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

TL;DR

This paper investigates how the slope of the symmetry energy influences neutron star properties across different models, highlighting the potential of the direct URCA process threshold to constrain the symmetry energy slope.

Contribution

It systematically analyzes the model dependence of symmetry energy slope effects on neutron star characteristics, introducing a new approach to constrain the slope using the direct URCA process.

Findings

The tidal parameter varies with the slope depending on the model.

Maximum L for direct URCA process is between 79 and 86 MeV.

The minimum mass for direct URCA process is sensitive to the symmetry energy slope.

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.