Tag Archives: Nuclear Theory

Relativistic description of dense matter equation of state and compatibility with neutron star observables: a Bayesian approach [CL]

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http://arxiv.org/abs/2201.12552


The general behavior of the nuclear equation of state (EOS), relevant for the description of neutron stars (NS), is studied within a Bayesian approach applied to a set of models based on a density dependent relativistic mean field description of nuclear matter. The EOS is subjected to a minimal number of constraints based on nuclear saturation properties and the low density pure neutron matter EOS obtained from a precise next-to-next-to-next-to-leading order (N$^{3}$LO) calculation in chiral effective field theory ($\chi$EFT). {The posterior distributions of the model parameters obtained under these minimal constraints are employed to construct the distributions of various nuclear matter properties and NS properties such as radii, tidal deformabilites, central energy densities and speeds of sound etc. We found that 90\% confidence interval (CI) for allowed NS mass – radius relationship and tidal deformabilites are compatible with GW170817 and recent NICER observations, without invoking the exotic degrees of freedom.}

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T. Malik, M. Ferreira, B. Agrawal, et. al.
Tue, 1 Feb 22
38/73

Comments: 20 pages, 10 figures

Cooking pasta with Lie groups [CL]

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http://arxiv.org/abs/2201.12598


We extend the (gauged) Skyrme model to the case in which the global isospin group (which usually is taken to be $SU(N)$) is a generic compact connected Lie group $G$. We analyze the corresponding field equations in (3+1) dimensions from a group theory point of view. Several solutions can be constructed analytically and are determined by the embeddings of three dimensional simple Lie groups into $G$, in a generic irreducible representation. These solutions represent the so-called nuclear pasta state configurations of nuclear matter at low energy. We employ the Dynkin explicit classification of all three dimensional Lie subgroups of exceptional Lie group to classify all such solutions in the case $G$ is an exceptional simple Lie group, and give all ingredients to construct them explicitly. As an example, we construct the explicit solutions for $G=G_{2}$. We then extend our ansatz to include the minimal coupling of the Skyrme field to a $U(1)$ gauge field. We extend the definition of the topological charge to this case and then concentrate our attention to the electromagnetic case. After imposing a “free force condition” on the gauge field, the complete set of coupled field equations corresponding to the gauged Skyrme model minimally coupled to an Abelian gauge field is reduced to just one linear ODE keeping alive the topological charge. We discuss the cases in which such ODE belongs to the (Whittaker-)Hill and Mathieu types.

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S. Cacciatori, F. Canfora, M. Lagos, et. al.
Tue, 1 Feb 22
45/73

Comments: 51 pages, accepted for publication in NPB

Probing neutron-star matter in the lab: connecting binary mergers to heavy-ion collisions [CL]

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http://arxiv.org/abs/2201.13150


As a way to find analogies and differences in the dynamics of hot and dense matter under extreme conditions, we present the first self-consistent relativistic-hydrodynamic calculations of both neutron-star mergers and low-energy heavy-ion collisions employing the same equation of state. By a direct comparison of the evolution of quantities such as temperature, entropy, and density, we show that neutron-star collision regimes can be probed directly at GSI beam energies. We provide concrete evidence that the physical conditions reached in binary neutron-star mergers can be studied in present and future laboratory experiments, thus bridging 18 orders of magnitude in length scale, from microscopic ion collisions to macroscopic astrophysical compact objects.

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E. Most, A. Motornenko, J. Steinheimer, et. al.
Tue, 1 Feb 22
66/73

Comments: 8 pages, 3 figures

Conservative finite volume scheme for first-order viscous relativistic hydrodynamics [CL]

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http://arxiv.org/abs/2201.12317


We present the first conservative finite volume numerical scheme for the causal, stable relativistic Navier-Stokes equations developed by Bemfica, Disconzi, Noronha, and Kovtun (BDNK). BDNK theory has arisen very recently as a promising means of incorporating entropy-generating effects (viscosity, heat conduction) into relativistic fluid models, appearing as a possible alternative to the so-called M\”uller-Israel-Stewart (MIS) theory successfully used to model quark-gluon plasma. Both BDNK and MIS-type theories may be understood in terms of a gradient expansion about the perfect (ideal) fluid, wherein BDNK arises at first order and MIS at second order. As such, BDNK has vastly fewer terms and undetermined model coefficients (as is typical for an effective field theory appearing at lower order), allowing for rigorous proofs of stability, causality, and hyperbolicity in full generality which have as yet been impossible for MIS. To capitalize on these advantages, we present the first fully conservative multi-dimensional fluid solver for the BDNK equations suitable for physical applications. The scheme includes a flux-conservative discretization, non-oscillatory reconstruction, and a central-upwind numerical flux, and is designed to smoothly transition to a high-resolution shock-capturing perfect fluid solver in the inviscid limit. We assess the robustness of our new method in a series of flat-spacetime tests for a conformal fluid, and provide a detailed comparison with previous approaches of Pandya & Pretorius (2021).

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A. Pandya, E. Most and F. Pretorius
Mon, 31 Jan 22
7/55

Comments: 23 pages, 9 figures; comments welcome

A theoretical overview of isospin and EOS effects in heavy-ion reactions at intermediate energies [CL]

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http://arxiv.org/abs/2201.09133


The isospin dependence of in-medium nuclear effective interactions is a fundamental issue in nuclear physics and has broad ramifications in astrophysics. Its uncertainties, especially the difference of neutron-proton interactions in the isosinglet and isotriplet channels, affect significantly the density and momentum dependence of the isovector single-nucleon potential and nucleon-nucleon short-range correlation in neutron-rich matter. Consequently, the neutron-proton effective mass splitting and the density dependence of nuclear symmetry energy are still rather uncertain. Heavy-ion reactions especially those involving rare isotopes is a useful tool for probing the isospin dependence of nuclear effective interactions through (1) the neutron-skin in coordinate and proton-skin in momentum of the initial state of colliding nuclei, (2) the density and momentum dependence of especially the isovector nuclear mean-field as well as (3) the isospin dependence of in-medium nucleon-nucleon cross sections. Observations of neutron stars especially since GW1710817 have also helped us significantly in understanding the isospin dependence of nuclear effective interactions. {\it We summarize here a review talk on these issues given at the 2021 International Workshop on multi-facets of EOS and Clustering. For details we refer the readers to the original publications and references therein}.

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B. Li, B. Cai, L. Chen, et. al.
Tue, 25 Jan 22
24/78

Comments: Proc. of the International Workshop on Multi-facets of EoS and Clustering, Caen, France, Nov. 23-26th, 2021

Implicit correlations within phenomenological parametric models of the neutron star equation of state [HEAP]

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http://arxiv.org/abs/2201.06791


The rapid increase in the number and precision of astrophysical probes of neutron stars in recent years allows for the inference of their equation of state. Observations target different macroscopic properties of neutron stars which vary from star to star, such as mass and radius, but the equation of state allows for a common description of all neutron stars. To connect these observations and infer the properties of dense matter and neutron stars simultaneously, models for the equation of state are introduced. Parametric models rely on carefully engineered functional forms that reproduce a large array of realistic equations of state. Such models benefit from their simplicity but are limited because any finite-parameter model cannot accurately approximate all possible equations of state. Nonparametric models overcome this by increasing model freedom at the cost of increased complexity. In this study, we compare common parametric and nonparametric models, quantify the limitations of the former, and study the impact of modeling on our current understanding of high-density physics. We show that parametric models impose strongly model-dependent, and sometimes opaque, correlations between density scales. Such inter-density correlations result in tighter constraints that are unsupported by data and can lead to biased inference of the equation of state and of individual neutron star properties.

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I. Legred, K. Chatziioannou, R. Essick, et. al.
Wed, 19 Jan 22
26/121

Comments: 20 pages, 12 figures

Thermal Relaxation and Cooling of Quark Stars with a Strangelet Crust [CL]

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http://arxiv.org/abs/2201.06928


In this article, we explore the cooling of isolated quark stars. These objects are structured of a homogeneous quark matter core and crusted by matter. To do this, we adopt two kinds of crust: (i) a crust made of purely nuclear matter following the Baym-Pethick-Sutherland (BPS) equation of state (EoS) and (ii) a crust made of nuggets of strange quark matter (strangelets). Both models have the same quark matter core described by the MIT bag model EoS. Our main purpose is to quantify the effects of a strangelet crust on the cooling and relaxation times of these strange stars. We also perform a thorough study of the thermal relaxation of quark stars, in which we have found that objects with a strangelet crust have a significantly different thermal relaxation time. Our study also includes the possible effects of color superconductivity in the quark core.

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J. Zapata, R. Negreiros, T. Sales, et. al.
Wed, 19 Jan 22
57/121

Comments: 7 pages, 8 figures

Gravitational search for near Earth black holes or other compact dark objects [CL]

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http://arxiv.org/abs/2201.06511


Primordial black holes, with masses comparable to asteroids, are an attractive possibility for dark matter. In addition, other forms of dark matter could form compact dark objects (CDO). We search for small tidal accelerations from low mass black holes or CDOs orbiting near the Earth, and find none. Using about 10 years of data from the superconducting gravimeters in the Black Forest Observatory in South-Western Germany and at Djougou, Northern Benin in Western Africa we set an upper limit on the maximum mass of any dark object orbiting the Earth as a function of orbital radius. For semi-major axis less than two earth radii we exclude all black holes or CDOs with masses larger than 6.7×10^{13} kg. Lower mass primordial black holes may be strongly constrained by Hawking radiation. We conclude that near Earth black holes are extremely unlikely.

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T. Namigata, C. Horowitz and R. Widmer-Schnidrig
Wed, 19 Jan 22
74/121

Comments: six pages, 6 figures

Taking Neutrino Pictures via Electrons [CL]

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http://arxiv.org/abs/2201.06733


In this paper we discuss the prospects to take a picture of an extended neutrino source, i.e., resolving its angular neutrino luminosity distribution. This is challenging since neutrino directions cannot be directly measured but only estimated from the directions of charged particles they interact with in the detector material. This leads to an intrinsic blurring effect. We first discuss the problem in general terms and then apply our insights to solar neutrinos scattering elastically with electrons. Despite the aforementioned blurring we show how with high statistics and precision the original neutrino distributions could be reconstructed.

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G. Lin, T. Nguyen, M. Spinrath, et. al.
Wed, 19 Jan 22
78/121

Comments: 34 pages, 15 figures

A stable and causal model of magnetohydrodynamics [CL]

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http://arxiv.org/abs/2201.06847


We formulate the theory of first-order dissipative magnetohydrodynamics in an arbitrary hydrodynamic frame under the assumption of parity-invariance and discrete charge symmetry. We study the mode spectrum of Alfv\’en and magnetosonic waves as well as the spectrum of gapped excitations and derive constraints on the transport coefficients such that generic equilibrium states with constant magnetic fields are stable and causal under linearised perturbations. We solve these constraints for a specific equation of state and show that there exists a large family of hydrodynamic frames that renders the linear fluctuations stable and causal. This theory does not require introducing new dynamical degrees of freedom and therefore is a promising and simpler alternative to M\”{u}ller-Israel-Stewart-type theories. Together with a detailed analysis of transport, entropy production and Kubo formulae, the theory presented here is well suited for studying dissipative effects in various contexts ranging from heavy-ion collisions to astrophysics.

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J. Armas and F. Camilloni
Wed, 19 Jan 22
115/121

Comments: v1:30pp

Neutron Stars with Baryon Number Violation, Probing Dark Sectors [CL]

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http://arxiv.org/abs/2201.02637


The neutron lifetime anomaly has been used to motivate the introduction of new physics with hidden-sector particles coupled to baryon number, and on which neutron stars provide powerful constraints. Although the neutron lifetime anomaly may eventually prove to be of mundane origin, we use it as motivation for a broader review of the ways that baryon number violation, be it real or apparent, and dark sectors can intertwine and how neutron star observables, both present and future, can constrain them.

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J. Berryman, S. Gardner and M. Zakeri
Tue, 11 Jan 22
52/95

Comments: 80 pages, 16 figures. Invited contribution to special issue of Symmetry, “The Neutron Star-Dark Matter Connection: Bridge Through the Baryon Symmetry Violation.”

Nuclear mass table in deformed relativistic Hartree-Bogoliubov theory in continuum: I. even-even nuclei [CL]

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http://arxiv.org/abs/2201.03216


Ground-state properties of even-even nuclei with $8\le Z\le120$ from the proton drip line to the neutron drip line have been investigated using the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the density functional PC-PK1. With the effects of deformation and continuum included simultaneously, 2583 even-even nuclei are predicted to be bound. The calculated binding energies, two-nucleon separation energies, root-mean-square (rms) radii of neutron, proton, matter, and charge distributions, quadrupole deformations, and neutron and proton Fermi surfaces are tabulated and compared with available experimental data. The rms deviation from the 637 mass data is 1.518 MeV, providing one of the best microscopic descriptions for nuclear masses. The drip lines obtained from DRHBc calculations are compared with other calculations, including the spherical relativistic continuum Hartree-Bogoliubov (RCHB) and triaxial relativistic Hartree-Bogoliubov (TRHB) calculations with PC-PK1. The deformation and continuum effects on the limits of the nuclear landscape are discussed. Possible peninsulas consisting of bound nuclei beyond the two-neutron drip line are predicted. The systematics of the two-nucleon separation energies, two-nucleon gaps, rms radii, quadrupole deformations, potential energy curves, neutron densities, neutron mean-field potentials, and pairing energies in the DRHBc calculations are also discussed. In addition, the $\alpha$ decay energies extracted are in good agreement with available data.

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D. Collaboration, K. Zhang, M. Cheoun, et. al.
Tue, 11 Jan 22
79/95

Comments: 217 pages, 15 figures, 2 tables, accepted for publication in Atomic Data and Nuclear Data Tables, data file in the TXT form is available for download under “Ancillary files”

Proto-neutron star evolution with improved charged-current neutrino-nucleon interactions [CL]

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http://arxiv.org/abs/2201.01955


We perform simulations of the Kelvin-Helmholtz cooling phase of proto-neutron stars with a new numerical code in spherical symmetry and using the quasi-static approximation. We use for the first time the full set of charged-current neutrino-nucleon reactions, including neutron decay and modified Urca processes, together with the energy-dependent numerical representation for the inclusion of nuclear correlations with random-phase approximation. Moreover, convective motions are taken into account within the mixing-length theory. As we vary the assumptions for computing neutrino-nucleon reaction rates, we show that the dominant effect on the cooling timescale, neutrino signal and composition of the neutrino-driven wind comes from the inclusion of convective motion. Computation of nuclear correlations within the random phase approximation, as compared to mean field approach, has a relatively small impact.

