Andre Sternbeck

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.

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

The Strong coupling and its running to four loops in a minimal MOM scheme

Abstract We introduce the minimal momentum subtraction (MiniMOM) scheme for QCD. Its definition allows the strong coupling to be fixed solely through a determination of the gluon and ghost propagators. In Landau gauge this scheme has been implicit in the early studies of these propagators, especially in relation to their non-perturbative behaviour in the infrared and the associated infrared fixed-point. Here we concentrate on its perturbative use. We give the explicit perturbative definition of the scheme and the relation of its β-function and running coupling to the MS ¯ scheme up to 4-loop order in general covariant gauges. We also demonstrate, by considering a selection of N f = 3 examples, that the apparent convergence of the relevant perturbative series can in some (though not all) cases be significantly improved by re-expanding the MS ¯ coupling version of this series in terms of the MiniMOM coupling, making the MiniMOM coupling also of potential interest in certain phenomenological applications.

Scaling behavior and positivity violation of the gluon propagator in full QCD

The Landau-gauge gluon propagator is studied using the coarse and fine dynamical MILC configurations. The effects of dynamical quarks are clearly visible and lead to a reduction of the nonperturbative infrared enhancement relative to the quenched case. Lattice spacing effects are studied and found to be small. The gluon spectral function is shown to clearly violate positivity in both quenched and full QCD.

Comparing SU(2) to SU(3) gluodynamics on large lattices

Also cited as: Lattice 2007, the XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, Germany / Gunnar Bali, Vladimir Braun, Christof Gattringer, Meinulf Gockeler, Andreas Schafer, Peter Weisz, Tilo Wettig (eds.): pp. 340/1-340/7.

The infrared behavior of lattice QCD green's functions

We investigate different aspects of lattice QCD in Landau gauge using Monte Carlo simulations. In particular, we focus on the low momentum behavior of gluon and ghost propagators. The gauge group is SU(3). Different systematic effects on the gluon and ghost propagators are studied, e.g. the dependence on the choice of Gribov copies or the influence of dynamical Wilson fermions. We compare our data with results from studies of Dyson-Schwinger equations for the gluon and ghost propagators. We demonstrate that the infrared behavior of both propagators, as found in this thesis, is consistent with different criteria for confinement. However, the running coupling constant, given as a renormalization-group-invariant combination of the gluon and ghost dressing functions, does not expose a finite infrared fixed point. We also report on a first nonperturbative computation of the SU(3) ghost-gluon-vertex renormalization constant and on an investigation of the spectral properties of the Faddeev-Popov operator.

A Numerical reinvestigation of the Aoki phase with N(f) = 2 Wilson fermions at zero temperature

We report on a numerical reinvestigation of the Aoki phase in lattice QCD with two flavors of Wilson fermions where the parity-flavor symmetry is spontaneously broken. For this purpose the Hybrid Monte Carlo algorithm was used and an explicit symmetry-breaking source term

Direct determinations of the nucleon and pion

h\bar{\psi} i \gamma_{5} \tau^{3}\psi

\sigma

was added to the Wilson fermion action. The order parameter

terms at nearly physical quark masses

\langle\bar{\psi}i\gamma_{5}\tau^{3}\psi\rangle