5th International Symposium on Nuclear Symmetry Energy NuSYM15, June 29 - July 2, 2015 Kraków, POLAND

Stefan Typel
GSI Helmholtzzentrum für Schwerionenforschung Darmstadt, GERMANY

Equation of State with Clustering in Low-Density Matter

The thermodynamic properties and the chemical composition of strongly interacting matter change substantially with density, temperature and isospin asymmetry. At subsaturation densities and not too high temperatures, the formation of clusters as many-body correlations has to be taken into account. Nucleons and clusters are considered as explicit degrees of freedom in a generalized relativistic density functional (gRDF) approach for the equation of state. It is an extension of standard relativistic mean-field models with density-dependent meson-nucleon couplings that are well constrained by fits to properties of finite nuclei. All constituents of the gRDF model are treated as quasiparticles with medium dependent properties. A particular feature is the explicit mass shift of clusters that is mainly driven by the Pauli exclusion principle. As a consequence, clusters dissolve with increasing density. Furthermore, the dissolution of nuclei with increasing temperature is described with temperature-dependent effective degeneracy factors. The gRDF model is primarily developed to provide an equation of state for astrophysical applications, e.g., for compact stars or core-collapse supernovae. In this contribution, the predictions of the gRDF model for matter at subsaturation densities are presented. The results are compared to an approach that uses the excluded-volume mechanism in order to describe the dissolution of nuclei.