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A. Pascal, J. Novak and M. Oertel
Fri, 7 Jan 22
13/34

Comments: N/A

Neural network reconstruction of the dense matter equation of state from neutron star observables [CL]

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http://arxiv.org/abs/2201.01756


The equation of state (EoS) of the strongly interacting cold and ultra-dense matter remains a major challenge in the field of nuclear physics. With the advancements in measurements of neutron star masses, radii, and tidal deformabilities from electromagnetic and gravitational wave observations, neutron stars play an important role in constraining the ultra-dense matter EoS. In this work, we present a novel method that exploits deep learning techniques to reconstruct the neutron star EoS from mass-radius (M-R) observations. We employ neural networks (NNs) to represent the EoS in a model-independent way, within the range of 1-7.4 times the nuclear saturation density. In an unsupervised manner, we implement the Automatic Differentiation (AD) framework to optimize the EoS, as to yield through TOV equations an M-R curve that best fits the observations. We demonstrate it in rebuilding the EoS on mock data, i.e., mass-radius pairs derived from a generated set of polytropic EoSs. The results show that it is possible to reconstruct the EoS with reasonable accuracy, using just 11 mock M-R pairs observations, which is close to the current number of observations.

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S. Soma, L. Wang, S. Shi, et. al.
Thu, 6 Jan 22
6/56

Comments: 12 pages, 11 figures

Reliable quark-nuclear hybrid EoS for neutron stars under modern observational constraints [CL]

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http://arxiv.org/abs/2201.00477


We study a family of equations of state (EoS) for hybrid neutron star (NS) matter. Our hybrid EoS are based on an instantaneous nonlocal version of NJL model in $SU(2)_f$ with vector interactions and color superconductivity describing the quark matter (QM) with a Maxwell construction phase transition to hadronic matter phase described by the “DD2” EoS with excluded volume and a crust at low baryonic densities. The form factor in the QM nonlocal model was fitted to lattice QCD (LQCD) results in the Coulomb gauge. To simultaneously fulfill constraints from NICER and tidal deformability from GW170817 it is necessary to consider a $\mu$ dependent bag constant that mimics confinement. Our results show an asymptotic constant behaviour for the speed of sound that reproduces the conjectured value of $1/3$ from QCD in the free case, and larger constant values in the range 0.4 – 0.6 when interactions are turned on.

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G. Contrera, D. Blaschke, J. Carlomagno, et. al.
Tue, 4 Jan 22
2/58

Comments: 17 pages, 7 figures

Neutron diffusion in magnetars as a source of astrophysical bursts [HEAP]

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http://arxiv.org/abs/2112.14817


Neutron tunneling in neutron star crusts can release enormous amounts of energy on a short timescale. We have clarified aspects of this process occurring in the outer crust regions of neutron stars when oscillations or cataclysmic events changes the crustal ambient density. We report a time-dependent Hartree-Fock-Bogoliubov model to determine the rate of neutron diffusion and conclude that a large amount of energy, in the range of 10^40 – 10^44 erg, can be released rapidly. We suggest that this mechanism may be the source of hitherto unknown phenomena such as the Fast Radio Bursts (FRBS).

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C. Bertulani and R. Lobato
Mon, 3 Jan 22
40/49

Comments: 10 pages, 4 figures, contribution to the XLIV Brazilian Workshop on Nuclear Physics to be published by the IOP

Tidal Deformability as a Probe of Dark Matter in Neutron Stars [HEAP]

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http://arxiv.org/abs/2112.14231


The concept of boson stars (BSs) was first introduced by Kaup and Ruffini-Bonazzola in the 1960s. Following this idea, we investigate an effect of self-interacting asymmetric bosonic dark matter (DM) according to Colpi et al. model for BSs (1986) on different observable properties of neutron stars (NSs). In this paper, the bosonic DM and baryonic matter (BM) are mixed together and interact only through gravitational force. The presence of DM as a core of a compact star or as an extended halo around it is examined by applying different boson masses and DM fractions for a fixed coupling constant. The impact of DM core/halo formations on a DM admixed NS properties is probed through the maximum mass and tidal deformability of NSs. Thanks to the recent detection of Gravitational-Waves (GWs) and the latest X-ray observations, the DM admixed NS’s features are compared to LIGO/Virgo and NICER results.

Read this paper on arXiv…

D. Karkevandi, S. Shakeri, V. Sagun, et. al.
Thu, 30 Dec 21
22/71

Comments: The article is prepared for the proceedings of the sixteenth Marcel Grossmann meeting (MG16)

Time-dependent extension of the self-consistent band theory for neutron star matter: Anti-entrainment effects in the slab phase [CL]

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http://arxiv.org/abs/2112.14350


Background: In the solid crust of neutron stars, a variety of crystalline structure may exist. Recently the band theory of solids has been applied to the inner crust of neutron stars and significance of the entrainment between dripped neutrons and the solid crust was advocated. Since it influences interpretations of various phenomena of neutron stars, it has been desired to develop deeper understanding of the microphysics behind.
Purpose: The purpose of the present article is to propose a fully self-consistent microscopic framework for describing time-dependent dynamics of neutron star matter, which allows us to explore diverse properties of nuclear matter, including the entrainment effect.
Results: As the first application of the time-dependent self-consistent band theory for nuclear systems, we investigate the slab phase of nuclear matter with various proton fractions. From a dynamic response of the system to an external force, we extract the collective mass of a slab, associated with entrained neutrons as well as bound nucleons. We find that the extracted collective mass is smaller than a naive estimation based on a potential profile and single-particle energies. We show that the reduction is mainly caused by “counterflow” of dripped neutrons towards the direction opposite to the motion of the slabs. We interpret it as an “anti-entrainment” effect. As a result, the number of effectively bound neutrons is reduced, indicating an enhancement of the number density of conduction neutrons. We demonstrate that those findings are consistent with a static treatment in the band theory of solids.
*shortened due to the arXiv’s word limit.

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K. Sekizawa, S. Kobayashi and M. Matsuo
Thu, 30 Dec 21
59/71

Comments: 19 pages, 9 figures, 3 tables

Dark matter effects on the compact star properties [HEAP]

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http://arxiv.org/abs/2112.14198


The neutron star properties are generally determined by the equation of state of $\beta$-equilibrated dense matter. In this work, we consider the interaction of fermionic dark matter (DM) particles with the nucleons via Higgs exchange and investigate its effect on the neutron star properties with the relativistic mean-field model equation of state coupled with DM. We deduce that DM significantly affects the neutron star properties, such as considerably reduce the maximum mass of the star, which depends on the percentage of the DM considered inside the neutron star. The tidal Love numbers both for electric and magnetic cases and surficial Love numbers are also studied for DM admixed NS. It is observed that the magnitude of tidal and surficial Love numbers increase with more DM percentage. Further, we point out that post-Newtonian tidal corrections to gravitational waves decreased by increasing DM percentage. Also, the DM effect on the GW signal is significant during the late inspiral and merger stages of binary evolution for GW frequencies >500 Hz.

Read this paper on arXiv…

H. Das, A. Kumar, B. Kumar, et. al.
Thu, 30 Dec 21
63/71

Comments: 15 pages, 8 figures, comments welcome, submitted to Galaxy journal (Special issues on Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics)

Time-dependent extension of the self-consistent band theory for neutron star matter: Anti-entrainment effects in the slab phase [CL]

Posted on by

http://arxiv.org/abs/2112.14350


Background: In the solid crust of neutron stars, a variety of crystalline structure may exist. Recently the band theory of solids has been applied to the inner crust of neutron stars and significance of the entrainment between dripped neutrons and the solid crust was advocated. Since it influences interpretations of various phenomena of neutron stars, it has been desired to develop deeper understanding of the microphysics behind.
Purpose: The purpose of the present article is to propose a fully self-consistent microscopic framework for describing time-dependent dynamics of neutron star matter, which allows us to explore diverse properties of nuclear matter, including the entrainment effect.
Results: As the first application of the time-dependent self-consistent band theory for nuclear systems, we investigate the slab phase of nuclear matter with various proton fractions. From a dynamic response of the system to an external force, we extract the collective mass of a slab, associated with entrained neutrons as well as bound nucleons. We find that the extracted collective mass is smaller than a naive estimation based on a potential profile and single-particle energies. We show that the reduction is mainly caused by “counterflow” of dripped neutrons towards the direction opposite to the motion of the slabs. We interpret it as an “anti-entrainment” effect. As a result, the number of effectively bound neutrons is reduced, indicating an enhancement of the number density of conduction neutrons. We demonstrate that those findings are consistent with a static treatment in the band theory of solids.
*shortened due to the arXiv’s word limit.

Read this paper on arXiv…

K. Sekizawa, S. Kobayashi and M. Matsuo
Thu, 30 Dec 21
2/71

Comments: 19 pages, 9 figures, 3 tables

Tidal Deformability as a Probe of Dark Matter in Neutron Stars [HEAP]

Posted on by

http://arxiv.org/abs/2112.14231


The concept of boson stars (BSs) was first introduced by Kaup and Ruffini-Bonazzola in the 1960s. Following this idea, we investigate an effect of self-interacting asymmetric bosonic dark matter (DM) according to Colpi et al. model for BSs (1986) on different observable properties of neutron stars (NSs). In this paper, the bosonic DM and baryonic matter (BM) are mixed together and interact only through gravitational force. The presence of DM as a core of a compact star or as an extended halo around it is examined by applying different boson masses and DM fractions for a fixed coupling constant. The impact of DM core/halo formations on a DM admixed NS properties is probed through the maximum mass and tidal deformability of NSs. Thanks to the recent detection of Gravitational-Waves (GWs) and the latest X-ray observations, the DM admixed NS’s features are compared to LIGO/Virgo and NICER results.

Read this paper on arXiv…

D. Karkevandi, S. Shakeri, V. Sagun, et. al.
Thu, 30 Dec 21
11/71

Comments: The article is prepared for the proceedings of the sixteenth Marcel Grossmann meeting (MG16)

Dark matter effects on the compact star properties [HEAP]

Posted on by

http://arxiv.org/abs/2112.14198


The neutron star properties are generally determined by the equation of state of $\beta$-equilibrated dense matter. In this work, we consider the interaction of fermionic dark matter (DM) particles with the nucleons via Higgs exchange and investigate its effect on the neutron star properties with the relativistic mean-field model equation of state coupled with DM. We deduce that DM significantly affects the neutron star properties, such as considerably reduce the maximum mass of the star, which depends on the percentage of the DM considered inside the neutron star. The tidal Love numbers both for electric and magnetic cases and surficial Love numbers are also studied for DM admixed NS. It is observed that the magnitude of tidal and surficial Love numbers increase with more DM percentage. Further, we point out that post-Newtonian tidal corrections to gravitational waves decreased by increasing DM percentage. Also, the DM effect on the GW signal is significant during the late inspiral and merger stages of binary evolution for GW frequencies >500 Hz.

Read this paper on arXiv…

H. Das, A. Kumar, B. Kumar, et. al.
Thu, 30 Dec 21
51/71

Comments: 15 pages, 8 figures, comments welcome, submitted to Galaxy journal (Special issues on Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics)

Cooling of Isolated Neutron Stars with Pion Condensation: Possible Fast Cooling in a Low-Symmetry-Energy Model [HEAP]

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http://arxiv.org/abs/2112.13302


We studied thermal evolution of isolated neutron stars (NSs) including the pion condensation core, with an emphasis on the stiffness of equation of state (EOS). Many temperature observations can be explained by the minimal cooling scenario which excludes the fast neutrino cooling process. However, several NSs are cold enough to require it. The most crucial problem for NS cooling theory is whether the nucleon direct Urca (DU) process is open. The DU process is forbidden if the nucleon symmetry energy is significantly low. Hence, another fast cooling process is required in such an EOS. As the candidate to solve this problem, we consider the pion condensation. We show that the low-symmetry-energy model can account for most cooling observations including cold NSs, with strong neutron superfluidity. Simultaneously, it holds the $2~M_{\odot}$ observations even if the pion condensation core exists. Thus, we propose the possibility of pion condensation, as an exotic state to solve the problem in low-symmetry-energy EOSs. We examined the consistency of our EOSs with other various observations as well.

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A. Dohi, H. Liu, T. Noda, et. al.
Tue, 28 Dec 21
20/55

Comments: 21 pages, 8 figures, accepted by Int. J. Mod. Phys. E

Analytical model on mass limit of strange stars [CL]

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http://arxiv.org/abs/2112.12807


In this paper, we present a new kind of stellar model using the Nariai IV metric. This model can be used to study the strange/quark stars(which is our present interest, though it can also be applicable to neutron stars). We present a mass-radius region where all the regularity conditions, energy conditions, the TOV equation, and stability conditions are satisfied. According to our model, strange stars having mass up to $1.9165M_{\odot}(=2.81 km)$ is stable. A strange star having a mass greater than $1.9165M_{\odot}$ violates the stability conditions. This model can be very useful to predict the radius of strange stars of mass greater than $1 M_{\odot}$.

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S. Molla, M. Murshid and M. Kalam
Tue, 28 Dec 21
36/55

Comments: 12 pages, 10 figures, 2 tables; Accepted in Astrophysics and Space Science

Quark-quark interaction and quark matter in neutron stars [CL]

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http://arxiv.org/abs/2112.12931


Hyperon ($Y$) mixing in neutron-star matter brings about a remarkable softening of the equation of state (EoS) and the maximum mass is reduced to a value far less than $2M_{\odot}$. One idea to avoid this “hyperon puzzle in neutron stars” is to assume that the many-body repulsions work universally for every kind of baryons. The other is to take into account the quark deconfinement phase transitions from a hadronic EoS to a sufficiently stiff quark-matter EoS. In the present approach, both effects are handled in a common framework. As well as the hadronic matter, the quark matter with the two-body quark-quark interactions are treated within the Brueckner-Bethe-Goldstone theory beyond the mean field frameworks, where interaction parameters are based on the terrestrial data. The derived mass-radius relations of neutron stars show that maximum masses reach over $2M_{\odot}$ even in the cases of including hadron-quark phase transitions, being consistent with the recent observations for maximum masses and radii of neutron stars by the NICER measurements and the other multimessenger data.

