M. Müller

Vacuum polarization of hadrons in lattice QCD

Abstract We investigate the QCD vacuum structure around static hadrons by calculating the correlations of Polyakov loops with the local chiral condensate ψ ψ( r ) and the color charge density ψ † ψ( r ) . We find that chiral symmetry is restored in the vicinity of static color sources as a consequence of gluon string creation and that virtual antiquarks screen static quarks in analogy to QED.

Chiral symmetry and charge density in mesons for Kogut-Susskind and Wilson fermions

Abstract We investigate the sea quark distribution around static quarks in the framework of lattice QCD by calculating the correlations of Polyakov loops with the local chiral condensate ψ ψ(r) and the color charge density ψ † ψ(r) . A comparison of dynamical quarks in Kogut-Susskind and Wilson discretization is performed. We observe a restoration of chiral symmetry in the vicinity of color sources for both fermion regularization schemes as a consequence of gluon string formation. It turns out that virtual antiquarks screen static quarks as expected from QED.

Vacuum polarization in compact QED

Abstract We analyze the vacuum structure of compact lattice QED affected by static electric sources. The potential and the energy density between a static charge and anticharge are computed. Potentials are screened by dynamical fermions and energy distributions are localized around the sources. We further compute the electric charge density ψ † ψ and find that static charges are screend by virtual anticharges as expected from ordinary QED. All effects are more pronounced at strong coupling and decrease with growing fermion mass.

Universality of the confinement string in multiplet potentials

Studying potentials between quark multiplets at finite temperature we find that at large distances all potentials become either screened or have the same string tension as the 3 - 3 potential. Thus, in the confining phase the string tension between different color sources depends only on triality zero or nonzero. The underlying mechanism is a screening of sources by virtual gluons either completely (e.g. octet sources) or partially (e.g. sextet sources) so that either singlet or triplet charges remain. Concerning the Coulomb part and the constant term of the potentials we achieve good agreement for the ratios of different multiplets with a Casimir scaling law already at β = 5.6.

Confinement in quantum field theories

Abstract We compare electromagnetic field distributions around a static charge-anticharge system for compact U(1) and SU(3) lattice gauge theories. We display flux tube formation for both internal symmetry groups in the confinement phase and its breaking beyond the deconfinement phase transition. The dependence of the string width on the dipole elongation is studied and the roughening mechanism is explored. Our results suggest that the energy density is restricted to a thin flux tube both in the SU(3) and U(1) case in the confinement regime.

Quark confinement with dynamical fermions in higher representations

Abstract We study the static interquark potential on a hypercubic lattice in pure gauge theory and with dynamical fermions in triplet and octet representation. Our computation shows that octet fermions in contraryto triplet fermions have no effect on the linear confinement behavior of the quark-antiquark potential. This fact gives interesting insight into the confinement mechanism of supersymmetric Yang-Mills theories if octet fermions are interpreted as a simple model for gluinos.

Chiral condensates for light dynamical quarks in mesons within lattice QCD

Abstract We investigate the QCD vacuum structure around static quarks and mesons by calculating the correlation of Polyakov loops with the local chiral condensate ψψ( r ) . We find that the restoration of chiral symmetry in the vicinity of static color sources increases with decreasing bare mass of virtual quarks.

Charge density in QED and QCD in both phases

Abstract The charge density around a static charge is investigated within finite temperature QCD and compact QED both in the chirally broken and symmetric phase. We analyze the functional behavior of the charge polarization and compare it to a weak coupling estimate. The total induced charge is found to be consistent with the results of the MILC Collaboration.

Surface Energy and Chiral Interface of A Coexisting Quark-Hadron System

In current heavy ion experiments at BNL and CERN the main aim is to create a new state of matter, the quark-gluon plasma (QGP). For this search energy densities of 2–3 GeV/fm3 corresponding to a temperature of ∼150 MeV or a matter density of 5–10 times nuclear density are required. The concept of the experiments is that two Lorentz-contracted nuclei collide and partly penetrate each other producing strong color-electric fields leading to a creation of free quarks and gluons. During expansion and cooling this QGP is converted to hadron matter. Most of the numerical investigations of QCD thermodynamics on space-time lattices indicate that this process may undergo a first order phase transition.1 At such a transition both phases can coexist at the critical temperature in thermodynamic equilibrium.

Chiral Symmetry in Mesons on the Lattice

We investigate chiral symmetry around static quarks and in mesons in the framework of lattice QCD by calculating the correlations of Polyakov loops with the local chiral condensate \( \bar{\psi }\psi \left( {\mathop{r}\limits^{ - } } \right)\). Dynamical quarks are taken into account by the Kogut-Susskind and the Wilson discretization. We observe a restoration of chiral symmetry in the vicinity of color sources for both fermion regularization schemes as a consequence of gluon string formation.