Special Issue "Compact Stars in the QCD Phase Diagram"

A special issue of Universe (ISSN 2218-1997).

Deadline for manuscript submissions: closed (6 January 2018)

Special Issue Editors

Guest Editor
Prof. Dr. David Blaschke

1 Institute of Theoretical Physics, University of Wroclaw, 50-204 Wroclaw, Poland
2 Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia
3 National Research Nuclear University (MEPhI), 115409 Moscow, Russia
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Guest Editor
Mr. Alexander Ayriyan

Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Moscow Region, Russia
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Guest Editor
Dr. Alexandra Friesen

Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Moscow Region, Russia
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Guest Editor
Dr. Hovik Grigorian

1 Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Moscow Region, Russia
2 Yerevan State University, Alek Manyukyan 1, 0025 Yerevan, Republic of Armenia
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Special Issue Information

Dear Colleagues,

This special issue is dedicated to the conference: Compact Stars in the QCD Phase Diagram VI http://theor.jinr.ru/~hmec16/csqcd6/.

This special issue will cover the following main topics:   

- QCD phase diagram for HIC vs. astrophysics   

- Quark deconfinement in HIC vs. supernovae, neutron stars and their mergers

- Strangeness in HIC and in compact stars   

- Equation of state and QCD phase transitions

Prof. Dr. David Blaschke
Dr. Hovik Grigorian
Mr. Alexander Ayriyan
Dr. Alexandra Friesen
Guest Editors

Manuscript Submission Information

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Published Papers (9 papers)

