Investigation of the existence of hybrid stars using Nambu-Jona-Lasinio models

TL;DR

This paper explores the potential existence of hybrid stars with quark matter cores by modifying the NJL model to produce a stiffer equation of state, addressing stability issues in neutron star models.

Contribution

It introduces a vector coupling in the NJL model to stiffen the equation of state, enabling more stable hybrid star configurations with quark matter cores.

Findings

Standard NJL model yields unstable hybrid stars.

Introducing a chemical potential-dependent cutoff does not fully stabilize stars.

Adding a vector coupling stiffens the EoS and improves stability.

Abstract

We investigate the hadron-quark phase transition inside neutron stars and obtain mass-radius relations for hybrid stars. The equation of state for the quark phase using the standard NJL model is too soft leading to an unstable star and suggesting a modification of the NJL model by introducing a momentum cutoff dependent on the chemical potential. However, even in this approach, the instability remains. In order to remedy the instability we suggest the introduction of a vector coupling in the NJL model, which makes the EoS stiffer, reducing the instability. We conclude that the possible existence of quark matter inside the stars require high densities, leading to very compact stars.