Neutron star properties: Constraining the nuclear matter EoS

Abstract

We examine the influence of the density dependence of the symmetry energy on several properties of neutron stars. In particular, we study the constraints set on the nuclear matter equation of state by the values of the tidal deformability and neutron star radius, using a diverse set of relativistic and non-relativistic mean field models consistent with bulk properties of finite nuclei and the observed lower bound on the maximum mass of neutron star. The tidal deformability and radius show a strong correlation with specific linear combinations of the isoscalar and isovector nuclear matter parameters associated with the EoS. Such correlations suggest that a precise value of the radius or the tidal deformability can put tight bounds on several EoS parameters, in particular, on the slope of the incompressibility and the curvature of the symmetry energy. We show that the density dependence of the symmetry energy has a direct influence on the amount of strangeness inside cold dense matter and, consequently, on the direct Urca process and cooling of neutron stars. We explain the low luminosity of SAX 1808.4-3658 as a result of hyperonic direct Urca processes. Finally, we discuss the strong influence of the density dependence of the symmetry energy on the extension of the crust-core transition region of a magnetized neutron star. The increase of the crust and its of complexity, due to the magnetic field effect, may have a role on the glitch mechanism or on the magnetic field decay.