Tag Archives: Nuclear Theory

Special point "trains" in the M-R diagram of hybrid stars [CL]

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http://arxiv.org/abs/2211.12626


We present a systematic investigation of the possible locations for the special point (SP), a unique feature of hybrid neutron stars in the mass-radius diagram. The study is performed within the two-phase approach where the high-density (quark matter) phase is described by the covariant nonlocal Nambu–Jona-Lasinio (nlNJL) model equation of state (EOS) which is shown to be equivalent to a constant-sound-speed (CSS) EOS. For the nuclear matter phase around saturation density different relativistic density functional EOSs are used: DD2p00, its excluded-volume modification DD2p40 and the hypernuclear EOS DD2Y-T. In the present contribution we apply the Maxwell construction scheme for the deconfinement transition and demonstrate that a simultaneous variation of the vector and diquark coupling constants results in the occurrence of SP “trains” which are invariant against changing the nuclear matter EOS. We propose that the SP train corresponding to a variation of the diquark coupling at constant vector coupling is special since it serves as a lower bound for the line of maximum masses and accessible radii of massive hybrid stars.

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D. Blaschke, A. Ayriyan, M. Cierniak, et. al.
Thu, 24 Nov 22
31/71

Comments: 8 pages, 5 figures, Contribution to Proceedings of Quark Confinement and the Hadron Spectrum XV, August 1-6, 2022, Stavanger, Norway

Probing the size and binding energy of the hypertriton in heavy ion collisions [CL]

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http://arxiv.org/abs/2211.12643


The hypertriton is predicted to have a small binding energy (a weighted average of about 170 keV), consistent with a large matter radius (~ 10 fm), large than the historical11Li halo discovered more than 35 years ago. But the reported experimental values of the binding energy of the hypertriton range from 50 to 500 keV. In this work I discuss the electromagnetic response and interaction radius of the hypertriton and how high energy heavy ion collisions (~ 1 – 2 GeV/nucleon) can help achieving a higher accuracy for the determination of its size and binding energy.

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C. Bertulani
Thu, 24 Nov 22
44/71

Comments: 8 pages, 9 figures

Probing the size and binding energy of the hypertriton in heavy ion collisions [CL]

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http://arxiv.org/abs/2211.12643


The hypertriton is predicted to have a small binding energy (a weighted average of about 170 keV), consistent with a large matter radius (~ 10 fm), large than the historical11Li halo discovered more than 35 years ago. But the reported experimental values of the binding energy of the hypertriton range from 50 to 500 keV. In this work I discuss the electromagnetic response and interaction radius of the hypertriton and how high energy heavy ion collisions (~ 1 – 2 GeV/nucleon) can help achieving a higher accuracy for the determination of its size and binding energy.

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C. Bertulani
Thu, 24 Nov 22
20/71

Comments: 8 pages, 9 figures

Special point "trains" in the M-R diagram of hybrid stars [CL]

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http://arxiv.org/abs/2211.12626


We present a systematic investigation of the possible locations for the special point (SP), a unique feature of hybrid neutron stars in the mass-radius diagram. The study is performed within the two-phase approach where the high-density (quark matter) phase is described by the covariant nonlocal Nambu–Jona-Lasinio (nlNJL) model equation of state (EOS) which is shown to be equivalent to a constant-sound-speed (CSS) EOS. For the nuclear matter phase around saturation density different relativistic density functional EOSs are used: DD2p00, its excluded-volume modification DD2p40 and the hypernuclear EOS DD2Y-T. In the present contribution we apply the Maxwell construction scheme for the deconfinement transition and demonstrate that a simultaneous variation of the vector and diquark coupling constants results in the occurrence of SP “trains” which are invariant against changing the nuclear matter EOS. We propose that the SP train corresponding to a variation of the diquark coupling at constant vector coupling is special since it serves as a lower bound for the line of maximum masses and accessible radii of massive hybrid stars.

Read this paper on arXiv…

D. Blaschke, A. Ayriyan, M. Cierniak, et. al.
Thu, 24 Nov 22
29/71

Comments: 8 pages, 5 figures, Contribution to Proceedings of Quark Confinement and the Hadron Spectrum XV, August 1-6, 2022, Stavanger, Norway

Early deconfinement of asymptotically conformal color-superconducting quark matter in neutron stars [CL]

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http://arxiv.org/abs/2211.12730


We present a relativistic density functional approach to color superconducting quark matter that mimics quark confinement by a fast growth of the quasiparticle selfenergy in the confining region. The approach is shown to be equivalent to a chiral model of quark matter with medium dependent couplings. While the (pseudo)scalar sector of the model is fitted to the vacuum phenomenology of quantum chromodynamics, the strength of interaction in the vector and diquark channels is varied in order to provide the best agreement with the observational constraints on the mass-radius relation and tidal deformability of neutron stars modelled with our approach. In order to recover the conformal behavior of quark matter at asymptotically high densities we introduce a medium dependence of the vector and diquark couplings motivated by the nonperturbative gluon exchange. Our analysis signals that the onset of deconfinement to color superconducting quark matter is likely to occur in neutron stars with masses below 1.0 $M_\odot$.

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O. Ivanytskyi, D. Blaschke, T. Fischer, et. al.
Thu, 24 Nov 22
46/71

Comments: 8 pages, 4 figuures, Contribution to Proceedings of Quark Confinement and the Hadron Spectrum XV, August 1-6, 2022, Stavanger, Norway

Peculiarity of the stellar CNO cycle with energetic particles [CL]

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http://arxiv.org/abs/2211.12093


A peculiarity of the stellar CNO cycle caused by MeV alpha-particles and protons generated in exoergic nuclear processes is analyzed. The main parameters of these particles and suprathermal reactions induced by them in a stellar core are calculated. It is shown that these reactions can trigger an abnormal nuclear flow in the second branch of the stellar CNO cycle. A conjecture is made that the phenomenon is of a general nature and can manifest in various stars at non-exploding stages of their evolution. The influence of the abnormal flow on some CNO characteristics is demonstrated.

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V. Voronchev
Wed, 23 Nov 22
19/71

Comments: 6 pages, 8 figures

Hybrid stars may have an inverted structure [CL]

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http://arxiv.org/abs/2211.12043


We propose a new stellar structure of compact stars, the “Cross stars” (CrSs) that consist of a hadronic matter core and a quark matter crust, with an inverted structure compared to the conventional hybrid stars. This distinct stellar structure naturally arises from the quark matter to hadronic matter transition associated with the chemical potential crossing, in the context of the quark matter hypothesis that either strange or up-down quark matter is the ground state of baryonic matter at low pressure. We find that the interplay between the hadronic matter and quark matter compositions of CrSs can help to reconcile the small radii constraints indicated by the LIGO/Virgo GW170817 event, the large radii constraints set for massive compact stars by recent NICER X-ray observations, and the recent observation of the most-massive pulsar PSR J0952-0607. This leaves more space open for the equation of states of both hadronic matter and quark matter.

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J. Ren and C. Zhang
Wed, 23 Nov 22
40/71

Comments: 10 pages, 6 figures

Thoughts about the utility of perturbative QCD in the cores of neutron stars [CL]

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http://arxiv.org/abs/2211.11414


In this contribution, I discuss the utility that perturbative QCD offers in studying the matter in the cores of neutron stars. I discuss the reasons why perturbative QCD can constrain the equation of state at densities far below the densities where we can perform controlled calculations. I discuss how perturbative QCD can inform nuclear modelling of neutron stars and how it influences equation-of-state inference. And finally, I discuss the implications to the QCD phase diagram and argue that interesting features in the equation of state revealed by the QCD input may be used to argue for the existence of quark-matter cores in most massive neutron stars.

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A. Kurkela
Tue, 22 Nov 22
8/83

Comments: 13 pages, 6 figures, zero equations. Contribution to a roundtable discussion on “neutron stars and QCD” at the 15th Quark Confinement and the Hadron Spectrum Conference (ConfXV)

Effect of the $σ$-cut potential on the properties of neutron stars with or without a hyperonic core [CL]

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http://arxiv.org/abs/2211.10616


Motivated by the recent observation of high-mass pulsars ($M \simeq 2 M_{\odot}$), we employ the $\sigma$-cut potential on the equation of state (EOS) of high-density matter and the properties of neutron stars within the relativistic mean-field (RMF) model using TM1$^{*}$ parameter set. The $\sigma$-cut potential is known to reduce the contributions of the $\sigma$ field, resulting in a stiffer EOS at high densities and hence leading to larger neutron star masses without affecting the properties of nuclear matter at normal saturation density. We also analyzed the effect of the same on pure neutron matter and also on the neutron star matter with and without hyperonic core and compared it with the available theoretical, experimental, and observational data. The corresponding tidal deformability ($\Lambda_{1.4}$) is also calculated. With the choice of meson-hyperon coupling fixed to hypernuclear potentials, we obtain $\approx 10~\%$ increase in mass by employing the $\sigma$-cut potential for $f_{s} = 0.6$. Our results are in good agreement with various experimental constraints and observational data, particularly with the GW170817 data.

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N. Patra, B. Sharma, A. Reghunath, et. al.
Tue, 22 Nov 22
68/83

Comments: 7 Pages, 6 Figures and 1 Table (Accepted in Phys. Rev. C)

How does dark matter affect compact star properties and high density constraints of strongly interacting matter [HEAP]

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http://arxiv.org/abs/2211.10510


We study the impact of asymmetric bosonic dark matter on neutron star properties, including possible changes of tidal deformability, maximum mass, radius, and matter distribution inside the star. The conditions at which dark matter particles tend to condensate in the star’s core or create an extended halo are presented. We show that dark matter condensed in a core leads to a decrease of the total gravitational mass and tidal deformability compared to a pure baryonic star, which we will perceive as an effective softening of the equation of state. On the other hand, the presence of a dark matter halo increases those observable quantities. Thus, observational data on compact stars could be affected by accumulated dark matter and, consequently, constraints we put on strongly interacting matter at high densities. To confirm the presence of dark matter in the compact star’s interior, and to break the degeneracy between the effect of accumulated dark matter and strongly interacting matter properties at high densities, several astrophysical and GW tests are proposed.

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V. Sagun, E. Giangrandi, O. Ivanytskyi, et. al.
Tue, 22 Nov 22
72/83

Comments: 8 pages, 3 figures, Proceeding of the 15th Quark Confinement and the Hadron Spectrum Conference

Probing phase transition in neutron stars via the crust-core interfacial mode [HEAP]

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http://arxiv.org/abs/2211.11529


Gravitational waves emitted from the binary neutron star (BNS) systems can carry information about the dense matter phase in these compact stars. The crust-core interfacial mode is an oscillation mode in a neutron star and it depends mostly on the equation of the state of the matter in the crust-core transition region. This mode can be resonantly excited by the tidal field of an inspiraling-in BNS system, thereby affecting the emitted gravitational waves, and hence could be used to probe the equation of state in the crust-core transition region. In this work, we investigate in detail how the first-order phase transition inside the neutron star affects the properties of the crust-core interfacial mode, using a Newtonian fluid perturbation theory on a general relativistic background solution of the stellar structure. Two possible types of phase transitions are considered: (1) the phase transitions happen in the fluid core but near the crust-core interface, which results in density discontinuities; and (2) the strong interaction phase transitions in the dense core (as in the conventional hybrid star case). These phase transitions’ impacts on interfacial mode properties are discussed. In particular, the former phase transition has a minor effect on the M-R relation and the adiabatic tidal deformability, but can significantly affect the interfacial mode frequency and thereby could be probed using gravitational waves. For the BNS systems, we discuss the possible observational signatures of these phase transitions in the gravitational waveforms and their detectability. Our work enriches the exploration of the physical properties of the crust-core interfacial mode and provides a promising method for probing the phase transition using the seismology of a compact star.

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J. Zhu, C. Wang, C. Xia, et. al.
Tue, 22 Nov 22
83/83

Comments: 18 pages, 14 figures

Dark particle mass effects on neutron star properties from a short-range correlated hadronic model [CL]

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http://arxiv.org/abs/2211.10263


In this work we study a relativistic mean-field (RMF) hadronic model, with nucleonic short-range correlations (SRC) included, coupled to dark matter (DM) through the Higgs boson. We study different parametrizations of this model by running the dark particle Fermi momentum, and its mass in the range of $50$ GeV $\leqslant M_\chi\leqslant 500$ GeV, compatible with experimental spin-independent scattering cross-sections. By using this RMF-SRC-DM model, we calculate some neutron star quantities, namely, mass-radius profiles, dimensionless tidal deformabilities, and crustal properties. Our findings show that is possible to construct RMF-SRC-DM parametrizations in agreement with constraints provided by LIGO and Virgo collaboration (LVC) on the GW170817 event, and recent observational data from the NICER mission. Furthermore, we show that the increase of $M_\chi$ favors the model to attain data from LVC regarding the tidal deformabilities. Higher values of $M_\chi$ also induce a reduction of the neutron star crust (mass and thickness), and cause a decrease of the crustal fraction of the moment of inertia ($I_{\rm{\tiny crust}}/I$). Nevertheless, we show that some RMF-SRC-DM parametrizations still exhibit $I_{\rm{\tiny crust}}/I>7\%$, a condition that explains the glitch activity in rotation-powered pulsars such as the Vela one. Therefore, dark matter content can also be used for describing such a phenomenon.

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M. Dutra, C. Lenzi and O. Lourenço
Mon, 21 Nov 22
3/66

Comments: 10 pages, 8 figures. Published in Monthly Notices of the Royal Astronomical Society

Exploring the Phase Diagram of V-QCD with Neutron Star Merger Simulations [HEAP]

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http://arxiv.org/abs/2211.10118


Determining the phase structure of Quantum Chromodynamics (QCD) and its Equation of State (EOS) at densities and temperatures realized inside neutron stars and their mergers is a long-standing open problem. The holographic V-QCD framework provides a model for the EOS of dense and hot QCD, which describes the deconfinement phase transition between a dense baryonic and a quark matter phase. We use this model in fully general relativistic hydrodynamic (GRHD) simulations to study the formation of quark matter and the emitted gravitational wave signal of binary systems that are similar to the first ever observed neutron star merger event GW170817.

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T. Demircik, C. Ecker, M. Järvinen, et. al.
Mon, 21 Nov 22
15/66

Comments: 8 pages, 3 figures, contribution to the proceedings of the XVth Quark Confinement and the Hadron Spectrum conference (1st-6th August 2022) at the University of Stavanger, Norway

Isotopic dependence of $(n,α)$ reaction cross sections for Fe and Sn nuclei [CL]

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http://arxiv.org/abs/2211.09411


The $(n,\alpha)$ reactions play an important role for the energy generation and the synthesis of chemical elements in the stars, as well as for nuclear engineering and medical applications. The aim of this study is to explore the evolution of $(n,\alpha)$ reactions in Fe and Sn isotope chains in order to assess their properties with the increase of neutrons in target nucleus, and compare with other relevant neutron induced reactions. Model calculations of the cross sections are based on the statistical Hauser-Feshbach model in TALYS implementation, using global optical model potential that is additionally adjusted by the $(n,\alpha)$ cross section data for $^{54}$Fe and $^{118}$Sn. The calculations of $(n,\alpha)$ reactions in Fe and Sn isotopes provide the insight into their isospin dependence and properties over the complete relevant range of neutron energies. The results show the evolution of the cross sections with pronounced maxima at low-mass isotopes, and rather strong decrease for neutron-rich nuclei consistent with the reduction of the reaction $Q$-value and increased contributions from other exit channels from compound nucleus. The analysis of the Maxwellian averaged cross sections at temperatures in stellar environment shows that while the $(n,\alpha)$ reactions contribute for the low-mass isotopes, in neutron induced reactions with nuclei with neutron excess, $\gamma$ and neutron emission dominate.

