Recent SU͑3͒ gauge field lattice data for the equation of state are interpreted by a quasiparticle model with effective thermal gluon masses. The model is motivated by lowest-order perturbative QCD and describes very well the data. The proposed quasiparticle approach can be applied to study color excitations in the nonperturbative regime. As an example we estimate the temperature dependence of the Debye screening mass and find that it declines sharply when approaching the confinement temperature from above, while the thermal mass continuously rises. ͓S0556-2821͑96͒02815-9͔

We study properties of a gluon plasma above the critical temperature Tc in a generalized quasiparticle approach with a Lorentz spectral function. The model parameters are determined by a fit of the entropy s to lattice QCD data. The effective degrees of freedom are found to be rather heavy and of a sizable width. With the spectral width being closely related to the interaction rate, we find a large effective cross section, which is comparable to the typical distance squared of the quasiparticles. This suggests that the system should be viewed as a liquid as also indicated by an estimate of the plasma parameter Gamma. Furthermore, within the quasiparticle approach we find a very low viscosity to entropy ratio, eta/s approximately 0.2 for T > 1.05 Tc, supporting the recent conjecture of an almost ideal quark-gluon liquid seen at RHIC.

A quasiparticle description of the thermodynamics of deconfined matter, reproducing both the perturbative limit and nonperturbative lattice QCD data at finite temperature, is generalized to finite chemical potential. By a flow equation resulting from Maxwell's relation, the equation of state is extended from zero to non-zero quark densities. The impact of the massive strange flavor is considered and implications for cold, charge-neutral deconfined matter in β-equilibrium in compact stars are given.