The nuclear symmetry energy in heavy ion collisions

Abstract

In this article we discuss the nuclear symmetry energy in the regime of hadronic degrees of freedom. The density dependence of the symmetry energy is important from very low densities in supernova explosions, to the structure of neutron-rich nuclei around saturation density, and to several times saturation density in neutron stars. Heavy ion collisions are the only means to study this density dependence in the laboratory, and transport theories are used to extract the symmetry energy. We finally discuss some examples, which relate particularly to the high density symmetry energy, which is of particular interest today. We point out the status and open problems in the theoretical analyses of HIC.