Effects of Nonperturbative Improvement in Quenched Hadron Spectroscopy

We discuss a comparative analysis of unimproved and nonperturbatively improved quenched hadron spectroscopy, on a set of 104 gauge configurations, at beta=6.2. We also present here our results for meson decay constants, including the constants f_D and f_Ds in the charm-quark region.Comment: LATTICE98(spectrum

Numerical Study of the Gluon Propagator in Lattice Landau Gauge: the Three-Dimensional Case

We study the infrared behavior of the gluon propagator in lattice Landau gauge, for pure SU(2) lattice gauge theory in a three-dimensional lattice. Simulations are done for nine different values of the coupling $\beta$, from $\beta = 0$ (strong coupling) to $\beta = 6.0$ (in the weak-coupling region). In the limit of large lattice volumes, we observe in all cases a gluon propagator decreasing as the momentum goes to zero.Comment: LATTICE98(confine

SU(2) lattice gluon propagators at finite temperatures in the deep infrared region and Gribov copy effects

We study numerically the SU(2) Landau gauge transverse and longitudinal gluon propagators at non-zero temperatures T both in confinement and deconfinement phases. The special attention is paid to the Gribov copy effects in the IR-region. Applying powerful gauge fixing algorithm we find that the Gribov copy effects for the transverse propagator D_T(p) are very strong in the infrared, while the longitudinal propagator D_L(p) shows very weak (if any) Gribov copy dependence. The value D_T(0) tends to decrease with growing lattice size; however, D_T(0) is non-zero in the infinite volume limit, in disagreement with the suggestion made in [1]. We show that in the infrared region D_T(p) is not consistent with the pole-type formula not only in the deconfinement phase but also for T < T_c. We introduce new definition of the magnetic infrared mass scale ('magnetic screening mass') m_M. The electric mass m_E has been determined from the momentum space longitudinal gluon propagator. We study also the (finite) volume and temperature dependence of the propagators as well as discretization errors.Comment: 11 pages, 14 figures, 3 tables. Few minor change

Lattice simulations for the running coupling constant of QCD

The strong coupling constant alpha_s(mu_0), taken at a fixed reference scale mu_0, is the single free parameter of QCD and should be known to the highest available precision. The value of alpha_s should also be determined with good accuracy over as large a range of scales as possible, in order to reveal potential anomalous running in the strength of the strong interaction. Lattice QCD is now able to calculate alpha_s with accuracy comparable to or better than experiment. We review the status of such lattice calculations in quenched and full QCD.Comment: 10 pages; invited seminar presented at the VIII International Workshop on Hadron Physics 2002, Bento Goncalves RS, Brazil, April 14-19, 200

Lattice Results in Coulomb Gauge

We discuss recent numerical results obtained for gluon and ghost propagators in lattice Coulomb gauge and the status of the so-called Gribov-Zwanziger confinement scenario in this gauge. Particular emphasis will be given to the eigenvalue spectrum of the Faddeev-Popov matrix.Comment: 7 pages; plenary talk presented at the QCHS7, Ponta Delgada Acores - Portugal (September 2006

Color-Coulomb Force Calculated from Lattice Coulomb Hamiltonian

The static color-Coulomb potential is calculated as the solution of a non-linear integral equation. This equation has been derived recently as a self-consistency condition which arises in the Coulomb Hamiltonian formulation of lattice gauge theory when the restriction to the interior of the Gribov horizon is implemented. The potential obtained is in qualitative agreement with expectations, being Coulombic with logarithmic corrections at short range and confining at long range. The values obtained for the string tension and $\Lambda_{\overline{MS}}$ are in semi-quantitative agreement with lattice Monte Carlo and phenomenological determinations.Comment: 4 pages (including 1 figure); (latex using espcrc2.sty). Talk presented at LATTICE96(poster

Confinement made simple in the Coulomb gauge

In Gribov's scenario in Coulomb gauge, confinement of color charge is due to a long-range instantaneous color-Coulomb potential V(R). This may be determined numerically from the instantaneous part of the gluon propagator D_{44, inst} = V(R) \delta(t). Confinement of gluons is reflected in the vanishing at k = 0 of the equal-time three-dimensionally transverse would-be physical gluon propagator D^{tr}(k). We present exact analytic results on D_{44} and D^{tr} (which have also been investigated numerically, A. Cucchieri, T. Mendes, and D. Zwanziger, this conference), in particular the vanishing of D^{tr}(k) at k = 0, and the determination of the running coupling constant from x_0 g^2(k) = k^2 D_{44, inst}, where x_0 = 12N/(11N-2N_f).Comment: 3 pages; talk presented by D. Zwanziger at Lattice2001(confinement), Berlin, August 20-24, 200

1) The Influence of Gribov Copies on Gluon and Ghost Propagators in Landau Gauge and 2) A New Implementation of the Fourier Acceleration Method

We study the influence of Gribov copies on gluon and ghost propagators in lattice Landau gauge. For the gluon propagator, Gribov noise seems to be of the order of magnitude of the numerical accuracy. On the contrary, for the ghost propagator, Gribov noise is clearly observable, at least in the strong- coupling regime. We also observe, in the limit of large lattice volume, a gluon propagator decreasing as the momentum goes to zero. Finally, we introduce an implementation of the method of Fourier Acceleration which avoids the use of the fast Fourier transform, being well suited for parallel and vector machines. We apply it to the case of Landau gauge fixing, and study its performance on APE computers.Comment: 3 pages, including one figure; poster presented at LATTICE9