Abstract
Isospin symmetry breaking effects on the mass-radius relation of a cold, non-accreting neutron star are studied on the basis of two Skyrme Energy Density Functionals (EDFs). One functional contains isospin symmetry breaking terms other than those typically included in Skyrme EDFs while its counterpart is of standard form. Both functionals are based on the same fitting protocol except for the observables and pseudo-observables sensitive to the isospin symmetry breaking channel. The quality of those functionals is similar in the description of terrestrial observables but choosing either of them has a non-negligible effect on the mass-radius relation and tidal deformability of a neutron star. Further investigations are needed to clarify the effects of isospin symmetry breaking on these and other observables of neutron stars that are, and will become, available.
Highlights
We first compare the results of SAMi and SAMi-Isospin symmetry breaking (ISB) for some ground and excited state properties of different nuclei as well as some relevant properties of the nuclear equation of state
It is seen that both neutron star Equation of State (EoS) predict a radius that would be compatible with this observation at the 2σ level and that the SAMi-ISB model does not reproduce a maximum mass of 2Msun
Even though large systematic uncertainties exist, it is clear from the figure that ISB effects that are known to be small in nuclei, may entail non-negligible effects on observables that are sensitive to large densities as those associated with the core of a neutron star
Summary
It is customary to assume the core of a neutron star as made of β-stable neutrons, protons and electrons [8,9,10,11,12,13] This allows calculating the mass-radius relation and compare to observational data in order to detect deviations from such an approximation. Nuclear energy density functionals (EDFs) were proven to predict with a good accuracy the ground state as well as some excited state properties in terrestrial nuclei and have been applied to predict the limits of nuclear existence [16,17] The use of these models to the study of neutron-star matter may be regarded as strong extrapolation due to the difference in average density within the interior of a neutron star (over 2ρ0) and the interior of the atomic nucleus (ρ0).
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