Hadron matter in neutron stars in view of gravitational wave observations

Abstract

In this review we highlight a few physical properties of neutron stars and their theoretical treatment inasmuch as they can be useful for nuclear and particle physicists concerned with matter at finite density (and newly, temperature). Conversely, we lay out some of the hadron physics necessary to test General Relativity with binary mergers including at least one neutron star, in view of the event GW170817: neutron stars and their mergers reach the highest matter densities known, offering access to the matter side of Einstein's equations. In addition to minimum introductory material for those interested in starting research in the field of neutron stars, we dedicate quite some effort to a discussion of the Equation of State of hadron matter in view of gravitational wave developments; we address phase transitions and how the new data may help; we show why transport is expected to be dominated by turbulence instead of diffusion through most if not all of the star, in view of the transport coefficients that have been calculated from microscopic hadron physics; and we relate many of the interesting physics topics in neutron stars to the radius and tidal deformability.

Stellar structure models in modified theories of gravity: Lessons and challenges

“…The models introduced so far can be further generalized to a family of theories encompassing those defined via scalars built out of the (symmetrized) Ricci tensor 44 and its contractions with the metric. This family of metric-affine theories is known as Ricci-Based Gravity theories (RBGs) [57].…”

“…Unfortunately, simultaneous measurements of mass and radius for the same neutron star, which would allow to place constraints upon the EOS, are hard to achieve [30,31]. There are further observational weapons available to this challenge, such as the measurement of neutron stars' moment of inertia [32], as well as the analysis of gravitational wave and gamma ray burst data from binary neutron star mergers [33,34,35,36], which allows to place constraints on tidal deformability [37] (and to infer the moment of inertia [38]), on the EOS at supranuclear densities [39,40,41,42,43] (for a recent review see [44]) and on further properties [45]. Conversely, the combined measurements of radii and tidal deformability can also place constraints on the EOS [46].…”

Interpreting binary neutron star mergers: describing the binary neutron star dynamics, modelling gravitational waveforms, and analyzing detections

“…This is valid for any and (44) is to be substituted for y when evaluating Λ from (42). A number of studies have computed examples of Λ for a wide range of EOS models and delineated interpretations of its physics content such as symmetry energy, phase transitions, and multi-body interactions [16,25,29,30,59,74,86,112,113,121,129,168,[204][205][206]213,223,239,246,254,267,270,282,293,305,307,319,328,329,[343][344][345][346][347][348][349][350][351][353][354][355]362,363,365,378,385,402,…”

Nuclear Physics and Astrophysics Constraints on the High Density Matter Equation of State

“…Oertel et al [3] reviewed comprehensively the status of our knowledge about the EoS of neutron stars (NSs) and core-collapse supernovae (CCSN) before the observation of gravitational waves (GW), detailing many theoretical methods and astrophysical and terrestrial data needed for constructing an EoS model and constraining its parameters. A more recent review [4], focussed on a wide range of aspects of the GW observation, and related them to a hybrid EoS, built on the chiral effective field theory (χEFT) at low density and the perturbative QCD (pQCD) at high densities. The recent status of the research of the EoS of neutron stars can be found in [5].…”