Tag Archives: Nuclear Theory

Dense Nuclear Matter with Baryon Overlap [CL]

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http://arxiv.org/abs/2208.09331


The possibility of new short-distance physics applicable inside the cores of NS is incorporated into the equation of state generated by the quark-meson coupling model. The contribution of this new physics to the energy density is taken to be proportional to the amount of overlap between the quark cores of the baryons involved. With no change to the properties of symmetric nuclear matter at saturation density, including an incompressibility compatible with data on giant monopole resonances, one can sustain neutron stars with a maximum mass $M_{max}>2.1$ M$_\odot$, even when hyperons are included.

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J. Leong, T. Motta, A. Thomas, et. al.
Mon, 22 Aug 22
49/53

Comments: 16 pages, 10 figures

MSW effect with quark matter: Neutron Star as a case study [CL]

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http://arxiv.org/abs/2208.08278


With the recent findings from various astrophysical results hinting towards possible existence of strange quark matters with the baryonic resonances such as $\Lambda^0, \Sigma^0, \Xi, \Omega$ in the core of neutron stars, we investigate the MSW effect, in general, in quark matter. We find that the resonance condition for the complete conversion of down-quark to strange quark requires estremely large matter density ($\rho_u \simeq 10^{5}\,\mbox{fm}^{-3} $). Nonetheless the neutron stars provide a best condition for the conversion to be statistically significant which is of the same order as is expected from imposing charge neutrality condition. This has a possibility of resolving the hyperon puzzle as well as the equation of state for dense baryonic matter.

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H. Mishra, P. Panigrahi, S. Patra, et. al.
Thu, 18 Aug 22
3/45

Comments: 5 pages, 5 figures, regular article

Neutrinos in Stellar Astrophysics [CL]

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http://arxiv.org/abs/2208.08050


The physics of the mysterious and stealthy neutrino is at the heart of many phenomena in the cosmos. These particles interact with matter and with each other through the aptly named weak interaction. At typical astrophysical energies the weak interaction is some twenty orders of magnitude weaker than the electromagnetic interaction. However, in the early universe and in collapsing stars neutrinos can more than make up for their feeble interaction strength with huge numbers. Neutrinos can dominate the dynamics in these sites and set the conditions that govern the synthesis of the elements. Here we journey through the history of the discovery of these particles and describe their role in stellar evolution and collapse, the big bang, and multi-messenger astrophysics. Neutrino physics is at the frontier of elementary particle physics, nuclear physics, astrophysics and cosmology. All of these fields overlap in the neutrino story.

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G. Fuller and W. Haxton
Thu, 18 Aug 22
26/45

Comments: 45 pages, 14 figures; To be published in Neutrino Physics and Astrophysics, edited by F. W. Stecker, in the Encyclopedia of Cosmology II, edited by G. G. Fazio, World Scientific Publishing Company, Singapore, 2022. arXiv admin note: text overlap with arXiv:1209.3743, arXiv:0808.0735

Dark matter effects on tidal deformabilities and moment of inertia in a hadronic model with short-range correlations [CL]

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http://arxiv.org/abs/2208.06067


In this work we study the outcomes related to dimensionless tidal deformability $(\Lambda)$ obtained through a relativistic mean-field (RMF) hadronic model including short-range correlations (SRC) and dark matter (DM) content [Phys. Rev. D 105, 023008 (2022)]. As a dark particle candidate, we use the lightest neutralino interacting with nucleons through the Higgs boson exchange. In particular, we test the model against the constraints regarding the observation of gravitational waves from the binary neutron star merger GW170817 event provided by LIGO and Virgo collaboration (LVC). We show that $\Lambda$ decreases as the dark particle Fermi momentum ($k_F^{DM}$) increases. This feature favors the RMF-SRC-DM model used here to satisfy the limits of $\Lambda_{1.4}=190^{+390}{-120}$ ($\Lambda$ of a $1.4M\odot$ neutron star), and $\tilde{\Lambda}=300^{+420}{-230}$ given by the LVC. We also show that as $k_F^{DM}$ increases, $\Lambda_1$ and $\Lambda_2$, namely, tidal deformabilities of the binary system, are also moved to the direction of the GW170817 observational data. Finally, we verify that the inclusion of DM in the system does not destroy the \mbox{$I$-Love} relation (correlation between $\Lambda$ and dimensionless moment of inertia, $\bar{I}$). The observation data for $\bar{I}\star\equiv\bar{I}(M_\star)=11.10^{+3.68}{-2.28}$, with $M\star=1.338M_\odot$, is attained by the RMF-SRC-DM model.

