E.-M. Ilgenfritz

Lattice gluodynamics computation of Landau-gauge Green's functions in the deep infrared

Abstract We present recent results for the Landau-gauge gluon and ghost propagators in SU ( 3 ) lattice gluodynamics obtained on a sequence of lattices with linear extension ranging from L = 64 to L = 96 at β = 5.70 , thus reaching “deep infrared” momenta down to 75 MeV. Our gauge-fixing procedure essentially uses a simulated annealing technique which allows us to reach gauge-functional values closer to the global maxima than standard approaches do. Our results are consistent with the so-called decoupling solutions found for Dyson–Schwinger and functional renormalization group equations.

Polarized and unpolarized nucleon structure functions from lattice QCD

We report on a high statistics quenched lattice QCD calculation of the deep-inelastic structure functions {ital F}{sub 1}, {ital F}{sub 2}, {ital g}{sub 1}, and {ital g}{sub 2} of the proton and neutron. The theoretical basis for the calculation is the operator product expansion. We consider the moments of the leading twist operators up to spin four. Using Wilson fermions the calculation is done for three values of {kappa}, and we perform the extrapolation to the chiral limit. The renormalization constants, which lead us from lattice to continuum operators, are calculated in perturbation theory to one loop order. {copyright} {ital 1996 The American Physical Society.}

Towards the infrared limit in SU(3) Landau gauge lattice gluodynamics

We study the behavior of the gluon and ghost dressing functions in SU(3) Landau gauge at low momenta available on lattice sizes 12{sup 4}-32{sup 4} at {beta}=5.8, 6.0 and 6.2. We demonstrate the ghost dressing function to be systematically dependent on the choice of Gribov copies, while the influence on the gluon dressing function is not resolvable. The running coupling given in terms of these functions is found to be decreasing for momenta q<0.6 GeV. We study also effects of the finite volume and of the lattice discretization.

Pion and Rho Structure Functions from Lattice QCD

We calculate the lower moments of the deep-inelastic structure functions of the {pi} and the {rho} meson on the lattice. Of particular interest to us are the spin-dependent structure functions of the {rho}. The calculations are done with Wilson fermions and for three values of the quark mass, so that we can perform an extrapolation to the chiral limit. {copyright} {ital 1997} {ital The American Physical Society}

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

I. L. Bogolubsky a, E.-M. Ilgenfritzb, M. Muller-Preusskerb, and A. Sternbeckc a Joint Institute for Nuclear Research, 141980 Dubna, Russia b Humboldt Universitat zu Berlin, Institut fur Physik, 12489 Berlin, Germany c CSSM, School of Chemistry & Physics, University of Adelaide, SA 5005, Australia E-mail: bogolubs@lxpub04.jinr.ru, ilgenfri@physik.hu-berlin.de, mmp@physik.hu-berlin.de, andre.sternbeck@adelaide.edu.au

Where the electroweak phase transition ends

We give a more precise characterisation of the end of the electroweak phase transition in the framework of the effective 3d SU(2)–Higgs lattice model than has been given before. The model has now been simulated at gauge couplings �G = 12 and 16 for Higgs masses M �

Exploring the structure of the quenched QCD vacuum with overlap fermions

Overlap fermions have an exact chiral symmetry on the lattice and are thus an appropriate tool for investigating the chiral and topological structure of the QCD vacuum. We study various chiral and topological aspects of quenched gauge field configurations. This includes the localization and chiral properties of the eigenmodes, the local structure of the ultraviolet-filtered field strength tensor, as well as the structure of topological charge fluctuations. We conclude that the vacuum has a multifractal structure.

Landau gauge gluon and ghost propagators from lattice QCD

We report on recent numerical computations of the Landau gauge gluon and ghost propagators as well as of the ghost-gluon-vertex function in pure SU(3) Yang-Mills theory and in full QCD on the lattice. Special emphasis is paid to the low momentum region. In particular, we present new data for the gluon propagator at momenta below 300 MeV. We also discuss different systematic effects as there are finite-size, lattice discretization and Gribov copy but also unquenching effects. A MOM-scheme running coupling as(q2) based on the ghost-gluon vertex is calculated and found to decrease for momenta below 550 MeV, even though the renormalization constant of the vertex deviates only weakly from being constant.

Practical problems to compute the ghost propagator inSU(2)lattice gauge theory

In SU(2) lattice pure gauge theory we study numerically the dependence of the ghost propagator G(p) on the choice of Gribov copies in Lorentz (or Landau) gauge. We find that the effect of Gribov copies is essential in the scaling window region, however, it tends to decrease with increasing beta. On the other hand, we find that at larger beta-values very strong fluctuations appear which can make problematic the calculation of the ghost propagator.

On the topological content of SU(2) gauge fields below T(c)

Finite temperature Euclidean SU(2) lattice gauge elds generated in the connement phase close to the deconnement phase transition are subjected to cooling. The aim is to identify long-living, almost-classical local excitations which carry (generically non-integer) topological charge. Two kinds of spatial boundary conditions (xed holonomy and standard periodic boundary conditions) are applied. For the lowest-action almost-classical congurations we nd that their relative probability semi-quantitatively agrees for both types of boundary conditions. We nd calorons with unit topological charge as well as (anti-)selfdual lumps (BPS-monopoles or dyons) combined in pairs of non-integer (equal or opposite sign) topological charge. For calorons and separated pairs of equal-sign dyons obtained by cooling we have found that (i) the gluon eld is well-described by Kraan-van Baal solutions of the Euclidean Yang-Mills eld equations and (ii) the lowest Wilsonfermion modes are well-described by analytic solutions of the corresponding Dirac equation. For metastable congurations found at higher action, the multi-center structure can be interpreted in terms of dyons and antidyons, using the gluonic and fermionic indicators as in the dyon-pair case. Additionally, the Abelian monopole structure and eld strength correlators between the centers are useful to analyse the congurations in terms of dyonic constituents. We argue that a semi-classical approximation of the non-zero temperature path integral should be built on superpositions of solutions with non-trivial holonomy.