Role of Glueballs in Non-Perturbative Quark-Gluon Plasma

In this work discussed is how such anomalous non-perturbative properties of quark gluon plasma recently discovered in RHIC experiment can be related to the scalar and pseudoscalar glueballs. It is shown that scalar glueball stays to be massive above the deconfinement temperature, $T_c$, but pseudoscalar glueball becomes massless from $T_c$. It is demonstrated that the mass difference between scalar and pseudoscalar glueballs gives rise to the change of sign of the gluon condensate at $T\approx T_c$ in the pure $SU(3)_c$ gauge theory. Coupling of the pseudoscalar glueball to light quarks in QGP is estimated