Gluon Condensate and Parton Propagation in a Quark-gluon Plasma

Finite temperature QCD can be used to describe properties of a quark-gluon plasma (QGP) possibly created in the fireball of relativistic heavy ion collisions and in the early Universe. There are two different methods available, namely lattice QCD and perturbation theory. Lattice QCD is a non-perturbative method, which can be used at all temperatures above and below the phase transition. However, it is very difficult to calculate dynamical quantities or to consider a system at finite baryon density or in non-equilibrium. Using perturbative QCD, on the other hand, one is able to compute static as well as dynamical quantities at zero and finite baryon density and even out of equilibrium. However, the strong coupling constant αs is small only for temperatures T ≫ Tc. Furthermore, infrared singularities show up in perturbative calculations even within the hard thermal loop (HTL) resummation scheme . Therefore it would be desirable to construct non-perturbative QCD Green functions. Here we suggest to include the gluon condensate into the parton propagators. Condensates of gluons and quarks describe the non-perturbative feature of the QCD ground state. They have been used in QCD sum rules to describe hadron properties at zero and finite temperature. Whereas the quark condensate is related to chiral symmetry breaking, the gluon condensate is associated with the breaking of the scale invariance. Therefore, in contrast to the quark condensate, it does not vanish above the phase transition.