Read this paper on arXiv…

Y. Yamamoto, N. Yasutake and T. Rijken
Tue, 28 Dec 21
54/55

Comments: N/A

Analytical model on mass limit of strange stars [CL]

Posted on by

http://arxiv.org/abs/2112.12807


In this paper, we present a new kind of stellar model using the Nariai IV metric. This model can be used to study the strange/quark stars(which is our present interest, though it can also be applicable to neutron stars). We present a mass-radius region where all the regularity conditions, energy conditions, the TOV equation, and stability conditions are satisfied. According to our model, strange stars having mass up to $1.9165M_{\odot}(=2.81 km)$ is stable. A strange star having a mass greater than $1.9165M_{\odot}$ violates the stability conditions. This model can be very useful to predict the radius of strange stars of mass greater than $1 M_{\odot}$.

Read this paper on arXiv…

S. Molla, M. Murshid and M. Kalam
Tue, 28 Dec 21
20/55

Comments: 12 pages, 10 figures, 2 tables; Accepted in Astrophysics and Space Science

Cooling of Isolated Neutron Stars with Pion Condensation: Possible Fast Cooling in a Low-Symmetry-Energy Model [HEAP]

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http://arxiv.org/abs/2112.13302


We studied thermal evolution of isolated neutron stars (NSs) including the pion condensation core, with an emphasis on the stiffness of equation of state (EOS). Many temperature observations can be explained by the minimal cooling scenario which excludes the fast neutrino cooling process. However, several NSs are cold enough to require it. The most crucial problem for NS cooling theory is whether the nucleon direct Urca (DU) process is open. The DU process is forbidden if the nucleon symmetry energy is significantly low. Hence, another fast cooling process is required in such an EOS. As the candidate to solve this problem, we consider the pion condensation. We show that the low-symmetry-energy model can account for most cooling observations including cold NSs, with strong neutron superfluidity. Simultaneously, it holds the $2~M_{\odot}$ observations even if the pion condensation core exists. Thus, we propose the possibility of pion condensation, as an exotic state to solve the problem in low-symmetry-energy EOSs. We examined the consistency of our EOSs with other various observations as well.

Read this paper on arXiv…

A. Dohi, H. Liu, T. Noda, et. al.
Tue, 28 Dec 21
34/55

Comments: 21 pages, 8 figures, accepted by Int. J. Mod. Phys. E

Quark-quark interaction and quark matter in neutron stars [CL]

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http://arxiv.org/abs/2112.12931


Hyperon ($Y$) mixing in neutron-star matter brings about a remarkable softening of the equation of state (EoS) and the maximum mass is reduced to a value far less than $2M_{\odot}$. One idea to avoid this “hyperon puzzle in neutron stars” is to assume that the many-body repulsions work universally for every kind of baryons. The other is to take into account the quark deconfinement phase transitions from a hadronic EoS to a sufficiently stiff quark-matter EoS. In the present approach, both effects are handled in a common framework. As well as the hadronic matter, the quark matter with the two-body quark-quark interactions are treated within the Brueckner-Bethe-Goldstone theory beyond the mean field frameworks, where interaction parameters are based on the terrestrial data. The derived mass-radius relations of neutron stars show that maximum masses reach over $2M_{\odot}$ even in the cases of including hadron-quark phase transitions, being consistent with the recent observations for maximum masses and radii of neutron stars by the NICER measurements and the other multimessenger data.

Read this paper on arXiv…

Y. Yamamoto, N. Yasutake and T. Rijken
Tue, 28 Dec 21
39/55

Comments: N/A

Influence of nuclear symmetry energy slope on compact stars with $Δ$-admixed hypernuclear matter [HEAP]

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http://arxiv.org/abs/2112.12629


In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter equation of state and its impact on neutron star observables (mass-radius, tidal response). We construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models with viability of heavier non-nucleonic degrees of freedom. The slope of symmetry energy parameter ($L_{\text{sym}}$) is adjusted following density-dependence of isovector meson coupling to baryons. We find that smaller values of $L_{\text{sym}}$ at saturation favour early appearance of $\Delta$-resonances in comparison to hyperons leading to latter’s threshold at higher matter densities. We also investigate the dependence of $L_{\text{sym}}$ on tidal deformability and compactness parameter of a $1.4~M_\odot$ neutron star for different equation of states and observe similar converging behaviour for larger $L_{\text{sym}}$ values.

Read this paper on arXiv…

V. Thapa and M. Sinha
Fri, 24 Dec 21
2/58

Comments: 14 pages, 10 figures, 8 tables; Accepted for publication in Phys. Rev. C

Dense and Hot QCD at Strong Coupling [CL]

Posted on by

http://arxiv.org/abs/2112.12157


We present a novel framework for the equation of state of dense and hot Quantum Chromodynamics (QCD), which focuses on the region of the phase diagram relevant for neutron star mergers and core-collapse supernovae. The model combines predictions from the gauge/gravity duality with input from lattice field theory, QCD perturbation theory, chiral effective theory and statistical modeling. It is therefore, by construction, in good agreement with theoretical constraints both at low and high densities and temperatures. The main ingredients of our setup are the non-perturbative V-QCD model based on the gauge/gravity duality, a van der Waals model for nucleon liquid, and the DD2 version of the Hempel-Schaffner-Bielich statistical model of nuclear matter. By consistently combining these models, we also obtain a description for the nuclear to quark matter phase transition and its critical endpoint. The parameter dependence of the model is represented by three (soft, intermediate and stiff) variants of the equation of state, all of which agree with observational constraints from neutron stars and their mergers. We discuss resulting constraints for the equation of state, predictions for neutron stars and the location of the critical point.

Read this paper on arXiv…

T. Demircik, C. Ecker and M. Järvinen
Fri, 24 Dec 21
11/58

Comments: 16 pages, 8 figures, comments welcome

Classical and Quantum Evolution in a Simple Coherent Neutrino Problem [CL]

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http://arxiv.org/abs/2112.12686


The extraordinary neutrino flux produced in extreme astrophysical environments like the early universe, core-collapse supernovae and neutron star mergers may produce coherent quantum neutrino oscillations on macroscopic length scales. The Hamiltonian describing this evolution can be mapped into quantum spin models with all-to-all couplings arising from neutrino-neutrino forward scattering. To date many studies of these oscillations have been performed in a mean-field limit where the neutrinos time evolve in a product state.
In this paper we examine a simple two-beam model evolving from an initial product state and compare the mean-field and many-body evolution. The symmetries in this model allow us to solve the real-time evolution for the quantum many-body system for hundreds or thousands of spins, far beyond what would be possible in a more general case with an exponential number ($2^N$) of quantum states. We compare mean-field and many-body solutions for different initial product states and ratios of one- and two-body couplings, and find that in all cases in the limit of infinite spins the mean-field (product state) and many-body solutions coincide for simple observables. This agreement can be understood as a consequence of the fact that the typical initial condition represents a very local but dense distribution about a mean energy in the spectrum of the Hamiltonian. We explore quantum information measures like entanglement entropy and purity of the many-body solutions, finding intriguing relationships between the quantum information measures and the dynamical behavior of simple physical observables.

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J. Martin, A. Roggero, H. Duan, et. al.
Fri, 24 Dec 21
38/58

Comments: 16 pages, 9 figures

Classical and Quantum Evolution in a Simple Coherent Neutrino Problem [CL]

Posted on by

http://arxiv.org/abs/2112.12686


The extraordinary neutrino flux produced in extreme astrophysical environments like the early universe, core-collapse supernovae and neutron star mergers may produce coherent quantum neutrino oscillations on macroscopic length scales. The Hamiltonian describing this evolution can be mapped into quantum spin models with all-to-all couplings arising from neutrino-neutrino forward scattering. To date many studies of these oscillations have been performed in a mean-field limit where the neutrinos time evolve in a product state.
In this paper we examine a simple two-beam model evolving from an initial product state and compare the mean-field and many-body evolution. The symmetries in this model allow us to solve the real-time evolution for the quantum many-body system for hundreds or thousands of spins, far beyond what would be possible in a more general case with an exponential number ($2^N$) of quantum states. We compare mean-field and many-body solutions for different initial product states and ratios of one- and two-body couplings, and find that in all cases in the limit of infinite spins the mean-field (product state) and many-body solutions coincide for simple observables. This agreement can be understood as a consequence of the fact that the typical initial condition represents a very local but dense distribution about a mean energy in the spectrum of the Hamiltonian. We explore quantum information measures like entanglement entropy and purity of the many-body solutions, finding intriguing relationships between the quantum information measures and the dynamical behavior of simple physical observables.

Read this paper on arXiv…

J. Martin, A. Roggero, H. Duan, et. al.
Fri, 24 Dec 21
19/58

Comments: 16 pages, 9 figures

Influence of nuclear symmetry energy slope on compact stars with $Δ$-admixed hypernuclear matter [HEAP]

Posted on by

http://arxiv.org/abs/2112.12629


In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter equation of state and its impact on neutron star observables (mass-radius, tidal response). We construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models with viability of heavier non-nucleonic degrees of freedom. The slope of symmetry energy parameter ($L_{\text{sym}}$) is adjusted following density-dependence of isovector meson coupling to baryons. We find that smaller values of $L_{\text{sym}}$ at saturation favour early appearance of $\Delta$-resonances in comparison to hyperons leading to latter’s threshold at higher matter densities. We also investigate the dependence of $L_{\text{sym}}$ on tidal deformability and compactness parameter of a $1.4~M_\odot$ neutron star for different equation of states and observe similar converging behaviour for larger $L_{\text{sym}}$ values.

Read this paper on arXiv…

V. Thapa and M. Sinha
Fri, 24 Dec 21
42/58

Comments: 14 pages, 10 figures, 8 tables; Accepted for publication in Phys. Rev. C

Dense and Hot QCD at Strong Coupling [CL]

Posted on by

http://arxiv.org/abs/2112.12157


We present a novel framework for the equation of state of dense and hot Quantum Chromodynamics (QCD), which focuses on the region of the phase diagram relevant for neutron star mergers and core-collapse supernovae. The model combines predictions from the gauge/gravity duality with input from lattice field theory, QCD perturbation theory, chiral effective theory and statistical modeling. It is therefore, by construction, in good agreement with theoretical constraints both at low and high densities and temperatures. The main ingredients of our setup are the non-perturbative V-QCD model based on the gauge/gravity duality, a van der Waals model for nucleon liquid, and the DD2 version of the Hempel-Schaffner-Bielich statistical model of nuclear matter. By consistently combining these models, we also obtain a description for the nuclear to quark matter phase transition and its critical endpoint. The parameter dependence of the model is represented by three (soft, intermediate and stiff) variants of the equation of state, all of which agree with observational constraints from neutron stars and their mergers. We discuss resulting constraints for the equation of state, predictions for neutron stars and the location of the critical point.

Read this paper on arXiv…

T. Demircik, C. Ecker and M. Järvinen
Fri, 24 Dec 21
57/58

Comments: 16 pages, 8 figures, comments welcome

Neutron stars with crossover to color superconducting quark matter [CL]

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http://arxiv.org/abs/2112.12145


We follow the idea that the QCD phase diagram may be described by a crossover from a hadron resonance gas to perturbative QCD using the switch function ansatz of Albright, Kapusta and Young [1]. While the switch function could be calibrated at vanishing baryon chemical potential with data from lattice QCD simulations, it has been suggested recently by Kapusta and Welle [2] that in the zero temperature limit, the switch function parameter $\mu_0$ could be constrained by neutron star phenomenology, in particular by massive pulsars like PSR J0740+6620 with a mass exceeding $2~M_\odot$. In this work we demonstrate that this procedure to constrain the QCD phase diagram does crucially depend on the fact that cold dense quark matter is very likely in a color superconducting state.

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D. Blaschke, E. Hanu and S. Liebing
Thu, 23 Dec 21
4/63

Comments: 9 pages, 6 figures

The Impact of Neutron Transfer Reactions on Heating and Cooling of Accreted Neutron Star Crusts [HEAP]

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http://arxiv.org/abs/2112.11544


Nuclear reactions heat and cool the crust of accreting neutron stars and need to be understood to interpret observations of X-ray bursts and of long-term cooling in transiently accreting systems. It was recently suggested that previously neglected neutron transfer reactions may play a significant role in the nuclear processes. We present results from full nuclear network calculations that now include these reactions and determine their impact on crust composition, crust impurity, heating, and cooling. We find that a large number of neutron transfer reactions indeed occur and impact crust models. In particular, we identify a new type of reaction cycle that brings a pair of nuclei across the nuclear chart into equilibrium via alternating neutron capture and neutron release, interspersed with a neutron transfer. While neutron transfer reactions lead to changes in crust model predictions, and need to be considered in future studies, previous conclusions concerning heating, cooling, and compositional evolution are remarkably robust.

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H. Schatz, Z. Meisel, E. Brown, et. al.
Thu, 23 Dec 21
9/63

Comments: 8 pages, 10 figures, accepted for Astrophysical Journal

Ensembles of unified crust and core equations of state in a nuclear-multimessenger astrophysics environment [HEAP]

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http://arxiv.org/abs/2112.12108


We present an ensemble of unified neutron star crust and core equations of state, constructed using an extended Skyrme energy density functional through the crust and outer core, and appended by two piecewise polytropes at higher densities. The equations of state are parameterized by the first three coefficients in the density expansion of the symmetry energy $J,L$ and $K_{\rm sym}$, the moment of inertia of a 1.338 M${\odot}$ star $I{1.338}$ and the maximum neutron star mass $M_{\rm max}$. We construct an ensemble with uniform priors on all five parameters, and then apply data filters to the ensemble to explore the effect of combining neutron skin data from PREX with astrophysical measurements of radii and tidal deformabilities from NICER and LIGO/VIRGO. Neutron skins are calculated directly using the EDFs. We demonstrate that both the nuclear data and astrophysical data play a role in constraining crust properties such as the mass, thickness and moment of inertia of the crust and the nuclear pasta layers therein, and that astrophysical data better constrains $K_{\rm sym}$ than PREX data.

