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3 pages, 159 KiB

Open AccessEditorial

Editorial for the Special Issue “The Modern Physics of Compact Stars and Relativistic Gravity 2017”

by Armen Sedrakian

Particles 2019, 2(4), 444-446; https://doi.org/10.3390/particles2040026 - 23 Sep 2019

Cited by 1 | Viewed by 2035

Abstract

This Special Issue arose from the presentations of the authors at the international conference “The Modern Physics of Compact Stars and Relativistic Gravity 2017” https://indico [...] Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

Research

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23 pages, 575 KiB

Open AccessArticle

Chirally Improved Quark Pauli Blocking in Nuclear Matter and Applications to Quark Deconfinement in Neutron Stars

by David Blaschke, Hovik Grigorian and Gerd Röpke

Particles 2020, 3(2), 477-499; https://doi.org/10.3390/particles3020033 - 17 Jun 2020

Cited by 21 | Viewed by 2930

Abstract

The relativistic mean field (RMF) model of the nuclear matter equation of state was modified by including the effect of Pauli-blocking owing to quark exchange between the baryons. Different schemes of a chiral enhancement of the quark Pauli blocking was suggested according to [...] Read more.

The relativistic mean field (RMF) model of the nuclear matter equation of state was modified by including the effect of Pauli-blocking owing to quark exchange between the baryons. Different schemes of a chiral enhancement of the quark Pauli blocking was suggested according to the adopted density dependence of the dynamical quark mass. The resulting equations of state for the pressure are compared to the RMF model DD2 with excluded volume correction. On the basis of this comparison a density-dependent nucleon volume is extracted which parameterizes the quark Pauli blocking effect in the respective scheme of chiral enhancement. The dependence on the isospin asymmetry is investigated and the corresponding density dependent nuclear symmetry energy is obtained in fair accordance with phenomenological constraints. The deconfinement phase transition is obtained by a Maxwell construction with a quark matter phase described within a higher order NJL model. Solutions for rotating and nonrotating (hybrid) compact star sequences are obtained, which show the effect of high-mass twin compact star solutions for the rotating case. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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13 pages, 2544 KiB

Open AccessArticle

Neutron Star Mergers: Probing the EoS of Hot, Dense Matter by Gravitational Waves

by Matthias Hanauske, Jan Steinheimer, Anton Motornenko, Volodymyr Vovchenko, Luke Bovard, Elias R. Most, L. Jens Papenfort, Stefan Schramm and Horst Stöcker

Particles 2019, 2(1), 44-56; https://doi.org/10.3390/particles2010004 - 2 Jan 2019

Cited by 45 | Viewed by 5825

Abstract

Gravitational waves, electromagnetic radiation, and the emission of high energy particles probe the phase structure of the equation of state of dense matter produced at the crossroad of the closely related relativistic collisions of heavy ions and of binary neutron stars mergers. 3 [...] Read more.

Gravitational waves, electromagnetic radiation, and the emission of high energy particles probe the phase structure of the equation of state of dense matter produced at the crossroad of the closely related relativistic collisions of heavy ions and of binary neutron stars mergers. 3 + 1 dimensional special- and general relativistic hydrodynamic simulation studies reveal a unique window of opportunity to observe phase transitions in compressed baryon matter by laboratory based experiments and by astrophysical multimessenger observations. The astrophysical consequences of a hadron-quark phase transition in the interior of a compact star will be focused within this article. Especially with a future detection of the post-merger gravitational wave emission emanated from a binary neutron star merger event, it would be possible to explore the phase structure of quantum chromodynamics. The astrophysical observables of a hadron-quark phase transition in a single compact star system and binary hybrid star merger scenario will be summarized within this article. The FAIR facility at GSI Helmholtzzentrum allows one to study the universe in the laboratory, and several astrophysical signatures of the quark-gluon plasma have been found in relativistic collisions of heavy ions and will be explored in future experiments. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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18 pages, 569 KiB

Open AccessArticle

Bulk Viscosity of Hot Quark Plasma from Non-Equilibrium Statistical Operator

by Arus Harutyunyan and Armen Sedrakian

Particles 2018, 1(1), 212-229; https://doi.org/10.3390/particles1010016 - 20 Aug 2018

Cited by 6 | Viewed by 2871

Abstract

We provide a discussion of the bulk viscosity of two-flavor quark plasma, described by the Nambu–Jona-Lasinio model, within the framework of Kubo-Zubarev formalism. This discussion, which is complementary to our earlier study, contains a new, detailed derivation of the bulk viscosity in the [...] Read more.

