Thermodynamic instabilities and statistical effects in protoneutron stars

We investigate the physical properties of the protoneutron stars in the framework of a relativistic mean-field model and we study the finite-temperature equation of state in Delta-stable matter at fxed entropy per baryon, in the presence of hyperons, Delta-isobar resonances and trapped neutrinos. In this context, we study the possible presence of thermodynamic instabilities and a phase transition from nucleonic matter to resonance-dominated Delta-matter can take place. Such a phase transition is characterized by both mechanical instability (fluctuations on the baryon density) and by chemical-dffusive instability (fluctuations on the isospin concentration) in asymmetric nuclear matter. We show that such statistical ffects could play a crucial role in the structure and in the evolution of the protoneutron stars.