Hyperonic Crystallization in Hadronic Matter

We propose a method for analyzing the formation of spatially ordered configurations in hadronic matter, related to the crystallization of the hyperonic sector in a lattice. The method allows the determination of the density ranges where such ordered configurations are energetically favoured with respect to the usual gaseous configurations. This leads to the determination of the parameters of a first order phase transition from the fluid to the crystallized state as well as the equation of state of the plasma in the ordered phase. We show some preliminary results obtained by the application of the method to a very simplified model which shows the efficiency of the mechanism of confinement of the hyperons in an ordered phase proposed here. The eventual existence of such a new phase should induce changes in the structure and cooling of dense stars. At densities about 1.5 times nuclear saturation and beyond, hyperons are present in hadronic matter. The equation of state taking into account the presence of nucleons and hyperons which interact through the exchange of several mesons has been extensively studied using phenomenological lagrangian models . In the mean field approximation, the hyperonic component (as the other hadronic components in the ground state) is supposed to form a spatially uniformly distributed Fermi fluid undergoing the action of the mesonic mean field created by the whole baryonic distribution in the plasma. The hadronic interaction in our model is reduced to the exchange of scalar and vector meson fields. Such a description is the simplest one allowing for an acceptable fit of nuclear saturation . We consider a unique species of neutral hyperons. The interaction Lagrangian for every baryon species B reads