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W. Newton, L. Balliet, S. Budimir, et. al.
Thu, 23 Dec 21
12/63

Comments: 11 Pages, 3 figures, 1 table; submitted to EPJA

Equation of state and neutrino transfer in supernovae and neutron stars [HEAP]

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http://arxiv.org/abs/2112.11159


We overview the progress of the tables of the equation of state for astrophysical simulations and the numerical methods of neutrino transfer. Hot and dense matter play essential roles in core-collapse supernovae and neutron stars. Equation of state determines the structure of compact objects and their dynamics through its behavior of thermodynamic quantities. In addition, neutrinos are trapped in supernova cores and neutron star mergers and frequently interact with matter to crucially affect dynamics in determining the explosion mechanism and the final form of compact objects. Therefore, it is essential to implement detailed processes of nuclear and neutrino physics in numerical simulations by having reliable data set of the equation of state and reaction rates. We show examples of developments of the equation of state and the neutrino transfer and discuss research directions toward understanding the explosive phenomena by the first principle calculation.

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K. Sumiyoshi
Wed, 22 Dec 21
7/67

Comments: 13 pages, 4 figures; contribution to the EPJ A topical issue “CompOSE: a repository for Neutron Star Equations of State and Transport Properties”

Constraining neutron star properties with a new equation of state insensitive approach [HEAP]

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http://arxiv.org/abs/2112.10824


Instead of parameterizing the pressure-density relation of a neutron star (NS), one can parameterize its macroscopic properties such as mass ($M$), radius ($R$), and dimensionless tidal deformability ($\Lambda$) to infer the equation of state (EoS) combining electromagnetic and gravitational wave (GW) observations. We present a new method to parameterize $R(M)$ and $\Lambda(M)$ relations, which approximate the candidate EoSs with accuracy better than 5\% for all masses and span a broad region of $M-R-\Lambda$ plane. Using this method we combine the $M-\Lambda$ measurement from GW170817 and GW190425, and simultaneous $M-R$ measurement of PSR J0030+0451 and PSR J0740+6620 to place joint constraints on NS properties. At 90 \% confidence, we infer $R_{1.4}=12.05_{-0.87}^{+0.98}$ km and $\Lambda_{1.4}=372_{-150}^{+220}$ for a $1.4 M_{\odot}$ NS, and $R_{2.08}=12.65_{-1.46}^{+1.36}$ km for a $2.08 M_{\odot}$ NS. Furthermore, we use the inferred values of the maximum mass of a nonrotating NS $M_{\rm max}=2.52_{-0.29}^{+0.33} M_{\odot}$ to investigate the nature of the secondary objects in three potential neutron star-black hole merger (NSBH) system.

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B. Biswas and S. Datta
Wed, 22 Dec 21
20/67

Comments: N/A

Predictions for neutron stars from holographic nuclear matter [HEAP]

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http://arxiv.org/abs/2112.10633


We discuss masses, radii, and tidal deformabilities of neutron stars constructed from the holographic Witten-Sakai-Sugimoto model. Using the same model for crust and core of the star, we combine our theoretical results with the latest astrophysical data, thus deriving more stringent constraints than given by the data alone. For instance, our calculation predicts — independent of the model parameters — an upper limit for the maximal mass of the star of about 2.46 solar masses and a lower limit of the (dimensionless) tidal deformability of a 1.4-solar-mass star of about 277.

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N. Kovensky, A. Poole and A. Schmitt
Tue, 21 Dec 21
34/86

Comments: 11 pages, 6 figures, Contribution to proceedings of XXXIII International (ONLINE) Workshop on High Energy Physics “Hard Problems of Hadron Physics: Non-Perturbative QCD & Related Quests”

Universal relations for rapidly rotating cold and hot hybrid star [HEAP]

Posted on by

http://arxiv.org/abs/2112.10439


Several global parameters of compact stars are related via empirical relations, which are (nearly) independent of the underlying equation of state of dense matter and, therefore, are said to be universal. We investigate the universality of relations that express the maximum mass and the radius of non-rotating and maximally rapidly rotating configurations, as well as their moment of inertia, in terms of the compactness of the star. For this, we first utilize a collection of cold (zero-temperature) and hot (isentropic) nucleonic EoS and confirm that the universal relations are holding for our collection of EoS. We then go on, to add to our collection and test for the same universality models of EoS which admit a strong first-order phase transition from nucleonic to deconfined quark matter. Also in this case we find that the universal relations hold, in particular for hot, isentropic hybrid stars. By fitting the universal relations to our computed data, we determine the coefficients entering these relations and the accuracy to which they hold.

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N. Largani, T. Fischer, A. Sedrakian, et. al.
Tue, 21 Dec 21
52/86

Comments: 15 pages, 6 figures

Future radioisotope measurements to clarify the origin of deep-ocean 244Pu [HEAP]

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http://arxiv.org/abs/2112.09607


244Pu has been discovered in deep-ocean deposits spanning the past 10 Myr, a period that includes two 60Fe pulses from nearby supernovae. 244Pu is among the heaviest $r$-process products, and we consider whether the 244Pu was created in the supernovae, which is disfavored by model calculations, or in an earlier kilonova that seeded 244Pu in the nearby interstellar medium, which was subsequently swept up by the supernova debris. We propose probing these possibilities by measuring other $r$-process radioisotopes such as 129I and 182Hf in deep-ocean deposits and in lunar regolith.

Read this paper on arXiv…

X. Wang, A. Clark, J. Ellis, et. al.
Mon, 20 Dec 21
13/59

Comments: 7 pages, 3 figures, 1 table, comments welcome

A Bayesian analysis of the properties of hybrid stars with the NJL model [HEAP]

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http://arxiv.org/abs/2112.09595


We implement a Bayesian analysis of the properties of non-rotating hybrid stars at equilibrium with quark matter cores, as described by the $SU(3)$ Nambu-Jona-Lasinio (NJL) model. The hadronic phase is described by a unified meta-modelling approach, with a prior parameter space covering the present uncertainties on nuclear matter properties with nucleonic degrees of freedom. The parameter space of the NJL model includes vector-isoscalar and vector-isovector couplings and additionnally, an effective bag constant for the quark pressure is introduced as a free parameter. The phase transition is assumed to be first order with charge neutral phases, following the Maxwell construction. Our Bayesian framework includes filters on the experimental and theoretical low-density nuclear physics knowledge (atomic masses, ab initio calculations of the EoS) and high density constraints from astrophysical observations (maximum mass of J0740+6620, binary tidal deformability of the GW170817 event). We find that microscopic vector interactions play an important role in quark matter in order to stiffen the equation of state sufficiently to reach high star masses, in agreement with previous studies. Even within a very large prior for both the hadronic and the quark phase and the important freedom brought by the effective bag constant, our posterior quark cores tend to be relatively small and only appear in very heavy stars ($M\gtrsim 2 M_\odot$). Coincidentally, the inclusion of the nucleon-quark transition (deconfinement transition) only weakly affects the radii of compact stars, foreshadowing a very low observability of a possible phase transition using X-ray radii measurements.

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A. Pfaff, H. Hansen and F. Gulminelli
Mon, 20 Dec 21
21/59

Comments: N/A

Alpha-alpha scattering in the Multiverse [CL]

Posted on by

http://arxiv.org/abs/2112.09409


We investigate the phase shifts of low-energy $\alpha$-$\alpha$ scattering under variations of the fundamental parameters of the Standard Model, namely the light quark mass, the electromagnetic fine-structure constant as well as the QCD $\theta$-angle. As a first step, we recalculate $\alpha$-$\alpha$ scattering in our Universe utilizing various improvements in the adiabatic projection method, which leads to an improved, parameter-free prediction of the S- and D-wave phase shifts for laboratory energies below 10~MeV. We find that positive shifts in the pion mass have a small effect on the S-wave phase shift, whereas lowering the pion mass tends to unbind the two-alpha system, limiting such variations to less than 7%. The effect on the D-wave phase shift turns out to be more pronounced as signaled by the D-wave resonance parameters. Variations of the fine-structure constant have almost no effect on the low-energy $\alpha$-$\alpha$ phase shifts. We further show that up-to-and-including next-to-leading order in the chiral expansion, variations of these phase shifts with respect to the QCD $\theta$-angle can be expressed in terms of the $\theta$-dependent pion mass.

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S. Elhatisari, T. Lähde, D. Lee, et. al.
Mon, 20 Dec 21
33/59

Comments: 22 pages, 8 figures

Locating the special point of hybrid neutron stars [CL]

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http://arxiv.org/abs/2112.09166


The special point is a feature unique to models of hybrid neutron stars. It represents a location on their mass–radius sequences that is insensitive to the phase transition density. We consider hybrid neutron stars with a core of deconfined quark matter that obeys a constant–sound–speed (CSS) equation of state model and provide a fit formula for the coordinates of the special point as functions of the squared sound speed ($c_s^2$) and pressure scale ($A$) parameters. Using the special point mass as a proxy for the maximum mass of the hybrid stars we derive limits for the CSS model parameters based on the recent NICER constraint on mass and radius of pulsar PSR J0740+6620, $0.36 < {c^2_s}{\rm min} < 0.43$ and $80<A [{\rm MeV/fm}^3]<160$. The upper limit for the maximum mass of hybrid stars depends on the upper limit for $c_s^2$ so that choosing $c^2{s,max} = 0.6$ results in $M_{\rm max}<2.7~M_\odot$, within the mass range of GW190814.

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M. Cierniak and D. Blaschke
Mon, 20 Dec 21
57/59

Comments: 8 pages, 5 figures, 1 table

Holographic approach to compact stars and their binary mergers [CL]

Posted on by

http://arxiv.org/abs/2112.08422


In this review article, we describe the role of holography in deciphering the physics of dense QCD matter, relevant for the description of compact stars and their binary mergers. We review the strengths and limitations of the holographic duality in describing strongly interacting matter at large baryon density, walk the reader through the most important results derived using the holographic approach so far, and highlight a number of outstanding open problems in the field. Finally, we discuss how we foresee holography contributing to compact-star physics in the coming years.

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C. Hoyos, N. Jokela and A. Vuorinen
Fri, 17 Dec 21
7/72

Comments: 84 pages, 19 figures; invited review article

Dark matter component in hadronic models with short-range correlations [CL]

Posted on by

http://arxiv.org/abs/2112.07716


A relativistic mean field hadronic model with a dark matter (DM) particle coupled to nucleons including short-range correlations (SRC) is applied to study neutron stars (NS). The lightest neutralino is chosen as the dark particle candidate, which interacts with nucleons by the exchange of Higgs bosons. A detailed thermodynamical analysis shows that the contribution of the DM fermions to the energy density of the matter composed by these particles and nucleons is completely dominated by the DM kinetic terms. The model reproduces satisfactorily the constraints on the mass-radius diagram obtained from the analysis of the combined data from the NICER mission, LIGO collaboration, and mass measurements from radio observations. We show that the SRC balance the reduction of the neutron star mass due to the DM component, and because of that the model is able to present more massive NS. We also present a study of the effect, in the NS mass-radius profiles, of the uncertainties in some bulk parameters related to the hadronic sector. We find that it is possible to generate parametrizations, with DM content, compatible with the recent astrophysical constraints and with the uncertainty in the symmetry energy slope obtained from the results reported by the updated Lead Radius EXperiment (PREX-2).

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O. Lourenço, T. Frederico and M. Dutra
Thu, 16 Dec 21
75/83

Comments: 12 pages, 12 figures. Accepted for publication in Phys. Rev. D

Transport coefficients in neutron star environment with the possibility of hadron-quark phase transition [CL]

Posted on by

http://arxiv.org/abs/2112.07404


We have attempted to visualize transport coefficients like shear viscosity and electrical conductivity with respect to density of neutron star environment, whose core may expect a hadron-quark phase transition due to acquiring much higher density than nuclear saturation density. By making sandwich between MIT bag model for quark phase and two different effective hadronic models for hadronic phase, we have estimated the transport coefficients of two phases. During sketching of the transport coefficients, we have discussed their detailed density profile of phase-space part and relaxation time part. By calculating shear viscosity to density ratio, we have also explored the nearly perfect fluid domain along the density axis of hadron-quark phase diagram.

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D. Sen, N. Alam and S. Ghosh
Wed, 15 Dec 21
67/85

Comments: 26 pages, 5 figures

Probing the incompressibility of nuclear matter at ultra-high density through the prompt collapse of asymmetric neutron star binaries [HEAP]

Posted on by

http://arxiv.org/abs/2112.05864


Using 250 neutron star merger simulations with microphysics, we explore for the first time the role of nuclear incompressibility in the prompt collapse threshold for binaries with different mass ratios. We demonstrate that observations of prompt collapse thresholds, either from binaries with two different mass ratios or with one mass ratio but combined with the knowledge of the maximum neutron star mass or compactness, will constrain the incompressibility at the maximum neutron star density, $K_{\rm max}$, to within tens of percent. This, otherwise inaccessible, measure of $K_{\rm max}$ can potentially reveal the presence of hyperons or quarks inside neutron stars.

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A. Perego, D. Logoteta, D. Radice, et. al.
Tue, 14 Dec 21
63/98

Comments: 8 pages, 5 figures, 2 tables

Hybrid stars from a constrained equation of state [CL]

Posted on by

http://arxiv.org/abs/2112.05546


We determine, within a meta-model, the properties of the nuclear matter equation of state (EoS) that allow for a phase transition to deconfinement matter. It is shown that the properties that define the isoscalar channel are the ones that are affected, in particular, a phase transition implies much larger values of the skewness and kurtosis. The effect of multi-quark interaction channels in the description of the quark phase in hybrid stars is also studied. NS properties, such as the mass and radius of the quark core, show an interplay dependence between the 8-quark vector and the 4-quark isovector-vector interactions. We show that low mass NS, $M\sim 1.4 M_\odot$, may already contain a quark core, and satisfy all existing NS observational constraints. We discuss the strangeness content of the quark core and its influence on the speed of sound.

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M. Ferreira, R. Pereira and C. Providência
Mon, 13 Dec 21
17/70

Comments: 8 pages, 5 figures, Contribution to the Virtual Tribute to Quark Confinement and the Hadron Spectrum 2021 conference proceedings (vConf21)

Hot neutron stars and their equation of state [CL]

Posted on by

http://arxiv.org/abs/2112.05323


A set of microscopic, covariant density-functional, and non-relativistic Skyrme-type equations of state is employed to study the structure of purely nucleonic neutron stars at finite temperature. After examining the agreement with presently available astrophysical observational constraints, we find that the magnitude of thermal effects depends on the nucleon effective mass as well as on the stiffness of the cold equation of state. We evidence a fairly small but model-dependent effect of finite temperature on stellar stability that is correlated with the relative thermal pressure inside the star.