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Open AccessArticle Prospects of Constraining the Dense Matter Equation of State from Timing Analysis of Pulsars in Double Neutron Star Binaries: The Cases of PSR J0737 ‒ 3039A and PSR J1757 ‒ 1854
Universe 2018, 4(2), 36; doi:10.3390/universe4020036
Received: 4 December 2017 / Revised: 8 February 2018 / Accepted: 8 February 2018 / Published: 12 February 2018
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Abstract
The Lense-Thirring effect from spinning neutron stars in double neutron star binaries contributes to the periastron advance of the orbit. This extra term involves the moment of inertia of the neutron stars. The moment of inertia, on the other hand, depends on the
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The Lense-Thirring effect from spinning neutron stars in double neutron star binaries contributes to the periastron advance of the orbit. This extra term involves the moment of inertia of the neutron stars. The moment of inertia, on the other hand, depends on the mass and spin of the neutron star, as well as the equation of state of the matter. If at least one member of the double neutron star binary (better the faster one) is a radio pulsar, then accurate timing analysis might lead to the estimation of the contribution of the Lense-Thirring effect to the periastron advance, which will lead to the measurement of the moment of inertia of the pulsar. The combination of the knowledge on the values of the moment of inertia, the mass and the spin of the pulsar will give a new constraint on the equation of state. Pulsars in double neutron star binaries are the best for this purpose as short orbits and moderately high eccentricities make the Lense-Thirring effect substantial, whereas tidal effects are negligible (unlike pulsars with main sequence or white-dwarf binaries). The most promising pulsars are PSR J0737 − 3039A and PSR J1757 − 1854. The spin-precession of pulsars due to the misalignment between the spin and the orbital angular momentum vectors affect the contribution of the Lense-Thirring effect to the periastron advance. This effect has been explored for both PSR J0737 − 3039A and PSR J1757 − 1854, and as the misalignment angles for both of these pulsars are small, the variation in the Lense-Thirring term is not much. However, to extract the Lense-Thirring effect from the observed rate of the periastron advance, more accurate timing solutions including precise proper motion and distance measurements are essential. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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Open AccessFeature PaperArticle A Phenomenological Equation of State of Strongly Interacting Matter with First-Order Phase Transitions and Critical Points
Universe 2018, 4(2), 32; doi:10.3390/universe4020032
Received: 12 December 2017 / Revised: 8 January 2018 / Accepted: 29 January 2018 / Published: 9 February 2018
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Abstract
An extension of the relativistic density functional approach to the equation of state for strongly interacting matter is suggested that generalizes a recently developed modified excluded-volume mechanism to the case of temperature- and density-dependent available-volume fractions. A parametrization of this dependence is presented
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An extension of the relativistic density functional approach to the equation of state for strongly interacting matter is suggested that generalizes a recently developed modified excluded-volume mechanism to the case of temperature- and density-dependent available-volume fractions. A parametrization of this dependence is presented for which, at low temperatures and suprasaturation densities, a first-order phase transition is obtained. It changes for increasing temperatures to a crossover transition via a critical endpoint. This provides a benchmark case for studies of the role of such a point in hydrodynamic simulations of ultrarelativistic heavy-ion collisions. The approach is thermodynamically consistent and extendable to finite isospin asymmetries that are relevant for simulations of neutron stars, their mergers, and core-collapse supernova explosions. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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Open AccessArticle Vector-Interaction-Enhanced Bag Model
Universe 2018, 4(2), 30; doi:10.3390/universe4020030
Received: 4 December 2017 / Revised: 23 January 2018 / Accepted: 24 January 2018 / Published: 8 February 2018
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Abstract
A commonly applied quark matter model in astrophysics is the thermodynamic bag model (tdBAG). The original MIT bag model approximates the effect of quark confinement, but does not explicitly account for the breaking of chiral symmetry, an important property of Quantum Chromodynamics (QCD).
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A commonly applied quark matter model in astrophysics is the thermodynamic bag model (tdBAG). The original MIT bag model approximates the effect of quark confinement, but does not explicitly account for the breaking of chiral symmetry, an important property of Quantum Chromodynamics (QCD). It further ignores vector repulsion. The vector-interaction-enhanced bag model (vBag) improves the tdBAG approach by accounting for both dynamical chiral symmetry breaking and repulsive vector interactions. The latter is of particular importance to studies of dense matter in beta-equilibriumto explain the two solar mass maximum mass constraint for neutron stars. The model is motivated by analyses of QCD based Dyson-Schwinger equations (DSE), assuming a simple quark-quark contact interaction. Here, we focus on the study of hybrid neutron star properties resulting from the application of vBag and will discuss possible extensions. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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Open AccessArticle On Cooling of Neutron Stars with a Stiff Equation of State Including Hyperons
Universe 2018, 4(2), 29; doi:10.3390/universe4020029
Received: 29 November 2017 / Revised: 14 January 2018 / Accepted: 15 January 2018 / Published: 8 February 2018
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Abstract
Exploiting a stiff equation of state of the relativistic mean-field model MKVORHϕ with σ-scaled hadron effective masses and couplings, including hyperons, we demonstrate that the existing neutron-star cooling data can be appropriately described within “the nuclear medium cooling scenario” under the
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Exploiting a stiff equation of state of the relativistic mean-field model MKVORH ϕ with σ -scaled hadron effective masses and couplings, including hyperons, we demonstrate that the existing neutron-star cooling data can be appropriately described within “the nuclear medium cooling scenario” under the assumption that different sources have different masses. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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Open AccessConference Report Cracking Strange Stars by Torsional Oscillations
Universe 2018, 4(2), 41; doi:10.3390/universe4020041 (registering DOI)
Received: 8 December 2017 / Revised: 19 January 2018 / Accepted: 29 January 2018 / Published: 17 February 2018
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Abstract
Strange stars are one of the possible compact stellar objects formed in the core collapse of supernovae. These hypothetical stars are made by deconfined quark matter and are selfbound. In our study, we focus on the torsional oscillations of a non bare strange
