scholarly journals COMPACT STARS IN HADRON AND QUARK-HADRON MODELS

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1455-1462 ◽  
Author(s):  
S. SCHRAMM ◽  
V. A. DEXHEIMER
Keyword(s):  
Phase Diagram ◽  
Neutron Star ◽  
Chiral Symmetry ◽  
Degrees Of Freedom ◽  
Dense Matter ◽  
Compact Stars ◽  
Chiral Symmetry Restoration ◽  
Hybrid Star ◽  
Nonlinear Realization ◽  
Model Approach

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.

scholarly journals Constraint on Hybrid Stars with Gravitational Wave Events

Universe ◽  
2020 ◽  
Vol 6 (12) ◽  
pp. 231
Author(s):  
Kilar Zhang ◽  
Feng-Li Lin
Keyword(s):  
Black Hole ◽  
Dark Matter ◽  
Neutron Star ◽  
Gravitational Wave ◽  
Compact Object ◽  
Compact Objects ◽  
Compact Stars ◽  
Hybrid Star ◽  
Hybrid Stars

Motivated by the recent discoveries of compact objects from LIGO/Virgo observations, we study the possibility of identifying some of these objects as compact stars made of dark matter called dark stars, or the mix of dark and nuclear matters called hybrid stars. In particular, in GW190814, a new compact object with 2.6 M⊙ is reported. This could be the lightest black hole, the heaviest neutron star, and a dark or hybrid star. In this work, we extend the discussion on the interpretations of the recent LIGO/Virgo events as hybrid stars made of various self-interacting dark matter (SIDM) in the isotropic limit. We pay particular attention to the saddle instability of the hybrid stars which will constrain the possible SIDM models.

scholarly journals Aspects on Effective Theories and the QCD Transition

Symmetry ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 945
Author(s):  
Angel Gómez Nicola
Keyword(s):  
Phase Diagram ◽  
Perturbation Theory ◽  
Quantum Chromodynamics ◽  
Chiral Symmetry ◽  
Current Knowledge ◽  
Chiral Symmetry Restoration ◽  
Chiral Perturbation ◽  
Ward Identities ◽  
Hadron Gas ◽  
Effective Theories

We review recent advances in the understanding of the Quantum Chromodynamics (QCD) transition and its nature, paying special attention to the analysis of chiral symmetry restoration within different approaches based on effective theories. After presenting some of the main aspects of the current knowledge of the phase diagram from the theoretical, experimental and lattice sides, we discuss some recent problems where approaches relying on effective theories have been particularly useful. In particular, the combination of ideas such as Chiral Perturbation Theory, unitarity and Ward Identities allows us to describe successfully several observables of interest. This is particularly relevant for quantities expected to be dominated by the light meson components of the hadron gas such as the scalar and topological susceptibilities. In addition, ward identities and effective Lagrangians provide systematic results regarding chiral and U ( 1 ) A partner degeneration properties which are of great importance for the interplay between those two transitions and the nature of chiral symmetry restoration. Special attention is paid to the connection of this theoretical framework with lattice simulations.

THE ROLE OF SELF-COUPLINGS OF SCALAR MESONS IN NEUTRON STAR MATTER

2002 ◽  
Vol 17 (21) ◽  
pp. 1335-1344 ◽  
Author(s):  
S. S. POCHA ◽  
A. R. TAURINES ◽  
C. A. Z. VASCONCELLOS ◽  
M. B. PINTO ◽  
M. DILLIG
Keyword(s):  
Neutron Star ◽  
Nuclear Matter ◽  
Degrees Of Freedom ◽  
Scalar Meson ◽  
Dense Matter ◽  
Meson Field ◽  
Static Properties ◽  
Hartree Approximation ◽  
Scalar Meson Field

The influence of nonlinear cubic and quartic self-couplings of the scalar meson field in nuclear matter is investigated. In summing the leading tadpole corrections for the Dirac-vacuum, we compare two approaches, the modified relativistic Hartree approximation, applied to the Walecka model, and the relativistic Hartree approximation, employed to the nonlinear model, respectively. These two approaches render similar expressions for the equation of state of nuclear matter up to the fifth order in the scalar meson field. We find that, by exploring the parameter dependence of the two models, they yield similar results for the bulk static properties of nuclear matter. However, increasing the baryon density the two models start to deviate significantly, such as in the predictions for the maximal mass of a neutron star or in the role of hyperon degrees of freedom in dense matter. The results indicate that with increasing density, scalar meson self-couplings beyond the fourth order seem to play a significant role.

scholarly journals QCD phase diagram from chiral symmetry restoration: analytic approach at high and low temperature using the Linear Sigma Model with Quarks