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S. Kucuksucu, M. Yigit and N. Paar
Fri, 18 Nov 22
19/70

Comments: 12 pages, 12 figures

Dark Matter or Regular Matter in Neutron Stars? How to tell the difference from the coalescence of compact objects [HEAP]

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http://arxiv.org/abs/2211.08590


The mirror twin Higgs model is a candidate for (strongly-interacting) complex dark matter, which mirrors SM interactions with heavier quark masses. A consequence of this model are mirror neutron stars — exotic stars made entirely of mirror matter, which are significantly smaller than neutron stars and electromagnetically dark. This makes mergers of two mirror neutron stars detectable and distinguishable in gravitational wave observations, but can we observationally distinguish between regular neutron stars and those that may contain some mirror matter? This is the question we study in this paper, focusing on two possible realizations of mirror matter coupled to standard model matter within a compact object: (i) mirror matter captured by a neutron star and (ii) mirror neutron star-neutron star coalescences. Regarding (i), we find that (non-rotating) mirror-matter-admixed neutron stars no longer have a single mass-radius sequence, but rather exist in a two-dimensional mass-radius plane. Regarding (ii), we find that binary systems with mirror neutron stars would span a much wider range of chirp masses and completely different binary Love relations, allowing merger remnants to be very light black holes. The implications of this are that gravitational wave observations with advanced LIGO and Virgo, and X-ray observations with NICER, could detect or constrain the existence of mirror matter through searches with wider model and parameter priors.

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M. Hippert, E. Dillingham, H. Tan, et. al.
Thu, 17 Nov 22
17/63

Comments: 22 pages, 16 figures

Detection of the 4.4-MeV gamma rays from $^{16}$O($ν, ν^{\prime}$)$^{16}$O(12.97 ${\rm MeV}, 2^-)$ with a water-Cherenkov detector in the supernova neutrino bursts [HEAP]

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http://arxiv.org/abs/2211.07851


We first discuss and determine the isospin mixing of the two $2^-$ states (12.53 MeV and 12.97 MeV) of $^{16}$O nucleus using the inelastic electron scattering data. We then evaluate the cross section of 4.4-MeV $\gamma$ rays produced in the neutrino neutral-current (NC) reaction $^{16}$O($\nu, \nu^{\prime}$)$^{16}$O$(12.97~{\rm MeV}, 2^-$) in a water Cherenkov detector at the low energy below 100 MeV. The detection of $\gamma$ rays for $E_{\gamma}>5$~MeV from the NC reaction $^{16}$O($\nu, \nu^{\prime}$)$^{16}$O$(E_x>16\ {\rm MeV}, T=1$) with a water Cherenkov detector in the supernova neutrino bursts has been proposed and discussed by several authors previously. In this article, we discuss a new NC reaction channel from $^{16}$O(12.97 ${\rm MeV}, 2^-$) producing a 4.4-MeV $\gamma$ ray, the cross section of which is more robust and even larger at the low energy ($E_{\nu}<25$ MeV) than the NC cross section from $^{16}$O$(E_x>16\ {\rm MeV}, T=1$). We also evaluate the number of such events induced by neutrinos from supernova explosion which can be observed by the Super-Kamiokande, a 32 kton water Cherenkov detector in the Earth.

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M. Sakuda, T. Suzuki, M. Reen, et. al.
Wed, 16 Nov 22
3/76

Comments: 23 Pages, 9 figures, Submitted for publication in PTEP journal on 13 November, 2022

On the sound velocity bound in neutron stars [HEAP]

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http://arxiv.org/abs/2211.07874


It has been suggested in the literature that the sound velocity of the nuclear matter $v_s$ violates the so-called sound velocity bound $v_s \le c/\sqrt{3}$ at high density, where $c$ is the speed of light. In this paper, we revisit this issue and confront the current measurements of mass, radius, and tidal deformability of neutron stars with $10^5$ different equations of state which are parametrized at low density and saturates the sound velocity bound beyond twice the saturation density where the equation of state has not been constrained yet, by which we can conservatively obtain the maximum mass of the neutron stars compatible both with the observed properties of neutron stars and the sound velocity bound. We find that majority of the models are eliminated by the incompatibility with the observations and, especially, the recently detected massive pulsar ($2.35\pm 0.17 M_\odot$) is hardly realized by our simulations. Our study strongly supports the violation of the sound velocity bound.

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S. Roy and T. Suyama
Wed, 16 Nov 22
15/76

Comments: 14 pages, 5 figures

Is the compact object associated with HESS J1731-347 a strange quark star? [HEAP]

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http://arxiv.org/abs/2211.07485


The analysis of the central compact object within the supernova (SN) remnant HESS J1731-347 suggests that it has a small radius and, even more interestingly, a mass of the order or smaller than one solar mass (Doroshenko et al. 2022, Nature Astronomy). This raises the question of which astrophysical process could lead to such a small mass, since the analysis of various types of SN explosions indicate that is it not possible to produce a neutron star (NS) with a mass smaller than about $1.17 M_\odot$. Here we show that masses of the order or smaller than one solar mass can be obtained in the case of strange quark stars (QSs) and that it is possible to build a coherent astrophysical scenario explaining not only the mass and the radius of that object, but also its slow cooling suggested in various analyses. Moreover, we will show that QSs can fulfill all the limits on masses and radii of the other astrophysical objects discussed in Doroshenko et al. 2022 and can also explain the possible existence of objects having a mass of the order or larger than $2.5 M_\odot$, as suggested by the analysis of GW190814.

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F. Clemente, A. Drago and G. Pagliara
Tue, 15 Nov 22
72/103

Comments: 6 pages, 1 Figure, 1 Table

Magnetised neutron star crust within effective relativistic mean-field model [HEAP]

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http://arxiv.org/abs/2211.07339


Even though the crystallize nature of the neutron star crust plays a pivotal role in describing various fascinating astrophysical observations, its microscopic structure is not fully understood in the presence of a colossal magnetic field. In the present work, we study the crustal properties of a neutron star within an effective relativistic mean field framework in the presence of magnetic field strength $\sim 10^{17}$ G. We calculate the equilibrium composition of the outer crust by minimizing the gibbs free energy using the most recent atomic mass evaluations. The magnetic field significantly affects the equation of state (eos) and the properties of the outer crust, such as neutron drip density, pressure, and melting temperature. For the inner crust, we use the compressible liquid drop model for the first time to study the crustal properties in a magnetic environment. The inner crust properties, such as mass and charge number distribution, isospin asymmetry, cluster density, etc. , show typical quantum oscillations (de haasvan alphen effect) sensitive to the magnetic field’s strength. The density-dependent symmetry energy influences the magnetic inner crust like the field-free case. We study the probable modifications in the pasta structures and it is observed that their mass and thickness changes by $\sim 10-15 \%$ depending upon the magnetic field strength. The fundamental torsional oscillation mode frequency is investigated for the magnetized crust in the context of quasiperiodic oscillations (qpo) in soft gamma repeaters. The magnetic field strengths considered in this work influences only the eos of outer and shallow regions of the inner crust, which results in no significant change in global neutron star properties. However, the outer crust mass and its moment of inertia increase considerably with increase in magnetic field strength.

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V. Parmar, H. Das, M. Sharma, et. al.
Tue, 15 Nov 22
73/103

Comments: 17 pages, 12 figures, 5 tables, comments welcome

Leptonic and semi-leptonic neutrino interactions with muons in the proto-neutron star cooling [HEAP]

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http://arxiv.org/abs/2211.06944


It is known that muons are scarce just after the birth of a proto-neutron star via a supernova explosion but get more abundant as the proto-neutron star cools via neutrino emissions on the Kelvin-Helmholtz timescale.
In this paper we evaluate all the relevant rates of the neutrino interactions with muons at different times in the proto-neutron star cooling.
We are particularly interested in the late phase ($ t \gtrsim 10 \operatorname{s}$), which will be accessible in the next Galactic supernova but has not been studied well so far.
We calculate both leptonic and semi-leptonic processes, for the latter of which we pay attention also to the form factors with their dependence on the transferred momentum as well as to the modification of the dispersion relations for nucleons on the mean field level.
We find that the flavor-exchange reactions $\nu_e + \mu^- \rightarrow \nu_{\mu} + e^-$ and $\bar{\nu}{\mu} + \mu^- \rightarrow \bar{\nu}_e + e^-$ can be dominant, particularly at low energies, over the capture of $\nu_e$ on neutron and the scatterings of $\bar{\nu}{\mu}$ on nucleons as the opacity sources for these species and that the inverse muon decay $ \bar{\nu}e + \nu{\mu} + e^- \leftrightarrows \mu^- $ can overwhelm the scatterings of $\bar{\nu}e$ and $\nu{\mu}$ on nucleons again at low energies.
At high energies, on the other hand, the corrections in the semi-leptonic processes mentioned above are more important.
We also show the non-trivial energy- and angular dependences of the flavor-exchange reactions and the inverse muon decay.
In the study of the diffusion coefficients from these reactions, we find that $\bar{\nu}_{\mu}$ is most affected.
These pieces of information are indispensable for numerical computations and the interpretation of results thereof for the proto-neutron star cooling particularly at the very late phase.

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K. Sugiura, S. Furusawa, K. Sumiyoshi, et. al.
Tue, 15 Nov 22
102/103

Comments: 53 pages, 19 Figures

Testing the phase transition parameters inside neutron stars with the production of protons and lambdas in relativistic heavy-ion collisions [CL]

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http://arxiv.org/abs/2211.04978


We demonstrate the consistency of the quark deconfinement phase transition parameters in the beta-stable neutron star matter and in the nearly symmetric nuclear matter formed in heavy-ion collisions (HICs). We investigate the proton and $\Lambda$ flow in Au+Au collisions at 3 and 4.5 GeV/nucleon incident beam energies with the pure hadron cascade version of a multi-phase transport model. The phase transition in HICs and neutron stars is described based on a class of hybrid equations of state from the quark mean-field model for the hadronic phase and a constant-speed-of-sound parametrization for the high-density quark phase. The measurements of the anisotropic proton flow at 3 GeV/nucleon by the STAR collaboration favor a relatively low phase transition density lower than $\sim 2.5$ times saturation density indicated by the gravitational wave and electromagnetic observations of neutron stars. And the proton flow data at the higher energy of 4.5 GeV/nucleon can be used to effectively constrain the softness of high-density quark matter equations of state. Finally, compared to the proton flow, the $\Lambda$ flow is found to be less sensitive and not constraining to the equations of state.

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A. Li, G. Yong and Y. Zhang
Thu, 10 Nov 22
23/78

Comments: 7 pages, 7 figures

Finite-temperature equation of state with hyperons [CL]

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http://arxiv.org/abs/2211.04855


We present the novel finite-temperature FSU2H$^*$ equation-of-state model that covers a wide range of temperatures and lepton fractions for the conditions in proto-neutron stars, neutron star mergers and supernovae. The temperature effects on the thermodynamical observables and the composition of the neutron star core are stronger when the hyperonic degrees of freedom are considered. We pay a special attention to the temperature and density dependence of the thermal index in the presence of hyperons and conclude that the true thermal effects cannot be reproduced with the use of a constant $\Gamma$ law.

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H. Kochankovski, A. Ramos and L. Tolos
Thu, 10 Nov 22
28/78

Comments: 8 pages, 5 figures, contribution to the proceedings of the XVth Quark confinement and the Hadron spectrum conference (ConfXV), University of Stavanger, August 1-6, 2022

PANDORA project: photo-nuclear reactions below $A=60$ [CL]

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http://arxiv.org/abs/2211.03986


Photo-nuclear reactions of light nuclei below a mass of $A=60$ are studied experimentally and theoretically by the PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project. Two experimental methods, virtual-photon excitation by proton scattering and real-photo absorption by a high-brilliance gamma-ray beam produced by laser Compton scattering, will be applied to measure the photo-absorption cross sections and the decay branching ratio of each decay channel as a function of the photon energy. Several nuclear models, {\em e.g.} anti-symmetrized molecular dynamics, mean-field type models, a large-scale shell model, and {\em ab initio} models, will be employed to predict the photo-nuclear reactions. The uncertainty in the model predictions will be evaluated from the discrepancies between the model predictions and the experimental data. The data and the predictions will be implemented in a general reaction calculation code \talys . The results will be applied to the simulation of the photo-disintegration process of ultra-high-energy cosmic rays in inter-galactic propagation.

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A. Tamii, L. Pellegri, P. Söderström, et. al.
Wed, 9 Nov 22
33/76

Comments: N/A

Counting States: A Combinatorial Analysis of SQM Fragmentation [HEAP]

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http://arxiv.org/abs/2211.03687


The Strange Quark matter (SQM) hypothesis states that at extreme pressure and density conditions a new ground state of matter would arise, in which half of the \textit{down} quarks become strange quarks. If true, it would mean that at least the core of neutron stars is made of SQM. In this hypothesis, SQM would be released in the inter-stellar medium when two of these objects merge. It is estimated that $10^{-2} M\odot$ of SQM would be released this way. This matter will undergo a sequence of processes that should result in a fraction of the released SQM becoming heavy nuclei through \textit{r-process}. In this work we are interested in characterizing the fragmentation of SQM, with the novelty of keeping track of the \textit{quark configuration} of the fragmented matter. This is accomplished by developing a methodology to estimate the energy of each fragment as the sum of its \textit{constituent quarks}, the Coulomb interaction among the quarks and fragments’ momenta. The determination of the fragmentation output is crucial to fully characterize the subsequent nucleosynthesis.

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A. Bernardo, L. Paulucci, L. Sá, et. al.
Tue, 8 Nov 22
26/79

Comments: 4 pages, 2 figures, 2 tables

Space-time variation of the s and c quark masses [CL]

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http://arxiv.org/abs/2211.03325


Space-time variation of fundamental physical constants in expanding Universe is predicted by a number of popular models. The masses of second generation quarks are larger than first generation quark masses by several orders of magnitude, therefore space-time variation in quark masses may significantly vary between each generation. We evaluate limits on variation in the s and c quark masses from Big Bang nucleosynthesis, Oklo natural nuclear reactor, Yb+, Cs and Rb clock data. The construction of 229Th nuclear clock is expected to enhance these limits by several orders of magnitude. Furthermore, constraints are obtained on an oscillating scalar or pseudoscalar cold dark matter field, as interactions of the field with quarks produce variations in quark masses.

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V. Flambaum and P. Munro-Laylim
Tue, 8 Nov 22
32/79

Comments: N/A

Long Range Plan: Dense matter theory for heavy-ion collisions and neutron stars [CL]

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http://arxiv.org/abs/2211.02224


Since the release of the 2015 Long Range Plan in Nuclear Physics, major events have occurred that reshaped our understanding of quantum chromodynamics (QCD) and nuclear matter at large densities, in and out of equilibrium. The US nuclear community has an opportunity to capitalize on advances in astrophysical observations and nuclear experiments and engage in an interdisciplinary effort in the theory of dense baryonic matter that connects low- and high-energy nuclear physics, astrophysics, gravitational waves physics, and data science

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A. Lovato, T. Dore, R. Pisarski, et. al.
Mon, 7 Nov 22
28/67

Comments: 70 pages, 3 figures, White Paper for the Long Range Plan for Nuclear Science

Connecting small-scale to large-scale structures of fast neutrino-flavor conversion [HEAP]

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http://arxiv.org/abs/2211.01398


We present a systematic study of fast neutrino-flavor conversion (FFC) with both small-scale and large-scale numerical simulations in spherical symmetry. We find that FFCs can, in general, reach in a quasi-steady state, and these features in the non-linear phase are not characterized by the growth rate of FFC instability but rather angular structures of electron neutrino lepton number (ELN) and heavy one (XLN). Our result suggests that neutrinos can almost reach a flavor equipartition even in cases with low growth rate of instability (e.g., shallow ELN crossing) and narrow angular regions (in momentum space) where flavor conversions occur vigorously. This exhibits that ELN and XLN angular distributions can not provide a sufficient information to determine total amount of flavor conversion in neutrinos and antineutrinos of all flavors. Based on the results of our numerical simulations, we provide a new approximate scheme of FFC that is designed so that one can easily incorporate effects of FFCs in existing classical neutrino transport codes for the study of core-collapse supernova (CCSN) and binary neutron star merger (BNSM). The scheme has an ability to capture key features of quasi-steady state of FFCs without solving quantum kinetic neutrino transport, which will serve to facilitate access to FFCs for CCSN and BNSM theorists.