We provide a discussion of the bulk viscosity of two-flavor quark plasma, described by the Nambu–Jona-Lasinio model, within the framework of Kubo-Zubarev formalism. This discussion, which is complementary to our earlier study, contains a new, detailed derivation of the bulk viscosity in the case of multiple conserved charges. We also provide some numerical details of the computation of the bulk viscosity close to the Mott transition line, where the dissipation is dominated by decays of mesons into quarks and their inverse processes. We close with a summary of our current understanding of this quantity, which stresses the importance of loop resummation for obtaining the qualitatively correct result near the Mott line. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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9 pages, 360 KiB

Open AccessArticle

Models of Compact Stars in the Bimetric Scalar-Tensor Theory of Gravitation

by Levon Sh. Grigorian, Hrant F. Khachatryan and Aram A. Saharian

Particles 2018, 1(1), 203-211; https://doi.org/10.3390/particles1010015 - 10 Aug 2018

Cited by 3 | Viewed by 3048

Abstract

We investigate static spherically-symmetric configurations of gravitating masses in the bimetric scalar-tensor theory of gravitation. In the gravitational sector, the theory contains the metric tensor, a scalar field and a background metric as an absolute variable of the theory. The analysis is presented [...] Read more.

We investigate static spherically-symmetric configurations of gravitating masses in the bimetric scalar-tensor theory of gravitation. In the gravitational sector, the theory contains the metric tensor, a scalar field and a background metric as an absolute variable of the theory. The analysis is presented for the simplest version of the theory with a constant coupling function and a zero cosmological function. We show that, depending on the value of the theory parameter, the masses for superdense compact configurations can be essentially larger compared to the configurations in general relativity. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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9 pages, 2812 KiB

Open AccessArticle

Thermal Spectrum and Neutrino Cooling Rate of the Vela Pulsar

by Dmitry D. Ofengeim and Dmitry A. Zyuzin

Particles 2018, 1(1), 194-202; https://doi.org/10.3390/particles1010014 - 30 Jul 2018

Cited by 7 | Viewed by 4551

Abstract

We reanalyse the X-ray spectrum of the PSR B0833–45 (the Vela pulsar) using the data of the Chandra space observatory. In contrast to previous works, we consider a wide range of possible masses and radii of the pulsar. The derived surface temperature of [...] Read more.

We reanalyse the X-ray spectrum of the PSR B0833–45 (the Vela pulsar) using the data of the Chandra space observatory. In contrast to previous works, we consider a wide range of possible masses and radii of the pulsar. The derived surface temperature of the star

T_{s}^{\infty} = 0 . 66_{- 0.01}^{+ 0.04}

MK (

1 σ

level over the entire mass and radius range of our study) is consistent with earlier results. However, the preferable values of Vela’s mass and radius given by the spectral analysis are different from those used previously; they are consistent with modern equation of state models of neutron star matter. In addition, we evaluate the Vela’s surface temperature as a function of assumed values of its mass and radius. This allows us to analyse the neutrino cooling rates consistent with the evaluated surface temperatures and explore the additional restrictions that could be set on the Vela’s mass and radius using different versions of the neutron star cooling theory. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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19 pages, 454 KiB

Open AccessArticle

Electromagnetic Vacuum Densities Induced by a Cosmic String

by Aram A. Saharian, Vardan F. Manukyan and Nvard A. Saharyan

Particles 2018, 1(1), 175-193; https://doi.org/10.3390/particles1010013 - 17 Jul 2018

Cited by 2 | Viewed by 2852

Abstract

We investigate the influence of a generalized cosmic string in

(D + 1)

-dimensional spacetime on the local characteristics of the electromagnetic vacuum. Two special cases are considered with flat and locally de Sitter background geometries. The topological contributions in the [...] Read more.

