\ast }$ propagators. The calculation is done on a quenched lattice of size $20^4$ and $a=0.148(2)$ fm using overlap fermions and an improved gauge action.

    hep-latNucl.Phys.B Proc.Suppl.(2002)·7 citations
11. 11*

    Mass renormalisation for improved staggered quarks

    J. Hein🇬🇧 · Q. Mason🇺🇸 · G.P. Lepage🇺🇸 · H. Trottier🇨🇦

    Improved staggered quark actions are designed to suppress flavour changing strong interactions. We discuss the perturbation theory for this type of actions and show the improvements to reduce the quark mass renormalisation compared to naive staggered quarks. The renormalisations are of similar size as for Wilson quarks.

    hep-latNucl.Phys.B Proc.Suppl.(2002)·16 citations
12. 12*

    Zero-modes of the QED Neuberger Dirac operator

    Bernd A. Berg🇺🇸 · Urs M. Heller🇺🇸 · Harald Markum🇦🇹 · Rainer Pullirsch🇦🇹 · Wolfgang Sakuler🇦🇹

    We consider $4d$ compact lattice QED in the quenched approximation. First, we briefly summarize the spectrum of the staggered Dirac operator and its connection with random matrix theory. Afterwards we present results for the low-lying eigenmodes of the Neuberger overlap-Dirac operator. In the strong coupling phase we find exact zero-modes. Subsequently we discuss possibly related topological excitations of the U(1) lattice gauge theory.

    hep-latNucl.Phys.B Proc.Suppl.(2002)·3 citations
13. 13*

    Instabilities in Molecular Dynamics Integrators used in Hybrid Monte Carlo Simulations

    B. Joo · UKQCD Collaboration

    We discuss an instability in the leapfrog integration algorithm, widely used in current Hybrid Monte Carlo (HMC) simulations of lattice QCD. We demonstrate the instability in the simple harmonic oscillator (SHO) system where it is manifest. We demonstrate the instability in HMC simulations of lattic QCD with dynamical Wilson-Clover fermions and discuss implications for future simulations of lattice QCD.

    hep-latNucl.Phys.B Proc.Suppl.(2002)·5 citations
14. 14*

    Lowest eigenvalues of the Dirac operator for two color QCD at nonzero chemical potential

    Elmar Bittner🇦🇹 · Maria-Paola Lombardo🇮🇹 · Harald Markum🇦🇹 · Rainer Pullirsch🇦🇹

    We investigate the eigenvalue spectrum of the staggered Dirac matrix in SU(3) and U(1) gauge theory as well as in full QCD with two colors and finite chemical potential. Along the strong-coupling axis up to the phase transition, the low-lying Dirac spectrum of these quantum field theories is well described by random matrix theory and exhibits universal behavior. Related results for gauge theories with minimal coupling are discussed in the chirally symmetric phase and no universality is seen for the microscopic spectral densities.

    hep-latNucl.Phys.B Proc.Suppl.(2002)·10 citations
15. 15*

    Lowest eigenvalues of the Dirac operator for two color QCD at finite density

    Elmar Bittner🇦🇹 · Maria-Paola Lombardo🇮🇹 · Harald Markum🇦🇹 · Rainer Pullirsch🇦🇹

    We investigate the eigenvalue spectrum of the staggered Dirac matrix in full QCD with two colors and finite chemical potential. Along the strong-coupling axis up to the temperature phase transition, the low-lying Dirac spectrum is well described by random matrix theory (RMT) and exhibits universal behavior. The situation is discussed in the chirally symmetric phase and no universality is seen for the microscopic spectral density.

    hep-lat0 citations
16. 16*

    Spins coupled to a $Z_2$-Regge lattice in 4d

    Elmar Bittner🇦🇹 · Wolfhard Janke🇩🇪 · Harald Markum🇦🇹

    We study an Ising spin system coupled to a fluctuating four-dimensional $Z_2$-Regge lattice and compare with the results of the four-dimensional Ising model on a regular lattice. Particular emphasis is placed on the phase transition of the spin system and the associated critical exponents. We present results from finite-size scaling analyses of extensive Monte Carlo simulations which are consistent with mean-field predictions.

    hep-latNucl.Phys.B Proc.Suppl.(2002)·0 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.