Interplay between the symmetry energy and the strangeness content of neutron stars

Abstract

The effect of the density dependence of the nucleonic equation of state and the hyperon meson couplings on the star properties, including strangeness content, mass and radius, are studied within a relativistic mean field formalism. It is shown that there is still lacking information on the nucleonic equation of state at supra-saturation densities and on the hyperon interactions in nuclear matter that will allow a clear answer to the question whether the mass of the pulsar J1614-2230 could rule out exotic degrees of freedom from the interior of compact stars. We show that some star properties are affected in a similar way by the density dependence of the symmetry energy and the hyperon content of the star. To disentangle these two effects it is essential to have a good knowledge of the equation of state at supra-saturation densities. A linear correlation between the radius and the strangeness content of a star with a fixed mass is obtained.

Hyperons in neutron star matter within relativistic mean-field models

“…The parameter values for GM1 can be found, e.g., in [32], figure 1 of [29]. It has the same properties as TM1 [33] at and below saturation density, but it is stiffer at suprasaturation densities, still within the constraints imposed by heavy-ion flow [34].…”

“…However, within this parametrization the slope of the symmetry energy at saturation is very large, L = 110 MeV. Since the radius of compact stars is very sensitive to L [35][36][37], we will consider a modified version with L = 55 MeV [29], too, introducing a non-linear ω ρ − term as in [35]. The resulting properties of homogeneous symmetric nuclear matter are listed in table 1 for all parametrizations employed within the present paper.…”

“…For the present study we will limit ourselves to two non-linear models, GM1 [28] and TM1-2 [29], and one density-dependent model, DDHδ [30,31]. The two non-linear ones have been chosen among the large number of existing models because they are widely used and they have been obtained assuming very different strategies for determining the parameters: GM1 has been adjusted to nuclear saturation properties imposing a certain effective mass and incompressibility, whereas TM1 has been fitted to ground state properties of nuclei and at high densities to DBHF calculations.…”

Effects of the symmetry energy on properties of neutron star crusts near the neutron drip density

“…An additional ω-ρ coupling term is added in the FSU and IUFSU parametrizations, and it plays an important role in modifying the density dependence of the symmetry energy and affecting the neutron star properties [16,29,[37][38][39][40]. The IUFSU parametrization was developed from FSU by reducing the neutron skin thickness of 208 Pb and increasing the maximum neutron star mass in the parameter fitting [37].…”

Effects of finite size and symmetry energy on the phase transition of stellar matter at subnuclear densities

“…These two models include nonlinear terms for both σ and ω mesons, while an additional ω-ρ coupling term is added in the IUFSU model. It was found that the ω-ρ coupling term plays an important role in modifying the density dependence of the symmetry energy and affecting the neutron star properties [58][59][60][61]. To examine the influence of the symmetry energy slope L on the liquid-gas phase transition of stellar matter, we adopt two sets of generated models based on the TM1 and IUFSU parametrizations, which was described in our previous work [26].…”