QCD equation of state and cosmological parameters in the early universe

The time evolution of cosmological parameters in the early Universe at the deconfinement transition is studied by an equation of state (EoS) which takes into account the finite baryon density and the background magnetic field. The nonperturbative dynamics is described by the field correlator method which gives, with a small number of free parameters, a good fit of lattice data. The entire system has two components, i.e., the quark-gluon plasma and the electroweak sector, and the solutions of the Friedmann equation show that the scale factors a(t) and H(t) = (1/a) da/dt are weakly dependent on the EoS, but the deceleration parameter q(t) and the jerk j(t) are strongly modified above the critical temperature T-c, corresponding to a critical time t(c) similar or equal to 20-25 mu s. The time evolution of the cosmological parameters suggests that above and around T-c, there is a transient state of acceleration typical of a matter-dominated universe; this is entailed by the QCD strong interaction. The effect of the hadronic matter below T-c does not qualitatively change the previous behavior and one can consistently follow the cosmological evolution up to 100 mu s.