We investigate the influence of a generalized cosmic string in

(D + 1)

-dimensional spacetime on the local characteristics of the electromagnetic vacuum. Two special cases are considered with flat and locally de Sitter background geometries. The topological contributions in the vacuum expectation values (VEVs) of the squared electric and magnetic fields are explicitly separated. Depending on the number of spatial dimensions and on the planar angle deficit induced by the cosmic string, these contributions can be either negative or positive. In the case of the flat bulk, the VEV of the energy–momentum tensor is evaluated as well. For the locally de Sitter bulk, the influence of the background gravitational field essentially changes the behavior of the vacuum densities at distances from the string larger than the curvature radius of the spacetime. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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12 pages, 5024 KiB

Open AccessArticle

Active Oxygen Target for Studies in Nuclear Astrophysics with Laser Compton Backscattered γ-ray Beams

by Robert Ajvazyan, John R. M. Annand, Dimiter L. Balabanski, Nersik Grigoryan, Vanik Kakoyan, Patrik Khachatryan, Vachik Khachatryan, Kenneth Livingston, Rachel Montgomery, Henrik Vardanyan, Branislav Vlahovic, Simon Zhamkochyan and Amur Margaryan

Particles 2018, 1(1), 126-137; https://doi.org/10.3390/particles1010009 - 20 May 2018

Cited by 1 | Viewed by 4001

Abstract

An active target is being developed to be used in low-energy nuclear astrophysics experiments. It is a position- and time-sensitive detector system based on the low-pressure Multi Wire Proportional Chamber (MWPC) technique. Methylal ((OCH₃)₂CH₂), at a pressure [...] Read more.

An active target is being developed to be used in low-energy nuclear astrophysics experiments. It is a position- and time-sensitive detector system based on the low-pressure Multi Wire Proportional Chamber (MWPC) technique. Methylal ((OCH₃)₂CH₂), at a pressure of a few Torr, serves as the working gas for MWPC operation, and in addition, the oxygen atoms of the methylal molecules serve as an experimental target. The main advantage of this new target detector system is that it has high sensitivity to the low-energy, highly-ionizing particles produced after photodisintegration of ¹⁶O and insensitivity to γ-rays and minimum ionizing particles. This allows users to detect only the products of the nuclear reaction of interest. The threshold energies for detection of α particles and ¹²C nuclei are about 50 keV and 100 keV, respectively. The main disadvantage of this detector is the small target thickness, which is around a few tens of μg/cm². However, reasonable luminosity can be achieved by using a multimodule detector system and an intense, Laser Compton Backscattered (LCB) γ-ray beam. This paper summarizes the architecture of the active target and reports test results of the prototype detector. The tests investigated the timing and position resolutions of 30 × 30 mm² low-pressure MWPC units using an α-particle source. The possibility of measuring the ¹⁶O(γ, α)¹²C cross-section in the 8–10 MeV energy region by using a LCB γ-ray beam is also discussed. A measurement of the ¹⁶O(γ, α)¹²C cross-section will enable the reaction rate of ¹²C(α, γ)¹⁶O to be determined with significantly improved precision compared to previous experiments. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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15 pages, 413 KiB

Open AccessArticle

Some Theoretical Aspects of Magnetars

by Monika Sinha

Particles 2018, 1(1), 111-125; https://doi.org/10.3390/particles1010008 - 9 May 2018

Cited by 1 | Viewed by 3776

Abstract

Magnetars have been observationally determined to have surface magnetic fields of order of

10^{14}

–

10^{15}

G, and the implied internal field strength may be even larger. We discuss the effect of strong field on the dense matter expected to be [...] Read more.

Magnetars have been observationally determined to have surface magnetic fields of order of

10^{14}

–

10^{15}

G, and the implied internal field strength may be even larger. We discuss the effect of strong field on the dense matter expected to be inside neutron stars. We describe the microphysics, phenomenology, and astrophysical implications of strong field induced unpairing effect that may occur in magnetars, if the local magnetic field in the core of a magnetar exceeds a critical value. The density dependence of the pairing of proton condensate implies that the critical value required for the unpairing effect to occur is maximal at the crust–core interface and decreases towards the center of the star. As a consequence, magnetar cores with homogeneous constant fields will be partially superconducting for “medium-field” magnetars, whereas “strong-field” magnetars will be void of superconductivity. We also discuss its effect on some observational phenomena which depend on the nature and composition of matter inside neutron stars. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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14 pages, 748 KiB

Open AccessArticle

Turbulence Generation by Shock-Acoustic-Wave Interaction in Core-Collapse Supernovae

by Ernazar Abdikamalov, César Huete, Ayan Nussupbekov and Shapagat Berdibek

Particles 2018, 1(1), 97-110; https://doi.org/10.3390/particles1010007 - 7 May 2018

Cited by 8 | Viewed by 3381

Abstract

Convective instabilities in the advanced stages of nuclear shell burning can play an important role in neutrino-driven supernova explosions. In our previous work, we studied the interaction of vorticity and entropy waves with the supernova shock using a linear perturbations theory. In this [...] Read more.