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H. Nagakura and M. Zaizen
Fri, 4 Nov 22
11/84

Comments: 22 pages, 18 figures

A Bayesian inference of relativistic mean-field model for neutron star matter from observation of NICER and GW170817/AT2017gfo [HEAP]

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http://arxiv.org/abs/2211.02007


The observations of optical and near-infrared counterparts of binary neutron star mergers not only enrich our knowledge about the abundance of heavy elements in the Universe, or help reveal the remnant object just after the merger as generally known, but also can effectively constrain dense nuclear matter properties and the equation of state (EOS) in the interior of the merging stars. Following the relativistic mean-field description of nuclear matter, we perform the Bayesian inference of the EOS and the nuclear matter properties using the first multi-messenger event GW170817/AT2017gfo, together with the NICER mass-radius measurements of pulsars. The kilonova is described by a radiation-transfer model with the dynamical ejecta, and light curves connect with the EOS through the quasi-universal relations between the ejecta properties (the ejected mass, velocity, opacity or electron fraction) and binary parameters (the mass ratio and reduced tidal deformability). It is found that the posterior distributions of the reduced tidal deformability from the AT2017gfo analysis display a bimodal structure, with the first peak enhanced by the GW170817 data, leading to slightly softened posterior EOSs, while the second peak cannot be achieved by a nuclear EOS with saturation properties in their empirical ranges. The inclusion of NICER data in our analyses results in stiffened EOS posterior because of the massive pulsar PSR J0740+6620. We give results at nuclear saturation density for the nuclear incompressibility, the symmetry energy and its slope, as well as the nucleon effective mass, from our analysis of those observational data.

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Z. Zhu, A. Li and T. liu
Fri, 4 Nov 22
41/84

Comments: 14 pages, 5 figures

Modeling Solids in Nuclear Astrophysics with Smoothed Particle Hydrodynamics [IMA]

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http://arxiv.org/abs/2211.01927


Smoothed Particle Hydrodynamics (SPH) is a frequently applied tool in computational astrophysics to solve the fluid dynamics equations governing the systems under study. For some problems, for example when involving asteroids and asteroid impacts, the additional inclusion of material strength is necessary in order to accurately describe the dynamics. In compact stars, that is white dwarfs and neutron stars, solid components are also present. Neutron stars have a solid crust which is the strongest material known in nature. However, their dynamical evolution, when modeled via SPH or other computational fluid dynamics codes, is usually described as a purely fluid dynamics problem. Here, we present the first 3D simulations of neutron-star crustal toroidal oscillations including material strength with the Los Alamos National Laboratory SPH code FleCSPH. In the first half of the paper, we present the numerical implementation of solid material modeling together with standard tests. The second half is on the simulation of crustal oscillations in the fundamental toroidal mode. Here, we dedicate a large fraction of the paper to approaches which can suppress numerical noise in the solid. If not minimized, the latter can dominate the crustal motion in the simulations.

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I. Sagert, O. Korobkin, I. Tews, et. al.
Fri, 4 Nov 22
42/84

Comments: 24 pages, 29 figures

Nuclei in Core-Collapse Supernovae Engine [CL]

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http://arxiv.org/abs/2211.01050


Herein, we review the nuclear equations of state (EOSs) %for core-collapse supernova simulations and the constituent nuclei of core-collapse supernovae (CCSNe) and their roles in CCSN simulations. Various nuclei such as deuterons, iron, and extremely neutron-rich nuclei compose in the central engines of CCSNe. The center of a collapsing core is dominated by neutron-rich heavy nuclei prior to the occurrence of core bounce. Their weak interactions significantly affect the neutrino emission and the size of the produced proto-neutron star. After a core bounce, heavy nuclei are dissolved to protons, neutrons, and light nuclei between the expanding shock wave and the newly formed neutron star (NS). Some of the key components in determining the shock-wave dynamics and supernova explosion of outer envelopes are neutrino interactions of nucleons and light nuclei such as deuterons. An EOS provides the relations between thermodynamical properties and the nuclear composition, and is needed to simulate this explosion. Further investigations on uniform and non-uniform nuclear matter are needed to improve the understanding of the mechanism of CCSNe and the properties of supernova nuclei. The knowledge of the EOS for uniform nuclear matter is being continually improved by a combination of microscopic calculations, terrestrial experiments, and NS observations. With reference to various nuclear experiments and current theories, the finite temperature effects on heavy nuclei, formation of light nuclei in dilute nuclear matter, and transition to uniform nuclear matter should be improved in the model of the EOS for non-uniform nuclear matter.

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S. Furusawa and H. Nagakura
Thu, 3 Nov 22
18/59

Comments: 57 pages, 23 figures, submitted to Prog. Part. Nucl. Phys

Effects of electromagnetic fluctuations in plasmas on solar neutrino fluxes [SSA]

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http://arxiv.org/abs/2211.00907


We explore the effects of electromagnetic (EM) fluctuations in plasmas on solar neutrino fluxes exploiting the fluctuation-dissipation theorem. We find that the EM spectrum in the solar core is enhanced by the EM fluctuations due to the high density of the Sun, which increases the radiation energy density and pressure. By the EM fluctuations involving the modified radiation formula, the central temperature decreases when the central pressure of the Sun is fixed. With a help of the empirical relation between central temperature and neutrino fluxes deduced from the numerical solar models, we present the change in each of the solar neutrino fluxes by the EM fluctuations. We also discuss the enhanced radiation pressure and energy density by the EM fluctuations for other astronomical objects.

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E. Hwang, D. Jang, K. Park, et. al.
Thu, 3 Nov 22
35/59

Comments: N/A

Bayesian analysis of neutron-star properties with parameterized equations of state: the role of the likelihood functions [CL]

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http://arxiv.org/abs/2211.00018


We have investigated the systematic differences introduced when performing a Bayesian-inference analysis of the equation of state of neutron stars employing either variable- or constant-likelihood functions. The former have the advantage that it retains the full information on the distributions of the measurements, making an exhaustive usage of the data. The latter, on the other hand, have the advantage of a much simpler implementation and reduced computational costs. In both approaches, the EOSs have identical priors and have been built using the sound-speed parameterization method so as to satisfy the constraints from X-ray and gravitational-waves observations, as well as those from Chiral Effective Theory and perturbative QCD. In all cases, the two approaches lead to very similar results and the $90\%$-confidence levels are essentially overlapping. Some differences do appear, but in regions where the probability density is extremely small and are mostly due to the sharp cutoff set on the binary tidal deformability $\tilde \Lambda \leq 720$ employed in the constant-likelihood analysis. Our analysis has also produced two additional results. First, a clear inverse correlation between the normalized central number density of a maximally massive star, $n_{\rm c, TOV}/n_s$, and the radius of a maximally massive star, $R_{\rm TOV}$. Second, and most importantly, it has confirmed the relation between the chirp mass $\mathcal{M}{\rm chirp}$ and the binary tidal deformability $\tilde{\Lambda}$. The importance of this result is that it relates a quantity that is measured very accurately, $\mathcal{M}{\rm chirp}$, with a quantity that contains important information on the micro-physics, $\tilde{\Lambda}$. Hence, once $\mathcal{M}_{\rm chirp}$ is measured in future detections, our relation has the potential of setting tight constraints on $\tilde{\Lambda}$.

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J. Jiang, C. Ecker and L. Rezzolla
Wed, 2 Nov 22
26/67

Comments: 16 pages, 6 figures, 2 tables

Deep Learning Detection and Classification of Gravitational Waves from Neutron Star-Black Hole Mergers [IMA]

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http://arxiv.org/abs/2210.15888


The Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo Interferometer Collaborations have now detected all three classes of compact binary mergers: binary black hole (BBH), binary neutron star (BNS), and neutron star-black hole (NSBH). For coalescences involving neutron stars, the simultaneous observation of gravitational and electromagnetic radiation produced by an event, has broader potential to enhance our understanding of these events, and also to probe the equation of state (EOS) of dense matter. However, electromagnetic follow-up to gravitational wave (GW) events requires rapid real-time detection and classification of GW signals, and conventional detection approaches are computationally prohibitive for the anticipated rate of detection of next-generation GW detectors. In this work, we present the first deep learning based results of classification of GW signals from NSBH mergers in \textit{real} LIGO data. We show for the first time that a deep neural network can successfully distinguish all three classes of compact binary mergers and separate them from detector noise. Specifically, we train a convolutional neural network (CNN) on $\sim 500,000$ data samples of real LIGO noise with injected BBH, BNS, and NSBH GW signals, and we show that our network has high sensitivity and accuracy. Most importantly, we successfully recover the two confirmed NSBH events to-date (GW200105 and GW200115) and the two confirmed BNS mergers to-date (GW170817 and GW190425), together with $\approx 90\%$ of all BBH candidate events from the third Gravitational Wave Transient Catalog, GWTC-3. These results are an important step towards low-latency real-time GW detection, enabling multi-messenger astronomy.

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R. Qiu, P. Krastev, K. Gill, et. al.
Mon, 31 Oct 22
6/60

Comments: 8 pages, 5 figures. arXiv admin note: text overlap with arXiv:2012.13101

Twin stars as probes of the nuclear equation of state: effects of rotation through the PSR J0952-0607 pulsar and constraints via the tidal deformability from the GW170817 event [HEAP]

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http://arxiv.org/abs/2210.15644


In agreement with the constantly increasing gravitational wave events, new aspects of the internal structure of compact stars can be considered. A scenario in which a first order transition takes place inside these stars is of particular interest as it can lead, under conditions, to a third gravitationally stable branch (besides white dwarfs and neutron stars), the twin stars. The new branch yields stars with the same mass as normal compact stars but quite different radii. In the present work, we focus on hybrid stars undergone a hadron to quark phase transition near their core and how this new stable configuration arises. Emphasis is to be given on the aspects of the phase transition and its parametrization in two different ways, namely with Maxwell and Gibbs construction. We systematically study the gravitational mass, the radius, and the tidal deformability, and we compare them with the predictions of the recent observation by LIGO/VIRGO collaboration, the GW170817 event, along with the mass and radius limits, suggesting possible robust constraints. Moreover, we extent the study in order to include rotation effects on the twin stars configurations. The recent discovery of the fast rotating supermassive pulsar PSR J0952-0607 triggered the effort to constrain the equation of state and moreover to examine possible predictions related to the phase transition in dense nuclear matter. We pay special attention to relate the PSR J0952-0607 pulsar properties with the twin stars predictions and mainly to explore the possibility that the existence of such a massive object would rule out the existence of twin stars. Finally, we discuss the constraints on the radius and mass of the recently observed compact object within the supernova remnant HESS J1731-347. The estimations implies that this object is either the lightest neutron star known, or a star with a more exotic equation of state.

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L. Tsaloukidis, P. Koliogiannis, A. Kanakis-Pegios, et. al.
Fri, 28 Oct 22
9/56

Comments: 16 pages, 17 figures

(Anti)kaon condensation in strongly magnetized dense matter [HEAP]

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http://arxiv.org/abs/2210.14565


Recent observations of several massive pulsars, with masses near and above $2~M_\odot$, point towards the existence of matter at very high densities, compared to normal matter that we are familiar with in our terrestrial world. This leads to the possibility of appearance of exotic degrees of freedom other than nucleons inside the core of the neutrons stars (NS). Another significant property of NSs is the presence of high surface magnetic field, with highest range of the order of $\sim~10^{16}$ G. We study the properties of highly dense matter with the possibility of appearance of heavier strange and non-strange baryons, and kaons in presence of strong magnetic field. We find that the presence of a strong magnetic field stiffens the matter at high density, delaying the kaon appearance and, hence, increasing the maximum attainable mass of NS family.

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D. Kundu, V. Thapa and M. Sinha
Thu, 27 Oct 22
14/55

Comments: 14 pages, 9 figures

Understanding the cosmic abundance of $^{22}$Na: lifetime measurements in $^{23}$Mg [CL]

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http://arxiv.org/abs/2210.14336


Simulations of explosive nucleosynthesis in novae predict the production of $^{22}$Na, a key astronomical observable to constrain nova models. Its gamma-ray line at 1.275 MeV has not yet been observed by the gamma-ray space telescopes. The $^{20}$Ne/$^{22}$Ne ratio in presolar grains, a possible tool to identify nova grains, also depends on $^{22}$Na produced. Uncertainties on its yield in classical novae currently originate from the rate of the $^{22}$Na(p, $\gamma$)$^{23}$Mg reaction. At peak novae temperatures, this reaction is dominated by a resonance at E${\text{R}}$=0.204 MeV, corresponding to the $E_x$=7.785 MeV excited state in $^{23}$Mg. The resonance strengths measured so far disagree by one order of magnitude. An experiment has been performed at GANIL to measure the lifetime and the proton branching ratio of this key state, with a femtosecond resolution for the former. The reactions populating states in $^{23}$Mg have been studied with a high resolution detection set-up, i.e. the particle VAMOS, SPIDER and gamma tracking AGATA spectrometers, allowing the measurements of lifetimes and proton branchings. We present here a comparison between experimental results and shell-model calculations, that allowed us to assign the spin and parity of the key state. Rather small values obtained for reduced $M1$ matrix elements, $|M(M1)|\lesssim 0.5$ $\mu_N$, and proton spectroscopic factors, $C^{2}S{\text{p}}$<10$^{-2}$, seem to be beyond the accuracy of the shell model. With the reevaluated $^{22}$Na(p, $\gamma$)$^{23}$Mg rate, the $^{22}$Na detectability limit and its observation frequency from novae are found promising for the future space telescopes.

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C. Fougères, F. Santos, N. Smirnova, et. al.
Thu, 27 Oct 22
34/55

Comments: 6 pages, 4 figures, proceedings of the conference Nuclear Physics in Astrophysics – X (NPA-X, Cern 2022), submitted in EPJ Web of Conferences

Bayesian Estimation of the $S$ Factor and Thermonuclear Reaction Rate for $^{16}$O(p,$γ$)$^{17}$F [CL]

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http://arxiv.org/abs/2210.14354


The $^{16}$O(p,$\gamma$)$^{17}$F reaction is the slowest hydrogen-burning process in the CNO mass region. Its thermonuclear rate sensitively impacts predictions of oxygen isotopic ratios in a number of astrophysical sites, including AGB stars. The reaction has been measured several times at low bombarding energies using a variety of techniques. The most recent evaluated experimental rates have a reported uncertainty of about 7.5\% below $1$~GK. However, the previous rate estimate represents a best guess only and was not based on rigorous statistical methods. We apply a Bayesian model to fit all reliable $^{16}$O(p,$\gamma$)$^{17}$F cross section data, and take into account independent contributions of statistical and systematic uncertainties. The nuclear reaction model employed is a single-particle potential model involving a Woods-Saxon potential for generating the radial bound state wave function. The model has three physical parameters, the radius and diffuseness of the Woods-Saxon potential, and the asymptotic normalization coefficients (ANCs) of the final bound state in $^{17}$F. We find that performing the Bayesian $S$ factor fit using ANCs as scaling parameters has a distinct advantage over adopting spectroscopic factors instead. Based on these results, we present the first statistically rigorous estimation of experimental $^{16}$O(p,$\gamma$)$^{17}$F reaction rates, with uncertainties ($\pm 4.2$\%) of about half the previously reported values.

