The Landau gauge gluon and ghost propagators in 4D SU(3) gluodynamics in large lattice volumes

We present recent results of the Landau gauge gluon and ghost propagators in SU(3) pure gauge theory at Wilson \beta=5.7 for lattice sizes up to 80^4 corresponding to physical volumes up to (13.2 fm)^4. In particular, we focus on finite-volume and Gribov copy effects. We employ a gauge fixing method that combines a simulated annealing algorithm with finalizing overrelaxation. We find the gluon propagator for the largest volumes and at q^2 ~ 0.01 GeV^2 to become flat. Although not excluded by our data, there is still no clear indication of a gluon propagator tending towards zero in the zero-momentum limit. New data for the ghost propagator are reported, too.Comment: 7 pages, 3 figures, poster presented at Lattice-2007, Regensburg, July 30 - August 4, 2007, 1 figure replace

Pseudoscalar correlators and the problem of the chiral limit in the compact lattice QED with Wilson fermions

The phase diagram for the compact lattice QED with Wilson fermions is shown. We discuss different methods for the calculation of the 'pion' mass $m_{\pi}$ near the chiral transition point $\kappa_c(\beta )$.Comment: 3 pages, TALK GIVEN AT THE LATTICE '94 INTERNATIONAL SYMPOSIUM LATTICE FIELD THEORY, BIELEFELD, GERMANY, SEPTEMBER 27 -- OCTOBER 1, 1994 Three figures are included as ps-files. Look for %%%%% FIG1.PS %%%% , et

Gauge-variant propagators and the running coupling from lattice QCD

On the occasion of the 70th birthday of Prof. Adriano Di Giacomo we report on recent numerical computations of the Landau gauge gluon and ghost propagators as well as of a non-symmetric MOM-scheme ghost-gluon vertex in quenched and full lattice QCD. Special emphasis is paid to the Gribov copy problem and to the unquenching effect. The corresponding running coupling \alpha_s(q^2) is found and shown to decrease for q^2 \le 0.3 GeV^2 in the infrared limit. No indication for a non-trivial infrared fixed point is seen in agreement with findings from truncated systems of Dyson-Schwinger equations treated on a four-dimensional torus.Comment: contribution to "Sense of Beauty in Physics", Festschrift in honor of Adriano Di Giacomo's 70-th birthda

Spectral properties of the Landau gauge Faddeev-Popov operator in lattice gluodynamics

Recently we reported on the infrared behavior of the Landau gauge gluon and ghost dressing functions in SU(3) Wilson lattice gluodynamics with special emphasis on the Gribov problem. Here we add an investigation of the spectral properties of the Faddeev-Popov operator at $\beta$=5.8 and 6.2 for lattice sizes 12^4, 16^4 and 24^4. The larger the volume the more of its eigenvalues are found accumulated close to zero. Using the eigenmodes for the spectral representation it turns out that for our smallest lattice O(200) eigenmodes are sufficient to saturate the ghost propagator at lowest momentum. We associate exceptionally large values of the ghost propagator to extraordinary contributions of low-lying eigenmodes.Comment: 7 pages, 8 figure

Calorons in SU(3) lattice gauge theory

We examine the semiclassical content of SU(3) Yang Mills theory on the lattice at finite temperature. Employing the cooling method, a set of classical fields is generated from a Monte Carlo ensemble. Various operators are used to inspect this set with respect to topological properties. We find pseudoparticle fields, so-called caloron solutions, possessing the remarkable features of (superpositions of) Kraan-van Baal solutions, i.e. extensions of Harrington-Shepard calorons to generic values of the holonomy.Comment: 14 pages, 16 figure

Background Configurations, Confinement and Deconfinement on a Lattice with BPS Monopole Boundary Conditions

Finite temperature SU(2) lattice gauge theory is investigated in a 3D cubic box with fixed boundary conditions provided by a discretized, static BPS monopole solution with varying core scale $\mu$. Using heating and cooling techniques we establish that for discrete $\mu$-values stable classical solutions either of self-dual or of pure magnetic type exist inside the box. Having switched on quantum fluctuations we compute the Polyakov line and other local operators. For different $\mu$ and at varying temperatures near the deconfinement transition we study the influence of the boundary condition on the vacuum inside the box. In contrast to the pure magnetic background field case, for the self-dual one we observe confinement even for temperatures quite far above the critical one.Comment: to appear in EPJ