Confronting GW190814 with hyperonization in dense matter and hypernuclear compact stars

We investigate strongly interacting dense matter and neutron stars using a flavor-SU(3) approach based on a nonlinear realization of chiral symmetry. We study chiral symmetry restoration and the equation of state of stellar matter and determine neutron star properties using different sets of degrees of freedom. Finally, we include quarks in the model approach. We show the resulting phase diagram as well as hybrid star solutions for this model.

Download Full-text

Strange matter in compact stars

EPJ Web of Conferences ◽

10.1051/epjconf/201817108001 ◽

2018 ◽

Vol 171 ◽

pp. 08001 ◽

Cited By ~ 3

Author(s):

Thomas Klähn ◽

David B. Blaschke

Keyword(s):

Quark Matter ◽

Strange Quark ◽

Chiral Symmetry Breaking ◽

Dense Matter ◽

Strange Quark Matter ◽

Compact Stars ◽

Hadronic Matter ◽

Model Description ◽

Severe Problem ◽

Strange Matter

We discuss possible scenarios for the existence of strange matter in compact stars. The appearance of hyperons leads to a hyperon puzzle in ab-initio approaches based on effective baryon-baryon potentials but is not a severe problem in relativistic mean field models. In general, the puzzle can be resolved in a natural way if hadronic matter gets stiffened at supersaturation densities, an effect based on the quark Pauli quenching between hadrons. We explain the conflict between the necessity to implement dynamical chiral symmetry breaking into a model description and the conditions for the appearance of absolutely stable strange quark matter that require both, approximately masslessness of quarks and a mechanism of confinement. The role of strangeness in compact stars (hadronic or quark matter realizations) remains unsettled. It is not excluded that strangeness plays no role in compact stars at all. To answer the question whether the case of absolutely stable strange quark matter can be excluded on theoretical grounds requires an understanding of dense matter that we have not yet reached.

Download Full-text

Dense Matter For Compact Stars

Chiral Nuclear Dynamics II ◽

10.1142/9789812814746_0010 ◽

2008 ◽

pp. 289-315

Keyword(s):

Dense Matter ◽

Compact Stars

Download Full-text

H-cluster stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312024416 ◽

2012 ◽

Vol 8 (S291) ◽

pp. 435-437

Author(s):

X. Y. Lai ◽

R. X. Xu

Keyword(s):

Low Temperature ◽

Experimental Evidence ◽

Lattice Qcd ◽

Dense Matter ◽

Experimental Tests ◽

Degree Of Freedom ◽

Compact Stars ◽

Maximum Mass ◽

Cold Dense Matter ◽

Stiffening Effect

AbstractThe study of dense matter at ultra-high density has a very long history, which is meaningful for us to understand not only cosmic events in extreme circumstances but also fundamental laws of physics. In compact stars at only a few nuclear densities but low temperature, quarks could be interacting strongly with each other. That might produce quarks grouped in clusters, although the hypothetical quark-clusters in cold dense matter have not been confirmed due to the lack of both theoretical and experimental evidence. A so-called H-cluster matter is proposed in this paper as the nature of dense matter in reality.Motivated by recent lattice QCD simulations of the H-dibaryons (with structure uuddss), we are therefore considering here a possible kind of quark-clusters, H-clusters, that could emerge inside compact stars during their initial cooling, as the dominant components inside (the degree of freedom could then be H-clusters there). We study the stars composed of H-clusters, i.e., H-cluster stars, and derive the dependence of their maximum mass on the in-medium stiffening effect, showing that the maximum mass could be well above 2 M⊙ as observed and that the resultant mass-radius relation fits the measurement of the rapid burster under reasonable parameters. Besides a general understanding of different manifestations of compact stars, we expect further observational and experimental tests for the H-cluster stars in the future.

Download Full-text

QUARK-CLUSTER STARS: HINTS FROM THE SURFACE

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512005855 ◽

2012 ◽

Vol 10 ◽

pp. 137-146

Author(s):

SHI DAI ◽

RENXIN XU

Keyword(s):

Dense Matter ◽

Compact Stars ◽

Cluster Star ◽

Cluster Phase ◽

Vacuum Gaps ◽

Cold Dense Matter ◽

Star Surface ◽

Absorption Features ◽

Bare Surface ◽

Contamination Problem

The matter inside pulsar-like compact stars could be in a quark-cluster phase since in cold dense matter at a few nuclear densities (ρ ~ 2 - 10ρ0), quarks could be coupled still very strongly and condensate in position space to form quark clusters. Quark-cluster stars are chromatically confined and could initially be bare, therefore the surface properties of quark-cluster stars would be quite different from that of conventional neutron stars. Some facts indicate that a bare and self-confined surface of pulsar-like compact stars might be necessary in order to naturally understand different observational manifestations. On one hand, as for explaining the drifting sub-pulse phenomena, the binding energy of particles on pulsar surface should be high enough to produce vacuum gaps, which indicates that pulsar's surface might be strongly self-confined. On the other hand, a bare surface of quark-cluster star can overcome the baryon contamination problem of γ-ray burst as well as promote a successful core-collapse supernova. What is more, the non-atomic thermal spectra of dead pulsars may indicate also a bare surface without atmosphere, and the hydro-cyclotron oscillation of the electron sea above the quark-cluster star surface could be responsible for those absorption features detected. These hints could reflect the property of compact star's surface and possibly the state of condensed matter inside, and then might finally result in identifying quark-cluster stars.

