KIDS Energy Density Functional and Mass–Radius Relation of Neutron Stars

Abstract

Many efforts are made to determine the nuclear equation of state which governs the properties and evolution of neutron stars. Especially important is to constrain the parameters of the nuclear symmetry energy. In those efforts, nuclear energy density functional (EDF) theory has been a very useful tool, as it provides a unified framework for the description both of nuclei, which can be studied on Earth, and of infinite matter and its nuclear equation of state, which is a necessary input in the modelling of neutron stars. In the present study, a new nuclear EDF, the KIDS functional, is explored with a focus on the nuclear symmetry energy. The form of the functional allows us to vary at will the poorly constrained high-order derivatives of the symmetry energy and examine how the maximum possible mass of a neutron star is affected. Some tentative constraints on the skewness are presented, which will help guide further refinements. It is noteworthy that the pressure of neutron-rich matter is found strongly affected by skewness variations, both at low and high densities.

From homogeneous matter to finite nuclei: Role of the effective mass

“…Future applications abound: Our method will allow us to vary independently and at will all relevant EoS parameters (e.g., compression modulus or symmetry energy parameters) around a baseline set of values (here, those of KIDS-ad2) and the effective mass and to examine their effects on predictions for nuclear observables. An exploration of symmetry-energy parameters is underway [46,47]. Explorations of giant resonances are also in progress [48].…”