Thermodynamics and in-medium hadron properties from lattice QCD

Non-perturbative studies of the thermodynamics of strongly interacting elementary particles within the context of lattice regularized QCD are being reviewed. After a short introduction into thermal QCD on the lattice we report on the present status of investigations of bulk properties. In particular, we discuss the present knowledge of the phase diagram including recent developments of QCD at non-zero baryon number density. We continue with the results obtained so far for the transition temperature as well as the temperature dependence of energy and pressure and comment on screening and the heavy quark free energies. A major section is devoted to the discussion of thermal modifications of hadron properties, taking special account of recent progress through the use of the maximum entropy method.Comment: prepared for "Quark-Gluon Plasma III", R.Hwa (ed.

Further Evidence for an unstable H-Dibaryon?

We present preliminary results for the mass of the 6q flavor-singlet state ($J^P=0^+$, $S=-2$) called H-dibaryon, calculated in quenched QCD on $16^3$x30 and $24^3$x30 lattices with improved gauge and fermion actions (Symanzik improvement, Clover action). For both lattice sizes we applied the fuzzing technique to enhance the overlap with the ground state. We observe a H-mass above the $\Lambda\Lambda$ threshold for strong decay. The difference in mass, $m_H - 2m_\Lambda$, increases with increasing lattice size.Comment: Poster at LATTICE99 (QCD Spectrum and Quark Masses), 3 pages, 4 figures, LaTeX2e using espcrc2.st

Quark Mass and Flavour Dependence of the QCD Phase Transition

We analyze the quark mass and flavour dependence of the QCD phase transition temperature. When the lightest pseudo-scalar meson mass (m_PS) is larger than 2 GeV the critical temperature is controlled by the gluonic sector of QCD alone. For smaller values of the lightest meson mass the pseudo-critical temperature decreases slowly with m_PS. For a large regime of meson masses the pseudo-critical temperature of 2-flavour QCD is about 10% larger than in the 3-flavour case. On lattices with temporal extent N_t=4 an extrapolation to the chiral limit yields T_c = 173(8) MeV and 154(8) MeV for 2 and 3-flavour QCD, respectively. We also analyze dynamical quark mass effects on the screening of the heavy quark potential. A detailed analysis of the heavy quark free energy in 3-flavour QCD shows that close to T_c screening effects are approximately quark mass independent already for pseudo-scalar meson masses m_PS = 800 MeV and screening sets in at distances r = 0.3 fm.Comment: 25 pages, LaTeX2e File, 11 EPS-file

The Phase Diagram of 2 flavour QCD with improved Actions

It has been proposed, that the chiral continuum limit of 2-flavour QCD with Wilson fermions is brought about by a phase in which flavour and parity symmetry are broken spontaneously at finite lattice spacing. At finite temperature this phase should retract from the weak coupling limit to form 5 cusps. This scenario is studied with tree level Symanzik improved actions for both gauge and fermion fields on lattices of size $8^3\times 4$ and $12^2\times 24\times 4$.Comment: Talk given at Conference on Strong and Electroweak Matter (SEWM 98), Copenhagen, Denmark, 2-5 Dec 199

Two Flavour QCD Phase Transition

Results on the phase transition in QCD with two flavours of light staggered fermions from an ongoing simulation are presented. We find the restoration of the chiral SU(2) x SU(2) symmetry, but not of the axial U_A(1) symmetry.Comment: LaTeX2e, amstex package. 4 pages, 2 figures. Talk presented at the 10th International Conference on Problems of Quantum Field Theory, Crime

Thermodynamics of two-colour QCD

We discuss the thermodynamics of two-colour QCD with four flavours of staggered quarks on 8^3x4 and 16^3x4 lattices. In our simulations we use the Naik action for the fermions and a (1,2) tree-level improved gauge action. We analyze the deconfinement and chiral phase transitions for four different quark masses (m=0.1,0.05,0.025,0.015). Contrary to three-colour QCD the peak in the Polyakov loop susceptibility decreases with decreasing quark mass. This reflects an early breaking of the string in the heavy quark potential, which we verify explicitly by calculating the heavy quark potential at finite temperature using Polyakov loop correlations.Comment: LATTICE98(hightemp), 3 pages, LaTeX2e File, 5 EPS-figures, espcrc2.st

Free Meson Spectral Functions on the Lattice

We present results from an analytic calculation of thermal meson spectral functions in the infinite temperature (free field) limit. We compare spectral functions for various lattice fermion formulations used at present in studies of in-medium properties of hadrons based on the maximum entropy method (MEM). In particular, we will present a new calculation of spectral functions performed with extended quark sources.Comment: 3 pages, Lattice2003(nonzero

Flavor and Quark Mass Dependence of QCD Thermodynamics

We calculate the transition temperature in 2 and 3-flavor QCD using improved gauge and staggered fermion actions on lattices with temporal extent Nt=4. We find Tc=173(8)MeV and 154(8)MeV for nf=2 and 3, respectively. In the case of 3-flavor QCD we present evidence that the chiral critical point, i.e. the second order endpoint of the line of first order chiral phase transitions, belongs to the universality class of the 3d Ising model.Comment: Talk given at Lattice 2000 (Finite Temperature), 4 pages, 6 EPS-figure