Influence of the interactions of scalar mesons on the behavior of the symmetry energy

Symmetry energy behavior of scalar mesons interactions is analyzed within the framework of the standard relativistic mean-field model. Whereas the presence of the $\delta$ meson itself makes the symmetry energy stiffer, the crossing term $\delta \text{−}\sigma$ allows its slope to decrease to the suggested experimental value. Moreover, such controlling of the symmetry energy does not significantly affect the stiffness of the equation of state and acceptable neutron star masses result. Interestingly, for the most plausible value of the symmetry energy slope, the phase transition occurs in the neutron star core.

Figure 1

Slope of symmetry energy $L\left[\mathrm{MeV}\right]$ as a function of $C_{\delta }^2\left[{\mathrm{fm}}^2\right]$ for different $g_{\alpha }$. For negative $g_{\alpha }$ the slope is decreasing.

Figure 2

Symmetry energy $E_{\text{sym}}$ for negative value of $g_{\alpha }$ with respect to various values of $C_{\delta }^2$ for both types of coupling.

Figure 3

The proton fraction and compressibility of beta-equilibrated matter for the quadratic model with various $C_{\delta }^2$.

Figure 4

Effective masses of protons (solid lines) and neutrons (dashed lines) for two values of $C_{\delta }^2$ for quadratic type of coupling.