  The time evolution of cosmological parameters in 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
non perturbative dynamics is described by the Field Correlator Method (FCM)
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 factor, $a(t)$, 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
$t_c \simeq 20-25 \mu s$. The time evolution of the cosmological parameters
suggest 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 driven by the presence of massive colored objects.