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C. Iliadis, V. Palanivelrajan and R. Souza
Thu, 27 Oct 22
47/55

Comments: 3 figures

Crustal failure as a tool to probe hybrid stars [HEAP]

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http://arxiv.org/abs/2210.14048


It is currently unknown if neutron stars are composed of nucleons only or are hybrid stars, i.e., in addition to nucleonic crusts and outer cores, they also possess quark cores. Quantum chromodynamics allows for such a phase transition possibility, but accurate calculations in the range of interest for compact stars are still elusive. Here we investigate some crust-breaking aspects of hybrid stars. We show that the crust-breaking orbital/gravitational wave frequency and maximum ellipticity are sensitive to the quark-hadron density jump and equation of state stiffness. Remarkably, the crust-breaking frequency related to static tides scales linearly with the mass of the star (for a given companion’s mass), and its slope encompasses information about the microphysics of the star. When a liquid quark core touches an elastic hadronic phase, which could be the result of a significant energy-density jump, the maximum ellipticity can increase orders of magnitude when compared to the case the liquid quark core touches a liquid hadronic phase, such as the outer core. Our analysis also suggests that a given upper limit to the ellipticity or a crust-breaking frequency could have representatives in stars with either small or very large energy-density jumps. Therefore, upper limits to the ellipticity from continuous gravitational wave observations of the LIGO-Virgo-KAGRA network for isolated stars, and gamma-ray precursors associated with crust breaking in inspiraling binary systems may constrain some aspects of phase transitions in neutron stars.

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J. Pereira, M. Bejger, P. Haensel, et. al.
Wed, 26 Oct 22
27/73

Comments: 10 pages, 6 figures. Comments welcome

Exotic Compact Objects with Two Dark Matter Fluids [CL]

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http://arxiv.org/abs/2210.13697


The generic properties of compact objects made of two different fluids of dark matter are studied in a scale invariant approach. We investigate compact objects with a core-shell structure, where the two fluids are separated, and with mixed dark matter components, where both dark matter fluids are immersed within each other. The constellations considered are combinations of incompressible fluids, free and interacting Fermi gases, and equations of state with a vacuum term, i.e. self-bound dark matter. We find novel features in the mass-radius relations for combined dark matter compact objects which distinguishes them from compact objects with a single dark matter fluid and compact stars made of ordinary baryonic matter, as white dwarfs, neutron stars and quark stars. The maximum compactness of certain combined dark matter stars can reach values up to the causality limit for compact stars but not beyond that limit if causality of the dark matter fluids is ensured.

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M. Cassing, A. Brisebois, M. Azeem, et. al.
Wed, 26 Oct 22
64/73

Comments: 11 pages, 13 figures

Cosmological consequences of first-order general-relativistic viscous fluid dynamics [CL]

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http://arxiv.org/abs/2210.13372


We investigate the out-of-equilibrium dynamics of viscous fluids in a spatially flat Friedmann-Lema\^itre-Robertson-Walker cosmology using the most general causal and stable viscous energy-momentum tensor defined at first order in spacetime derivatives. In this new framework a pressureless viscous fluid having density $\rho$ can evolve to an asymptotic future solution in which the Hubble parameter approaches a constant while $\rho \rightarrow 0$, even in the absence of a cosmological constant (i.e., $\Lambda = 0$). Thus, while viscous effects in this model drive an accelerated expansion of the universe, the density of the viscous component itself vanishes, leaving behind only the acceleration. This behavior emerges as a consequence of causality in first-order theories of relativistic fluid dynamics and it is fully consistent with Einstein’s equations.

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F. Bemfica, M. Disconzi, J. Noronha, et. al.
Tue, 25 Oct 22
85/111

Comments: 14 pages, no figures

Nuclear data activities for medium mass and heavy nuclei at Los Alamos [CL]

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http://arxiv.org/abs/2210.12136


Nuclear data is critical for many modern applications from stockpile stewardship to cutting edge scientific research. Central to these pursuits is a robust pipeline for nuclear modeling as well as data assimilation and dissemination. We summarize a small portion of the ongoing nuclear data efforts at Los Alamos for medium mass to heavy nuclei. We begin with an overview of the NEXUS framework and show how one of its modules can be used for model parameter optimization using Bayesian techniques. The mathematical framework affords the combination of different measured data in determining model parameters and their associated correlations. It also has the advantage of being able to quantify outliers in data. We exemplify the power of this procedure by highlighting the recently evaluated 239-Pu cross section. We further showcase the success of our tools and pipeline by covering the insight gained from incorporating the latest nuclear modeling and data in astrophysical simulations as part of the Fission In R-process Elements (FIRE) collaboration.

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M. Mumpower, T. Sprouse, T. Kawano, et. al.
Mon, 24 Oct 22
7/56

Comments: 6 pages, 5 figures, Nuclear Data (2022) conference proceedings. Comments welcome!

Neutron Lifetime Anomaly and Big Bang Nucleosynthesis [CL]

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http://arxiv.org/abs/2210.12031


We calculate the Big Bang Nucleosynthesis abundances for helium-4 and deuterium for a range of neutron lifetimes, $\tau_n = 840 – 1050$ s, using the state-of-the-art Python package \textsc{PRyMordial}. We show the results for two different nuclear reaction rates, calculated by NACRE II [1] and the PRIMAT [2] collaborations.

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T. Chowdhury and S. Ipek
Mon, 24 Oct 22
15/56

Comments: N/A

Core-collapse supernovae simulations with reduced nucleosynthesis networks [HEAP]

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http://arxiv.org/abs/2210.11848


We present core-collapse supernovae simulations including nuclear reaction networks which impact explosion dynamics and nucleosynthesis. The different composition treatment can lead to changes in the neutrino heating in the vicinity of the shock, by modifying the amount of nucleons and thus the $\mathrm{\nu}$-opacity of the region. This reduces the ram pressure outside the shock and allows an easier expansion. The energy released by the nuclear reactions during collapse also slows down the accretion, and aids the shock expansion. In addition, nuclear energy generation in the post-shocked matter produces more energetic explosions, up to $20\,\%$. Nucleosynthesis is affected due to the different dynamic evolution of the explosion. Our results indicate that the energy generation from nuclear reactions helps to sustain late outflows from the vicinity of the proto-neutron star (PNS), synthesizing more neutron-rich species. Furthermore, we show that there are systematic discrepancies between the ejecta calculated with in-situ and ex-situ reaction networks. The mass fractions of some Ca, Ti, Cr, and Fe isotopes are consistently under-produced in post-processing calculations, leading to different nucleosynthesis paths. Therefore, large in-situ nuclear reaction networks are needed for a more accurate nucleosynthesis.

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G. Navó, M. Reichert, M. Obergaulinger, et. al.
Mon, 24 Oct 22
18/56

Comments: Submitted to ApJ on 20 October 2022

Spatial Structure of the $^{12}$C Nucleus in a 3$α$ Model with Deep Potentials Containing Forbidden States [CL]

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http://arxiv.org/abs/2210.11763


The spatial structure of the lowest 0$_1^+$, 0$_2^+$, 2$_1^+$ and 2$_2^+$ states of the $^{12}$C nucleus is studied within the 3$\alpha$ model with the Buck, Friedrich, and Wheatley $\alpha \alpha$ potential with Pauli forbidden states in the $S$ and $D$ waves. The Pauli forbidden states in the three-body system are treated by the exact orthogonalization method. The largest contributions to the ground and excited 2$_1^+$ bound states energies come from the partial waves $(\lambda, \ell)=(2,2)$ and $(\lambda, \ell)=(4,4)$. In contrast to the bound states, for the Hoyle resonance 0$_2^+$ and its analog state 2$_2^+$, dominant contributions come from the $(\lambda, \ell)=(0,0)$ and $(\lambda, \ell)=(2,2)$ configurations, respectively. The estimated probability density functions for the $^{12}$C(0$_1^+$) ground and 2$_1^+$ excited bound states show mostly a triangular structure, where the $\alpha$ particles move at a distance of about 2.5 fm from each other. However, the spatial structure of the Hoyle resonance and its analog state have a strongly different structure, like $^8$Be + $\alpha$. In the Hoyle state, the last $\alpha$ particle moves far from the doublet at the distance between $R=3.0$ fm and $R=5.0$ fm. In the Hoyle analog 2$_2^+$ state the two alpha particles move at a distance of about 15 fm, but the last $\alpha$ particle can move far from the doublet at the distance up to $R=30.0$ fm.

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E. Tursunov, M. Saidov and M. Begijonov
Mon, 24 Oct 22
32/56

Comments: 12 pages, 4 figures, 2 tables

Neutron star mass formula with nuclear saturation parameters for asymmetric nuclear matter [CL]

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http://arxiv.org/abs/2210.11651


Low-mass neutron stars are directly associated with the nuclear saturation parameters because their central density is definitely low. We have already found a suitable combination of nuclear saturation parameters for expressing the neutron star mass and gravitational redshift, i.e., $\eta\equiv (K_0L^2)^{1/3}$ with the incompressibility for symmetric nuclear matter, $K_0$, and the density-dependent nuclear symmetry energy, $L$. In this study, we newly find another suitable combination given by $\eta_\tau\equiv (-K_\tau L^5)^{1/6}$ with the isospin dependence of incompressibility for asymmetric nuclear matter, $K_\tau$, and derive the empirical relations for the neutron star mass and gravitational redshift as a function of $\eta_\tau$ and the normalized central number density. With these empirical relations, one can evaluate the mass and gravitational redshift of the neutron star, whose central number density is less than threefold the saturation density, within $\sim 10\%$ accuracy, and the radius within a few \% accuracies. In addition, we discuss the neutron star mass and radius constraints from the terrestrial experiments, using the empirical relations, together with those from the astronomical observations. Furthermore, we find a tight correlation between $\eta_\tau$ and $\eta$. With this correlation, we derive the constraint on $K_\tau$ as $-348\le K_\tau\le -237$ MeV, assuming that $L=60\pm 20$ and $K_0=240\pm 20$ MeV.

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H. Sotani and S. Ota
Mon, 24 Oct 22
55/56

Comments: Accepted for publication in RPD. arXiv admin note: text overlap with arXiv:2203.09004

Nuclear Equation of State and Single-nucleon Potential from Gogny-like Energy Density Functionals Encapsulating Effects of Nucleon-nucleon Short-range Correlations [CL]

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http://arxiv.org/abs/2210.10924


Nucleon-nucleon short-range correlations (SRCs) induce a high momentum tail (HMT) in the single-nucleon momentum distribution function $n_{\v{k}}^J(\rho,\delta)$ in cold neutron-rich matter. While there are clear experimental evidences that the SRC/HMT effects are different for neutrons and protons and their strengths depend strongly on the isospin asymmetry of finite nuclei mostly based on electron-nucleus scattering experiments, much less is known experimentally about the SRC/HMT effects in the dense neutron-rich matter. To facilitate further explorations of SRC/HMT effects in dense neutron-rich matter especially with heavy-ion reactions involving high-energy radioactive beams as well as multimessenger observations of neutron stars and their mergers, by incorporating the SRC-induced HMT in $n_{\v{k}}^J(\rho,\delta)$ into a Gogny-like energy density functional we study SRC/HMT effects on the equation of state (EOS) especially its symmetry energy term and single-nucleon potential in the dense asymmetric nucleonic matter (ANM). Using a parametrization as a surrogate for the momentum-dependent kernel in the Gogny-like energy density functional (EDF) we derive analytical expressions for all components of the ANM EOS and their characteristics (e.g., magnitude, slope and curvature as well as nucleon effective mass) at saturation density $\rho_0$ as well as the momentum-dependent single-nucleon optical potential in neutron-rich matter using parameters characterizing nuclear interactions as well as the size, shape and isospin dependence of the HMT at $\rho_0$. Some consequences of the SRC/HMT effects on properties of neutron stars are also studied.

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B. Cai and B. Li
Fri, 21 Oct 22
73/76

Comments: 35 pages including 16 figures

Evolution of collisional neutrino flavor instabilities in spherically symmetric supernova models [HEAP]

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http://arxiv.org/abs/2210.08254


We implement a multi-group and discrete-ordinate neutrino transport model in spherical symmetry which allows to simulate collective neutrino oscillations by including realistic collisional rates in a self-consistent way. We utilize this innovative model, based on strategic parameter rescaling, to study a recently proposed collisional flavor instability caused by the asymmetry of emission and absorption rates between $\nu_e$ and $\bar\nu_e$ for four different static backgrounds taken from different stages in a core-collapse supernova simulation. Our results confirm that collisional instabilities generally exist around the neutrinosphere during the SN accretion and post-accretion phase, as suggested by [arXiv:2104.11369]. However, the growth and transport of flavor instabilities can only be fully captured by models with global simulations as done in this work. With minimal ingredient to trigger collisional instabilities, we find that the flavor oscillations and transport mainly affect (anti)neutrinos of heavy lepton flavors around their decoupling sphere, which then leave imprints on their energy spectra in the free-streaming regime. For electron (anti)neutrinos, their properties remain nearly intact. We also explore various effects due to the decoherence from neutrino-nucleon scattering, artificially enhanced decoherence from emission and absorption, neutrino vacuum mixing, and inhomogeneous matter profile, and discuss the implication of our work.

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Z. Xiong, M. Wu, G. Martínez-Pinedo, et. al.
Tue, 18 Oct 22
60/99

Comments: 20 pages, 12 figures

Constraining the equation of state of hybrid stars using recent information from multidisciplinary physics [HEAP]

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http://arxiv.org/abs/2210.09077


At the ultra-high densities existing in the core of neutron stars, it is expected that a phase transition from baryonic to deconfined quark matter may occur. Such a phase transition would affect the underlying equation of state (EoS) as well as the observable astrophysical properties of neutron stars. Comparison of EoS model predictions with astronomical data from multi-messenger signals then provides us an opportunity to probe the behaviour of dense matter. In this work, we restrict the allowed parameter space of EoS models in neutron stars for both nucleonic (relativistic mean field model) and quark matter (bag model) sectors by imposing state-of-the-art constraints from nuclear calculations, multi-messenger astrophysical data and perturbative QCD (pQCD). We systematically investigate the effect of each constraint on the parameter space of uncertainties using a cut-off filter scheme, as well as the correlations among the parameters and with neutron star astrophysical observables. Using the constraints, we obtain limits for maximum NS mass, maximum central density, as well as for NS radii and tidal deformability. Although pQCD constraints are only effective at very high densities, they significantly reduce the parameter space of the quark model. We also conclude that astrophysical data supports high values of the bag parameter B and disfavors the existence of a pure quark matter core in hybrid stars.

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S. Shirke, S. Ghosh and D. Chatterjee
Tue, 18 Oct 22
77/99

Comments: 16 pages, 11 figures, 2 tables

Collision-induced flavor instability in dense neutrino gases with energy-dependent scattering [CL]

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http://arxiv.org/abs/2210.09218


We investigate the collision-induced flavor instability in homogeneous, isotropic, dense neutrino gases in the two-flavor mixing scenario with energy-dependent scattering. We find that the growth rate of such an instability, if it exists, is the negative average of the flavor-decohering collision rates of the neutrinos weighted by the electron lepton number distribution of the neutrinos. This growth rate is independent of the neutrino mass-splitting, the matter density, and the neutrino density, although the initial amplitude of the unstable oscillation mode can be suppressed by a large matter density. Our results suggest that neutrinos are likely to experience collision-induced flavor conversions deep inside a core-collapse supernova even when both the fast and slow collective flavor oscillations are suppressed. However, this phenomenon may not occur in a neutron star merger because the electron antineutrinos have a larger average energy and more abundance than the electron neutrinos in such an environment.