Convective instabilities in the advanced stages of nuclear shell burning can play an important role in neutrino-driven supernova explosions. In our previous work, we studied the interaction of vorticity and entropy waves with the supernova shock using a linear perturbations theory. In this paper, we extend our work by studying the effect of acoustic waves. As the acoustic waves cross the shock, the perturbed shock induces a field of entropy and vorticity waves in the post-shock flow. We find that, even when the upstream flow is assumed to be dominated by sonic perturbations, the shock-generated vorticity waves contain most of the turbulent kinetic energy in the post-shock region, while the entropy waves produced behind the shock are responsible for most of the density perturbations. The entropy perturbations are expected to become buoyant as a response to the gravity force and then generate additional turbulence in the post-shock region. This leads to a modest reduction of the critical neutrino luminosity necessary for producing an explosion, which we estimate to be less than ~5%. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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15 pages, 358 KiB

Open AccessArticle

Azimuthal Fermionic Current in the Cosmic String Spacetime Induced by a Magnetic Tube

by Mikael Souto Maior de Sousa, Rubens Freire Ribeiro and Eugênio Ramos Bezerra de Mello

Particles 2018, 1(1), 82-96; https://doi.org/10.3390/particles1010006 - 16 Mar 2018

Cited by 2 | Viewed by 3005

Abstract

In this paper, we calculate the vacuum expectation value of the azimuthal fermionic current, associated with a massive fermionic quantum field in the spacetime of an idealized cosmic string, considering the presence of a magnetic tube of radius a, coaxial to the [...] Read more.

In this paper, we calculate the vacuum expectation value of the azimuthal fermionic current, associated with a massive fermionic quantum field in the spacetime of an idealized cosmic string, considering the presence of a magnetic tube of radius a, coaxial to the string. In this analysis three distinct configurations of magnetic field are considered: (i) a magnetic field concentrated on a surface of the tube; (ii) a magnetic field presenting a

1 / r

radial dependence; and (iii) an homogeneous magnetic field. In order to develop this analysis , we construct the complete set of normalized solution of the Dirac equation in the region outside the tube. By using the mode-sum formula, we show that the azimuthal induced current is formed by two contributions: the first being the current induced by a line of magnetic flux running along the string, and the second, named core-induced current, is induced by the non-vanishing extension of the magnetic tube. The first contribution depends only on the fractional part of the ration of the magnetic flux inside the tube by the quantum one; as to the second contribution, it depends on the total magnetic flux. We specifically analyze the core-induced current in several limits of the parameters and distance to the tube. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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13 pages, 770 KiB

Open AccessArticle

Limits on the Reconstruction of a Single Dark Energy Scalar Field Potential from SNe Ia Data

by Arpine Piloyan, Sergey Pavluchenko and Luca Amendola

Particles 2018, 1(1), 23-35; https://doi.org/10.3390/particles1010003 - 28 Feb 2018

Cited by 12 | Viewed by 3606

Abstract

In this paper we perform a reconstruction of the scalar field potential responsible for cosmic acceleration using SNe Ia data. After describing the method, we test it with real SNe Ia data—Union2.1 and JLA SNe datasets. We demonstrate that with the current data [...] Read more.

