Gluon condensates in a cold quark-gluon plasma

The quark-gluon plasma which has been observed at RHIC is a strongly interacting system and has been called sQGP. This is a system at high temperatures and almost zero baryon chemical potential. A similar system with high chemical potential and almost zero temperature may exist in the core of compact stars. Most likely it is also a strongly interacting system. The strong interactions may be partly due to non-perturbative effects, which survive after the deconfinement transition and which can be related with the non-vanishing gluon condensates in the sQGP. In this work, starting from the QCD Lagrangian we perform a gluon field decomposition in low (“soft”) and high (“hard”) momentum components, we make a mean field approximation for the hard gluons and take the matrix elements of the soft gluon fields in the plasma. The latter are related to the condensates of dimension two and four. With these approximations we derive an analytical expression for the equation of state, which is compared to the MIT bag model one. The effect of the condensates is to soften the equation of state whereas the hard gluons significantly increase the energy density and the pressure.