Dynamical instabilities of warm $npe^-$ matter: the $\delta$ meson effects

The effects of $\delta$ mesons on the dynamical instabilities of cold and warm nuclear and stellar matter at subsaturation densities are studied in the framework of relativistic mean-field hadron models (NL3, NL$\rho$ and NL$\rho\delta$) with the inclusion of the electromagnetic field. The distillation effect and the spinodals for all the models considered are discussed. The crust-core transition density and pressure are obtained as a function of temperature for $\beta$-equilibrium matter with and without neutrino trapping. An estimation of the size of the clusters formed in the non-homogeneous phase is made. It is shown that cluster sizes increase with temperature. The effects of the $\delta$-meson on the instability region are larger for low temperatures, very asymmetric matter and densities close to the spinodal surface. It increases the distillation effect above $\sim 0.4\rho_0$ and has the opposite effect below that density.