arXiv subjects

M. Thies

Publications and source records attributed to M. Thies.

16 recordsLinked to original sources

arXiv2007

Confining Effective Theories Based on Instantons and Merons

An effective theory based on ensembles of either regular gauge instantons or merons is shown to produce confinement in SU(2) Yang-Mills theory. When the scale is set by the string tension, the action density, topological susceptibility and low-lying glueball spectrum are similar to those arising in lattice QCD. The physical mechanism producing confinement is explained, and a number of analytical insights into the effective theory are presented.

hep-ph↗

arXiv2004

Diffusion of Wilson Loops

A phenomenological analysis of the distribution of Wilson loops in SU(2) Yang-Mills theory is presented in which Wilson loop distributions are described as the result of a diffusion process on the group manifold. It is shown that, in the absence of forces, diffusion implies Casimir scaling and, conversely, exact Casimir scaling implies free diffusion. Screening processes occur if diffusion takes place in a potential. The crucial distinction between screening of fundamental and adjoint loops is formulated as a symmetry property related to the center symmetry of the underlying gauge theory. The results are expressed in terms of an effective Wilson loop action and compared with various limits of SU(2) Yang-Mills theory.

hep-th↗

arXiv2004

Confinement from Instantons or Merons

In contrast to ensembles of singular gauge instantons, which are well known to fail to produce confinement, it is shown that effective theories based on ensembles of merons or regular gauge instantons do produce confinement. Furthermore, when the scale is set by the string tension, the action density, topological susceptibility, and glueball masses are similar to those arising in lattice QCD.

hep-lat↗

arXiv2004

Chiral Symmetry in Light-Cone Field Theory

An analysis of spontaneously broken chiral symmetry in light-cone field theory is presented. The non-locality inherent to light-cone field theory requires revision of the standard procedure in the derivation of Ward-Takahashi identities. We derive the general structure of chiral Ward-Takahashi identities and construct them explicitly for various model field theories. Gell-Mann-Oakes-Renner relations and relations between fermion propagators and the structure functions of Nambu-Goldstone bosons are discussed and the necessary modifications of the Ward-Takahashi identities due to the axial anomaly are indicated.

hep-th↗

arXiv2003

Confinement from Merons

It is shown that an effective theory with meron degrees of freedom produces confinement in SU(2) Yang Mills theory. This effective theory is compatible with center symmetry. When the scale is set by the string tension, the action density and topological susceptibility are similar to those arising in lattice QCD.

hep-th↗

arXiv2001

Vacancy-mediated domain growth in a driven lattice gas

Using Monte Carlo simulations and a mean-field theory, we study domain growth in a driven lattice gas. Mediated by a single vacancy, two species of particles (``charges'') unmix, so that a disordered initial configuration develops charge-segregated domains which grow logarithmically slowly. An order parameter is defined and shown to satisfy dynamic scaling. Its scaling form is computed analytically, in excellent agreement with simulations.

cond-mat.stat-mech↗

arXiv2000

Chiral Condensates in the Light-Cone Vacuum

In light-cone quantization, the standard procedure to characterize the phases of a system by appropriate ground state expectation values fails. The light-cone vacuum is determined kinematically. We show that meaningful quantities which can serve as order parameters are obtained as expectation values of Heisenberg operators in the equal (light-cone) time limit. These quantities differ from the purely kinematical expectation values of the corresponding Schroedinger operators. For the Nambu--Jona-Lasinio and the Gross-Neveu model, we describe the spontaneous breakdown of chiral symmetry; we derive within light-cone quantization the corresponding gap equations and the values of the chiral condensate.

hep-th↗

arXiv1999

Field-induced vacancy localization in a driven lattice gas: Scaling of steady states

With the help of Monte Carlo simulations and a mean-field theory, we investigate the ordered steady-state structures resulting from the motion of a single vacancy on a periodic lattice which is filled with two species of oppositely ``charged'' particles. An external field biases particle-vacancy exchanges according to the particle's charge, subject to an excluded volume constraint. The steady state exhibits charge segregation, and the vacancy is localized at one of the two characteristic interfaces. Charge and hole density profiles, an appropriate order parameter and the interfacial regions themselves exhibit characteristic scaling properties with system size and field strength. The lattice spacing is found to play a significant role within the mean-field theory.

