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We calculate the equation of state in 2+1 flavor QCD at finite temperature with physical strange quark mass and almost physical light quark masses using lattices with temporal extent Nt=8. Calculations have been performed with two different improved staggered fermion actions, the asqtad and p4 actions. Overall, we find good agreement between results obtained with these two O(a^2) improved staggered fermion discretization schemes. A comparison with earlier calculations on coarser lattices is performed to quantify systematic errors in current studies of the equation of state. We also present results for observables that are sensitive to deconfining and chiral aspects of the QCD transition on Nt=6 and 8 lattices. We find that deconfinement and chiral symmetry restoration happen in the same narrow temperature interval. In an Appendix we present a simple parametrization of the equation of state that can easily be used in hydrodynamic model calculations. In this parametrization we also incorporated an estimate of current uncertainties in the lattice calculations which arise from cutoff and quark mass effects. We estimate these systematic effects to be about 10 MeV, Comment: 31 pages, 24 EPS-figures

We calculate correlation functions of the energy-momentum tensor in the vicinity of the deconfinement phase transition of (3+1)-dimensional SU(2) gauge theory and discuss their critical behavior in the vicinity of the second order deconfinement transition. We show that correlation functions of the trace of the energy momentum tensor diverge uniformly at the critical point in proportion to the specific heat singularity. Correlation functions of the pressure, on the other hand, stay finite at the critical point. We discuss the consequences of these findings for the analysis of transport coefficients, in particular the bulk viscosity, in the vicinity of a second order phase transition point., Comment: 24 pages, 6 figures

We calculate the spatial string tension in (2+1) flavor QCD with physical strange quark mass and almost physical light quark masses using lattices with temporal extent N_tau=4,6 and 8. We compare our results on the spatial string tension with predictions of dimensionally reduced QCD. This suggests that also in the presence of light dynamical quarks dimensional reduction works well down to temperatures 1.5T_c., Comment: 8 pages ReVTeX, 4 figures

We study the free energy of static three quark systems in singlet, octet, decuplet and average color channels in the quenched approximation and in 2-flavor QCD at finite temperature. We show that in the high temperature phase singlet and decuplet free energies of three quark systems are well described by the sum of the free energies of three diquark systems plus self energy contributions of the three quarks. In the confining low temperature phase we find evidence for a Y-shaped flux tube in SU(3) pure gauge theory, which is less evident in 2-flavor QCD due to the onset of string breaking. We also compare the short distance behavior of octet and decuplet free energies to the free energies of single static quarks in the corresponding color representations., Comment: 11 pages, 17 figures

We analyze the screening of static diquark sources in 2-flavor QCD and compare results with the screening of static quark-antiquark pairs. We show that a two quark system in a fixed color representations is screened at short distances like a single quark source in the same color representation whereas at large distances the two quarks are screened independently. At high temperatures we observe that the relative strength of the interaction in diquark and quark-antiquark systems, respectively, obeys Casimir scaling. We use this result to examine the possible existence of heavy quark-quark bound states in the high temperature phase of QCD. We find support for the existence of $bb$ states up to about $2T_c$ while $cc$ states are unlikely to be formed above $T_c$., Comment: 8 pages, 6 figures

We investigate the Polyakov loop in different representations of SU(3) in pure gauge at finite $T$. We discuss Casimir scaling for the Polyakov loop in the deconfined phase and test and generalize the renormalization procedure for the Polyakov loop from \cite{Kaczmarek:2002mc} to arbitrary representations. In the confined phase we extract the renormalized adjoint Polyakov loop, which is finite in the thermodynamic limit. For our numerical calculations we used the tree-level improved Symanzik action on $32^3\times 4,6,8$ lattices., Comment: 4 pages, 4 figures, to appear in the proceedings of International Conference on Strong & Electroweak Matter 2006, Brookhaven National Laboratory, USA, May 10-13, 2006

We investigate the behaviour of heavy $QQ$- and $QQQ$-free energies in SU(3) pure gauge theory at finite temperature. After stating some general properties of the free energies, we discuss the $QQ$-antitriplet and -sextet channels as well as free energies in different $QQQ$-channels. We perform a detailed finite volume scaling analysis of $QQ$-free energies below and above $T_c$. Moreover, we also discuss the relation of the $QQ$-antitriplet to the $Q\bar Q$-singlet free energies. A comparison of the effective running coupling indicates that the $r$-dependence of the free energies differs by a factor of two in agreement with the different Casimir factors. We observe that the baryonic free energies can be decomposed into a sum of two particle interactions., Comment: 6 pages, 8 figures, talk presented at Lattice 2005 (Nonzero Temperature and Density), Dublin, July 25-30, 2005

We study the behaviour of free energies of baryonic systems composed of three heavy quarks on the lattice in SU(3) pure gauge theory at finite temperature. For all temperatures above $T_c$ we find that the connected part of the singlet (decuplet) free energy of the three quark system is given by the sum of the connected parts of the free energies of $qq$-triplets (-sextets). Using renormalized free energies we can compare free energies in different colour channels as well as those of $qq$- and $qqq$-systems on an unique energy scale., Comment: 5 pages, 6 figures, Contribution to Strong and Electroweak Matter 2004 (SEWM04), Helsinki, Finland 16-19 June 2004