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Y. Lin and H. Duan
Tue, 18 Oct 22
87/99

Comments: 6 pages, 4 figures

3XMM J185246.6+003317: an isolated massive neutron star with a low magnetic field and a carbon atmosphere [HEAP]

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http://arxiv.org/abs/2210.06648


3XMM J185246.6+003317 is a slowly rotating soft-gamma repeater (neutron star) in the vicinity of the supernova remnant Kes\,79. So far, observations have only set upper limits to its surface magnetic field and spindown, and there is no estimate for its mass and radius. Using ray-tracing modelling and Bayesian inference for the analysis of several light curves spanning a period of around three weeks, we have found that it may be one of the most massive neutron stars to date. In addition, our analysis suggests a multipolar magnetic field structure with a subcritical field strength and a carbon atmosphere composition. Due to the time-resolution limitation of the available light curves, we estimate the surface magnetic field and the mass to be $\log_{10} (B/{\rm G}) = 11.89^{+0.19}{-0.93}$ and $M=2.09^{+0.16}{-0.09}$~$M_{\odot}$ at $1\sigma$ confidence level, while the radius is estimated to be $R=12.02^{+1.44}_{-1.42}$ km at $2\sigma$ confidence level. The robustness of these estimates was verified by simulations, i.e., data injections with known model parameters, and their subsequent recovery. The best-fit model has three small hot spots, two of them in the southern hemisphere. We interpret the above results as due to accretion of supernova layers/interstellar medium onto 3XMM J185246.6+003317 leading to burying and a subsequent re-emergence of the magnetic field, and a carbon atmosphere being formed possibly due to hydrogen/helium diffusive nuclear burning. Finally, we briefly discuss some consequences of our findings for superdense matter constraints.

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R. Lima, J. Pereira, J. Coelho, et. al.
Fri, 14 Oct 22
46/75

Comments: 23 pages, 10 figures, 2 tables. Comments welcome

Big Bang nucleosynthesis as a probe of new physics [CL]

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http://arxiv.org/abs/2210.04071


The Big Bang Nucleosynthesis (BBN) model is a cornerstone for the understanding of the evolution of the early universe, making seminal predictions that are in outstanding agreement with the present observation of light element abundances in the universe. Perhaps, the only remaining issue to be solved by theory is the so-called “lithium abundance problem”. Dedicated experimental efforts to measure the relevant nuclear cross sections used as input of the model have lead to an increased level of accuracy in the prediction of the light element primordial abundances. The rise of indirect experimental techniques during the preceding few decades has permitted the access of reaction information beyond the limitations of direct measurements. New theoretical developments have also opened a fertile ground for tests of physics beyond the standard model of atomic, nuclear, statistics, and particle physics. We review the latest contributions of our group for possible solutions of the lithium problem.

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C. Bertulani, F. Hall and B. Santoyo
Tue, 11 Oct 22
47/92

Comments: 9 pages, 7 figures, to be published

Supernova Neutrinos as a Precise Probe of Nuclear Neutron Skin [CL]

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http://arxiv.org/abs/2210.04534


A precise and model-independent determination of the neutron distribution radius $R_{\rm n}$ and thus the neutron skin thickness $R_{\rm skin}$ of atomic nuclei is of fundamental importance in nuclear physics, particle physics and astrophysics but remains a big challenge in terrestrial labs. We argue that the nearby core-collapse supernova (CCSN) in our Galaxy may render a neutrino flux with unprecedentedly high luminosity, offering perfect opportunity to determine the $R_{\rm n}$ and $R_{\rm skin}$ through the coherent elastic neutrino-nucleus scattering (CE$\nu$NS). We evaluate the potential of determining the $R_{\rm n}$ of lead (Pb) via CE$\nu$NS with the nearby CCSN neutrinos in the RES-NOVA project which is designed to hunt CCSN neutrinos using an array of archaeological Pb based cryogenic detectors. We find that an ultimate precision of $\sim 0.1 \%$ for the $R_{\rm n}$ ($\sim 0.006$ fm for the $R_{\rm skin}$) of Pb can be achieved via RES-NOVA if the CCSN explosion were to occur at a distance of $\sim 1$ kpc from the Earth.

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X. Huang and L. Chen
Tue, 11 Oct 22
74/92

Comments: 6 pages, 3 figures, 1 table

Internal Heating in Magnetars: Role of Electron Captures [HEAP]

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http://arxiv.org/abs/2210.02790


The role of electron captures by nuclei in the shallow heating of magnetars is further investigated using both nuclear measurements and the theoretical atomic mass table HFB-27. Starting from the composition of the outer crust in full equilibrium, we have calculated the onset of electron captures and the heat released due to the slow decay of the magnetic field. Numerical results are found to be similar to those previously obtained with the HFB-24 atomic mass model and are consistent with neutron-star cooling data.

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N. Chamel, A. Fantina, L. Suleiman, et. al.
Fri, 7 Oct 22
24/62

Comments: 6 pages, 1 figure. Contribution to the proceedings of the XLIV Brazilian Workshop on Nuclear Physics

Solar neutrino physics [CL]

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http://arxiv.org/abs/2209.14832


As a free, intensive, rarely interactive and well directional messenger, solar neutrinos have been driving both solar physics and neutrino physics developments for more than half a century. Since more extensive and advanced neutrino experiments are under construction, being planned or proposed, we are striving toward an era of precise and comprehensive measurement of solar neutrinos in the next decades. In this article, we review recent theoretical and experimental progress achieved in solar neutrino physics. We present not only an introduction to neutrinos from the standard solar model and the standard flavor evolution, but also a compilation of a variety of new physics that could affect and hence be probed by solar neutrinos. After reviewing the latest techniques and issues involved in the measurement of solar neutrino spectra and background reduction, we provide our anticipation on the physics gains from the new generation of neutrino experiments.

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X. Xu, Z. Wang and S. Chen
Fri, 30 Sep 22
26/71

Comments: 68 pages, many figures, review invited by Progress in Particle and Nuclear. Comments and suggestions are welcome

The Nuclear Physics of Neutron Stars [CL]

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http://arxiv.org/abs/2209.14877


Neutron stars — compact objects with masses similar to that of our Sun but radii comparable to the size of a city — contain the densest form of matter in the universe that can be probed in terrestrial laboratories as well as in earth- and space-based observatories. The historical detection of gravitational waves from a binary neutron star merger has opened the brand new era of multimessenger astronomy and has propelled neutron stars to the center of a variety of disciplines, such as astrophysics, general relativity, nuclear physics, and particle physics. The main input required to study the structure of neutron stars is the pressure support generated by its constituents against gravitational collapse. These include neutrons, protons, electrons, and perhaps even more exotic constituents. As such, nuclear physics plays a prominent role in elucidating the fascinating structure, dynamics, and composition of neutron stars.

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J. Piekarewicz
Fri, 30 Sep 22
65/71

Comments: 15 pages, 6 figures, submitted to Oxford Research Encyclopedia of Physics

Elastic properties of nuclear pasta in a fully three-dimensional geometry [CL]

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http://arxiv.org/abs/2209.13310


Realistic estimations on the elastic properties of neutron star matter are carried out with a large strain ($\varepsilon \lesssim 0.5$) in the framework of relativistic-mean-field model with Thomas-Fermi approximation, where various crystalline configurations are considered in a fully three-dimensional geometry with reflection symmetry. Our calculation confirms the validity of assuming Coulomb crystals for the droplet phase above neutron drip density, which nonetheless does not work at large densities since the elastic constants are found to be decreasing after reaching their peaks. Similarly, the analytic formulae derived in the incompressible liquid-drop model gives excellent description for the rod phase at small densities, which overestimates the elastic constants at larger densities. For slabs, due to the negligence on the variations of their thicknesses, the analytic formulae from liquid-drop model agree qualitatively but not quantitatively with our numerical estimations. By fitting to the numerical results, these analytic formulae are improved by introducing dampening factors. The impacts of nuclear symmetry energy are examined adopting two parameter sets, corresponding to the slope of symmetry energy $L = 41.34$ and 89.39 MeV. Even with the uncertainties caused by the anisotropy in polycrystallines, the elastic properties of neutron star matter obtained with $L = 41.34$ and 89.39 MeV are distinctively different, results in detectable differences in various neutron star activities.

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C. Xia, T. Maruyama, N. Yasutake, et. al.
Wed, 28 Sep 22
56/89

Comments: N/A

Rotating Solar Models in Agreement with Helioseismic Results and Updated Neutrino Fluxes [SSA]

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http://arxiv.org/abs/2209.13483


Standard solar models (SSMs) constructed in accordance with old solar abundances are in reasonable agreement with seismically inferred results, but SSMs with new low-metal abundances disagree with the seismically inferred results. The constraints of neutrino fluxes on solar models exist in parallel with those of helioseismic results. The solar neutrino fluxes were updated by Borexino Collaboration. We constructed rotating solar models with new low-metal abundances where the effects of enhanced diffusion and convection overshoot were included. A rotating model using OPAL opacities and the Caffau abundance scale has better sound-speed and density profiles than the SSM with the old solar abundances and reproduces the observed $p$-mode frequency ratios $r_{02}$ and $r_{13}$. The depth and helium abundance of the convection zone of the model agree with the seismically inferred ones at the level of $1\sigma$. The updated neutrino fluxes are also reproduced by the model at the level of $1\sigma$. The effects of rotation and enhanced diffusion not only improve the model’s sound-speed and density profiles but bring the neutrino fluxes predicted by the model into agreement with the detected ones. Moreover, the calculations show that OP may underestimate opacities for the regions of the Sun with $T\gtrsim5\times10^{6}$ K by around $1.5\%$, while OPAL may underestimate opacities for the regions of the Sun with $2\times10^{6}$ K $\lesssim T \lesssim 5\times10^{6}$ K by about $1-2\%$.

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W. Yang
Wed, 28 Sep 22
60/89

Comments: 32 pages, 10 figures, 7 tables. Accepted for publication in ApJ

Role of vector self-interaction in Neutron Star properties [CL]

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http://arxiv.org/abs/2209.12657


Previous studies have claimed that there exist correlations among certain nuclear saturation parameters and neutron star observables, such as the slope of the symmetry energy and the radius of a $1.4M_{\odot}$ neutron star. However, it is not clear whether such correlations are physical or spurious, as they are not observed universally for all equation of state models. In this work, we probe the role of vector self-interaction within the framework of the Relativistic Mean Field model and its role in governing the observable stellar properties and their correlations with nuclear parameters. We confirm that the effect of this term is not only to control the high density properties of the equation of state but also in governing such correlations. We also impose a limit on the maximum strength of the vector self-interaction using recent astrophysical data.

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B. Pradhan, D. Chatterjee, R. Gandhi, et. al.
Tue, 27 Sep 22
8/89

Comments: 14 pages, 10 figures

The Radius of PSR J0740+6620 from NICER with NICER background estimates [HEAP]

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http://arxiv.org/abs/2209.12840


We report a revised analysis for the radius, mass, and hot surface regions of the massive millisecond pulsar PSR J0740+6620, studied previously with joint fits to NICER and XMM data by Riley et al. 2021 and Miller et al. 2021. We perform a similar Bayesian estimation for the pulse-profile model parameters, except that instead of fitting simultaneously the XMM data, we use the best available NICER background estimates to constrain the number of photons detected from the source. This approach eliminates any potential issues in the cross-calibration between these two instruments, providing thus an independent check of the robustness of the analysis. The obtained neutron star parameter constraints are compatible with the already published results, with a slight dependence on how conservative the imposed background limits are. A tighter lower limit causes the inferred radius to increase, and a tighter upper limit causes it to decrease. We also extend the study of the inferred emission geometry to examine the degree of deviation from antipodality of the hot regions. We show that there is a significant offset to an antipodal spot configuration, mainly due to the non-half-cycle azimuthal separation of the two emitting spots. The offset angle from the antipode is inferred to be above 25 degrees with 84 % probability. This seems to exclude a centered-dipolar magnetic field in PSR J0740+6620.

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T. Salmi, S. Vinciguerra, D. Choudhury, et. al.
Tue, 27 Sep 22
31/89

Comments: 29 pages, 18 figures (10 of which are figure sets), 1 animation, 10 tables. Accepted for publication in ApJ

Accreting neutron stars from the nuclear energy-density functional theory. II. Equation of state and global properties [HEAP]

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http://arxiv.org/abs/2209.11457


The accretion of matter onto the surface of a neutron star in a low-mass X-ray binary triggers X-ray bursts, whose ashes are buried and further processed thus altering the composition and the properties of the stellar crust. In this second paper of a series, the impact of accretion on the equation of state and on the global properties of neutron stars is studied in the framework of the nuclear energy-density functional theory. Considering ashes made of $^{56}$Fe, we calculated the equations of state using the same Brussels-Montreal nuclear energy-density functionals BSk19, BSk20, and BSk21, as those already employed for determining the crustal heating in our previous study for the same ashes. All regions of accreting neutron stars were treated in a unified and thermodynamically consistent way. With these equations of state, we determined the mass, radius, moment of inertia, and tidal deformability of accreted neutron stars and compared with catalyzed neutron stars for which unified equations of state based on the same functionals are available. The equation of state of accreted neutron stars is found to be significantly stiffer than that of catalyzed matter, with an adiabatic index $\Gamma \approx 4/3$ throughout the crust. For this reason, accreting neutron stars have larger radii. However, their crustal moment of inertia and their tidal deformability are hardly changed provided density discontinuities at the interface between adjacent crustal layers are properly taken into account. The enhancement of the stiffness of the equation of state of accreting neutron stars is mainly a consequence of nuclear shell effects, thus confirming the importance of a quantum treatment as stressed in our first study. With our previous calculations of crustal heating using the same functionals, we have thus obtained consistent microscopic inputs for simulations of accreting neutron stars.

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A. Fantina, J. Zdunik, N. Chamel, et. al.
Mon, 26 Sep 22
37/62

Comments: 10 pages, 7 figures. The tables of the equations of state are available at the CDS

Stellar neutron capture reactions at low and high temperature [CL]

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http://arxiv.org/abs/2209.11480


The determination of astrophysical reaction rates requires different approaches depending on the conditions in hydrostatic and explosive burning. The focus here is on astrophysical reaction rates for radiative neutron capture reactions. Relevant nucleosynthesis processes not only involve the s-process but also the i-, r- and $\gamma$-processes, which from the nuclear perspective mainly differ in the relative interaction energies of neutrons and nuclei, and in the nuclear level densities of the involved nuclei. Emphasis is put on the difference between reactions at low and high temperature. Possible complications in the prediction and measurement of these reaction rates are illustrated and the connection between theory and experiment is addressed.

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T. Rauscher
Mon, 26 Sep 22
58/62

Comments: 11 pages, 6 figures; to be published in the EPJA Special Issue “From reactors to Stars, in memoriam Franz K\”appeler”

Chiral restoration of strange baryons [CL]

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http://arxiv.org/abs/2209.10980


We review the results of a phenomenological model for cold and dense nuclear matter exhibiting a chiral phase transition. The idea is to model the quark-hadron phase transition under neutron star conditions within a single model, but without adding quark degrees of freedom by hand. To this end, strangeness is included in the form of hyperonic degrees of freedom, whose light counterparts provide the strangeness in the chirally restored phase. In the future, the model can be used for instance to compute the surface tension at the (first-order) chiral phase transition and to study the possible existence of inhomogeneous phases.

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E. Fraga, R. Mata, S. Pitsinigkos, et. al.
Fri, 23 Sep 22
62/70

Comments: 6 pages, 4 figures, contribution to proceedings of QCD@Work, 27-30 June 2022

Parameterisations of thermal bomb explosions for core-collapse supernovae and 56Ni production [HEAP]

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http://arxiv.org/abs/2209.10989


Thermal bombs are a widely used method to artificially trigger explosions of core-collapse supernovae (CCSNe) to determine their nucleosynthesis or ejecta and remnant properties. Recently, their use in spherically symmetric (1D) hydrodynamic simulations led to the result that {56,57}Ni and 44Ti are massively underproduced compared to observational estimates for Supernova 1987A, if the explosions are slow, i.e., if the explosion mechanism of CCSNe releases the explosion energy on long timescales. It was concluded that rapid explosions are required to match observed abundances, i.e., the explosion mechanism must provide the CCSN energy nearly instantaneously on timescales of some ten to order 100 ms. This result, if valid, would disfavor the neutrino-heating mechanism, which releases the CCSN energy on timescales of seconds. Here, we demonstrate by 1D hydrodynamic simulations and nucleosynthetic post-processing that these conclusions are a consequence of disregarding the initial collapse of the stellar core in the thermal-bomb modelling before the bomb releases the explosion energy. We demonstrate that the anti-correlation of 56Ni yield and energy-injection timescale vanishes when the initial collapse is included and that it can even be reversed, i.e., more 56Ni is made by slower explosions, when the collapse proceeds to small radii similar to those where neutrino heating takes place in CCSNe. We also show that the 56Ni production in thermal-bomb explosions is sensitive to the chosen mass cut and that a fixed mass layer or fixed volume for the energy deposition cause only secondary differences. Moreover, we propose a most appropriate setup for thermal bombs.