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J. Wei, G. Burgio, A. Raduta, et. al.
Mon, 13 Dec 21
21/70

Comments: 10 pages, 8 figures

Determination of the symmetry energy from the neutron star equation of state [CL]

Posted on by

http://arxiv.org/abs/2112.05551


We analyze the uncertainties introduced in the determination of the neutron star matter proton fraction, in a range of densities close to the saturation density, if the cold $\beta$-equilibrium neutron star matter equation of state (EoS) is known. In particular, we discuss the effect of neglecting the muon contribution and of considering that the energy density of nuclear matter is well described by taking only terms until second order in the proton-neutron asymmetry. It is shown that two types of uncertainties may be associated with the extraction of the symmetry energy from the $\beta$-equilibrium equation of state: an overestimation if terms above the parabolic approximation on the asymmetry parameter are neglected, or an underestimation if the muon contribution is not considered. The effect of the uncertainty on the symmetric nuclear matter EoS on the determination of the proton fraction is discussed. It could be shown that the neutron star mass-radius curve is sensitive to the parabolic approximation on the asymmetry parameter.

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P. Tovar, M. Ferreira and C. Providência
Mon, 13 Dec 21
52/70

Comments: 13 pages, 8 figures, Accepted for publication in Physical Review D

Translating neutron star observations to nuclear symmetry energy via artificial neural networks [CL]

Posted on by

http://arxiv.org/abs/2112.04089


One of the most significant challenges involved in efforts to understand the equation of state of dense neutron-rich matter is the uncertain density dependence of the nuclear symmetry energy. Because of its broad impact, pinning down the density dependence of the nuclear symmetry energy has been a longstanding goal of both nuclear physics and astrophysics. Recent observations of neutron stars, in both electromagnetic and gravitational-wave spectra, have already constrained significantly the nuclear symmetry energy at high densities. Training deep neural networks to learn a computationally efficient representation of the mapping between astrophysical observables of neutron stars, such as masses, radii, and tidal deformabilities, and the nuclear symmetry energy allows its density dependence to be determined reliably and accurately. In this work we use a deep learning approach to determine the nuclear symmetry energy as a function of density directly from observational neutron star data. We show for the first time that artificial neural networks can precisely reconstruct the nuclear symmetry energy from a set of available neutron star observables, such as, masses and radii as those measured by, e.g., the NICER mission, or masses and tidal deformabilities as measured by the LIGO/VIRGO/KAGRA gravitational-wave detectors. These results demonstrate the potential of artificial neural networks to reconstruct the symmetry energy, and the equation of state, directly from neutron star observational data, and emphasize the importance of the deep learning approach in the era of Multi-Messenger Astrophysics.

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P. Krastev
Thu, 9 Dec 21
16/63

Comments: 16 pages, 6 figures. Invited article for Galaxies for the Special Issue “Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics”

Surface properties of neutron star within coherent density fluctuation model using the relativistic mean-field density [CL]

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http://arxiv.org/abs/2112.03519


A detailed study of the structural properties of neutron star (NS) is performed within the coherent density fluctuation model using the recently developed G3 and widely used NL3 and IU-FSU parameter sets in the relativistic mean-field formalism. The masses, moment of inertia, and density profiles of the NS at various mass limits are studied. The incompressibility $K^{star}$, symmetry energy $S^{star}$, slope parameter $L_{sym}^{star}$ and curvature coefficient $K_{sym}^{star}$ of the NS at various masses are analyzed. The surface properties ($K^{star}$, $S^{star}$, $L_{sym}^{star}$ and $K_{sym}^{star}$) are found to be model dependent, NL3 is the stiffest equation of state gives the higher magnitude of surface quantities as compared to the G3 and IU-FSU forces.

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A. Kumar, H. Das, J. Pattnaik, et. al.
Wed, 8 Dec 21
54/77

Comments: 9 pages, 8 figures, 2 tables, comments welcome

Finite-temperature electron-capture rates for neutron-rich nuclei around N=50 and effects on core-collapse supernovae simulations [CL]

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http://arxiv.org/abs/2112.01626


The temperature dependence of stellar electron-capture (EC) rates is investigated, with a focus on nuclei around $N=50$, just above $Z=28$, which play an important role during the collapse phase of core-collapse supernovae (CCSN). Two new microscopic calculations of stellar EC rates are obtained from a relativistic and a non-relativistic finite-temperature quasiparticle random-phase approximation approaches, for a conventional grid of temperatures and densities. In both approaches, EC rates due to Gamow-Teller transitions are included. In the relativistic calculation contributions from first-forbidden transitions are also included, and add strongly to the EC rates. The new EC rates are compared with large-scale shell model calculations for the specific case of $^{86}$Kr, providing insight into the finite-temperature effects on the EC rates. At relevant thermodynamic conditions for core-collapse, the discrepancies between the different calculations of this work are within about one order of magnitude. Numerical simulations of CCSN are performed with the spherically-symmetric GR1D simulation code to quantify the impact of such differences on the dynamics of the collapse. These simulations also include EC rates based on two parametrized approximations. A comparison of the neutrino luminosities and enclosed mass at core bounce shows that differences between simulations with different sets of EC rates are relatively small ($\approx 5\%$), suggesting that the EC rates used as inputs for these simulations have become well constrained.

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S. Giraud, E. Ney, A. Ravlić, et. al.
Mon, 6 Dec 21
23/61

Comments: N/A

Ab initio predictions link the neutron skin of ${}^{208}$Pb to nuclear forces [CL]

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http://arxiv.org/abs/2112.01125


Heavy atomic nuclei have an excess of neutrons over protons. This leads to the formation of a neutron skin whose thickness, $R_\mathrm{skin}$, is sensitive to details of the nuclear force — linking atomic nuclei to properties of neutron stars, thereby relating objects that differ in size by 18 orders of magnitude [1, 2]. ${}^{208}$Pb is of particular interest here because it exhibits a simple structure and is accessible to experiment. However, computing such a heavy nucleus has been out of reach for ab initio theory. By combining advances in quantum many-body methods, statistical tools, and emulator technology, we make quantitative predictions for the properties of ${}^{208}$Pb starting from nuclear forces that are consistent with symmetries of low-energy quantum chromodynamics. We explore $10^9$ different nuclear-force parameterisations via history matching, confront them with data in select light nuclei, and arrive at an importance-weighted ensemble of interactions. We accurately reproduce bulk properties of ${}^{208}$Pb and find $R_\mathrm{skin}({}^{208}\mathrm{Pb}) = 0.14-0.20$ fm which is smaller than a recent extraction from parity-violating electron scattering [3] but in agreement with other experimental probes. The allowable range of $R_\mathrm{skin}({}^{208}\mathrm{Pb})$ is significantly constrained by nucleon-nucleon scattering data, ruling out very thick skins. This work demonstrates that nuclear forces constrained to light systems extrapolate reliably to even the heaviest nuclei, and that we can make quantitative predictions across the nuclear landscape.

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B. Hu, W. Jiang, T. Miyagi, et. al.
Fri, 3 Dec 21
33/81

Comments: N/A

Perturbative and non-perturbative effects in ultraperipheral production of lepton pairs [CL]

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http://arxiv.org/abs/2112.00358


Perturbative and non-perturbative terms of the cross sections of ultraperipheral production of lepton pairs in ion collisions are taken into account. It is shown that production of low-mass $e^+e^-$ pairs is strongly enhanced (compared to perturbative estimates) due to the non-perturbative Sommerfeld-Gamow-Sakharov (SGS) factor. Coulomb attraction of the non-relativistic components of those pairs leads to the finite value of their mass distribution at lowest relative velocities. Their annihilation can result in the increased intensity of 511 keV photons. It can be recorded at the NICA collider and is especially crucial in astrophysical implications regarding the 511 keV line emitted from the Galactic center. The analogous effect can be observed in lepton pairs production at LHC. Energy spectra of lepton pairs created in ultraperipheral nuclear collisions and their transverse momenta are calculated.

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I. Dremin
Fri, 3 Dec 21
60/81

Comments: 9 p., 2 Figs. arXiv admin note: text overlap with arXiv:2008.13184, arXiv:2101.04679

Statistical Hauser-Feshbach model description of $(n,α)$ reaction cross sections for s-process nuclei [CL]

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http://arxiv.org/abs/2111.14980


The $(n,\alpha)$ reaction contributes in many processes of energy generation and nucleosynthesis in stellar environment. Since experimental data are available for a limited number of nuclei and in restricted energy ranges, at present only theoretical studies can provide predictions for all astrophysically relevant $(n,\alpha)$ reaction cross sections. The purpose of this work is to study $(n,\alpha)$ reaction cross sections for a set of nuclei contributing in the s-process nucleosynthesis. Theory framework is based on the statistical Hauser-Feshbach model implemented in TALYS code and supplemented with nuclear properties based on Skyrme energy density functional. In addition to the analysis of the properties of calculated $(n,\alpha)$ cross sections, the Mawellian averaged cross sections are described and analyzed for the range of temperatures in stellar environment. Model calculations determined astrophysically relevant energy windows in which $(n,\alpha)$ reactions occur in massive stars. In order to reduce the uncertainties in modeling $(n,\alpha)$ reaction cross sections for the s-process, novel experimental studies are called for. The results on the predicted relevant $(n,\alpha)$ reaction energy windows for the s-process nuclei provide a guidance for the priority energy ranges for the future experimental studies.

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S. Küçüksucu, M. Yiğit and N. Paar
Wed, 1 Dec 21
59/110

Comments: 25 pages, 9 figures

Hypermassive quark cores [CL]

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http://arxiv.org/abs/2111.13732


Using a quantum hadrodynamics (QHD) and MIT based models we construct hybrid stars within the Maxwell criteria of hadron-quark phase transition. We are able to produce a hybrid star with maximum mass of 2.15$M_\odot$. Furthermore, a 2.03$M_\odot$ star with a quark core corresponding to more than $80\%$ of both, its total mass and radius, is also possible.

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L. Lopes, C. Biesdorf and D. Menezes
Tue, 30 Nov 21
20/105

Comments: 13 pages, 11 figures, 15 tables

Neutrino flavor mixing with moments [CL]

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http://arxiv.org/abs/2111.13722


The successful transition from core-collapse supernova simulations using classical neutrino transport to simulations using quantum neutrino transport will require the development of methods for calculating neutrino flavor transformations that mitigate the computational expense. One potential approach is the use of angular moments of the neutrino field, which has the added appeal that there already exist simulation codes which make use of moments for classical neutrino transport. Evolution equations for quantum moments based on the quantum kinetic equations can be straightforwardly generalized from the evolution of classical moments based on the Boltzmann equation. We present an efficient implementation of neutrino transformation using quantum angular moments in the free streaming, spherically symmetric bulb model. We compare the results against analytic solutions and the results from more exact multi-angle neutrino flavor evolution calculations. We find that our moment-based methods employing scalar closures predict, with good accuracy, the onset of collective flavor transformations seen in the multi-angle results. However, they over-estimate the coherence between neutrinos traveling along different trajectories in tests that neglect neutrino-neutrino interactions. More sophisticated quantum closures may improve the agreement between the inexpensive moment-based methods and the multi-angle approach.

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M. Myers, T. Cooper, M. Warren, et. al.
Tue, 30 Nov 21
73/105

Comments: N/A

Constraints on the fermionic dark matter from observations of neutron stars [HEAP]

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http://arxiv.org/abs/2111.13289


We study an impact of asymmetric fermionic dark matter on neutron star properties, including tidal deformability, mass, radius, etc. We present the conditions at which dark matter particles tend to form a compact structure in a core of the star or create an extended halo around it. We show that compact core of dark matter leads to a decrease of the total gravitational mass and tidal deformability compared to a pure baryonic star, while presence of a dark matter halo increases those observable quantities. By imposing an existing astrophysical and gravitational wave constraints set by LIGO/Virgo Collaboration together with the recent results on the spatial distribution of dark matter in the Milky Way we determine a new upper limit on the mass and fraction of dark matter particles inside compact stars. Furthermore, we show that the formation of an extended halo around a NS is incompatible with the GW170817 tidal deformability constraint.

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V. Sagun, E. Giangrandi, O. Ivanytskyi, et. al.
Mon, 29 Nov 21
54/94

Comments: 5 pages, 4 figures

Holographic QCD in the NICER era [CL]

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http://arxiv.org/abs/2111.12101


We analyze families of hybrid equations of state of cold QCD matter, which combine input from gauge/gravity duality and from various ab initio methods for nuclear matter at low density, and predict that all neutron stars are fully hadronic without quark matter cores. We focus on constraints from recent measurements by the NICER telescope on the radius and mass of the millisecond pulsar PSR J0740+6620. These results are found to be consistent with our approach: they set only mild constraints on the hybrid equations of state, and favor the most natural models which are relatively stiff at low density. Adding an upper bound on the maximal mass of neutron stars, as suggested by the analysis of the GW170817 neutron star merger event, tightens the constraints considerably. We discuss updated predictions on observables such as the transition density and latent heat of the nuclear to quark matter transition as well as the masses, radii, and tidal deformabilities of neutron stars.

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N. Jokela, M. Järvinen and J. Remes
Thu, 25 Nov 21
47/60

Comments: 21 pages, 8 figures

A moderately-sized nuclear network to assist multi-D hydrodynamic simulations of supernova explosions [SSA]

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http://arxiv.org/abs/2111.12353


A key ingredient in any numerical study of supernova explosions is the nuclear network routine that is coupled with the hydrodynamic simulation code. When these studies are performed in more than one dimension, the size of the network is severely limited by computational issues. In this work, we propose a nuclear network, net87, which is close to one hundred nuclei and could be appropriate to simulate supernova explosions in multidimensional studies. One relevant feature is that electron and positron captures on free protons and neutrons have been incorporated to the network. Such addition allows for a better track of both, the neutronized species and the gas pressure. A second important feature is that the reactions are implicitly coupled with the temperature, which enhances the stability in the nuclear statistical equilibrium (NSE) regime. Here we analyze the performance of net87 in light of both: the computational overhead of the algorithm and the outcome in terms of the released nuclear energy and produced yields in typical Type Ia Supernova conditions.

