From confinement to new states of dense QCD matter

Transitions between centre sectors are related to confinement in pure Yang-Mills theories. We study the impact of these transitions in QCD-like theories for which centre symmetry is explicitly broken by the presence of matter. For low temperatures, we provide numerical evidence that centre transitions do occur with matter merely providing a bias towards the trivial centre sector until centre symmetry is spontaneously broken at high temperatures. The phenomenological consequences of these transitions for dense hadron matter are illustrated in an SU(3) effective quark theory: centre dressed quarks undergo condensation due to Bose-type statistics forming a hitherto unknown state of dense but cold quark matter.Comment: 7 pages, 7 figures, talk presented at the International School of Nuclear Physics "From Quarks and Gluons to Hadrons and Nuclei", 16-24 Sept 2011, Erice, Sicily, Ital

Singular gauge potentials and the gluon condensate at zero temperature

We consider a new cooling procedure which separates gluon degrees of freedom from singular center vortices in SU(2) LGT in a gauge invariant way. Restricted by a cooling scale $\kappa^4/\sigma^2$ fixing the residual SO(3) gluonic action relative to the string tension, the procedure is RG invariant. In the limit $\kappa \to 0$ a pure Z(2) vortex texture is left. This {\it minimal} vortex content does not contribute to the string tension. It reproduces, however, the lowest glueball states. With an action density scaling like $a^4$ with $\beta$, it defines a finite contribution to the action density at T=0 in the continuum limit. We propose to interpret this a mass dimension 4 condensate related to the gluon condensate. Similarly, this vortex texture is revealed in the Landau gauge.Comment: 3 pages, 4 figures, Contribution to ''Lattice 2001'' (confinement) to appear in the Proceedings (Nucl. Phys. B Proc. Suppl.

Chiral symmetry breaking in strongly coupled QED?

The coupled system of renormalized Dyson-Schwinger equations for the electron self-energy and the photon propagator are supplied with the tree level vertex as Ansatz for the renormalized three point function. The system is investigated numerically. In the case of a massive electron, the theory is ``weakly renormalizable'', i.e.\ cutoff independent for values of the cutoff below an upper limit. In this regime of cutoff independence, the quenched approximation yields good results for the electron self-energy. In the chiral limit, a logarithmic cutoff dependence of the electron self-energy is found. The question, whether a regime of cutoff independence with a spontaneously broken chiral symmetry exists in strongly coupled QED, remains open.Comment: 13 pages, 5 figures, complete uu-file avaiable on reques

Quantum diffusion of magnetic fields in a numerical worldline approach

We propose a numerical technique for calculating effective actions of electromagnetic backgrounds based on the worldline formalism. As a conceptually simple example, we consider scalar electrodynamics in three dimensions to one-loop order. Beyond the constant-magnetic-field case, serving as a benchmark test, we analyze the effective action of a step-function-like magnetic field -- a configuration that is inaccessible to derivative expansions. We observe magnetic-field diffusion, i.e., nonvanishing magnetic action density at space points near the magnetic step where the classical field vanishes.Comment: 15 pages, 3 figures, v2: numerical analysis in Sect.3 improved, references added, typos corrected, version to appear in NP