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L. Imasheva, H. Janka and A. Weiss
Fri, 23 Sep 22
68/70

Comments: 24 pages, 12 figures

Causal, stable first-order viscous relativistic hydrodynamics with ideal gas microphysics [CL]

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http://arxiv.org/abs/2209.09265


We present the first numerical analysis of causal, stable first-order relativistic hydrodynamics with ideal gas microphysics, based in the formalism developed by Bemfica, Disconzi, Noronha, and Kovtun (BDNK theory). The BDNK approach provides definitions for the conserved stress-energy tensor and baryon current, and rigorously proves causality, local well-posedness, strong hyperbolicity, and linear stability (about equilibrium) for the equations of motion, subject to a set of coupled nonlinear inequalities involving the undetermined model coefficients (the choice for which defines the “hydrodynamic frame”). We present a class of hydrodynamic frames derived from the relativistic ideal gas “gamma-law” equation of state which satisfy the BDNK constraints, and explore the properties of the resulting model for a series of (0+1)D and (1+1)D tests in 4D Minkowski spacetime. These tests include a comparison of the dissipation mechanisms in Eckart, BDNK, and Muller-Israel-Stewart theories, as well as investigations of the impact of hydrodynamic frame on the causality and stability properties of Bjorken flow, planar shockwave, and heat flow solutions.

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A. Pandya, E. Most and F. Pretorius
Wed, 21 Sep 22
3/68

Comments: 22 pages, 7 figures, to be submitted to PRD

Hyperonic equation of state at finite temperature for neutron stars [CL]

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http://arxiv.org/abs/2209.09739


We review the composition and the equation of state of the hyperonic core of neutron stars at finite temperature within a relativistic mean-field approach. We make use of the new FSU2H* model, which is built upon the FSU2H scheme by improving on the Xi potential according to the recent analysis on the Xi atoms, and we extend it to include finite temperature corrections. The calculations are done for a wide range of densities, temperatures and charge fractions, thus exploring the different conditions that can be found in protoneutron stars, binary mergers remnants and supernovae explosions. The inclusion of hyperons has a strong effect on the composition and the equation of state at finite temperature, which consequently would lead to significant changes in the properties and evolution of hot neutron stars.

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H. Kochankovski, A. Ramos and L. Tolos
Wed, 21 Sep 22
36/68

Comments: 4 pages, 1 figure, Conference proceeding HYP2022

dmscatter: A Fast Program for WIMP-Nucleus Scattering [CL]

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http://arxiv.org/abs/2209.09187


Recent work, using an effective field theory framework, has shown the number of possible couplings between nucleons and the dark-matter-candidate Weakly Interacting Massive Particles (WIMPs) is larger than previously thought. Inspired by an existing Mathematica script that computes the target response, we have developed a fast, modern Fortran code, including optional OpenMP parallelization, along with a user-friendly Python wrapper, to swiftly and efficiently explore many scenarios, with output aligned with practices of current dark matter searches. A library of most of the important target nuclides is included; users may also import their own nuclear structure data, in the form of reduced one-body density matrices. The main output is the differential event rate as a function of recoil energy, needed for modeling detector response rates, but intermediate results such as nuclear form factors can be readily accessed.

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O. Gorton, C. Johnson, C. Jiao, et. al.
Tue, 20 Sep 22
27/81

Comments: 15 pages, 6 figures, preprint submitted to Computer Physics Communications, code available at this https URL

Extracting nuclear matter properties from neutron star matter EoS using deep neural networks [CL]

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http://arxiv.org/abs/2209.09085


The extraction of the nuclear matter properties from neutron star observations is nowadays an important issue, in particular, the properties that characterize the symmetry energy which are essential to describe correctly asymmetric nuclear matter. We use deep neural networks (DNN) to map the relation between cold $\beta$-equilibrium neutron star matter and the nuclear matter properties. Assuming a quadratic dependence on the isospin asymmetry for the energy per particle of homogeneous nuclear matter and using a Taylor expansion up to fourth order in the iso-scalar and iso-vector contributions, we generate a dataset of different realizations of $\beta$-equilibrium NS matter and the corresponding nuclear matter properties. The DNN model was successfully trained, attaining great accuracy in the test set. Finally, a real case scenario was used to test the DNN model, where a set of 33 nuclear models, obtained within a relativistic mean field approach or a Skyrme force description, were fed into the DNN model and the corresponding nuclear matter parameters recovered with considerable accuracy, in particular, the standard deviations $\sigma(L_{\text{sym}})= 12.85$ MeV and $\sigma(K_{\text{sat}})= 41.02$ MeV were obtained, respectively, for the slope of the symmetry energy and the nuclear matter incompressibility at saturation.

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M. Ferreira, V. Carvalho and C. Providência
Tue, 20 Sep 22
30/81

Comments: 10 pages, 5 figures

Vector dark boson mediated feeble interaction between fermionic dark matter and strange quark matter in quark stars [CL]

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http://arxiv.org/abs/2209.09021


We study the structural properties like the gravitational mass, radius and tidal deformability of dark matter (DM) admixed strange quark stars (SQSs). For the purpose we consider the vector MIT Bag model to describe the strange quark matter (SQM) and investigate the possible presence of accreted DM in the SQSs consequently forming DM admixed SQSs. We introduce feeble interaction between SQM and the accreted fermionic DM via a vector dark boson mediator. Considering the present literature, in the context of possible presence of DM in SQSs, this work is the first to consider interaction between DM and SQM in the DM admixed SQSs. The mass of the DM fermion ($m_{\chi}$) and the vector mediator ($m_{\xi}$) and the coupling ($y_{\xi}$) between them are determined in accordance with the constraint from Bullet cluster and the present day relic abundance, respectively. We find that the presence of DM reduces both the mass and radius of the star compared to the no-DM case. The massive the DM fermion, the lower the values of maximum mass and radius of the DM admixed SQSs. For the chosen values of $m_{\chi}$ and corresponding values of $m_{\xi}$ and $y_{\xi}$, the computed structural properties of the DM admixed SQSs satisfy all the various present day astrophysical constraints.We obtain massive DM admixed SQSs configurations consistent with the GW190814 observational data. Hence the secondary compact object associated with this event may be a DM admixed SQS.

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D. Sen and A. Guha
Tue, 20 Sep 22
61/81

Comments: Accepted for Publication in Monthly Notices of the Royal Astronomical Society

Theory of Neutrino Physics — Snowmass TF11 (aka NF08) Topical Group Report [CL]

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http://arxiv.org/abs/2209.07983


This is the report for the topical group Theory of Neutrino Physics (TF11/NF08) for Snowmass 2021. This report summarizes the progress in the field of theoretical neutrino physics in the past decade, the current status of the field, and the prospects for the upcoming decade.

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A. Gouvêa, I. Mocioiu, S. Pastore, et. al.
Mon, 19 Sep 22
10/50

Comments: 26 pages, 5 figures

Snowmass 2021 Cosmic Frontier White Paper: The Dense Matter Equation of State and QCD Phase Transitions [HEAP]

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http://arxiv.org/abs/2209.07412


Our limited understanding of the physical properties of matter at ultra-high density, high proton/neutron number asymmetry, and low temperature is presently one of the major outstanding problems in physics. As matter in this extreme state is known to only exist stably in the cores of neutron stars (NSs), complementary measurements from electromagnetic and gravitational wave astrophysical observations of NSs, combined with terrestrial laboratory constraints and further theoretical investigations, hold the promise to provide important insight into the properties of matter in a region of the quantum chromodynamics phase space that is otherwise inaccessible. This multidisciplinary endeavor imposes the following requirements for facilities and resources in the upcoming decade and beyond:
* A next generation of gravitational wave detectors to uncover more double NS and neutron star-black hole mergers;
* Sensitive radio telescopes to find the most massive and fastest spinning NSs;
* Large-area, high-time-resolution and/or high angular resolution X-ray telescopes to constrain the NS mass-radius relation;
* Suitable laboratory facilities for nuclear physics experiments to constrain the dense matter equation of state;
* Funding resources for theoretical studies of matter in this regime;
* The availability of modern large-scale high performance computing infrastructure.
The same facilities and resources would also enable significant advances in other high-profile fields of inquiry in modern physics such as the nature of dark matter, alternative theories of gravity, nucleon superfluidity and superconductivity, as well as an array of astrophysics, including but not limited to stellar evolution, nucleosynthesis, and primordial black holes.

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S. Bogdanov, E. Fonseca, R. Kashyap, et. al.
Fri, 16 Sep 22
6/84

Comments: Submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021) under Cosmic Frontier (CF07: Cosmic probes of fundamental physics); 30 pages, 8 figures

Compact Star Twins with a Dark Matter Core [HEAP]

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http://arxiv.org/abs/2209.06602


We present a model of compact stars with a dark matter core. The hadronic equation of state is based on the parity doublet model and does not present a phase transition to quark matter. Instead, a strong first-order phase transition to dark matter described by a constant speed of sound model leads to the scenario of compact star mass twins. Compact star structural properties which obey state-of-the-art measurements and constraints are presented.

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D. Alvarez-Castillo and M. Marczenko
Thu, 15 Sep 22
3/67

Comments: 9 pages, 2 figures, Proceedings of the XXVII Cracow EPIPHANY Conference on Recent Advances in Astroparticle Physics (2022)

Magnetic-Field Induced Deformation in Hybrid Stars [CL]

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http://arxiv.org/abs/2209.06016


The effects of strong magnetic fields on the deconfinement phase transition expected to take place in the interior of massive neutron stars is studied in detail for the first time. For hadronic matter, the very general density-dependent relativistic mean-field (DD-RMF) model is employed, while the simple, but effective Vector-Enhanced Bag model (vBag) model is used to study quark matter. Magnetic-field effects are incorporated into the matter equation of state and in the general-relativity solutions, which also satisfy Maxwell’s equations. We find that, for large values of magnetic dipole moment, the maximum mass, canonical-mass radius, and dimensionless tidal deformability obtained for stars using spherically-symmetric TOV equations and axisymmetric solutions attained through the LORENE library differ considerably. The deviations depend on the stiffness of the equation of state and on the star mass being analyzed. This points to the fact that, unlike what was assumed previously in the literature, magnetic field thresholds for the correct assumption of isotropic stars and the proper use of TOV equations depend on the matter composition and interactions.

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I. Rather, A. Rather, V. Dexheimer, et. al.
Wed, 14 Sep 22
18/90

Comments: 15 pages, 7 figures

Polytropic fits of modern and unified equations of state [CL]

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http://arxiv.org/abs/2209.06052


Equations of state for a cold neutron star’s interior are presented in three-column tables that relate the baryonic density, the energy density, and the pressure. A few analytical expressions for those tables have been established these past two decades, as a convenient way to present a large number of nuclear models for neutron star matter. Some of those analytical representations are based on nonunified equations of state, in the sense that the high and the low density part of the star are not computed with the same nuclear model. Fits of equations of state based on a piecewise polytropic representation are revised by using unified tables of equations of state, that is to say models which have been calculated consistently for the core and the crust. A set of 52 unified equations of state is chosen. Each one is divided in seven polytropes via an adaptive segmentation, and two parameters per polytrope are fitted to the tabulated equation of state. The total mass, radius, tidal deformability and moment of inertia of neutron stars are modelled from the fits and compared with the quantities calculated from the original tables to ensure the accuracy of the fits on macroscopic parameters. We provide the polytropes parameters for 15 nucleonic relativistic mean field models, seven hyperonic relativistic mean field models, five hybrid relativistic mean-field models, 24 nucleonic Skyrme models, and one ab initio model. The fit error on the macroscopic parameters of neutron stars is small and well within the estimated measurement accuracy from current and next generation telescopes.

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S. Lami, F. Morgane, Z. Julian-Leszek, et. al.
Wed, 14 Sep 22
37/90

Comments: 28 pages, 11 figures, 7 tables and 3 ancillary materials (tables in ASCII format and routine in Python). Accepted for publication with PRC

Massive relativistic compact stars from SU(3) symmetric quark models [CL]

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http://arxiv.org/abs/2209.05699


We construct a set of hyperonic equations of state (EoS) by assuming SU(3) symmetry within the baryon octet and by using a covariant density functional (CDF) theory approach. The low-density regions of our EoS are constrained by terrestrial experiments, while the high-density regime is modeled by systematically varying the nuclear matter skewness coefficient $Q_{\rm sat}$ and the symmetry energy slope $L_{\rm sym}$. The sensitivity of the EoS predictions is explored in terms of $z$ parameter of the SU(3) symmetric model that modifies the meson-hyperon coupling constants away from their SU(6) symmetric values. Our results show that model EoS based on our approach can support static Tolman-Oppenheimer-Volkof (TOV) masses in the range $2.3$-$2.5\,M_{\odot}$ in the large-$Q_{\rm sat}$ and small-$z$ regime, however, such stars contain only a trace amount of hyperons compared to SU(6) models. We also construct uniformly rotating Keplerian configurations for our model EoS for which the masses of stellar sequences may reach up to $3.0\,M_{\odot}$. These results are used to explore the systematic dependence of the ratio of maximum masses of rotating and static stars, the lower bound on the rotational frequency of the models that will allow secondary masses in the gravitational waves events to be compact stars with $M_2 \lesssim 3.0\,M_{\odot}$ and the strangeness fraction on the model parameters. We conclude that very massive stellar models can be, in principle, constructed within the SU(3) symmetric model, however, they are nucleonic-like as their strangeness fraction drops below 3\%.

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H. Fu, J. Li, A. Sedrakian, et. al.
Wed, 14 Sep 22
66/90

Comments: 10 pages, 7 figures

Neutron star inner crust: reduction of shear modulus by nuclei finite size effect [HEAP]

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http://arxiv.org/abs/2209.05821


The elasticity of neutron star crust is important for adequate interpretation of observations. To describe elastic properties one should rely on theoretical models. The most widely used is Coulomb crystal model (system of point-like charges on neutralizing uniform background), in some works it is corrected for electron screening. These models neglect finite size of nuclei. This approximation is well justified except for the innermost crustal layers, where nuclei size becomes comparable with the inter-nuclear spacing. Still, even in those dense layers it seems reasonable to apply the Coulomb crystal result, if one assumes that nuclei are spherically symmetric: Coulomb interaction between them should be the same as interaction between point-like charges. This argument is indeed correct, however, as we point here, shear of crustal lattice generates (microscopic) quadrupole electrostatic potential in a vicinity of lattice cites, which induces deformation on the nuclei. We analyze this problem analytically within compressible liquid drop model, using ionic spheroid model (which is generalization of well known ion sphere model). In particular, for ground state crust composition the effective shear modulus is reduced for a factor of $1-u^{5/3}/(2+3\,u-4\,u^{1/3})$, where u is the filling factor (ratio of the nuclei volume to the volume of the cell). This result is universal and does not depend on the applied nucleon interaction model. For the innermost layers of inner crust u~0.2 leading to reduction of the shear modulus by ~25%, which can be important for correct interpretation of quasi-periodic oscillations in the tails of magnetar flares.