cond-mat.stat-mech↗

arXiv1998

Polyakov Loop Dynamics in the Center Symmetric Phase

A study of the center symmetric phase of SU(2) Yang Mills theory is presented. Realization of the center symmetry is shown to result from non-perturbative gauge fixing. Dictated by the center symmetry, this phase exhibits already at the perturbative level confinement like properties. The analysis is performed by investigating the dynamics of the Polyakov loops. The ultralocality of these degrees of freedom implies significant changes in the vacuum structure of the theory. General properties of the confined phase and of the transition to the deconfined phase are discussed. Perturbation theory built upon the vacuum of ultralocal Polyakov loops is presented and used to calculate, via the Polyakov loop correlator, the static quark-antiquark potential.

hep-th↗

arXiv1998

QCD_{1+1} with Static Quarks as Supersymmetric Quantum Mechanics

We reexamine the solvable model problem of two static, fundamental quarks interacting with a SU(2) Yang-Mills field on a spatial circle, introduced by Engelhardt and Schreiber. If the quarks are at the same point, the model exhibits a quantum mechanical supersymmetry. At finite separation, the supersymmetry is explicitly broken in a way which naturally explains the geometrical nature of spectrum and state vectors of this system.

hep-th↗

arXiv1997

Magnetic and Thermodynamic Stability of SU(2) Yang-Mills Theory

SU(2) Yang-Mills theory at finite extension or, equivalently, at finite temperature is probed by a homogeneous chromomagnetic field. We use a recent modified axial gauge formulation which has the novel feature of respecting the center symmetry in perturbation theory. The characteristic properties of the Z_2-symmetric phase, an extension-dependent mass term and antiperiodic boundary conditions, provide stabilization against magnetic field formation for sufficiently small extension or high temperature. In an extension of this investigation to the deconfined phase with broken center symmetry, the combined constraints of thermodynamic and magnetic stability are shown to yield many of the high temperature properties of lattice SU(2) gauge theory.

hep-ph↗

arXiv1997

QCD at Finite Extension

A study of QCD at finite extension is presented and the relation to QCD at finite temperature and in the infinite momentum frame is discussed. The dynamics of Polyakov loops is investigated and shown to be described by functional integrals with finite range of integration. Consequences of this non-Gaussian form of the generating functional concerning the QCD vacuum, gluonic excitations and confinement are discussed.

hep-ph↗

arXiv1995

QCD in the axial gauge

We review a recent attempt to deal with non-perturbative features of QCD by analytical means, using a manifestly gauge invariant, canonical approach.

hep-ph↗

arXiv1995

Higgs Mechanism and Symmetry Breaking without Redundant Variables

The Higgs mechanism is reconsidered in the canonical Weyl gauge formulation of quantized gauge theories, using an approach in which redundant degrees of freedom are eliminated. As a consequence, its symmetry aspects appear in a different light. All the established physics consequences of the Higgs mechanism are recovered without invoking gauge symmetry breaking. The occurence of massless vector bosons in non-abelian Higgs models is interpreted as signal of spontaneous breakdown of certain global symmetries. Characteristic differences between the relevant ``displacement symmetries'' of QED and the Georgi Glashow model are exhibited. Implications for the symmetry aspects of the electroweak sector of the standard model and the interpretation of the physical photon as Goldstone boson are pointed out.

hep-th↗

arXiv1994

Signatures of Confinement in Axial Gauge QCD

A comparative dynamical study of axial gauge QED and QCD is presented. Elementary excitations associated with particular field configurations are investigated. Gluonic excitations analogous to linearly polarized photons are shown to acquire infinite energy. Suppression of this class of excitations in QCD results from quantization of the chromelectric flux and is interpreted as a dual Meissner effect, i.e. as expulsion from the QCD vacuum of chromo-electric fields which are constant over significant distances. This interpretation is supported by a comparative evaluation of the interaction energy of static charges in the axial gauge representation of QED and QCD.

hep-th↗

arXiv1994

Quantum Mechanics of the Vacuum State in Two-Dimensional QCD with Adjoint Fermions

A study of two-dimensional QCD on a spatial circle with Majorana fermions in the adjoint representation of the gauge groups SU(2) and SU(3) has been performed. The main emphasis is put on the symmetry properties related to the homotopically non-trivial gauge transformations and the discrete axial symmetry of this model. Within a gauge fixed canonical framework, the delicate interplay of topology on the one hand and Jacobians and boundary conditions arising in the course of resolving Gauss's law on the other hand is exhibited. As a result, a consistent description of the residual $Z_N$ gauge symmetry (for SU(N)) and the ``axial anomaly" emerges. For illustrative purposes, the vacuum of the model is determined analytically in the limit of a small circle. There, the Born-Oppenheimer approximation is justified and reduces the vacuum problem to simple quantum mechanics. The issue of fermion condensates is addressed and residual discrepancies with other approaches are pointed out.

hep-th↗