Prof. i. R. Dr. sc. nat. Michael Müller-Preußker

• SFB/TR 9/1-3: Chiral invariante Formulierungen der QCD auf dem Gitter (TP A 04)

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  Dieses Projekt dient der methodischen Untersuchung und physikalischen Anwendung von chiral invarianten Formulierungen der Quantenchromodynamik auf dem Gitter. Es stellt eine prinzipiell wichtige Forschungsaktivität dar, die für eine Vielzahl von Aussagen der Theorie der starken Wechselwirkungen von Interesse ist, bei denen die chirale Invarianz eine entscheidende Rolle spielt. Im Rahmen des Projektes sollen insbesondere die Ergebnisse numerischer Simulationen und Rechnungen in der chiralen Störungstheorie miteinander verknüpft werden.

• Semiclassical structure of (lattice) QCD at non-zero temperature: caloron solutions with nontrivial holonomy

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  At present, different models of the vacuum state are used to explain non-perturbative features of Quantum Chromodynamics. Instantons as carriers of topological charge are believed to be responsible for axial and chiral symmetry breaking, Abelian monopoles and/or centre vortices for quark confinement. The present project has the aim to verify, in lattice gauge theory simulations, a generalization of the semiclassical approach which promises to unify the carriers of topological charge with monopoles or dyons in finite temperature Yang-Mills theory. Such a synthesis seems to be viable since the discovery of caloron solutions with non-trivial asymptotic holonomy. The complete moduli space contains solutions which are dissociated into `instanton constituents' with variable action and topological charge. The possible relevance of such solutions has been overlooked in the past in ab-initio lattice investigations of topological structure. Lattice investigations of our own have given evidence for the existence of dyonic instanton constituents in SU(2) gluodynamics just below the deconfinement temperature. With the present project we want to strengthen joint efforts of groups at HU Berlin and ITEP Moscow, (1) to explore the dynamical relevance of these solutions at lower temperatures for SU(2) and to exclude it in the deconfined phase, (2) to find corresponding signatures for SU(3) gluodynamics and (3) to figure out the modifications in the presence of dynamical quarks.

• FG 465: Gitter-Hadronen-Phänomenologie - Teilprojekt 2: Topological Gauge Field Structure of Lattice QCD in the Ground State and at Non-Vanishing Temperature

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  The purpose of the project is to pursue thorough investigations of the topological structure of lattice QCD emphasizing the effects of dynamical quarks. The cases of the ground state (T=0) as well as of the thermal equilibrium at temperatures near the deconfinement and chiral phase transition (T=Tc) are studied and compared. The investigationen will rely on large volume, zero-temperature gauge field configurations obtained by the Forschergruppe ant those available, thanks to the QCDSF collaboration with UKQCD. Additional less extensive Hybrid Monte Carlo simulations are required for the finite T-case. With respect to a semi-classical view of the QCD vacuum we are going to investigate the relevance of dissociated non- Abelian monopoles or calorons (Kraan-van Baal Solutions) in pure gauge theory and - at a later stage - in full QCD. With respect to an effective long-range description of non-perturbative QCD the Abelian and centre degrees of freedom (monopoles and vortices) are studied in suitable gauges in order to understand their mutual relation and their correlation with semi-classical excitations as mentioned above. We shall focus on the local correlation of fermionic degrees of freedom with monpole and vortex excitations, the formation and breaking of flux tubes between static quarks and the computation of order parameters of the condensation of those topological excitations.

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