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N. Zemlyakov and A. Chugunov
Wed, 14 Sep 22
68/90

Comments: 7 pages, submitted to MNRAS on Sept. 8

Stability of spherical nuclei in the inner crust of neutron stars [CL]

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http://arxiv.org/abs/2209.05851


Neutron stars are the densest objects in the Universe. In this paper we consider so-called inner crust – the layer, where neutron-excess nuclei are immersed into degenerate gas of electrons and sea of quasi-free neutrons. It was generally believed that spherical nuclei become unstable with respect to quadrupole deformations at high densities and here we consider this instability. Within perturbative approach we show that spherical nuclei with equilibrium number density are, in fact, stable with respect to infinitesimal quadrupole deformation. This is due to background of degenerate electrons and associated electrostatic potential which maintain stability of spherical nuclei. However, if the number of atomic nuclei per unit volume is much less than the equilibrium value, instability can arise. To avoid confusion we stress that our results are limited to infinitesimal deformations and do not guaranty strict thermodynamic stability of spherical nuclei. In particular, they does not exclude that substantially non-spherical nuclei (so-called pasta phase) represent thermodynamic equilibrium state of the densest layers of neutron star crust. Rather our results points that spherical nuclei can be metastable even if they are not energetically favourable and the timescale of transformation of spherical nuclei to the pasta phases should be estimated subsequently.

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N. Zemlyakov and A. Chugunov
Wed, 14 Sep 22
82/90

Comments: 10 pages, 2 figures

Bulk Viscosity of Relativistic $npeμ$ Matter in Neutron-Star Mergers [HEAP]

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http://arxiv.org/abs/2209.04717


We discuss the bulk viscosity of hot and dense $npe\mu$ matter arising from weak-interaction direct Urca processes. We consider two regimes of interest: (a) the neutrino-transparent regime with $T\leq T_{\rm tr}$ ($T_{\rm tr}\simeq 5\div 10$ MeV is the neutrino-trapping temperature); and (b) the neutrino-trapped regime with $T\geq T_{\rm tr}$. Nuclear matter is modeled in relativistic density functional approach with density-dependent parametrization DDME2. The maximum of the bulk viscosity is achieved at temperatures $T \simeq 5\div 6$ MeV in the neutrino-transparent regime, then it drops rapidly at higher temperatures where neutrino-trapping occurs. As an astrophysical application, we estimate the damping timescales of density oscillations by the bulk viscosity in neutron star mergers and find that, e.g., at the oscillation frequency $f=10$ kHz, the damping will be very efficient at temperatures $4\leq T\leq 7$ MeV where the bulk viscosity might affect the evolution of the post-merger object.

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M. Alford, A. Harutyunyan and A. Sedrakian
Tue, 13 Sep 22
12/85

Comments: 16 pages, 9 figures, matches published version

Effects of finite sizes of atomic nuclei on shear modulus and torsional oscillations in neutron stars [CL]

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http://arxiv.org/abs/2209.05416


The shear modulus of neutron star matter is one of the important properties for determining torsional oscillations in neutron stars. We take into account the effects of finite sizes of spherical nuclei on the shear modulus and examine the frequencies of crustal torsional oscillations. The shear modulus decreases owing to the finite-size effect, which in turn decreases the frequencies of torsional oscillations. In particular, the finite-size effect becomes more crucial for oscillations with a larger azimuthal quantum number and for neutron star models with a weaker density dependence of nuclear symmetry energy. In practice, when one identifies the quasi-periodic oscillations from a neutron star, where the magnetic effect is negligible, with crustal torsional oscillations, the finite-size effect can be more significant at frequencies higher than $\sim 100$ Hz.

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H. Sotani, H. Togashi and M. Takano
Tue, 13 Sep 22
17/85

Comments: Accepted for publication in MNRAS

Nucleonic metamodelling in light of multimessenger, PREX-II and CREX data [CL]

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http://arxiv.org/abs/2209.05177


The need of reconciling our understanding of the behavior of hadronic matter across a wide range of densities, especially at the time when data from multimessenger observations and novel experimental facilities are flooding in, has provided new challenges to the nuclear models. Particularly, the density dependence of the isovector channel of the nuclear energy functionals seems hard to pin down if experiments like PREX-II (or PREX) and CREX are required to be taken on the same footing. We put to test this anomaly in a semi-agnostic modelling technique, by performing a full Bayesian analysis of static properties of neutron stars, together with global properties of nuclei as binding energy, charge radii and neutron skin calculated at the semi-classical level. Our results show that the interplay between bulk and surface properties, and the importance of high order empirical parameters that effectively decouple the subsaturation and the supersaturation density regime, might partially explain the tension between the different measurements and observations. If the surface behaviors, however, are decoupled from the bulk properties, we found a rather harmonious situation among experimental and observational data.

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C. Mondal and F. Gulminelli
Tue, 13 Sep 22
60/85

Comments: 13 pages, 12 figures

Bound states and electromagnetic radiation of relativistically rotating cylindrical wells [CL]

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http://arxiv.org/abs/2209.03991


We compute the effect of rigid rotation on the non-relativistic bound states. The energy levels of the bound states increase with the angular velocity of rotation until at certain value of the angular velocity they are completely pushed out into the continuum which corresponds to dissociation of the bound states. When the angular velocity exceeds the critical value at which the ground state disappears into the continuum, no bound state is possible. This effect should have important consequences for the phenomenology of the quark-gluon plasma. One of the ways to study it experimentally is to observe the electromagnetic radiation emitted by a rotating bound state. We compute the corresponding intensity of electromagnetic radiation and show that it strongly depends on the angular velocity of rotation.

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M. Buzzegoli and K. Tuchin
Mon, 12 Sep 22
38/54

Comments: 13 pages, 5 figures

Cold dense quark matter with phenomenological medium effects: a self-consistent formulation of the quark-mass density-dependent model [CL]

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http://arxiv.org/abs/2209.03455


We revisit the quark-mass density-dependent model — a phenomenological equation of state for deconfined quark matter in the high-density low-temperature regime — and show that thermodynamic inconsistencies that have plagued the model for decades, can be solved if the model is formulated in the canonical ensemble instead of the grand canonical one. Within the new formulation, the minimum of the energy per baryon occurs at zero pressure, and the Euler’s relation is verified. Adopting a typical mass-formula, we first analyze in detail a simple model with one particle species. We show that a “bag” term that produces quark confinement naturally appears in the pressure (and not in the energy density) due to density dependence of the quark masses. Additionally, the chemical potential gains a new term as in other models with quark repulsive interactions. Then, we extend the formalism to the astrophysically realistic case of charge-neutral three-flavor quark matter in equilibrium under weak interactions, focusing on two different mass formulae: a flavor dependent and a flavor blind one. For these two models, we derive the equation of state and analyze its behavior for several parameter choices. We systematically analyze the parameter space and identify the regions corresponding to self-bound 2-flavor and 3-flavor quark matter, hybrid matter and causal behavior.

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G. Lugones and A. Grunfeld
Fri, 9 Sep 22
8/76

Comments: 14 pages, 10 figures

Neutron stars as extreme laboratories for gravity tests [CL]

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http://arxiv.org/abs/2209.03351


Neutron stars are versatile in their application to studying various important aspects of fundamental physics, in particular strong-field gravity tests and the equation of state for super-dense nuclear matter at low temperatures. However, in many cases these two objectives are degenerate to each other. We discuss how pulsar timing and gravitational waves provide accurate measurements of neutron star systems and how to effectively break the degeneracy using tools like universal relations. We also present perspectives on future opportunities and challenges in the field of neutron star physics.

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L. Shao and K. Yagi
Fri, 9 Sep 22
9/76

Comments: 5 pages, 2 figures; accepted by Science Bulletin

Light Curves and Event Rates of Axion Instability Supernovae [HEAP]

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http://arxiv.org/abs/2209.03517


It was recently proposed that exotic particles can trigger a new stellar instability which is analogous to the e-e+ pair instability if they are produced and reach equilibrium in the stellar plasma. In this study, we construct axion instability supernova (AISN) models caused by the new instability to predict their observational signatures. We focus on heavy axion-like particles (ALPs) with masses of ~400 keV–2 MeV and coupling with photons of g_{ag}~10^{-5} GeV^{-1}. It is found that the 56Ni mass and the explosion energy are significantly increased by ALPs for a fixed stellar mass. As a result, the peak times of the light curves of AISNe occur earlier than those of standard pair-instability supernovae by 10–20 days when the ALP mass is equal to the electron mass. Also, the event rate of AISNe is 1.7–2.6 times higher than that of pair-instability supernovae, depending on the high mass cutoff of the initial mass function.

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K. Mori, T. Moriya, T. Takiwaki, et. al.
Fri, 9 Sep 22
58/76

Comments: 9 pages, 6 figures, 1 table, submitted to ApJ

Neutron Star Crust Can Support A Large Ellipticity [CL]

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http://arxiv.org/abs/2209.03222


Non-axisymmetrical deformations of the crust on rapidly rotating neutron stars are one of the main targets of searches for continuous gravitational waves. The maximum ellipticity, or fractional difference in moments of inertia, that can be supported by deformations of the crust (known as “mountains”) provides an important upper limit on the strength of these continuous gravitational wave sources. We use the formalism of Gittins et al 2021, along with a deforming force that acts mainly in the transverse direction, to obtain a maximum ellipticity of 7.4$\times$10$^{-6}$. This is larger than the original results of Gittins et al 2021 but consistent with earlier calculations by Ushomirsky et al 2000. This suggests that rotating neutron stars could be strong sources of continuous gravitational waves.

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J. Morales and C. Horowitz
Thu, 8 Sep 22
45/77

Comments: 9 pages, 5 figures

Low-energy nuclear physics and global neutron star properties [CL]

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http://arxiv.org/abs/2209.03257


We address the question of the role of low-energy nuclear physics data in constraining neutron star global properties, e.g., masses, radii, angular momentum, and tidal deformability, in the absence of a phase transition in dense matter. To do so, we assess the capacity of 415 relativistic mean field and non-relativistic Skyrme-type interactions to reproduce the ground state binding energies, the charge radii and the giant monopole resonances of a set of spherical nuclei. The interactions are classified according to their ability to describe these characteristics and we show that a tight correlation between the symmetry energy and its slope is obtained providing $N=Z$ and $N\ne Z$ nuclei are described with the same accuracy (mainly driven by the charge radius data). By additionally imposing the constraints from isobaric analog states and neutron skin radius in $^{208}$Pb, we obtain the following estimates: $E_{sym,2}=31.8\pm 0.7$ MeV and $L_{sym,2}=58.1\pm 9.0$ MeV. We then analyze predictions of neutron star properties and we find that the 1.4$M_\odot$ neutron star (NS) radius lies between 12 and 14 km for the “better” nuclear interactions. We show that i) the better reproduction of low-energy nuclear physics data by the nuclear models only weakly impacts the global properties of canonical mass neutron stars and ii) the experimental constraint on the symmetry energy is the most effective one for reducing the uncertainties in NS matter. However, since the density region where constraints are required are well above densities in finite nuclei, the largest uncertainty originates from the density dependence of the EDF, which remains largely unknown.

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B. Carlson, M. Dutra, O. Lourenço, et. al.
Thu, 8 Sep 22
59/77

Comments: 26 pages, 20 figures

Deducing Neutron Star Equation of State Parameters Directly From Telescope Spectra with Uncertainty-Aware Machine Learning [HEAP]

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http://arxiv.org/abs/2209.02817


Neutron stars provide a unique laboratory for studying matter at extreme pressures and densities. While there is no direct way to explore their interior structure, X-rays emitted from these stars can indirectly provide clues to the equation of state (EOS) of superdense nuclear matter through the inference of the star’s mass and radius. However, inference of EOS directly from a star’s X-ray spectra is extremely challenging and is complicated by systematic uncertainties. The current state of the art is to use simulation-based likelihoods in a piece-wise method, which first infer the star’s mass and radius to reduce the dimensionality of the problem, and from those quantities infer the EOS. We demonstrate a series of enhancements to the state of the art, in terms of realistic uncertainty quantification and improved regression of physical properties with machine learning. We also demonstrate novel inference of the EOS directly from the high-dimensional spectra of observed stars, avoiding the intermediate mass-radius step. Our network is conditions on the sources of uncertainty of each star, allowing for natural and complete propagation of uncertainties to the EOS.

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D. Farrell, P. Baldi, J. Ott, et. al.
Thu, 8 Sep 22
62/77

Comments: 22 pages, 20 figures

Holographic cold dense matter constrained by neutron stars [CL]

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http://arxiv.org/abs/2209.00766


The equation of state (EoS) for cold dense matter inside neutron stars is investigated by using holographic QCD models in the framework of the Einstein-Maxwell-dilaton (EMD) system and the improved Karch-Katz-Son-Stephanov (KKSS) action for matter part. This method of describing holographic nuclear matter in the EMD$+$KKSS framework is different from that by using the Dirac-Born-Infeld (DBI) action and the Chern-Simons (CS) terms. Combining with the Hebeler-Lattimer-Pethick-Schwenk (HLPS) intermediate equation of state (EoS), the hybrid EoS inside the neutron stars is constructed. The obtained hybrid EoS is located in the range that is defined by the low-density chiral effective theory, the high-density perturbative QCD, and the polytropic interpolations between them, and is constrained by the astrophysics observations. The square of the sound velocity reaches a maximum value larger than $0.8$ in the region of $2-5$ times the saturation baryon number density and approaches the conformal limit at the high baryon density range. The mass-radius relation and the tidal deformability of the neutron stars are in agreement with astrophysical measurements. The possible maximum mass for the neutron star is about $2.5 M_{\odot}$ and the radius is about $12 \mathrm{km}$ then. It is noticed that the holographic quark matter branch in the mass-radius relation is always unstable and the holographic nuclear matter can produce a stable branch. These results indicate that even in the core of the NS, the matter is still in the confinement phase and the quark matter is not favored.

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L. Zhang and M. Huang
Mon, 5 Sep 22
21/53

Comments: N/A

Holographic cold dense matter constrained by neutron stars [CL]

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http://arxiv.org/abs/2209.00766


The equation of state (EoS) for cold dense matter inside neutron stars is investigated by using holographic QCD models in the framework of the Einstein-Maxwell-dilaton (EMD) system and the improved Karch-Katz-Son-Stephanov (KKSS) action for matter part. This method of describing holographic nuclear matter in the EMD$+$KKSS framework is different from that by using the Dirac-Born-Infeld (DBI) action and the Chern-Simons (CS) terms. Combining with the Hebeler-Lattimer-Pethick-Schwenk (HLPS) intermediate equation of state (EoS), the hybrid EoS inside the neutron stars is constructed. The obtained hybrid EoS is located in the range that is defined by the low-density chiral effective theory, the high-density perturbative QCD, and the polytropic interpolations between them, and is constrained by the astrophysics observations. The square of the sound velocity reaches a maximum value larger than $0.8$ in the region of $2-5$ times the saturation baryon number density and approaches the conformal limit at the high baryon density range. The mass-radius relation and the tidal deformability of the neutron stars are in agreement with astrophysical measurements. The possible maximum mass for the neutron star is about $2.5 M_{\odot}$ and the radius is about $12 \mathrm{km}$ then. It is noticed that the holographic quark matter branch in the mass-radius relation is always unstable and the holographic nuclear matter can produce a stable branch. These results indicate that even in the core of the NS, the matter is still in the confinement phase and the quark matter is not favored.

