High-Density behavior of symmetry energy and speed of sound in the dense matter within an effective chiral model

With an effective chiral model, we investigate how the mesonic cross couplings $\sigma-\rho$ and $\omega-\rho$ affect the density content of the symmetry energy and its higher-order slope parameters. Earlier mentioned cross-couplings are crucial to controlling the density content of symmetry energy. For this purpose, we did a case study for different values of the symmetry energy $J_1$, defined at density 0.1 fm$^{-3}$ in the range (23.4 - 25.2) for a fixed value of the slope of the symmetry energy $L_0 = 60$ MeV at saturation density and investigate its effect on the higher-order coefficients and their influence on the underlying equation of state. We found that the model with $J_1= 24.6$ MeV is more favorable with the pure neutron matter (PNM) constraints obtained from $\chi$EFT calculations. In addition, we show that all of our models predict a monotonically increasing speed of sound up to four times the saturation density. The speed of sound decreases/saturates above that point and approaches the conformal limit approximately $\sqrt{1/3}~c$ at the center of the maximum mass star.
Comment: The manuscript contain 9 figures and 2 tables