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Dense QCD and neutron stars
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Dense QCD and neutron stars

A special issue of Particles (ISSN 2571-712X).

Deadline for manuscript submissions: closed (30 June 2019) | Viewed by 13429

Special Issue Editor

Dr. Andreas Schmitt

E-Mail Website
Guest Editor
Mathematical Sciences and STAG Research Centre, University of Southampton, Southampton SO17 1BJ, United Kingdom
Interests: quantum chromodynamics; neutron stars; gauge/string duality; superfluidity

Special Issue Information

Dear Colleagues,

This Special Issue intends to collect modern research articles in the field of neutron star physics, broadly defined. The goal is to bring together new ideas and results that advance our understanding of matter at large baryon densities and of the properties and composition of neutron stars. Articles may have a theoretical emphasis or may be centred around phenomenological aspects, or combine both. Highly encouraged are for instance contributions to the QCD phase diagram, addressing questions such as chiral and deconfinement transitions at high density, quark–hadron continuity, inhomogeneous chiral condensates, or color superconducitvity. This includes various possible theoretical approaches, which may range from perturbative QCD and the sign problem of lattice QCD to effective theories, phenomenological models, and the gauge/gravity correspondence. Particularly important are open theoretical questions with direct relevance to astrophysical observations such as the equation of state of neutron star matter, multi-fluid hydrodynamics and dissipative properties of dense matter, or rotational vortices and magnetic flux tubes. Purely phenomenological studies are also highly welcome, dealing for instance with the neutron star crust, the emission of gravitational waves from mergers and isolated neutron stars, the evolution of the magnetic field in a neutron star, or aspects of the mass/radius relation.

Dr. Andreas Schmitt
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Particles is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Neutron Stars
  • Quark Matter
  • Nuclear Matter
  • Color Superconductivity
  • QCD Phase Diagram
  • Neutron Star Mergers
  • Superfluidity
  • Transport in Dense Matter

Published Papers (4 papers)

