Toward a unified equation of state for multi-messenger astronomy

Abstract

Aims. We aim to present a first step in developing a benchmark equation-of-state (EoS) model for multi-messenger astronomy that unifies the thermodynamics of quark and hadronic degrees of freedom. Methods. A Lagrangian approach to the thermodynamic potential of quark-meson-nucleon matter was used. In this approach, dynamical chiral-symmetry breaking is described by the scalar mean-field dynamics coupled to quarks and nucleons and their chiral partners, whereby its restoration occurs in the hadronic phase by parity doubling, as well as in the quark phase. Quark confinement was achieved by an auxiliary scalar field that parametrizes a dynamical infrared cut-off in the quark sector, serving as an ultraviolet cut-off for the nucleonic phase space. The gap equations were solved for the isospin-symmetric case, as well as for neutron star (NS) conditions. We also calculated the mass-radius (MR) relation of NSs and their tidal deformability (TD) parameter. Results. The obtained EoS is in accordance with nuclear matter properties at saturation density and with the flow constraint from heavy ion collision experiments. For isospin-asymmetric matter, a sequential occurrence of light quark flavors is obtained, allowing for a mixed phase of chirally-symmetric nucleonic matter with deconfined down quarks. The MR relations and TDs for compact stars fulfill the constraints from the latest astrophysical observations for PSR J0740+6620, PSR J0030+0451, and the NS merger GW170817, whereby the tension between the maximum mass and compactness constraints rather uniquely fixes the model parameters. The model predicts the existence of stars with a core of chirally restored but purely hadronic (confined) matter for masses beyond 1.8 M⊙. Stars with pure-quark matter cores are found to be unstable against the gravitational collapse. This instability is shifted to even higher densities if repulsive interactions between quarks are included.

Unified Quark–Hadron EoS and Critical Endpoint in the QCD Phase Diagram

“…This is a remarkable result for such a simple unified model of quark-nucleon matter. In a parallel attempt at a unified description of quark-nuclear matter applied in [29] to Astrophysics of compact stars, the aspect of nucleonic parity doubling at the chiral restoration transition has been included and leads to another corner of first-order phase transition at low temperatures in the QCD phase diagram.…”

“…This is a remarkable result for such a simple unified model of quark-nucleon matter. In a parallel attempt at a unified description of quark-nuclear matter applied in [29] to Astrophysics of compact stars, the aspect of nucleonic parity Fig. 2.…”

Interplay between chiral dynamics and repulsive interactions in hot hadronic matter

“…Such properties of the chiral partners can be described in the framework of the parity doublet model [11,12,13]. The model has been applied to hot and dense hadronic matter, neutron stars, as well as the vacuum phenomenology of QCD (see, e.g., [14,15,16,17,18,19,20,21,22,23,24,25,26]).…”

Maximum mass of compact stars from gravitational wave events with finite-temperature equations of state

“…Among the events in the last category, the GW170817 event is currently outstanding, since it has been possible to measure not only the neutron star tidal deformability during inspiral, but also electromagnetic counterparts [12,13]. As a result, the GW170817 event has triggered a large number of works which are aimed at constraining neutron star properties and the EoS, either from the analysis of the tidal deformability alone (see for example [14][15][16][17][18][19][20][21][22]), or from a combination of tidal deformability and the electromagnetic signal [23][24][25][26][27][28][29][30]. Including the information from the electromagnetic signal requires as an input numerical modeling of the merger process, which introduces additional uncertain-ties but, at the same time, broadens the experimental base of the analysis.…”