Cosmological model with variable vacuum pressure

Scenarios of the cosmological evolution are studied by using an equation of state (EoS) having points where the specific enthalpy of the cosmological fluid vanishes. A large class of barotropic equations of state admits, depending upon initial conditions, analogues of the Big Rip [R. R. Caldwell, M. Kamionkowski, and N. N. Weinberg, Phys. Rev. Lett. 91, 071301 (2003)], as well as solutions describing exponential inflation followed by usual matter dominance; their classification is proposed. We discuss extensions to a more general two-parametric EoS dealing with a preinflationary evolution and yielding stages with both increasing and decreasing energy density as a function of time. Possible cosmological scenarios with transitions from collapse to an expanding Universe or a closed oscillating one, without reaching a singularity, are included.