2018 ◽  
Vol 64 (3) ◽  
pp. 302 ◽  
Author(s):  
Luis Hernandez ◽  
Alejandro Ayala ◽  
Saul Hernandez-Ortiz
Keyword(s):  
Phase Diagram ◽  
Chiral Symmetry ◽  
Low Temperatures ◽  
Sigma Model ◽  
Chemical Potential ◽  
Linear Sigma Model ◽  
Transition Line ◽  
Chiral Symmetry Restoration ◽  
Qcd Phase Diagram ◽  
End Point

We use the linear sigma model with quarks to study the QCD phase diagram from the point of view of chiral symmetry restoration. We compute the leading order effective potential for high and low temperatures and finite quark chemical potential, up to the contribution of the ring diagrams to account for the plasma screening effects. We fix the values of the model couplings using physical values for the input parameters such as  the vacuum pion and sigma masses, the critical temperature at vanishing quark chemical potential and the conjectured end point value of the baryon chemical potential of the transition line at vanishing temperature. We find that the critical end point (CEP) is located at low temperatures and high quark chemical potentials $(\mu^{\text{CEP}}>320\ {\mbox{MeV}},T^{\text{CEP}}<40\ {\mbox{MeV}})$.

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

2019 ◽  
Vol 622 ◽  
pp. A174 ◽  
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.

scholarly journals Neutron-Star-Merger Equation of State

Universe ◽  
2019 ◽  
Vol 5 (5) ◽  
pp. 129 ◽  
Author(s):  
Veronica Dexheimer ◽  
Constantinos Constantinou ◽  
Elias R. Most ◽  
L. Jens Papenfort ◽  
Matthias Hanauske ◽  
...  
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Temperature Effects ◽  
Degrees Of Freedom ◽  
Mean Field ◽  
Dense Matter ◽  
Light Nuclei ◽  
Excluded Volume ◽  
Small Admixture ◽  
Consistent Manner

In this work, we discuss the dense matter equation of state (EOS) for the extreme range of conditions encountered in neutron stars and their mergers. The calculation of the properties of such an EOS involves modeling different degrees of freedom (such as nuclei, nucleons, hyperons, and quarks), taking into account different symmetries, and including finite density and temperature effects in a thermodynamically consistent manner. We begin by addressing subnuclear matter consisting of nucleons and a small admixture of light nuclei in the context of the excluded volume approach. We then turn our attention to supranuclear homogeneous matter as described by the Chiral Mean Field (CMF) formalism. Finally, we present results from realistic neutron-star-merger simulations performed using the CMF model that predict signatures for deconfinement to quark matter in gravitational wave signals.

scholarly journals LOW-MOMENTUM PION ENHANCEMENT INDUCED BY CHIRAL SYMMETRY RESTORATION

2004 ◽  
Vol 19 (03) ◽  
pp. 341-346
Author(s):  
PENGFEI ZHUANG
Keyword(s):  
Phase Transition ◽  
Chiral Symmetry ◽  
Finite Temperature ◽  
Pion Production ◽  
Dense Matter ◽  
Chiral Symmetry Restoration ◽  
Chiral Phase ◽  
Chiral Phase Transition ◽  
Symmetric Phase

The thermal and nonthermal pion production by sigma decay and its relation with chiral symmetry restoration in a hot and dense matter are investigated. The nonthermal decay into pions of sigma mesons which are popularly produced in chiral symmetric phase leads to a low-momentum pion enhancement as a possible signature of chiral phase transition at finite temperature and density.

scholarly journals Estimating the Variation of Neutron Star Observables by Dense Symmetric Nuclear Matter Properties

Universe ◽  
2019 ◽  
Vol 5 (6) ◽  
pp. 153 ◽  
Author(s):  
Péter Pósfay ◽  
Gergely Gábor Barnaföldi ◽  
Antal Jakovác
Keyword(s):  
Neutron Star ◽  
Nuclear Matter ◽  
Dense Matter ◽  
Effective Field ◽  
Symmetric Nuclear Matter ◽  
The Other ◽  
Compact Stars ◽  
Field Theories ◽  
Star Model ◽  
Dense Nuclear Matter

Recent multi-channel astrophysics observations and the soon-to-be published new measured electromagnetic and gravitation data provide information on the inner structure of the compact stars. These macroscopic observations can significantly increase our knowledge on the neutron star enteriors, providing constraints on the microscopic physical properties. On the other hand, due to the masquarade problem, there are still uncertainties on the various nuclear-matter models and their parameters as well. Calculating the properties of the dense nuclear matter, effective field theories are the most widely-used tools. However, the values of the microscopical parameters need to be set consistently to the nuclear and astrophysical measurements. In this work, we investigate how uncertainties are induced by the variation of the microscopical parameters. We use a symmetric nuclear matter in an extended σ - ω model to see the influence of the nuclear matter parameters. We calculate the dense matter equation of state and give the mass-radius diagram for a simplistic neutron star model. We present that the Landau mass and compressibility modulus of the nuclear matter have definite linear relation to the maximum mass of a Schwarzschild neutron star.

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