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A. Sanz, R. Cabezón and D. García-Senz
Thu, 25 Nov 21
56/60

Comments: 3 pages, 2 Figures and 1 Table. in Proceedings of The 16th International Symposium on Nuclei in the Cosmos (NIC-XVI)

A moderately-sized nuclear network to assist multi-D hydrodynamic simulations of supernova explosions [SSA]

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http://arxiv.org/abs/2111.12353


A key ingredient in any numerical study of supernova explosions is the nuclear network routine that is coupled with the hydrodynamic simulation code. When these studies are performed in more than one dimension, the size of the network is severely limited by computational issues. In this work, we propose a nuclear network, net87, which is close to one hundred nuclei and could be appropriate to simulate supernova explosions in multidimensional studies. One relevant feature is that electron and positron captures on free protons and neutrons have been incorporated to the network. Such addition allows for a better track of both, the neutronized species and the gas pressure. A second important feature is that the reactions are implicitly coupled with the temperature, which enhances the stability in the nuclear statistical equilibrium (NSE) regime. Here we analyze the performance of net87 in light of both: the computational overhead of the algorithm and the outcome in terms of the released nuclear energy and produced yields in typical Type Ia Supernova conditions.

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A. Sanz, R. Cabezón and D. García-Senz
Thu, 25 Nov 21
15/60

Comments: 3 pages, 2 Figures and 1 Table. in Proceedings of The 16th International Symposium on Nuclei in the Cosmos (NIC-XVI)

Holographic QCD in the NICER era [CL]

Posted on by

http://arxiv.org/abs/2111.12101


We analyze families of hybrid equations of state of cold QCD matter, which combine input from gauge/gravity duality and from various ab initio methods for nuclear matter at low density, and predict that all neutron stars are fully hadronic without quark matter cores. We focus on constraints from recent measurements by the NICER telescope on the radius and mass of the millisecond pulsar PSR J0740+6620. These results are found to be consistent with our approach: they set only mild constraints on the hybrid equations of state, and favor the most natural models which are relatively stiff at low density. Adding an upper bound on the maximal mass of neutron stars, as suggested by the analysis of the GW170817 neutron star merger event, tightens the constraints considerably. We discuss updated predictions on observables such as the transition density and latent heat of the nuclear to quark matter transition as well as the masses, radii, and tidal deformabilities of neutron stars.

Read this paper on arXiv…

N. Jokela, M. Järvinen and J. Remes
Thu, 25 Nov 21
55/60

Comments: 21 pages, 8 figures

QHC21 equation of state of neutron star matter — in light of 2021 NICER data [HEAP]

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http://arxiv.org/abs/2111.11919


The recent NICER measurement of the radius of the neutron star PSR J0740+6620, and the inferred small variation in neutron star radii from $1.4M_\odot$ to $2.1M_\odot$, suggest that the neutron star equation of state remains relatively stiff up to baryon densities $n \sim$ 2-4 times nuclear saturation density, $n_0$ — the region where we expect hadronic matter to be undergoing transformation into quark matter. To delineate the physics from the nuclear to the quark matter regimes we use the quark-hadron-crossover (QHC) template to construct an updated equation of state, QHC21. We include nuclear matter results primarily based on chiral effective field theory, but also note results of using nuclear matter variational calculations based on empirical nuclear forces, thus covering the range of uncertainties in the nuclear equation of state. To allow for a possible early transition to quark degrees of freedom we begin the crossover regime from nucleons to quarks at $1.5n_0$. The resulting equations of state are stiffer than our earlier QHC19 at $\lesssim 2n_0$, predicting larger radii in substantial agreement with the NICER data, with accompanying peaks in sound velocity at 2-4$n_0$. We discuss possible microscopic mechanisms underlying stiffening of the equation of state.

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T. Kojo, G. Baym and T. Hatsuda
Wed, 24 Nov 21
34/61

Comments: 10 pages, 11 figures

Modulation of pulse profile as a signal for phase transitions in a pulsar core [HEAP]

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http://arxiv.org/abs/2111.10805


We calculate detailed modification of pulses from a pulsar arising from the effects of phase transition induced density fluctuations on the pulsar moment of inertia. We represent general statistical density fluctuations using a simple model where the initial moment of inertia tensor of the pulsar (taken to be diagonal here) is assumed to get random additional contributions for each of its component which are taken to be Gaussian distributed with certain width characterized by the strength of density fluctuations $\epsilon$. Using sample values of $\epsilon$, (and the pulsar deformation parameter $\eta$) we numerically calculate detailed pulse modifications by solving Euler’s equations for the rotational dynamics of the pulsar. We also give analytical estimates which can be used for arbitrary values of $\epsilon$ and $\eta$. We show that there are very specific patterns in the perturbed pulses which are observable in terms of modulations of pulses over large time periods. In view of the fact that density fluctuations fade away eventually leading to a uniform phase in the interior of pulsar, the off-diagonal components of MI tensor also vanish eventually. Thus, the modification of pulses due to induced wobbling (from the off-diagonal MI components) will also die away eventually. This allows one to distinguish these transient pulse modulations from the effects of any wobbling originally present. Further, the decay of these modulations in time directly relates to relaxation of density fluctuations in the pulsar giving valuable information about the nature of phase transition occurring inside the pulsar.

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P. Bagchi, B. Layek, A. Sarkar, et. al.
Tue, 23 Nov 21
66/84

Comments: 10 pages, 6 figures, submitted to MNRAS

The slope, the hill, the drop, and the swoosh: Learning about the nuclear matter equation of state from the binary Love relations [HEAP]

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http://arxiv.org/abs/2111.10260


Analyses that connect astrophysical observations of neutron stars with nuclear matter properties sometimes rely on equation-of-state insensitive relations. We show that the slope of the binary Love relations (i.e.~between the tidal deformabilities of binary neutron stars) encodes the rate of change of the nuclear matter speed of sound below three times nuclear saturation density. Twin stars lead to relations that present a signature ”hill”, ”drop”, and ”swoosh” due to the second (mass-radius) stable branch, requiring a new description of the binary love relations.

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H. Tan, V. Dexheimer, J. Noronha-Hostler, et. al.
Mon, 22 Nov 21
39/53

Comments: 8 pages, 3 figures

Hadron-quark Pasta Phase in Massive Neutron Stars [CL]

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http://arxiv.org/abs/2111.08909


The structured hadron-quark mixed phase, known as the pasta phase, is expected to appear in the core of massive neutron stars. Motivated by the recent advances in astrophysical observations, we explore the possibility of the appearance of quarks inside neutron stars and check its compatibility with current constraints. We investigate the properties of the hadron-quark pasta phases and their influences on the equation of state (EOS) for neutron stars. In this work, we extend the energy minimization (EM) method to describe the hadron-quark pasta phase, where the surface and Coulomb contributions are included in the minimization procedure. By allowing different electron densities in the hadronic and quark matter phases, the total electron chemical potential with the electric potential remains constant, and local ? equilibrium is achieved inside the Wigner-Seitz cell. The mixed phase described in the EM method shows the features lying between the Gibbs and Maxwell constructions, which is helpful for understanding the transition from the Gibbs construction (GC) to the Maxwell construction (MC) with increasing surface tension. We employ the relativistic mean-field model to describe the hadronic matter, while the quark matter is described by the MIT bag model with vector interactions. It is found that the vector interactions among quarks can significantly stiffen the EOS at high densities and help enhance the maximum mass of neutron stars. Other parameters like the bag constant can also affect the deconfinement phase transition in neutron stars. Our results show that hadron-quark pasta phases may appear in the core of massive neutron stars that can be compatible with current observational constraints.

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M. Ju, J. Hu and H. Shen
Thu, 18 Nov 21
50/92

Comments: N/A

Neutrino flavor evolution in dense environments and the r-process [CL]

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http://arxiv.org/abs/2111.08250


In dense environments, standard and non-standard neutrino interactions with the background particles trigger a variety of flavor mechanisms, which can impact r-process nucleosynthetic abundances. Future observations of a(n) (extra)galactic supernova will tell us about properties of neutrinos and of the astrophysical source that produce them. The upcoming measurement of the diffuse supernova neutrino background constitute a unique source of information. We highlight some recent developments.

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M. Volpe
Wed, 17 Nov 21
20/64

Comments: 5 pages, Proceedings for PANIC2021

Skyrme-based extrapolation for the static response of neutron matter [CL]

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http://arxiv.org/abs/2111.08056


The study of inhomogeneous neutron matter can provide insights into the structure of neutron stars as well as their dynamics in neutron-star mergers. In this work we tackle pure neutron matter in the presence of a periodic external field by considering a finite (but potentially large) number of particles placed in periodic boundary conditions. We start with the simpler setting of a noninteracting gas and then switch to a Skyrme-Hartree-Fock approach, showing static-response results for five distinct Skyrme parametrizations. We explain both the technical details of our computational approach, as well as the significance of these results as a general finite-size extrapolation scheme that may be used by ab initi} practitioners to approach the static-response problem of neutron matter in the thermodynamic limit.

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M. Buraczynski, S. Martinello and A. Gezerlis
Wed, 17 Nov 21
27/64

Comments: 18 pages, 20 figures

NICER view on holographic QCD [CL]

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http://arxiv.org/abs/2111.07940


The holographic models for dense QCD matter work surprisingly well. A general implication seems that the deconfinement phase transition dictates the maximum mass of neutron stars. The nuclear matter phase turns out to be rather stiff which, if continuously merged with nuclear matter models based on effective field theories, leads to the conclusion that neutron stars do not have quark matter cores in the light of all current astrophysical data. We comment that as the perturbative QCD results are in stark contrast with strong coupling results, any future simulations of neutron star mergers incorporating corrections beyond ideal fluid should proceed cautiously. For this purpose, we provide a model which treats nuclear and quark matter phases in a unified framework at strong coupling.

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N. Jokela
Tue, 16 Nov 21
24/97

Comments: 9 pages, 4 figures. Talk at the (virtual) “Quark Confinement and the Hadron Spectrum 2021” conference on 2 — 6 August 2021 in Stavanger, Norway

Crustal properties of the neutron star within effective relativistic mean-field model [CL]

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http://arxiv.org/abs/2111.07278


We use the effective relativistic mean-field (E-RMF) model to study the crustal properties of the neutron star. The unified equations of state (EoS) are constructed using recently developed E-RMF parameter sets, such as FSUGarnet, IOPB-I, and G3. The outer crust composition is determined using the Atomic Mass Evaluation 2020 data [\textbf{Chinese Physics C 45, 030002 (2021)}] along with the available Hartree-Fock-Bogoliubov mass models [\textbf{bf Phys. Rev. C 88, 024308 (2013)}] for neutron-rich nuclei. The structure of the inner crust is estimated by performing the compressible liquid drop model calculations using the same E-RMF functional as that for the uniform nuclear matter in the liquid core. Various neutron star properties such as mass-radius ($M-R$) relation, the moment of inertia ($I$), the fractional crustal moment of inertia ($I_{crust}/I$), mass ($M_{crust})$ and thickness ($l_{crust}$) of the crust are calculated with three unified EoSs. The crustal properties are found to be sensitive to the density-dependent symmetry energy and slope parameter advocating the importance of the unified treatment of neutron star EoS. The three unified EoSs, IOPB-I-U, FSUGarnet-U, and G3-U, reproduced the observational data obtained with different pulsars, NICER, and glitch activity and are found suitable for further description of the structure of the neutron star.

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V. Parmar, H. Das, A. Kumar, et. al.
Tue, 16 Nov 21
53/97

Comments: 18 pages, 13 figures, 6 tables, comments are welcome

A modified Brink-Axel hypothesis for astrophysical Gamow-Teller transitions [CL]

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http://arxiv.org/abs/2111.06242


Weak interaction charged current transition strengths from highly excited nuclear states are fundamental ingredients for accurate modeling of compact object composition and dynamics, but are difficult to obtain either from experiment or theory. For lack of alternatives, calculations have often fallen back upon a generalized Brink-Axel hypothesis, that is, assuming the strength function (transition probability) is independent of the initial nuclear state but depends only upon the transition energy and the weak interaction properties of the parent nucleus ground state. Here we present numerical evidence for a modified `local’ Brink-Axel hypothesis for Gamow-Teller transitions for $pf$-shell nuclei relevant to astrophysical applications. Specifically, while the original Brink-Axel hypothesis does not hold globally, strength functions from initial states nearby in energy are similar within statistical fluctuations. This agrees with previous work on strength function moments. Using this modified hypothesis, we can tackle strength functions at previously intractable initial energies, using semi-converged initial states at arbitrary excitation energy. Our work provides a well-founded method for computing accurate thermal weak transition rates for medium-mass nuclei at temperatures occurring in stellar cores near collapse. We finish by comparing to previous calculations of astrophysical rates.

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R. Herrera and C. Fuller
Fri, 12 Nov 21
16/53

Comments: 19 pages, 10 figures

The Second Love Number of Dark Compact Planets and Neutron Stars with Dark Matter [HEAP]

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http://arxiv.org/abs/2111.06197


We study the mass-radius relation and the second Love number of compact objects made of ordinary matter and non-selfannihilating fermionic dark matter for a wide range of dark matter particle masses, and for the cases of weakly and strongly interacting dark matter. We obtain stable configurations of compact objects with radii smaller than 10 km and masses similar to Earth- or Jupiter-like stellar objects. In certain parameter ranges we find second Love numbers which are markedly different compared to those expected for neutron stars without dark matter. Thus, by obtaining the compactness of these compact objects and measuring their tidal deformability from gravitational wave detections from binary neutron star mergers, the extracted value of second Love number would allow to determine the existence of dark matter inside neutron stars irrespective of the equation of state of ordinary matter.

