The equation of state and symmetry energy of low-density nuclear matter

The symmetry energy of nuclear matter is a fundamental ingredient in the investigation of exotic nuclei, heavy-ion collisions and astrophysical phenomena. A recently developed quantum statistical (QS) approach that takes the formation of clusters into account predicts low-density symmetry energies far above the usually quoted mean-field limits. A consistent description of the symmetry energy has been developed that joins the correct low-density limit with values calculated from quasiparticle approaches valid near the saturation density. The results are confronted with experimental values for free symmetry energies and internal symmetry energies, determined at sub-saturation densities and temperatures below 10MeV using data from heavy-ion collisions. There is very good agreement between the experimental symmetry energy values and those calculated in the QS approach. (orig.)