Download Full-text

Dichotomy of Baryons as Quantum Hall Droplets and Skyrmions: Topological Structure of Dense Matter

Symmetry ◽

10.3390/sym13101888 ◽

2021 ◽

Vol 13 (10) ◽

pp. 1888

Author(s):

Yong-Liang Ma ◽

Mannque Rho

Keyword(s):

Field Theory ◽

Nuclear Matter ◽

Effective Field Theory ◽

Topological Structure ◽

Dense Matter ◽

Local Symmetry ◽

Effective Field ◽

Compact Stars ◽

Nonlinear Sigma Model ◽

Baryonic Matter

We review a new development on the possible direct connection between the topological structure of the Nf=1 baryon as a FQH droplet and that of the Nf≥2 baryons (such as nucleons and hyperons) as skyrmions. This development suggests a possible “domain-wall (DW)” structure of compressed baryonic matter at high density expected to be found in the core of massive compact stars. Our theoretical framework is anchored on an effective nuclear effective field theory that incorporates two symmetries either hidden in the vacuum in QCD or emergent from strong nuclear correlations. It presents a basically different, hitherto undiscovered structure of nuclear matter at low as well as high densities. Hidden “genuine dilaton (GD)” symmetry and hidden local symmetry (HLS) gauge-equivalent at low density to nonlinear sigma model capturing chiral symmetry, put together in nuclear effective field theory, are seen to play an increasingly important role in providing hadron–quark duality in baryonic matter. It is argued that the FQH droplets could actually figure essentially in the properties of the vector mesons endowed with HLS near chiral restoration. This strongly motivates incorporating both symmetries in formulating “first-principles” approaches to nuclear dynamics encompassing from the nuclear matter density to the highest density stable in the Universe.

Download Full-text

Tidal deformability and other global parameters of compact stars with strong phase transitions

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833969 ◽

2019 ◽

Vol 622 ◽

pp. A174 ◽

Cited By ~ 24

Author(s):

M. Sieniawska ◽

W. Turczański ◽

M. Bejger ◽

J. L. Zdunik

Keyword(s):

Phase Transition ◽

Phase Transitions ◽

Neutron Star ◽

Neutron Stars ◽

Equations Of State ◽

Dense Matter ◽

Compact Stars ◽

High Mass ◽

Density Jump ◽

Strong Phase

Context. Using parametric equations of state (relativistic polytropes and a simple quark bag model) to model dense-matter phase transitions, we study global, measurable astrophysical parameters of compact stars such as their allowed radii and tidal deformabilities. We also investigate the influence of stiffness of matter before the onset of the phase transitions on the parameters of the possible exotic dense phase. Aims. The aim of our study is to compare the parameter space of the dense matter equation of state permitting phase transitions to a sub-space compatible with current observational constraints such as the maximum observable mass, tidal deformabilities of neutron star mergers, radii of configurations before the onset of the phase transition, and to give predictions for future observations. Methods. We studied solutions of the Tolman-Oppenheimer-Volkoff equations for a flexible set of parametric equations of state, constructed using a realistic description of neutron-star crust (up to the nuclear saturation density), and relativistic polytropes connected by a density-jump phase transition to a simple bag model description of deconfined quark matter. Results. In order to be consistent with recent observations of massive neutron stars, a compact star with a strong high-mass phase transition cannot have a radius smaller than 12 km in the range of masses 1.2 − 1.6 M⊙. We also compare tidal deformabilities of stars with weak and strong phase transitions with the results of the GW170817 neutron star merger. Specifically, we study characteristic phase transition features in the Λ1 − Λ2 relation, and estimate the deviations of our results from the approximate formulæ for Λ∼ − R (M1) and Λ-compactness proposed in the literature. We find constraints on the hybrid equations of state to produce stable neutron stars on the twin branch. For the exemplary equations of state most of the high-mass twins occur for the minimum values of the density jump λ = 1.33 − 1.54; corresponding values of the square of the speed of sound are α = 0.7 − 0.37. We compare results with observations of gravitational waves and with the theoretical causal limit and find that the minimum radius of a twin branch is between 9.5 and 10.5 km, and depends on the phase transition baryon density. For these solutions the phase transition occurs below 0.56 fm−3.

Download Full-text

Exact solutions for compact stars with CFL quark matter

International Journal of Modern Physics D ◽

10.1142/s0218271820500443 ◽

2020 ◽

Vol 29 (07) ◽

pp. 2050044 ◽

Cited By ~ 1

Author(s):

L. S. Rocha ◽

A. Bernardo ◽

M. G. B. De Avellar ◽

J. E. Horvath

Keyword(s):

Exact Solutions ◽

Quark Matter ◽

Dense Matter ◽

Compact Stars ◽

Einstein Field Equations ◽

Field Equations ◽

Strange Matter ◽

Mit Bag Model ◽

Wide Range ◽

The One

The search for the true ground state of the dense matter remains open since Bodmer, Terazawa and others raised the possibility of stable quark matter, boosted by Witten’s strange matter hypothesis in 1984. Within this proposal, the strange matter is assumed to be composed of [Formula: see text] quarks in addition to the usual [Formula: see text]s and [Formula: see text]s, having an energy per baryon lower than the strangeless counterpart, and even lower than that of nuclear matter. In this sense, neutron stars should actually be strange stars. Later work showed that a paired, symmetric in flavor, color-flavor locked (CFL) state would be preferred to the one without any pairing for a wide range of the parameters (gap [Formula: see text], strange quark mass [Formula: see text] and bag constant B). We use an approximate, yet very accurate, CFL equation-of-state (EoS) that generalizes the MIT bag model to obtain two families of exact solutions for the static Einstein Field Equations (EFE) constructing families of anisotropic compact relativistic objects. In this fashion, we provide exact useful solutions directly connected with microphysics.

Download Full-text