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Y. Dengler, J. Schaffner-Bielich and L. Tolos
Fri, 12 Nov 21
52/53

Comments: 9 pages, 2 figures, 1 table

Density dependence of symmetry energy and neutron skin thickness revisited [CL]

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http://arxiv.org/abs/2111.05743


The correlation between neutron skin-thickness of a neutron-rich nucleus and slope parameter of symmetry energy is assessed as a function of density using relativistic mean field models containing non-linear couplings among different mesons. Models with larger skin were found to probe the slope parameter even at suprasaturation densities, whereas models with smaller skin were observed to be sensitive only at specific subsaturation density, connected to the average density of nuclei. Possible reasons behind this density dependence are explored systematically. These results might be model specific, which need to be reassessed in other type of interactions existing in the literature. Nevertheless, extrapolating the predictions at high densities from models, which are optimized by data at saturation or subsaturation densities, needs to be handled with care

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C. Mondal
Thu, 11 Nov 21
5/60

Comments: 6 figures, 6 pages

How perturbative QCD constrains the Equation of State at Neutron-Star densities [CL]

Posted on by

http://arxiv.org/abs/2111.05350


We demonstrate in a general and analytic way how high-density information about the equation of state (EoS) of strongly interacting matter obtained using perturbative Quantum Chromodynamics (pQCD) constrains the same EoS at densities reachable in physical neutron stars. Our approach is based on utilizing the full information of the thermodynamic potentials at the high-density limit together with thermodynamic stability and causality. The results can be used to propagate the pQCD calculations reliable around $40 n_s$ to lower densities in the most conservative way possible. We constrain the EoS starting from only few times the nuclear saturation density $n \gtrsim 2.2 n_s$ and at $n = 5 n_s$ we exclude at least 65% of otherwise allowed area in the $\epsilon – p$-plane. These purely theoretical results are independent of astrophysical neutron-star input and hence they can also be used to test theories of modified gravity and BSM physics in neutron stars.

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O. Komoltsev and A. Kurkela
Thu, 11 Nov 21
14/60

Comments: 9 pages, 6 figures

Light scalars in neutron star mergers [CL]

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http://arxiv.org/abs/2111.05852


Due to their unique set of multimessenger signals, neutron star mergers have emerged as a novel environment for studies of new physics beyond the Standard Model (SM). As a case study, we consider the simplest extension of the SM scalar sector involving a light CP-even scalar singlet $S$ mixing with the SM Higgs boson. These $S$ particles can be produced abundantly in neutron star mergers via the nucleon bremsstrahlung process. We show that the $S$ particles may either be trapped in or stream freely out of the merger remnant, depending on the $S$ mass, its mixing with the SM Higgs boson, and the temperature and baryon density in the merger. In the free-streaming region, the scalar $S$ will provide an extra channel to cool down the merger remnant, with cooling timescales as small as ${\cal O}$(ms). On the other hand, in the trapped region, the Bose gas of $S$ particles could contribute a larger thermal conductivity than the trapped neutrinos in some parts of the parameter space, thus leading to faster thermal equilibration than expected. Therefore, future observations of the early postmerger phase of a neutron star merger could effectively probe a unique range of the $S$ parameter space, largely complementary to the existing and future laboratory and supernova limits. In view of these results, we hope the merger simulation community will be motivated to implement the effects of light CP-even scalars into their simulations in both the free-streaming and trapped regimes.

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P. Dev, J. Fortin, S. Harris, et. al.
Thu, 11 Nov 21
55/60

Comments: 44 pages, 10 figures

Modeling general-relativistic plasmas with collisionless moments and dissipative two-fluid magnetohydrodynamics [HEAP]

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http://arxiv.org/abs/2111.05752


Relativistic plasmas are central to the study of black hole accretion, jet physics, neutron star mergers, and compact object magnetospheres. Despite the need to accurately capture the dynamics of these plasmas and the implications for relativistic transients, their fluid modeling is typically done using a number of (overly) simplifying assumptions, which do not hold in general. This is especially true when the mean free path in the plasma is large compared to the system size, and kinetic effects start to become important. Going beyond common approaches used in the literature, we describe a fully relativistic covariant 14-moment based two-fluid system appropriate for the study of electron-ion or electron-positron plasmas. This generalized Israel-Stewart-like system of equations of motion is obtained directly from the relativistic Boltzmann-Vlasov equation. Crucially, this new formulation can account for non-ideal effects, such as anisotropic pressures and heat fluxes. We show that a relativistic two-fluid plasma can be recast as a single fluid coupled to electromagnetic fields with (potentially large) out-of-equilibrium corrections. In particular, we keep all electron degrees of freedom, which provide self-consistent evolution equations for electron temperature and momentum. The equations outlined in this paper are able to capture the full two-fluid character of collisionless plasmas found in black hole accretion and flaring processes around compact objects, as well Braginskii-like two-fluid magnetohydrodynamics applicable to weakly collisional plasmas inside accretion disks. This new formulation will be instrumental in the construction of a large class of next-generation simulations of relativistic transient phenomena produced around black holes and neutron stars.

Read this paper on arXiv…

E. Most, J. Noronha and A. Philippov
Thu, 11 Nov 21
56/60

Comments: 14 pages

The effect of the energy functional on the pasta-phase properties of catalysed neutron stars [HEAP]

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http://arxiv.org/abs/2111.04374


Nuclear pasta, that is an inhomogeneous distribution of nuclear matter characterised by non-spherical clustered structures, is expected to occur in a narrow spatial region at the bottom of the inner crust of neutron stars, but the width of the pasta layer is strongly model dependent. In the framework of a compressible liquid-drop model, we use Bayesian inference to analyse the constraints on the sub-saturation energy functional and surface tension imposed by both ab-initio chiral perturbation theory calculations and experimental measurements of nuclear masses. The posterior models are used to obtain general predictions for the crust-pasta and pasta-core transition with controlled uncertainties. A correlation study allows extracting the most influential parameters for the calculation of the pasta phases. The important role of high-order empirical parameters and the surface tension is underlined.

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H. Thi, A. Fantina and F. Gulminelli
Tue, 9 Nov 21
31/102

Comments: 15 pages, 11 figures. Contribution to the EPJ A topical issue “CompOSE: a repository for Neutron Star Equations of State and Transport Properties”

Can we decipher the composition of the core of a neutron star? [CL]

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http://arxiv.org/abs/2111.04520


Recent developments in the multi-messenger astronomy through gravitational waves (LIGO/Virgo) or X-ray timing data (NICER) have provided new constraints on the theories of nuclear physics, where an absolute energy density functional from ab-initio modelling is still not available. General relativity guarantees a unique one-to-one correspondence between static observables of neutron stars (NSs) such as mass-radius or tidal deformability and the equation of state (EoS) of beta equilibrated matter. However, these static properties are not enough to predict the composition of the interiors of NSs, even if one assumes that hadrons present in the neutron star core are only neutrons and protons. This statement is demonstrated through a simple analytical method based on a polynomial expansion of the EoS, and it is further reinforced by a full Bayesian analysis. We show that even additional empirical information on symmetric matter at high densities are not sufficient to pin down the composition, if uncertainties on measurements are accounted for. We conclude that only constraints on the symmetry energy at high densities can make some meaningful impact to decipher the composition of neutron star core. Our results give a lower limit to the uncertainty on the NS core composition that can be obtained with astrophysical and terrestrial experiments.

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C. Mondal and F. Gulminelli
Tue, 9 Nov 21
53/102

Comments: 6 pages, 5 figures

Building a realistic neutron star from holography [CL]

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http://arxiv.org/abs/2111.03374


We employ the recently improved description of dense baryonic matter within the Witten-Sakai-Sugimoto model to construct neutron stars. In contrast to previous holographic approaches, the presence of an isospin asymmetry allows us to implement beta equilibrium and electric charge neutrality. As a consequence, we are able to model the crust of the star within the same formalism and compute the location of the crust-core transition dynamically. After showing that a simple pointlike approximation for the baryons fails to satisfy astrophysical constraints, we demonstrate that our improved description does account for neutron stars that meet the current experimental constraints for mass, radius, and tidal deformability. However, we also point out tensions in the parameter fit and large-$N_c$ artifacts and discuss how to potentially resolve them in the future.

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N. Kovensky, A. Poole and A. Schmitt
Mon, 8 Nov 21
21/69

Comments: 19 pages, 12 figures

A New Constraint on the Nuclear Equation of State from Statistical Distributions of Compact Remnants of Supernovae [HEAP]

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http://arxiv.org/abs/2111.01815


Understanding how matter behaves at the highest densities and temperatures is a major open problem in both nuclear physics and relativistic astrophysics. This physics is often encapsulated in the so-called high-temperature nuclear equation of state, which influences compact binary mergers, core-collapse supernovae, and many more phenomena. One such case is the type (either black hole or neutron star) and mass of the remnant of the core collapse of a massive star. For each of six candidate equations of state, we use a very large suite of spherically symmetric supernova models to generate a suite of synthetic populations of such remnants. We then compare these synthetic populations to the observed remnant population. We thus provide a novel constraint on the high-temperature nuclear equation of state and describe which EOS candidates are more or less favored by this metric.

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M. Meskhi, N. Wolfe, Z. Dai, et. al.
Thu, 4 Nov 21
48/73

Comments: Submitted to ApJL

On the nature of the mass-gap object in the GW190814 event [CL]

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http://arxiv.org/abs/2111.02247


In this letter, we discuss the possibility of the mass-gap object in the GW190814 event being different classes of compact objects: hadronic neutron stars with nucleons only, hadronic stars with nucleons and hyperons, hybrid stars with nucleons and quarks, hybrid stars with nucleons, hyperons and quarks, and strange stars satisfying the Bodmer-Witten conjecture. We show that for the current limit of the observational constraints none of these possibilities can be ruled out.

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L. Lopes and D. Menezes
Thu, 4 Nov 21
54/73

Comments: 5 pages, 5 figures, 3 tables

Dissipative superfluid relativistic magnetohydrodynamics of a multicomponent fluid: the combined effect of particle diffusion and vortices [HEAP]

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http://arxiv.org/abs/2111.00999


We formulate dissipative magnetohydrodynamic equations for finite-temperature superfluid and superconducting charged relativistic mixtures, taking into account the effects of particle diffusion and possible presence of Feynman-Onsager and/or Abrikosov vortices in the system. The equations depend on a number of phenomenological transport coefficients, which describe, in particular, relative motions of different particle species and their interaction with vortices. We demonstrate how to relate these transport coefficients to the mutual friction parameters and momentum transfer rates arising in the microscopic theory. The resulting equations can be used to study, in a unified and coherent way, a very wide range of phenomena associated with dynamical processes in neutron stars, e.g., the magnetothermal evolution, stellar oscillations and damping, as well as development and suppression of various hydrodynamic instabilities in neutron stars.

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V. Dommes and M. Gusakov
Tue, 2 Nov 21
28/93

Comments: 30 pages, accepted for publication in PRD

Radial oscillations of quark stars admixed with dark matter [CL]

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http://arxiv.org/abs/2111.00091


We investigate compact stars consisting of cold quark matter and fermionic dark matter treated as two admixed fluids. We compute the stellar structure and fundamental radial oscillation frequency for different masses of the dark fermion in the cases of weak and strong self-interacting dark matter. We find that the fundamental frequency can be dramatically modified and, in some cases, stable dark strange planets and dark strangelets with very low masses and radii can be formed.

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J. Jiménez and E. Fraga
Tue, 2 Nov 21
52/93

Comments: 11 pages, 8 figures, 1 table

Bayesian reconstruction of nuclear matter parameters from the equation of state of neutron star matter [CL]

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http://arxiv.org/abs/2110.15776


The nuclear matter parameters (NMPs), those underlie in the construction of the equation of state (EoS) of neutron star matter, are not directly accessible. The Bayesian approach is applied to reconstruct the posterior distributions of NMPs from the EoS of neutron star matter. The constraints on lower-order parameters as imposed by the finite nuclei observables are incorporated through appropriately chosen prior distributions. The calculations are performed with two sets of pseudo data on the EoS whose true models are known. The median values of second or higher order NMPs show sizeable deviations from their true values and associated uncertainties are also larger. The sources of these uncertainties are intrinsic in nature, identified as (i) the correlations among various NMPs and (ii) the variations in the EoS of symmetric nuclear matter, symmetry energy, and the neutron-proton asymmetry in such a way that the neutron star matter EoS remain almost unaffected.

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S. Imam, N. Patra, C. Mondal, et. al.
Mon, 1 Nov 21
58/58

Comments: 11 pages, 7 figures, Submitted to PRC

Constraining exotic compact stars composed of bosonic and fermionic dark matter with gravitational wave events [HEAP]

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http://arxiv.org/abs/2110.12972


We investigate neutron star-black hole (NS-BH) merger candidates as a test for compact exotic objects. Using the events GW190814, GW200105 and GW200115 measured by the LIGO-Virgo collabration, which represent a broad profile of the masses in the NS mass spectrum, we demonstrate the constraining power for the parameter spaces of compact stars consisting of dark matter for future measurements. We consider three possible cases of dark matter stars: self-interacting, purely bosonic or fermionic dark matter stars, stars consisting of a mixture of interacting bosonic and fermionic matter, as well as the limiting case of selfbound stars. We find that the scale of those hypothetical objects are dominated by the one of the strong interaction. The presence of fermionic dark matter requires a dark matter particle of the GeV mass scale, while the bosonic dark matter particle mass can be arbitrarily large or small. In the limiting case of a selfbound linear equation of state, we find that the vacuum energy of those configurations has to be similar to the one of QCD.

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S. Wystub, J. Schaffner-Bielich, J. Christian, et. al.
Tue, 26 Oct 21
51/109

Comments: 6 pages, 4 figures, 3 tables

Probing dense matter physics with transiently-accreting neutron stars: the case of source MXB 1659-29 [CL]

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http://arxiv.org/abs/2110.11077


Recent observational data on transiently-accreting neutron stars has unequivocally shown fast-cooling sources, such as in the case of neutron star MXB 1659-29. Previous calculations have estimated its total neutrino luminosity and heat capacity, as well as suggested that direct Urca reactions take place in $1 \%$ of the volume of the core. In this paper, we reproduce the inferred luminosity of this source with detailed models of equations of state (EOS) and nuclear pairing gaps. We show that three superfluidity gap models are inconsistent with data for all EOS and another three are disfavoured because of fine tuning arguments. We also calculate the total heat capacity for all constructed stars and show that independent observations of mass and luminosity could set constraints on the core superfluidity of a source as well as the density slope of the symmetry energy, L. This is an important step towards defining a universal equation of state for neutron stars and therefore, towards a better understanding of the phase diagram of asymmetric matter at high densities.

