Speed of sound and quark confinement inside neutron stars

TL;DR

This paper investigates the equation of state of dense matter inside neutron stars using a hybrid quark-meson-nucleon model, highlighting the role of confinement in explaining observed neutron star properties.

Contribution

It introduces a unified hadron-quark matter model with a dynamical confinement mechanism to better understand neutron star observations.

Findings

Speed of sound likely exceeds the conformal limit in neutron stars.

Dynamical confinement significantly influences the equation of state.

Model can accommodate 2 solar mass neutron stars.

Abstract

Several observations of high-mass neutron stars (NSs), as well as the first historic detection of the binary neutron star merger GW170817, have delivered stringent constraints on the equation of state (EoS) of cold and dense matter. Recent studies suggest that, in order to simultaneously accommodate a $2M_\odot$ NS and the upper limit on the compactness, the pressure has to swiftly increase with density and the corresponding speed of sound likely exceeds the conformal limit. In this work, we employ a unified description of hadron-quark matter, the hybrid quark-meson-nucleon (QMN) model, to investigate the EoS under NS conditions. We show that the dynamical confining mechanism of the model plays an important role in explaining the observed properties of NSs.