Speed of sound and quark confinement inside 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 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.

Excluded-volume model for quarkyonic matter II: Three-flavor shell-like distribution of baryons in phase space

“…[c 2 s ] 0.7) for the strong (weak) correlation assumption for the confined quark momenta. Although the Quarkyonic matter would not have the evident first-order phase transition nature, the EoS looks similar to the result of the previously reported works where the phase transition is implied [34,35,61]. Beyond the saturation moments of the quark Fermi sea, the stiffness of EoS becomes moderate and converges to the conformal limit at the high density regime.…”

“…The multiple peaks and the scale of sound velocity is compatible with the results from Ref. [34,35,61]. As discussed in Sec.…”

“…This evolution look similar to the results presented in Refs. [34,35] where the first-order phase transition is implied via the hybrid quark-meson-nucleon model [32][33][34][35]. However, as one can find in the sound velocity plots (Figs.…”

“…The resulting stellar mass number and evolution tendency are comparable with the results of Refs. [25,34,35,61], although the fundamental physical principle is different from the Quarkyonic matter concept.…”

Hybrid quark-hadron equation of state for multi-messenger astronomy

“…In this contribution, we briefly present our recent studies based on the hybrid quark-meson-nucleon (QMN) model [8,9,10,11,12,13]. The model has the characteristic feature that the chiral symmetry is restored within the hadronic phase by lifting the mass splitting between chiral partner states, before the quark deconfinement takes place.…”