Quasiparticles in Qcd Thermodynamics and Dilepton Radiation∗

A first-principles understanding of the equation of state (EOS) of hot QCD is of great interest in order to reliably identify and calculate experimental signatures of that elusive state in ultra-relativistic heavy-ion collisions. However, perturbative results show bad convergence, and current experiments only probe that non-perturbative temperature regime close to the critical temperature Tc where the underlying physics, the confinement and chiral symmetry breaking mechanism, is not sufficiently understood. Phenomenological models incorporating as much physics as is known are therefore necessary. Here, we propose a new quasiparticle model of the quark-gluon plasma (QGP) that incorporates a parametrization of confinement, supplemented by thermal masses compatible with lattice results. Details can be found in [1]. From asymptotic freedom, we expect that at very high temperatures the plasma consists of quasifree quarks and gluons. As long as the spectral function of the thermal excitations at lower temperatures resembles qualitatively this asymptotic form, a quasiparticle description of the QGP is expected to be applicable. Their dispersion relation reads