An investigation of the phase transition in the extended bag model

By proposing an Ansatz for the pressure (measured in terms of the bag constant) of the hadronic gas in equilibrium, we have formulated a rather simple method which allows one to analytically investigate the bulk thermodynamic propertities in the vicinity of the phase transition. This makes it also possible to take into account the nonperturbative vacuum effects from both sides of the equilibrium condition. As an example of our approach, we have calculated the crossover (critical or transition) temperature $T_c$ and the critical chemical potential $\mu_c$ (as functions of the bag constant) from the noninteracting quark-gluon plasma state equation. Our results for $T_c(N_f=0)=241.5 MeV$ and $T_c(N_f=2)=160.6 MeV$ are in good agreement with recent lattice data. The extensive densities such as the entropy density, specific heat, etc. are calculated as well. A general scheme how to calculate the latent heat, the critical density, etc. within the extended bad model is also described and it is applied to the two models of the hadronic gas phase.