Hadronic fluctuations in the QGP

We analyze fluctuations of quark number and electric charge, in 2-flavour QCD at finite temperature and vanishing net baryon number density. In the hadronic phase we find that an enhancement of charge fluctuations arises from contributions of doubly charged hadrons to the thermodynamics. The rapid suppression of fluctuations seen in the high temperature phase suggests that in the QGP quark number and electric charge are predominantly carried by quasi-particles with the quantum numbers of quarks.Comment: 4 pages, 6 EPS-files, talk presented at Quark Matter 2005, Budapes

Hadron Resonance Mass Spectrum and Lattice QCD Thermodynamics

We confront lattice QCD results on the transition from the hadronic phase to the quark--gluon plasma with hadron resonance gas and percolation models. We argue that for T < T_c the equation of state derived from Monte--Carlo simulations of (2+1) quark--flavor QCD can be well described by a hadron resonance gas. We examine the quark mass dependence of the hadron spectrum on the lattice and discuss its description in terms of the MIT bag model. This is used to formulate a resonance gas model for arbitrary quark masses which can be compared to lattice calculations. We finally apply this model to analyze the quark mass dependence of the critical temperature obtained in lattice calculations. We show that the value of T_c for different quark masses agrees with lines of constant energy density in a hadron resonance gas. For large quark masses a corresponding contribution from a glueball resonance gas is required.Comment: 18 pages, LaTex2

Thermodynamics of 2 and 3 flavour QCD

We discuss recent results on the thermodynamics of QCD in the presence of light dynamical quark degrees of freedom. In particular, we concentrate on an analysis of the flavour and quark mass dependence of the QCD phase diagram, the equation of state and the transition temperature. Moreover, we present recent results on the heavy quark free energy.Comment: 10 pages, To appear in the proceedings of QCD@Work: International Conference on QCD: Theory and Experiment, Martina Franca, Italy, 16-20 Jun 200

Charmonium at finite temperature

We study charmoinum correlators and spectral functions at finite temperature within the quenched approximation using isotropic lattices with lattice spacing a^-1=4.86 GeV and 9.72 GeV. Although we observe some medium modifications of the ground state charmonium spectral function above deconfinement, we find that ground state charmonia (J/psi and eta_c) exist in the deconfined phase at least up to temperatures as high as 1.5Tc. P-wave charmonia (chi_c) on the other hand are dissociated already at 1.12Tc.Comment: Contribution to Lattice 2003 (non-zero) LaTeX, 3 pages, 3 figures, uses espcrc2 styl

Fluctuations of Goldstone modes and the chiral transition in QCD

We provide evidence for the influence of thermal fluctuations of Goldstone modes on the chiral condensate at finite temperature. We show that at fixed temperature, T<Tc, in the vicinity of the chiral transition temperature this leads to a characteristic dependence of the chiral condensate on the square root of the light quark mass (m_l), which is expected for 3-dimensional models with broken O(N) symmetry. As a consequence the chiral susceptibility shows a strong quark mass dependence for all temperatures below Tc and diverges like 1/sqrt(m_l) in the chiral limit.Comment: 4 pages,presented in Strong and ElectroWeak Matter, August 2008, Amsterdam, The Netherland

Lattice QCD at High Temperature and the QGP

We review recent progress in studies of bulk thermodynamics of strongly interacting matter, present results on the QCD equation of state and discuss the status of studies of the phase diagram at non-vanishing quark chemical potential.Comment: 9 pages, plenary talk given at PANIC05, Particles and Nuclei International Conference, Santa Fe, NM, Oct. 24-28, 200

The finite temperature transition for 3-flavour lattice QCD at finite isospin density

We simulate 3-flavour lattice QCD with a small chemical potential $\mu_I$ for isospin, at temperatures close to the finite temperature transition. Using quark masses just above the critical mass for zero chemical potential, we determine the position of the transition from hadronic matter to a quark-gluon plasma as a function of $\mu_I$. We see evidence for a critical endpoint where the transition changes from a crossover to a first-order transition as $\mu_I$ is increased. We argue that QCD at finite $\mu_I$ and QCD at finite quark-numberchemical potential $\mu$ should behave similarly in this region.Comment: 3 pages LaTex, 2 postscript figures. Parallel talk presented at Lattice 2004 (non-zero), Fermila

Lattice Regularized QCD at Finite Temperature

During the first part of this review we will focus on the thermodynamics of $SU(N)$ gauge theories at finite temperature. We will present results from a calculation of electric and magnetic screening masses for the gluons, discuss calculations of the critical temperature in units of the string tension and bulk thermodynamic quantities like the energy density and pressure. In particular, the latter calculations have now reached a stage where $O(a^2)$ cut-off effects can be controlled systematically and an extrapolation to the continuum limit can be performed. In the second part we discuss the critical behaviour of QCD with light quarks. We analyze the chiral transition in 2-flavour QCD and present results on the temperature dependence of hadron properties.Comment: 20 pages, 13 Postscript figure

Lattice Simulations of the Thermodynamics of Strongly Interacting Elementary Particles and the Exploration of New Phases of Matter in Relativistic Heavy Ion Collisions

At high temperatures or densities matter formed by strongly interacting elementary particles (hadronic matter) is expected to undergo a transition to a new form of matter - the quark gluon plasma - in which elementary particles (quarks and gluons) are no longer confined inside hadrons but are free to propagate in a thermal medium much larger in extent than the typical size of a hadron. The transition to this new form of matter as well as properties of the plasma phase are studied in large scale numerical calculations based on the theory of strong interactions - Quantum Chromo Dynamics (QCD). Experimentally properties of hot and dense elementary particle matter are studied in relativistic heavy ion collisions such as those currently performed at the relativistic heavy ion collider (RHIC) at BNL. We review here recent results from studies of thermodynamic properties of strongly interacting elementary particle matter performed on Teraflops-Computer. We present results on the QCD equation of state and discuss the status of studies of the phase diagram at non-vanishing baryon number density.Comment: 10 pages, invited plenary talk given at the conference 'Scientific Discovery through Advanced Computing', SciDAC 2006, June 25-29, Denver, US