Proto-neutron and Neutron Stars

It has been shown that effective chiral hadronic models can satisfactorily describe nuclear matter, properties of finite nuclei as well as the structure of neutron stars1. While most of the approaches are based on variations of the linear sigma model or its non-linear realization, in the approach discussed here the scalar sigma meson serves to split the nucleon and its chiral partner (particle with opposite parity), while in the chirally restored phase both baryonic states become degenerate but not massless. The presence of the chiral partner allows to have a bare mass term m0 in the Lagrangian density in such a way that it does not break chirality because the physical fields in this case are a mixture of the fields of the particles and their chiral partners2,3,4.