Low Density Symmetry Energy Effects and the Neutron Star Crust Properties

The form of the nuclear symmetry energy Es around saturation point density leads to a different crust-core transition point in the neutron star and affects the crust properties. We show that the knowledge of Es close to the saturation point is not sufficient to determine the position of the transition point and the very low density behaviour is required. We also claim that crust properties are strongly influenced by the very high density behaviour of Es, so in order to conclude about the form of low density part of the symmetry energy from astrophysical data one must isolate properly the high density part. (authors)