Basic Models and Properties of Dense Nuclear Matter

Abstract

There are numerous models to describe cold and dense interacting nuclear matter. Some of them have been used to obtain the curves in Figs. 2.2 and 2.3. From these curves we see that the models may differ significantly in their predictions of the properties of neutron stars and hybrid stars. The reason is that they all are extrapolated into a regime where there is little theoretical control. In other words, for densities below the nuclear ground state density there are experimental data for instance from atomic nuclei or neutron scattering which serve to fit the parameters of the nuclear models unambiguously. However, it is very challenging to construct a model which reliably predicts the properties of nuclear matter for larger densities. Put another way, currently the only “experiments” in this density regime are astrophysical observations which themselves are naturally less controlled than experiments in the laboratory. Therefore, the state of the art in describing interacting nuclear matter at high densities is a competition between several models which all are prone to uncertainties. In these lectures we do not attempt to give an overview over these models. We rather focus on two basic models and discuss them in detail. The first is the Walecka model and its extensions. The second is chiral perturbation theory, which is an effective model based on chiral symmetry of QCD and spontaneous breaking thereof in nuclear matter. We shall use it to discuss kaon condensation in nuclear matter.