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O. Lourenço, C. Lenzi, T. Frederico, et. al.
Mon, 15 Aug 22
9/54

Comments: 8 pages, 4 figures. Published in Phys. Rev. D

The Influence of Beta Decay Rates on r-Process Observables [HEAP]

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http://arxiv.org/abs/2208.06373


The rapid neutron capture process (r-process) is one of the main mechanisms whereby elements heavier than iron are synthesized, and is entirely responsible for the natural production of the actinides. Kilonova emissions are modeled as being largely powered by the radioactive decay of species synthesized via the r -process. Given that the r -process occurs far from nuclear stability, unmeasured beta decay rates play an essential role in setting the time scale for the r -process. In an effort to better understand the sensitivity of kilonova modeling to different theoretical global beta-decay descriptions, we incorporate these into nucleosynthesis calculations. We compare the results of these calculations and highlight differences in kilonova nuclear energy generation and light curve predictions, as well as final abundances and their implications for nuclear cosmochronometry. We investigate scenarios where differences in beta decay rates are responsible for increased nuclear heating on time scales of days that propagates into a significantly increased average bolometric luminosity between 1-10 days post-merger. We identify key nuclei, both measured and unmeasured, whose decay rates are directly impact nuclear heating generation on timescales responsible for light curve evolution. We also find that uncertainties in beta decay rates significantly impact ages estimates from cosmochronometry.

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K. Lund, J. Engel, G. McLaughlin, et. al.
Mon, 15 Aug 22
45/54

Comments: N/A

Precise Calculations of Nucleosynthesis Parameters and Electron Self-mass [HEAP]

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http://arxiv.org/abs/2208.04896


We study the effect of temperature on beta decay rate during primordial nucleosynthesis. Using thermal contributions to the renormalized mass of electron, we re-compute thermal effects to the nucleosynthesis parameters in the early universe in relation to the thermal self-mass of electron. In this study we show how the presence of fermions in a medium cause the variation in nucleosynthesis parameters with temperature. Before and after nucleosynthesis, temperature contribution from the electron self-mass goes away. The temperature dependence of beta decay rate, helium abundance and energy density of the universe are calculated as a function of temperature during nucleosynthesis. The values of these nucleosynthesis parameters before and after the nucleosynthesis are also calculated.

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S. Masood and J. Singh
Wed, 10 Aug 22
15/66

Comments: 10 pages, 8 figures and 2 tables

Nuclear mass predictions with machine learning reaching the accuracy required by $r$-process studies [CL]

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http://arxiv.org/abs/2208.04783


Nuclear masses are predicted with the Bayesian neural networks by learning the mass surface of even-even nuclei and the correlation energies to their neighbouring nuclei. By keeping the known physics in various sophisticated mass models and performing the delicate design of neural networks, the proposed Bayesian machine learning (BML) mass model achieves an accuracy of $84$~keV, which crosses the accuracy threshold of the $100$~keV in the experimentally known region. It is also demonstrated the corresponding uncertainties of mass predictions are properly evaluated, while the uncertainties increase by about $50$~keV each step along the isotopic chains towards the unknown region. The shell structures in the known region are well described and several important features in the unknown region are predicted, such as the new magic numbers around $N = 40$, the robustness of $N = 82$ shell, the quenching of $N = 126$ shell, and the smooth separation energies around $N = 104$.