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M. Mendes, F. Fattoyev, A. Cumming, et. al.
Tue, 26 Oct 21
68/109

Comments: Talk given at the XVI Marcel Grossmann Meeting (2021), to be published on their proceedings

Jet Launching from Merging Magnetized Binary Neutron Stars with Realistic Equations of State [HEAP]

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http://arxiv.org/abs/2110.11968


We perform general relativistic, magnetohydrodynamic (GRMHD) simulations of binary neutron stars in quasi-circular orbit that merge and undergo delayed or prompt collapse to a black hole (BH). The stars are irrotational and modeled using an SLy or an H4 nuclear equation of state. To assess the impact of the initial magnetic field configuration on jet launching, we endow the stars with a purely poloidal magnetic field that is initially unimportant dynamically and is either confined to the stellar interior or extends from the interior into the exterior as in typical pulsars. Consistent with our previous results, we find that only the BH + disk remnants originating from binaries that form hypermassive neutron stars (HMNSs) and undergo delayed collapse can drive magnetically-powered jets. We find that the closer the total mass of the binary is to the threshold value for prompt collapse, the shorter is the time delay between the gravitational wave peak amplitude and jet launching. This time delay also strongly depends on the initial magnetic field configuration. We also find that seed magnetic fields confined to the stellar interior can launch a jet over~$\sim 25\,\rm ms$ later than those with pulsar-like magnetic fields. The lifetime of the jet [$\Delta t\lesssim 150\,\rm ms$] and its outgoing Poynting luminosity [$L_{\rm EM}\sim 10^{52\pm 1}\rm erg/s$] are consistent with typical short gamma-ray burst central engine lifetimes, as well as with the Blandford–Znajek mechanism for launching jets and their associated Poynting luminosities. Our numerical results also suggest that the dynamical ejection of matter can be enhanced by the magnetic field. Therefore, GRMHD studies are required to fully understand kilonova signals from GW170818-like events.

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M. Ruiz, A. Tsokaros and S. Shapiro
Tue, 26 Oct 21
75/109

Comments: 21 pages, 12 figures

Chiral anomalous processes in magnetospheres of pulsars and black holes [HEAP]

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http://arxiv.org/abs/2110.11380


We propose that chirally asymmetric plasma can be produced in the gap regions of the magnetospheres of pulsars and black holes. We show that, in the case of supermassive black holes situated in active galactic nuclei, the chiral charge density and the chiral chemical potential are very small and unlikely to have any observable effects. In contrast, the chiral asymmetry produced in the magnetospheres of magnetars can be substantial. It can trigger the chiral plasma instability that, in turn, can lead to observable phenomena in magnetars. In particular, the instability should trigger circularly polarized electromagnetic radiation in a wide window of frequencies, spanning from radio to near-infrared. As such, the produced chiral charge has the potential to affect some features of fast radio bursts.

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E. Gorbar and I. Shovkovy
Mon, 25 Oct 21
42/76

Comments: 9 pages, 1 figure, 1 table

Quantifying modelling uncertainties when combining multiple gravitational-wave detections from binary neutron star sources [HEAP]

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http://arxiv.org/abs/2110.11835


With the increasing sensitivity of gravitational-wave detectors, we expect to observe multiple binary neutron-star systems through gravitational waves in the near future. The combined analysis of these gravitational-wave signals offers the possibility to constrain the neutron-star radius and the equation of state of dense nuclear matter with unprecedented accuracy. However, it is crucial to ensure that uncertainties inherent in the gravitational-wave models will not lead to systematic biases when information from multiple detections are combined. To quantify waveform systematics, we perform an extensive simulation campaign of binary neutron-star sources and analyse them with a set of four different waveform models. Based on our analysis with about 38 simulations, we find that statistical uncertainties in the neutron-star radius decrease to $\pm 250\rm m$ ($2\%$ at $90\%$ credible interval) but that systematic differences between currently employed waveform models can be twice as large. Hence, it will be essential to ensure that systematic biases will not become dominant in inferences of the neutron-star equation of state when capitalizing on future developments.

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N. Kunert, P. Pang, I. Tews, et. al.
Mon, 25 Oct 21
48/76

Comments: 11 pages, 5 figures

Reconciling multi-messenger constraints with chiral symmetry restoration [CL]

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http://arxiv.org/abs/2110.11056


We analyze the recent nuclear and astrophysical constraints in the context of a hadronic equation of state (EoS), in which the baryonic matter is subject to chiral symmetry restoration. We show that it is possible to reconcile the modern constraints on the neutron star (NS) radius and tidal deformability (TD) in the light of recent neutron skin thickness measurement by PREX-II experiment. We find that the softening of the EoS (required by the TD constraint) followed by a subsequent stiffening (required by the $2~M_\odot$ constraint) is driven by the appearance of $\Delta$ matter due to partial restoration of chiral symmetry. Sufficiently early onset of $\Delta$ matter lifts the tension between the results from the PREX-II experiment and TD from GW170817. We argue that a purely hadronic EoS that accounts for the fundamental properties of quantum chromodynamics (QCD) linked to the dynamical emergence of parity doubling with degenerate masses can be fully consistent with the nuclear and astrophysical constraints.

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M. Marczenko, K. Redlich and C. Sasaki
Fri, 22 Oct 21
29/133

Comments: N/A

Thermal effects on tidal deformability of a coalescing binary neutron star system [HEAP]

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http://arxiv.org/abs/2110.10270


The study of neutron star mergers by the detection of the emitted gravitational waves is one of the most promised tools to study the properties of dense nuclear matter at high densities. It is worth claiming that, at the moment, strong evidence that the temperature of the stars is zero during the last orbits before coalescing does not exist. Contrariwise, there are some theoretical predictions suggesting that the star’s temperature might even be a few MeV. According to the main theory, the tides transfer mechanical energy and angular momentum to the star at the expense of the orbit, where friction within the star converts the mechanical energy into heat. During the inspiral these effects are potentially detectable. Different treatments have been used to estimate the transfer of the mechanical energy and the size of the tidal friction, leading to different conclusions about the importance of pre-merger tidal effects. The present work is dedicated to the study of the effect of temperature on the tidal deformability of neutron stars during the inspiral of a neutron star system just before the merger. We applied a class of hot equations of state originated from various nuclear models and found that even for low values of temperature ($T<1$ MeV) the effects on the basic ingredients of tidal deformability are not negligible. However, according to the main finding, the effect of the temperature on the tidal deformability is indistinguishable. The consequences of this unexpected result are discussed and analyzed.

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A. Kanakis-Pegios, P. Koliogiannis and C. Moustakidis
Fri, 22 Oct 21
36/133

Comments: 6 pages, 5 figures, 1 table; to be published in the proceedings of the International Workshop “Shapes and Dynamics of Atomic Nuclei: Contemporary Aspects” (SDANCA-21)

Electron Captures and Stability of White Dwarfs [SSA]

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http://arxiv.org/abs/2110.11038


Electron captures by atomic nuclei in dense matter are among the most important processes governing the late evolution of stars, limiting in particular the stability of white dwarfs. Despite considerable progress in the determination of the equation of state of dense Coulomb plasmas, the threshold electron Fermi energies are still generally estimated from the corresponding $Q$ values in vacuum. Moreover, most studies have focused on nonmagnetized matter. However, some white dwarfs are endowed with magnetic fields reaching $10^9$ G. Even more extreme magnetic fields might exist in super Chandrasekhar white dwarfs, the progenitors of overluminous type Ia supernovae like SN 2006gz and SN 2009dc. The roles of the dense stellar medium and magnetic fields on the onset of electron captures and on the structure of white dwarfs are briefly reviewed. New analytical formulas are derived to evaluate the threshold density for the onset of electron captures for arbitrary magnetic fields. Their influence on the structure of white dwarfs is illustrated by simple analytical formulas and numerical calculations.

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N. Chamel, L. Perot, A. Fantina, et. al.
Fri, 22 Oct 21
81/133

Comments: 20 pages, 5 figures, contribution to the Sixteenth Marcel Grossmann Meeting – MG16

Quiescent luminosities of transiently accreting neutron stars with neutrino heating due to charged pion decay [HEAP]

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http://arxiv.org/abs/2110.09729


We study the quiescent luminosities of accreting neutron stars by a new mechanism as neutrino heating for additional deep crustal heating, where the neutrino heating is produced by charged pions decay from the nuclear collisions on the surface of neutron star during its active accretion. For low mass neutron star($\lesssim1.4~M_{\odot}$), as the neutrino heating is little($\lesssim1$ MeV per accreted nucleon) or there would be no neutrino heating, the quiescent luminsoity will be not affected or slightly affected. While for massive neutron star ($\gtrsim2~M_{\odot}$), the quiescent luminosity will be enhanced more obviously with neutrino heating in the range 2-6 MeV per accreted nucleon. The observations on cold neutron stars such as 1H 19605+00, SAX J1808.4-3658 can be explained with neutrino heating if a fast cooling and heavy elements surface are considered. The observations on a hot neutron star such as RX J0812.4-3114 can be explained with neutrino heating if the direct Urca process is forbidden for a massive star with light elements surface, which is different from the previous work that the hot observations should be explained with small mass neutron star and the effect of superfluidity.

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H. Liu, Z. Dai, G. Lv, et. al.
Wed, 20 Oct 21
49/67

Comments: 9 pages, 5 figures, accepted for publication in Phys. Rev. D

Quiescent luminosities of transiently accreting neutron stars with neutrino heating due to charged pion decay [HEAP]

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http://arxiv.org/abs/2110.09729


We study the quiescent luminosities of accreting neutron stars by a new mechanism as neutrino heating for additional deep crustal heating, where the neutrino heating is produced by charged pions decay from the nuclear collisions on the surface of neutron star during its active accretion. For low mass neutron star($\lesssim1.4~M_{\odot}$), as the neutrino heating is little($\lesssim1$ MeV per accreted nucleon) or there would be no neutrino heating, the quiescent luminsoity will be not affected or slightly affected. While for massive neutron star ($\gtrsim2~M_{\odot}$), the quiescent luminosity will be enhanced more obviously with neutrino heating in the range 2-6 MeV per accreted nucleon. The observations on cold neutron stars such as 1H 19605+00, SAX J1808.4-3658 can be explained with neutrino heating if a fast cooling and heavy elements surface are considered. The observations on a hot neutron star such as RX J0812.4-3114 can be explained with neutrino heating if the direct Urca process is forbidden for a massive star with light elements surface, which is different from the previous work that the hot observations should be explained with small mass neutron star and the effect of superfluidity.

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H. Liu, Z. Dai, G. Lv, et. al.
Wed, 20 Oct 21
25/67

Comments: 9 pages, 5 figures, accepted for publication in Phys. Rev. D

Holographic modeling of nuclear matter and neutron stars [CL]

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http://arxiv.org/abs/2110.08281


I review holographic models for (dense and cold) nuclear matter, neutron stars, and their mergers. I start by a brief general discussion on current knowledge of cold QCD matter and neutron stars, and go on discussing various approaches to model cold nuclear and quark matter by using gauge/gravity duality, pointing out their strengths and weaknesses. Then I concentrate on recent results for a complex bottom-up holographic framework (V-QCD), which also takes input from lattice QCD results, effective field theory, and perturbative QCD. Dense nuclear matter is modeled in V-QCD through a homogeneous non-Abelian bulk gauge field. Feasible “hybrid” equations of state for cold nuclear (and quark) matter can be constructed by using traditional methods (e.g., effective field theory) at low densities and the holographic V-QCD model at higher densities. I discuss the constraints from this approach to the properties of the nuclear to quark matter transition as well as to properties of neutron stars. Using such hybrid equations of state as an input for numerical simulations of neutron star mergers, I also derive predictions for the spectrum of produced gravitational waves.

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M. Jarvinen
Tue, 19 Oct 21
62/98

Comments: Review article submitted to Eur.Phys.J.C. 56 pages, 24 figures, 2 tables

Hybrid stars with color superconducting cores in an extended FCM model [CL]

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http://arxiv.org/abs/2110.08892


We investigate the influence of repulsive vector interactions and color superconductivity on the structure of neutron stars using an extended version of the field correlator method (FCM) for the description of quark matter. The hybrid equation of state is constructed using the Maxwell description, which assumes a sharp hadron-quark phase transition. The equation of state of hadronic matter is computed for a density-dependent relativistic lagrangian treated in the mean-field approximation, with parameters given by the SW4L nuclear model. This model described the interactions among baryons in terms of $\sigma, \omega, \rho, \sigma^*$, and $\phi$ mesons. Quark matter is assumed to be in either the CFL or the 2SC+s color superconducting phase. The possibility of sequential (hadron-quark, quark-quark) transitions in ultra-dense matter is investigated. Observed data related to massive pulsars, gravitational-wave events, and NICER are used to constrain the parameters of the extended FCM model. The successful equations of state are used to explore the mass-radius relationship, radii, and tidal deformabilities of hybrid stars. A special focus lies on investigating consequences that slow or fast conversions of quark-hadron matter have on the stability and the mass-radius relationship of hybrid stars. We find that if slow conversion should occur, a new branch of stable massive stars would exist whose members have radii that are up to 1.5~km smaller than those of conventional neutron stars of the same mass. Such objects could be possible candidates for the stellar high-mass object of the GW190425 binary system.

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D. Curin, I. Ranea-Sandoval, M. Mariani, et. al.
Tue, 19 Oct 21
89/98

Comments: This article has the same content as the one published in Universe 2021, 7(10), 370

Supernova Preshock Neutronization Burst as a Probe of Non-Standard Neutrino Interactions [HEAP]

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http://arxiv.org/abs/2110.07249


It is believed that there is a preshock neutronization burst of $\nu_e$ before the shock-breakout burst in a core-collapse supernova (CCSN). The preshock burst essentially consists of only $\nu_e$ produced from the electron capture of nuclei in the early stage of the core collapse and is sensitive to the low-energy coherent elastic neutrino-nucleus scattering (CE$\nu$NS) which dominates the neutrino opacity and significantly influences the early $\nu_e$ emission in the CCSN. Since the CE$\nu$NS depends strongly on the largely uncertain non-standard neutrino interactions (NSI), the detection of the preshock burst thus provides a clean way to extract the NSI information. Within the spherically symmetric general-relativistic hydrodynamic simulation for the CCSN, we investigate the NSI effects on the preshock burst. We find that the NSI can maximally enhance the peak luminosity of the preshock burst almost by a factor of three, reaching a value to be comparable with that of the shock-breakout burst. The future detection of the preshock burst will have critical implications on astrophysics, neutrino physics and physics beyond the standard model.

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X. Huang, S. Zha and L. Chen
Fri, 15 Oct 21
1/56

Comments: 5 pages, 3 figures