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Research

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24 pages, 777 KiB  
Article
Dissipation Triggers Dynamical Two-Stream Instability
by Nils Andersson and Andreas Schmitt
Particles 2019, 2(4), 457-480; https://doi.org/10.3390/particles2040028 - 31 Oct 2019
Cited by 7 | Viewed by 2664
Abstract
Two coupled, interpenetrating fluids suffer instabilities beyond certain critical counterflows. For ideal fluids, an energetic instability occurs at the point where a sound mode inverts its direction due to the counterflow, while dynamical instabilities only occur at larger relative velocities. Here, we discuss [...] Read more.
Two coupled, interpenetrating fluids suffer instabilities beyond certain critical counterflows. For ideal fluids, an energetic instability occurs at the point where a sound mode inverts its direction due to the counterflow, while dynamical instabilities only occur at larger relative velocities. Here, we discuss two relativistic fluids, one of which is dissipative. Using linearized hydrodynamics, we show that, in this case, the energetic instability turns dynamical, i.e., there is an exponentially growing mode, and this exponential growth only occurs in the presence of dissipation. This result is general and does not rely on an underlying microscopic theory. It can be applied to various two-fluid systems, for instance, in the interior of neutron stars. We also point out that, under certain circumstances, the two-fluid system exhibits a mode analogous to the r-mode in neutron stars that can become unstable for arbitrarily small values of the counterflow. Full article
(This article belongs to the Special Issue Dense QCD and neutron stars)
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10 pages, 1223 KiB  
Article
Strange Stars in the Vector Interaction Enhanced Bag Model
by Marc Salinas, Thomas Klähn and Prashanth Jaikumar
Particles 2019, 2(4), 447-456; https://doi.org/10.3390/particles2040027 - 18 Oct 2019
Cited by 5 | Viewed by 2319
Abstract
The vector interaction enhanced Bag model (vBag) for dense quark matter extends the commonly used thermodynamic Bag model (tdBag) by incorporating effects of dynamical chiral symmetry breaking (D χ SB) and vector repulsion. Motivated by the suggestion that the stability of strange matter [...] Read more.
The vector interaction enhanced Bag model (vBag) for dense quark matter extends the commonly used thermodynamic Bag model (tdBag) by incorporating effects of dynamical chiral symmetry breaking (D χ SB) and vector repulsion. Motivated by the suggestion that the stability of strange matter is in tension with chiral symmetry breaking (D χ SB) we examine the parameter space for its stability in the vBag model in this work. Assuming the chiral transition occurs at sufficiently low density, we determine the stability region of strange matter as a function of the effective Bag constant and the vector coupling. As an astrophysical application, we construct contours of maximum mass M max and radius at maximum mass R max in this region of parameter space. We also study the stability of strange stars in the vBag model with maximum mass in the 2 M ⊙ range by computing the spectrum of radial oscillations, and comparing to results from the tdBag model, find some notable differences. Full article
(This article belongs to the Special Issue Dense QCD and neutron stars)
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20 pages, 3445 KiB  
Article
Simulating Binary Neutron Stars with Hybrid Equation of States: Gravitational Waves, Electromagnetic Signatures and Challenges for Numerical Relativity
by Henrique Gieg, Tim Dietrich and Maximiliano Ujevic
Particles 2019, 2(3), 365-384; https://doi.org/10.3390/particles2030023 - 8 Aug 2019
Cited by 15 | Viewed by 4101
Abstract
The gravitational wave and electromagnetic signatures connected to the merger of two neutron stars allow us to test the nature of matter at supranuclear densities. Since the Equation of State governing the interior of neutron stars is only loosely constrained, there is even [...] Read more.
The gravitational wave and electromagnetic signatures connected to the merger of two neutron stars allow us to test the nature of matter at supranuclear densities. Since the Equation of State governing the interior of neutron stars is only loosely constrained, there is even the possibility that strange quark matter exists inside the core of neutron stars. We investigate how strange quark matter cores affect the binary neutron star coalescence by performing numerical relativity simulations. Interestingly, the strong phase transition can cause a reduction of the convergence order of the numerical schemes to first order if the numerical resolution is not high enough. Therefore, an additional challenge is added in producing high-quality gravitational wave templates for Equation of States with a strong phase transition. Focusing on one particular configuration of an equal mass configuration consistent with GW170817, we compute and discuss the associated gravitational wave signal and some of the electromagnetic counterparts connected to the merger of the two stars. We find that existing waveform approximants employed for the analysis of GW170817 allow describing this kind of systems within the numerical uncertainties, which, however, are several times larger than for pure hadronic Equation of States, which means that even higher resolutions have been employed for an accurate gravitational wave model comparison. We also show that for the chosen Equation of State, quasi-universal relations describing the gravitational wave emission after the moment of merger seem to hold and that the electromagnetic signatures connected to our chosen setup would not be bright enough to explain the kilonova associated to GW170817. Full article
(This article belongs to the Special Issue Dense QCD and neutron stars)
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Review

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33 pages, 1923 KiB  
Review
Meson Condensation
by Massimo Mannarelli
Particles 2019, 2(3), 411-443; https://doi.org/10.3390/particles2030025 - 13 Sep 2019
Cited by 53 | Viewed by 3877
Abstract
We give a pedagogical review of the properties of the various meson condensation phases triggered by a large isospin or strangeness imbalance. We argue that these phases are extremely interesting and powerful playground for exploring the properties of hadronic matter. The reason is [...] Read more.
We give a pedagogical review of the properties of the various meson condensation phases triggered by a large isospin or strangeness imbalance. We argue that these phases are extremely interesting and powerful playground for exploring the properties of hadronic matter. The reason is that they are realized in a regime in which various theoretical methods overlap with increasingly precise numerical lattice QCD simulations, providing insight on the properties of color confinement and of chiral symmetry breaking. Full article
(This article belongs to the Special Issue Dense QCD and neutron stars)
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