Quark Confinement from Correlation Functions

We study quark confinement by computing the Polyakov loop potential in Yang--Mills theory within different non-perturbative functional continuum approaches [1]. We extend previous studies in the formalism of the functional renormalisation group and complement those with findings from Dyson--Schwinger equations and two-particle-irreducible functionals. These methods are formulated in terms of low order Green functions. This allows to identify a criterion for confinement solely in terms of the low-momentum behaviour of correlators.Comment: 8 pages, 3 figures. Talk given at "Xth Quark Confinement and the Hadron Spectrum", Munich, Germany, Oct. 8-12, 201

Two-colour QCD with heavy quarks at finite densities

We extend the density-of-states approach to gauge systems (LLR method) to QCD at finite temperature and density with heavy quarks. The approach features an exponential error suppression and yields the Polyakov loop probability distribution function over a range of more than hundred orders of magnitude. SU(2) gauge theory is considered in the confinement and the high-temperature phase, and at finite densities of heavy quarks. In the latter case, a smooth rise of the density with the chemical potential is observed, and no critical phenomenon associated with deconfinement due to finite densities is found.Comment: 4 pages, 5 figure

Improved real-time dynamics from imaginary frequency lattice simulations

The computation of real-time properties, such as transport coefficients or bound state spectra of strongly interacting quantum fields in thermal equilibrium is a pressing matter. Since the sign problem prevents a direct evaluation of these quantities, lattice data needs to be analytically continued from the Euclidean domain of the simulation to Minkowski time, in general an ill-posed inverse problem. Here we report on a novel approach to improve the determination of real-time information in the form of spectral functions by setting up a simulation prescription in imaginary frequencies. By carefully distinguishing between initial conditions and quantum dynamics one obtains access to correlation functions also outside the conventional Matsubara frequencies. In particular the range between $\omega_0$ and $\omega_1=2\pi T$, which is most relevant for the inverse problem may be more highly resolved. In combination with the fact that in imaginary frequencies the kernel of the inverse problem is not an exponential but only a rational function we observe significant improvements in the reconstruction of spectral functions, demonstrated in a simple 0+1 dimensional scalar field theory toy model.Comment: 8 pages, 5 figures, Talk given at the XXXVth International Symposium on Lattice Field Theory, June 18-24, 2017, Granada, Spai