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Strange stars are one of the possible compact stellar objects formed in the core collapse of supernovae. These hypothetical stars are made by deconfined quark matter and are selfbound. In our study, we focus on the torsional oscillations of a non bare strange star, i.e., a strange star with a thin crust made of standard nuclear matter. We construct a theoretical model assuming that the inner parts of the star are in two different phases, namely the color flavour locked phase and the crystalline colour superconducting phase. Since the latter phase is rigid, with a large shear modulus, it corresponds to a first stellar crust. Above this crust a second small crust made by standard nuclear matter is suspended thanks to a strong electromagnetic dipolar moment. We focus on the electromagnetically coupled oscillations of the two stellar crusts. Notably, we find that if a small fraction of the energy of a glitch event like a typical Vela glitch is conveyed in torsional oscillations, the small nuclear crust will likely break. This is due to the fact that in this model the maximum stress, due to torsional oscillations, is likely located near the star surface. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
Open AccessConference Report Strangeness Production in Nucleus-Nucleus Collisions at SIS Energies
Universe 2018, 4(2), 37; doi:10.3390/universe4020037
Received: 30 November 2017 / Revised: 8 January 2018 / Accepted: 15 January 2018 / Published: 13 February 2018
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Abstract
Simulating Many Accelerated Strongly-interacting Hadrons (SMASH) is a new hadronic transport approach designed to describe the non-equilibrium evolution of heavy-ion collisions. The production of strange particles in such systems is enhanced compared to elementary reactions (Blume and Markert 2011), providing an interesting signal
[...] Read more.
Simulating Many Accelerated Strongly-interacting Hadrons (SMASH) is a new hadronic transport approach designed to describe the non-equilibrium evolution of heavy-ion collisions. The production of strange particles in such systems is enhanced compared to elementary reactions (Blume and Markert 2011), providing an interesting signal to study. Two different strangeness production mechanisms are discussed: one based on resonances and another using forced canonical thermalization. Comparisons to experimental data from elementary collisions are shown. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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Open AccessConference Report From Heavy-Ion Collisions to Compact Stars: Equation of State and Relevance of the System Size
Universe 2018, 4(1), 14; doi:10.3390/universe4010014
Received: 30 November 2017 / Revised: 11 January 2018 / Accepted: 16 January 2018 / Published: 23 January 2018
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Abstract
In this article, we start by presenting state-of-the-art methods allowing us to compute moments related to the globally conserved baryon number, by means of first principle resummed perturbative frameworks. We focus on such quantities for they convey important properties of the finite temperature
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In this article, we start by presenting state-of-the-art methods allowing us to compute moments related to the globally conserved baryon number, by means of first principle resummed perturbative frameworks. We focus on such quantities for they convey important properties of the finite temperature and density equation of state, being particularly sensitive to changes in the degrees of freedom across the quark-hadron phase transition. We thus present various number susceptibilities along with the corresponding results as obtained by lattice quantum chromodynamics collaborations, and comment on their comparison. Next, omitting the importance of coupling corrections and considering a zero-density toy model for the sake of argument, we focus on corrections due to the small size of heavy-ion collision systems, by means of spatial compactifications. Briefly motivating the relevance of finite size effects in heavy-ion physics, in opposition to the compact star physics, we present a few preliminary thermodynamic results together with the speed of sound for certain finite size relativistic quantum systems at very high temperature. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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Open AccessConference Report Charged ρ Meson Condensate in Neutron Stars within RMF Models
Universe 2018, 4(1), 1; doi:10.3390/universe4010001
Received: 30 November 2017 / Revised: 12 December 2017 / Accepted: 12 December 2017 / Published: 26 December 2017
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Abstract
Knowledge of the equation of state (EoS) of cold and dense baryonic matter is essential for the description of properties of neutron stars (NSs). With an increase of the density, new baryon species can appear in NS matter, as well as various meson
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Knowledge of the equation of state (EoS) of cold and dense baryonic matter is essential for the description of properties of neutron stars (NSs). With an increase of the density, new baryon species can appear in NS matter, as well as various meson condensates. In previous works, we developed relativistic mean-field (RMF) models with hyperons and Δ -isobars, which passed the majority of known experimental constraints, including the existence of a 2 M neutron star. In this contribution, we present results of the inclusion of ρ -meson condensation into these models. We have shown that, in one class of the models (so-called KVOR-based models, in which the additional stiffening procedure is introduced in the isoscalar sector), the condensation gives only a small contribution to the EoS. In another class of the models (MKVOR-based models with additional stiffening in isovector sector), the condensation can lead to a first-order phase transition and a substantial decrease of the NS mass. Nevertheless, in all resulting models, the condensation does not spoil the description of the experimental constraints. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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Open AccessConference Report Directed Flow in Heavy-Ion Collisions and Its Implications for Astrophysics
Universe 2017, 3(4), 79; doi:10.3390/universe3040079
Received: 17 October 2017 / Revised: 6 November 2017 / Accepted: 7 November 2017 / Published: 14 November 2017
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Abstract
Analysis of directed flow (v1) of protons, antiprotons and pions in heavy-ion collisions is performed in the range of collision energies sNN = 2.7–39 GeV. Simulations have been done within a three-fluid model employing a purely hadronic equation
[...] Read more.
Analysis of directed flow ( v 1 ) of protons, antiprotons and pions in heavy-ion collisions is performed in the range of collision energies s N N = 2.7–39 GeV. Simulations have been done within a three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS with deconfinement transitions: a first-order phase transition and a smooth crossover transition. The crossover EoS is unambiguously preferable for the description of experimental data at lower collision energies s N N 20 Gev. However, at higher collision energies s N N 20 Gev. the purely hadronic EoS again becomes advantageous. This indicates that the deconfinement EoS in the quark-gluon sector should be stiffer at high baryon densities than those used in the calculation. The latter finding is in agreement with that discussed in astrophysics in connection with existence of hybrid stars with masses up to about two solar masses. Full article
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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