The Landau gauge gluon propagator for the pure gauge theory is evaluated on a 32 3 × 64 lattice with a physical volume of (3.35 3 × 6.7) fm 4 . Comparison with two smaller lattices at different lattice spacings allows an assessment of finite volume and finite lattice spacing errors. Cuts on the data are imposed to minimize these errors. Scaling of the gluon propagator is verified between β = 6.0 and β = 6.2. The tensor structure is evaluated and found to be in good agreement with the Landau gauge form, except at very small momentum values, where some small finite volume errors persist. A number of functional forms for the momentum dependence of the propagator are investigated. The form D(q 2 ) = D IR + D UV , where D IR (q 2 ) ∝ (q 2 + M 2 ) −η and D UV is an infrared regulated one-loop asymptotic form, is found to provide an adequate description of the data over the entire momentum region studied -thereby bridging the gap between the infrared confinement region and the ultraviolet asymptotic region. The best estimate for the exponent η is 3.2−0.3, where the first set of errors represents the uncertainty associated with varying the fitting range, while the second set of errors reflects the variation arising from different choices of infrared regulator in D UV . Fixing the form of D UV , we find that the mass parameter M is (1020 ± 100) MeV.

A new method for computing all elements of the lattice quark propagator is proposed. The method combines the spectral decomposition of the propagator, computing the lowest eigenmodes exactly, with noisy estimators which are 'diluted', i.e. taken to have support only on a subset of time, space, spin or colour. We find that the errors are dramatically reduced compared to traditional noisy estimator techniques.Comment: 24 pages, 18 figure

We present a lattice QCD calculation of the charge diffusion coefficient, the electrical conductivity and various susceptibilities of conserved charges, for a range of temperatures below and above the deconfinement crossover. The calculations include the contributions from up, down and strange quarks. We find that the diffusion coefficient is of the order of 1/(2πT ) and has a dip around the crossover temperature. Our results are obtained with lattice simulations containing 2+1 dynamical flavours on anisotropic lattices. The Maximum Entropy Method is used to construct spectral functions from correlators of the conserved vector current.

Abstract. We study SU(2) lattice gauge theory with two flavors of Wilson fermion at non-zero chemical potential µ and low temperature on a 8 3 × 16 system. We identify three régimes along the µ-axis. For µ mπ/2 the system remains in the vacuum phase, and all physical observables considered remain essentially unchanged. The intermediate régime is characterised by a non-zero diquark condensate and an associated increase in the baryon density, consistent with what is expected for Bose-Einstein condensation of tightly bound diquarks. We also observe screening of the static quark potential here. In the high-density deconfined régime we find a non-zero Polyakov loop and a strong modification of the gluon propagator, including significant screening in the magnetic sector in the static limit, which must have a non-perturbative origin. The behaviour of thermodynamic observables and the superfluid order parameter are consistent with a Fermi surface disrupted by a BCS diquark condensate. The energy per baryon as a function of µ exhibits a minimum in the deconfined régime, implying that macroscopic objects such as stars formed in this theory are largely composed of quark matter.

A lattice calculation is presented for the electrical conductivity σ of the QCD plasma with 2+1 dynamical flavors at nonzero temperature. We employ the conserved lattice current on anisotropic lattices using a tadpole-improved clover action and study the behavior of the conductivity over a wide range of temperatures, both below and above the deconfining transition. The conductivity is extracted from a spectral-function analysis using the maximal entropy method, and a discussion of its systematics is provided. We find an increase of σ/T across the transition.