Role of the symmetry energy slope in neutron stars: exploring the model-dependency

Abstract

Using six different parametrizations of the quantum hadrodynamics (one of which is original), I study how different values of the symmetry energy slope ($L)$ affect some microscopic and macroscopic properties of neutron stars, such as the proton fraction, the maximum mass, the radius of the canonical 1.4$M_\odot$ star and its dimensionless tidal parameter $\Lambda$. I show that while most quantities present the same qualitative results, the tidal parameter can increase or decrease with the slope, depending on the model. Moreover, special attention is given to the minimum mass that enables the direct URCA process to occur in neutron stars' interiors ($M_{DU})$. Assuming the weak constraint $M_{DU}~>~1.35M_\odot$, we see that the maximum value of $L$ that satisfies it lies between 79 and 86 MeV. A range of only 7 MeV. Therefore, $M_{DU}$ is an easy way to impose upper bounds to the slope.