In this paper we perform a reconstruction of the scalar field potential responsible for cosmic acceleration using SNe Ia data. After describing the method, we test it with real SNe Ia data—Union2.1 and JLA SNe datasets. We demonstrate that with the current data precision level, the full reconstruction is not possible. We discuss the problems which arise during the reconstruction process and the ways to overcome them. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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20 pages, 658 KiB

Open AccessArticle

Relativistic Mean-Field Models with Different Parametrizations of Density Dependent Couplings

by Stefan Typel

Particles 2018, 1(1), 3-22; https://doi.org/10.3390/particles1010002 - 2 Feb 2018

Cited by 29 | Viewed by 4771

Abstract

Relativistic mean-field models are successfully used for the description of finite nuclei and nuclear matter. Approaches with density-dependent meson-nucleon couplings assume specific functional forms and a dependence on vector densities in most cases. In this work, parametrizations with a larger sample of functions [...] Read more.

Relativistic mean-field models are successfully used for the description of finite nuclei and nuclear matter. Approaches with density-dependent meson-nucleon couplings assume specific functional forms and a dependence on vector densities in most cases. In this work, parametrizations with a larger sample of functions and dependencies on vector and scalar densities are investigated. They are obtained from fitting properties of finite nuclei. The quality of the description of nuclei and the obtained equations of state of symmetric nuclear matter and neutron matter below saturation are very similar. However, characteristic nuclear matter parameters, the equations of state and the symmetry energy at suprasaturation densities show some correlations with the choice of the density dependence and functional form of the couplings. Conditions are identified that can lead to problems for some of the parametrizations. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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Review

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26 pages, 661 KiB

Open AccessReview

Scalar Fields as Sources for Wormholes and Regular Black Holes

by Kirill A. Bronnikov

Particles 2018, 1(1), 56-81; https://doi.org/10.3390/particles1010005 - 14 Mar 2018

Cited by 57 | Viewed by 4372

Abstract

We review nonsingular static, spherically symmetric solutions of general relativity with minimally coupled scalar fields. Considered are wormholes and regular black holes (BHs) without a center, including black universes (BHs with expanding cosmology beyond the horizon). Such configurations require a “ghost” field with [...] Read more.

We review nonsingular static, spherically symmetric solutions of general relativity with minimally coupled scalar fields. Considered are wormholes and regular black holes (BHs) without a center, including black universes (BHs with expanding cosmology beyond the horizon). Such configurations require a “ghost” field with negative kinetic energy K. Ghosts can be invisible under usual conditions if

K < 0

only in strong-field region (“trapped ghost”), or they rapidly decay at large radii. Before discussing particular examples, some general results are presented, such as the necessity of anisotropic matter for asymptotically flat or AdS wormholes, no-hair and global structure theorems for BHs with scalar fields. The stability properties of scalar wormholes and regular BHs under spherical perturbations are discussed. It is stressed that the effective potential

V_{eff}

for perturbations has universal shapes near generic wormhole throats (a positive pole regularizable by a Darboux transformation) and near transition surfaces from canonical to ghost scalar field behavior (a negative pole at which the perturbation finiteness requirement plays a stabilizing role). Positive poles of

V_{eff}

emerging at “long throats” (with the radius

r \approx r_{0} + const \cdot x^{2 n}

,

n > 1

,

x = 0

is the throat) may be regularized by repeated Darboux transformations for some values of n. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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20 pages, 927 KiB

Open AccessReview

Realistic Compactification Models in Einstein–Gauss–Bonnet Gravity

by Sergey Pavluchenko

Particles 2018, 1(1), 36-55; https://doi.org/10.3390/particles1010004 - 4 Mar 2018

Cited by 11 | Viewed by 3694

Abstract

We report the results of a study on the dynamical compactification of spatially flat cosmological models in Einstein–Gauss–Bonnet gravity. The analysis was performed in the arbitrary dimension in order to be more general. We consider both vacuum and

Λ

-term cases. Our results [...] Read more.

We report the results of a study on the dynamical compactification of spatially flat cosmological models in Einstein–Gauss–Bonnet gravity. The analysis was performed in the arbitrary dimension in order to be more general. We consider both vacuum and

Λ

-term cases. Our results suggest that for vacuum case, realistic compactification into the Kasner (power law) regime occurs with any number of dimensions (D), while the compactification into the exponential solution occurs only for

D ⩾ 2

. For the

Λ

-term case only compactification into the exponential solution exists, and it only occurs for

D ⩾ 2

as well. Our results, combined with the bounds on Gauss–Bonnet coupling and the

Λ

-term (

α, Λ

, respectively) from other considerations, allow for the tightening of the existing constraints and forbid

α < 0

. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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