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L. Zhang and M. Huang
Mon, 5 Sep 22
10/53

Comments: N/A

Impact of Neutrino Cooling on Type-I X-ray Bursts and X-ray Superbursts [HEAP]

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http://arxiv.org/abs/2208.14622


We investigate the impacts of neutrino cooling mechanism inside the neutron star (NS) core on the light curves of type-I X-ray bursts and X-ray superbursts. From several observations of NS thermal evolution, physical processes of fast neutrino cooling, such as the direct Urca (DU) process, are indicated. They significantly decrease the surface temperature of NSs, though the cooling effect could be suppressed by nucleon superfluidity. In the present study, focusing on the DU process and nucleon superfluidity, we investigate the effects of NS cooling on the X-ray bursts using a general-relativistic stellar-evolution code. We find that the DU process leads find the longer recurrence time and the higher peak luminosity, which could be obstructed by the neutrons superfluidity. We also apply our burst models to the comparison with {\it Clocked burster} GS 1826$-$24, and to the recurrence time of superburst triggered by carbon ignition. These effects are significant within a certain range of binary parameters and uncertainty of the NS equation of state.

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A. Dohi, N. Nishimura, H. Sotani, et. al.
Thu, 1 Sep 22
35/68

Comments: 12 pages, 8 figures, 3 Tables, Accepted for publication in ApJ

Hyperon bulk viscosity and $r$-modes of neutron stars [HEAP]

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http://arxiv.org/abs/2208.14436


We propose and apply a new parameterization of the modified chiral effective model to study rotating neutron stars with hyperon cores in the framework of the relativistic mean-field theory. The inclusion of mesonic cross couplings in the model has improved the density content of the symmetry energy slope parameters, which are in agreement with the findings from recent terrestrial experiments. The bulk viscosity of the hyperonic medium is analyzed to investigate its role in the suppression of gravitationally driven $r$-modes. The hyperonic bulk viscosity coefficient caused by non-leptonic weak interactions and the corresponding damping timescales are calculated and the $r$-mode instability windows are obtained. The present model predicts a significant reduction of the unstable region due to a more effective damping of oscillations. We find that from $\sim 10^8$ K to $\sim 10^{9}$ K, hyperonic bulk viscosity completely suppresses the $r$-modes leading to a stable region between the instability windows. Our analysis indicates that the instability can reduce the angular velocity of the star up to $\sim$0.3~$\Omega_K$, where $\Omega_K$ is the Kepler frequency of the star.

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O. Jyothilakshmi, P. Krishnan, P. Thakur, et. al.
Wed, 31 Aug 22
30/86

Comments: 9 pages, 9 figures; Accepted for publication in MNRAS

Neutrino propagation in the neutron star with uncertainties from nuclear, hadron, and particle physics [CL]

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http://arxiv.org/abs/2208.13971


In the present work, we investigate the neutral-current neutrino-nucleon scattering in the nuclear medium using various energy-density functional (EDF) models such as the KIDS (Korea-IBS-Daegu-SKKU) and SLy4, together with the quark-meson coupling (QMC) model for the nucleon form factors at finite density. The differential cross section (DCS) and neutrino mean free path (NMFP) are computed numerically, considering the density-dependent nucleon form factors (DDFF) and neutrino structural properties such as the neutrino magnetic moment (NMM) and its electric charge radius (NCR). It turns out that the DDFF decreases the scattering cross-section, while the NCR increases it considerably. The effect of the NMM turns out to be almost negligible. We also observe that the value of the neutron effective mass is of importance in the neutron-star cooling process, indicating that for the neutron effective mass larger than the mass in free space, the neutrino can interact with matter at densities $\rho \gtrsim 1.5 \rho_0$ in the neutron star with radius 13 km.

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P. Hutauruk, H. Gil, S. Nam, et. al.
Wed, 31 Aug 22
39/86

Comments: 15 pages, 2 tables, 11 figures

Inferring the dense matter equation of state from neutron star observations via artificial neural networks [CL]

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http://arxiv.org/abs/2208.13163


The difficulty in describing the equation of state (EoS) for nuclear matter at densities above the saturation density ($\rho_0$) has led to the emergence of a multitude of models based on different assumptions and techniques. These EoSs, when used to describe a neutron star (NS), lead to differing values of observables. An outstanding goal in astrophysics is to constrain the dense matter EoS by exploiting astrophysical and gravitational wave measurements. Nuclear matter parameters appear as Taylor coefficients in the expansion of the EoS around the saturation density of symmetric and asymmetric nuclear matter, and provide a physically-motivated representation of the EoS. In this paper, we introduce a deep learning-based methodology to predict key neutron star observables such as the NS mass, NS radius, and tidal deformability from a set of nuclear matter parameters. Using generated mock data, we confirm that the neural network model is able to accurately capture the underlying physics of finite nuclei and replicate inter-correlations between the symmetry energy slope, its curvature and the tidal deformability arising from a set of physical constraints. We also perform a systematic Bayesian estimation of NMPs in light of recent observational data with the trained neural network and study the effects of correlations among these NMPs. We show that by not considering inter-correlations arising from finite nuclei constraints, an intrinsic uncertainty of upto 30% can be observed on higher-order NMPs.

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A. Thete, K. Banerjee and T. Malik
Tue, 30 Aug 22
25/76

Comments: 23 pages, 5 figures, 7 tables

Unified neutron star EOSs and neutron star structures in RMF models [CL]

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http://arxiv.org/abs/2208.12893


In the framework of Thomas-Fermi approximation, we study systematically the EOSs and microscopic structures of neutron star matter in a vast density range with $n_\mathrm{b}\approx 10^{-10}$-2 $\mathrm{fm}^{-3}$, where various covariant density functionals are adopted, i.e., those with nonlinear self couplings (NL3, PK1, TM1, GM1, MTVTC) and density-dependent couplings (DD-LZ1, DDME-X, PKDD, DD-ME2, DD2, TW99). It is found that the EOSs generally coincide with each other at $n_\mathrm{b}\lesssim 10^{-4}$ fm${}^{-3}$ and 0.1 fm${}^{-3}\lesssim n_\mathrm{b} \lesssim 0.3$ fm${}^{-3}$, while in other density regions they are sensitive to the effective interactions between nucleons. By adopting functionals with larger slope of symmetry energy $L$, the curvature parameter $K_\mathrm{sym}$ and neutron drip density generally increase, while the droplet size, proton number of nucleus, core-crust transition density, and onset density of non-spherical nuclei decrease. All functionals predict neutron stars with maximum masses exceeding the two-solar-mass limit, while those of DD2, DD-LZ1, DD-ME2, and DDME-X predict optimum neutron star radii according to the observational constraints. Nevertheless, the corresponding skewness coefficients $J$ are much lager than expected, while only the functionals MTVTC and TW99 meet the start-of-art constraints on $J$. More accurate measurements on the radius of PSR J0740+6620 and the maximum mass of neutron stars are thus essential to identify the functional that satisfies all constraints from nuclear physics and astrophysical observations. Approximate linear correlations between neutron stars’ radii at $M=1.4 M_{\odot}$ and $2 M_{\odot}$, the slope $L$ and curvature parameter $K_\mathrm{sym}$ of symmetry energy are observed as well, which is mainly attributed to the curvature-slope correlations in the functionals adopted here.

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C. Xia, T. Maruyama, A. Li, et. al.
Tue, 30 Aug 22
29/76

Comments: The EOS tables can be found at: teacher.yzu.edu.cn/CJXia/en/lwcg/492393/content/79242.htm

Probing nuclear observables via primordial nucleosynthesis [CL]

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http://arxiv.org/abs/2208.12600


We study the dependence of primordial nuclear abundances on fundamental nuclear observables such as binding energies, scattering lengths, neutron lifetime, \textit{etc.} by varying these quantities. The numerical computations were performed with four publicly available codes, thus facilitating an investigation of the model-dependent (systematic) uncertainties on these dependences. Indeed deviations of the order of a few percent are found. Moreover, accounting for the temperature dependence of the sensitivity of the rates to some relevant parameters leads to a reduction of the sensitivity of the final primordial abundances, which in some cases is appreciable. These effects are considered to be relevant for studies of the dependence of the nuclear abundances on fundamental parameters such as quark masses or couplings underlying the nuclear parameters studied here.

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U. Meißner and B. Metsch
Mon, 29 Aug 22
10/49

Comments: 13 pages, 6 figures

$I-$Love$-C$ relation for anisotropic neutron star [CL]

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http://arxiv.org/abs/2208.12566


One of the most common assumptions has been made that the pressure inside the star is isotropic in nature. However, the pressure is locally anisotropic in nature which is a more realistic case. In this study, we investigate certain properties of anisotropic neutron stars with the scalar pressure anisotropy model. Different perfect fluid conditions are tested within the star with the relativistic mean-field model equation of states (EOSs). The anisotropic neutron star properties such as mass ($M$), radius ($R$), compactness ($C$), Love number ($k_2$), dimensionless tidal deformability ($\Lambda$), and the moment of inertia ($I$) are calculated. The magnitude of the quantities as mentioned above increases (decreases) with the positive (negative) value of anisotropy except $k_2$ and $\Lambda$. The Universal relation $I-$Love$-C$ is calculated with almost 58 EOSs spans from relativistic to non-relativistic cases. We observed that the relations between them get weaker when we include anisotropicity. With the help of the GW170817 tidal deformability limit and radii constraints from different approaches, we find that the anisotropic parameter is less than 1.0 if one uses the BL model. Using the universal relation and the tidal deformability bound given by the GW170817, we put a theoretical limit for the canonical radius, $R_{1.4}=10.74_{-1.36}^{+1.84}$ km, and the moment of inertia, $I_{1.4} = 1.77_{-0.09}^{+0.17}\times10^{45}$ g cm$^2$ with 90% confidence limit for isotropic stars. Similarly, for anisotropic stars with $\lambda_{\rm BL}=1.0$, the values are $R_{1.4}=11.74_{-1.54}^{+2.11}$ km, $I_{1.4} = 2.40_{-0.08}^{+0.17} \times10^{45}$ g cm$^2$ respectively.

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H. Das
Mon, 29 Aug 22
32/49

Comments: 12 pages, 15 figures, 4 tables, comments welcome

Early quark deconfinement in compact star astrophysics and heavy-ion collisions [CL]

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http://arxiv.org/abs/2208.09085


Based on a recently developed relativistic density functional approach to color-superconducting quark matter and a novel quark-hadron transition construction which phenomenologically accounts for the effects of inhomogeneous pasta phases and quark-hadron continuity, we construct a class of hybrid equations of state applicable at the regimes typical for compact star astrophysics and heavy ion collisions. We outline that early quark deconfinement is a notable consequence of strong diquark pairing providing a good agreement with the observational data and driving the trajectories of the matter evolution during the supernovae explosions toward the regimes typical for the compact star mergers and heavy-ion collisions.

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O. Ivanytskyi, D. Blaschke, T. Fischer, et. al.
Fri, 26 Aug 22
6/49

Comments: Presented at the $29^{\rm th}$ Conference ”Quark Matter 2022” on ultrarelativistic nucleus-nucleus collisions, April 4-10, 2022, Krak\’ow, Poland; minor typo corrections in v2

Explosion of a Minimum-Mass Neutron Star within Relativistic Hydrodynamics [HEAP]

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http://arxiv.org/abs/2208.11514


The relativistic hydrodynamics equations are adapted for the spherically symmetric case and the Lagrangian form. They are used to model the explosive disruption of a minimum-mass neutron star: a key ingredient of the stripping model for short gamma-ray bursts. The shock breakout from the neutron star surface accompanied by the acceleration of matter to ultrarelativistic velocities is studied. A comparison with the results of previously published nonrelativistic calculations is made.

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A. Yudin
Thu, 25 Aug 22
3/43

Comments: 17 pages, 5 figs

Vortex Pinning in Neutron Stars, Slip-stick Dynamics, and the Origin of Spin Glitches [HEAP]

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http://arxiv.org/abs/2208.11494


We study pinning and unpinning of superfluid vortices in the inner crust of a neutron star using 3-dimensional dynamical simulations. Strong pinning occurs for certain lattice orientations of an idealized, body-centered cubic lattice, and occurs generally in an amorphous or impure nuclear lattice. The pinning force per unit length is $\sim 10^{16}$ dyn cm$^{-1}$ for a vortex-nucleus interaction that is repulsive, and $\sim 10^{17}$ dyn cm$^{-1}$ for an attractive interaction. The pinning force is strong enough to account for observed spin jumps (glitches). Vortices forced through the lattice move with a slip-stick character; for a range of superfluid velocities, the vortex can be in either a cold, pinned state or a hot unpinned state, with strong excitation of Kelvin waves on the vortex. This two-state nature of vortex motion sets the stage for large-scale vortex movement that creates an observable spin glitch. We argue that the vortex array is likely to become tangled as a result of repeated unpinnings and repinnings. We conjecture that during a glitch, the Kelvin-wave excitation spreads rapidly along the direction of the mean superfluid vorticity and slower in the direction perpendicular to it, akin to an anisotropic deflagration.

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B. Link and Y. Levin
Thu, 25 Aug 22
23/43

Comments: 12 pages, 7 figures (two animations)

Determination of asymptotic normalization coefficients for the channel $^{16}$O$\to α+^{12}$C. Excited state $^{16}$O($0^+; 6.05$ MeV) [CL]

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http://arxiv.org/abs/2208.09587


Asymptotic normalization coefficients (ANC) determine the overall normalization of cross sections of peripheral radiative capture reactions. In the present paper, we treat the ANC $C$ for the virtual decay $^{16}$O$(0^+; 6.05$ MeV)$\to \alpha+^{12}$C(g.s.), the known values of which are characterized by a large spread $(0.29-1.65)\times 10^3$ fm$^{-1/2}$. The ANC $C$ is found by analytic continuation in the energy of the $\alpha^{12}$C $s$-wave scattering amplitude, known from the phase-shift analysis of experimental data, to the pole corresponding to the $^{16}$O bound state and lying in the unphysical region of negative energies. To determine $C$, two different methods of analytic continuation are used. In the first method, the scattering data are approximated by the sum of polynomials in energy in the physical region and then extrapolated to the pole. The best way of extrapolation is chosen on the basis of the exactly solvable model. Within the second approach, the ANC $C$ is found by solving the Schr\”odinger equation for the two-body $\alpha^{12}$C potential, the parameters of which are selected from the requirement of the best description of the phase-shift analysis data at a fixed experimental binding energy of $^{16}$O$(0^+; 6.05$ MeV) in the $\alpha+^{12}$C channel. The values of the ANC $C$ obtained within these two methods lie in the interval (886–1139) fm$^{-1/2}$.

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L. Blokhintsev, A. Kadyrov, A. Mukhamedzhanov, et. al.
Tue, 23 Aug 22
47/79

Comments: arXiv admin note: text overlap with arXiv:1710.10767

High-order isospin-dependent surface tension contribution to the fourth-order symmetry energy of finite nuclei [CL]

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http://arxiv.org/abs/2208.10438


The relation between the fourth-order symmetry energy $E_{\rm{sym,4}}(\rho_0)$ of nuclear matter at saturation density $\rho_0$ and its counterpart $a_{\rm{sym,4}}(A)$ of finite nuclei in a semi-empirical nuclear mass formula is revisited by considering the high-order isospin-dependent surface tension contribution to the latter. We derive the full expression of $a_{\rm{sym,4}}(A)$ which includes explicitly the high-order isospin-dependent surface tension effects, and find that the value of $E_{\rm{sym,4}}(\rho_0)$ cannot be extracted from the measured $a_{\rm{sym,4}}(A)$ before the high-order surface tension is well constrained. Our results imply that a large $a_{\rm{sym,4}}(A)$ value of several MeVs obtained from analyzing nuclear masses can nicely agree with the empirical constraint of $E_{\rm{sym,4}}(\rho_0)\lesssim 2$ MeV from mean-field models and does not necessarily lead to a large $E_{\rm{sym,4}}(\rho_0)$ value of $\sim 20$ MeV obtained previously without considering the high-order surface tension. Furthermore, we also give the expression for the sixth-order symmetry energy $a_{\rm{sym,6}}(A)$ of finite nuclei, which involves more nuclear matter bulk parameters and the higher-order isospin-dependent surface tension.

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B. Cai, R. Wang, Z. Zhang, et. al.
Tue, 23 Aug 22
70/79

Comments: 7 pages, 2 figures