Reconciling nuclear and astrophysical constraints

In view of new constraints put forth by recent observations and measurements in the realm of astrophysics and nuclear physics, we update the nonlinear realization of the $\sigma$ model as to reflect such constraints. By doing this, we obtain new equations of state that may be used to describe neutron stars. Such equations of state are obtained by investigating different ways by which the vector mesons self-interact. Furthermore, we also investigate the role played by $\delta$ mesons in the model. As a result, we are able to develop equations of state that are in better agreement with data, such as nuclear compressibility and slope of the symmetry energy at saturation, star masses, radii, and cooling profiles.

Figure 1

Slope of the symmetry energy at saturation as a function of the coupling constant of the $\delta$ meson for different coupling schemes.

Figure 2

Maximum possible star mass as a function of the coupling constant of the $\delta$ meson for different coupling schemes.

Figure 3

Radius of the maximum possible star mass as a function of the coupling constant of the $\delta$ meson for different coupling schemes.

Figure 4

Maximum possible star masses and respective radii for each coupling scheme obtained by varying $g_{\delta }$ from 0 to 15.

Figure 5

Normalized density threshold for the direct Urca process as a function of the coupling constant of the $\delta$ meson for different coupling schemes.

Figure 6

Surface temperature as observed at infinity of neutron stars with $1.4{\mathrm{M}}_{\odot }$ for the parameters described in Table 1.

Figure 7

Same as Fig. 6 but for neutron stars with the maximum possible mass.

Figure 8

Combination of Figs. 6 and 7 with the inclusion of pairing effects. The thermal evolutions of $1.4{\mathrm{M}}_{\odot }$ stars from all parameter sets fall within the dark band. The thermal evolutions of the maximum mass stars are indicated by individual curves.