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Z. Niu and H. Liang
Wed, 10 Aug 22
56/66

Comments: 14 pages, 5 figures

Emergence of microphysical viscosity in binary neutron star post-merger dynamics [HEAP]

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http://arxiv.org/abs/2207.00442


In nuclear matter in neutron stars the flavor content (e.g., proton fraction) is subject to weak interactions, establishing flavor ($\beta$-)equilibrium. During the merger of two neutron stars there can be deviations from this equilibrium. By incorporating Urca processes into general-relativistic hydrodynamics simulations, we study the resulting out-of-equilibrium dynamics during the collision. We provide the first direct evidence that microphysical transport effects at late times reach a hydrodynamic regime with a nonzero bulk viscosity, making neutron star collisions intrinsically viscous. Finally, we identify signatures of this process in the post-merger gravitational wave emission.

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E. Most, A. Haber, S. Harris, et. al.
Mon, 4 Jul 22
54/62

Comments: N/A

Formation of Chiral Soliton Lattice [CL]

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http://arxiv.org/abs/2207.00212


The Chiral Soliton Lattice (CSL) is a lattice structure composed of domain walls aligned in parallel at equal intervals, which is energetically stable in the presence of a background magnetic field and a finite (baryon) chemical potential due to the topological term originated from the chiral anomaly. We study its formation from the vacuum state, with describing the CSL as a layer of domain-wall disks surrounded by the vortex or string loop, based on the Nambu-Goto-type effective theory. We show that the domain wall nucleates via quantum tunneling when the magnetic field is strong enough. We evaluate its nucleation rate and determine the critical magnetic field strength with which the nucleation rate is no longer exponentially suppressed. We apply this analysis to the neutral pion in the two-flavor QCD as well as the axion-like particles (ALPs) with a finite (baryon) chemical potential under an external magnetic field. In the former case, even though the CSL state is more energetically stable than the vacuum state and the nucleation rate becomes larger for sufficiently strong magnetic field, it cannot be large enough so that the nucleation of the domain walls is not exponentially suppressed and promoted, without suffering from the tachyonic instability of the charged pion fluctuations. In the latter case, we confirm that the effective interaction of the ALPs generically includes the topological term required for the CSL state to be energetically favored. We show that the ALP CSL formation is promoted if the magnetic field strength and the chemical potential of the system is slightly larger than the scale of the axion decay constant.

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T. Higaki, K. Kamada and K. Nishimura
Mon, 4 Jul 22
56/62

Comments: 21 pages, 5 figures

Kaon-baryon coupling schemes and kaon condensation in hyperon-mixed matter [CL]

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http://arxiv.org/abs/2207.00242


Possible coexistence of kaon condensation and hyperons in highly dense matter [the ($Y+K$) phase] is investigated on the basis of the relativistic mean-field theory combined with the effective chiral Lagrangian. Two coupling schemes for the $s$-wave kaon-baryon interaction are compared regarding the onset density of kaon condensation in the hyperon-mixed matter and equation of state for the developed ($Y+K$) phase: One is the contact interaction scheme related to the nonlinear effective chiral Lagrangian. The other is the meson-exchange scheme, where the interaction vertices between the kaon field and baryons are described by exchange of mesons (sigma, sigma^* mesons for scalar coupling, and omega, rho, phi mesons for vector coupling). It is shown that in the meson exchange scheme, the contribution from the nonlinear scalar self-interaction gives rise to a repulsive effect for kaon effective energy, pushing up the onset density of kaon condensation as compared with the case of the contact interaction scheme. In general, the difference of kaon-baryon dynamics between the contact interaction scheme and the meson-exchange scheme relies on the specific forms of the nonlinear self-interacting meson terms. It is shown that the nonlinear self-interacting term is not relevant to repulsive energy leading to stiffening of the equation of state at high densities and that it cannot be compensated with large attractive energy due to the appearance of the ($Y$+$K$) phase in the case of the contact interaction scheme. We also discuss in the contact interaction scheme what effects are necessary so as to make the equation of state with (Y+K) phase stiff enough to be consistent with recent observations of massive neutron stars.

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T. Muto, T. Maruyama and T. Tatsumi
Mon, 4 Jul 22
60/62

Comments: 44 pages, 14 figures

Equation of state in neutron stars and supernovae [CL]

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http://arxiv.org/abs/2207.00033


Neutron stars and supernovae provide cosmic laboratories of highly compressed matter at supra nuclear saturation density which is beyond the reach of terrestrial experiments. The properties of dense matter is extracted by combining the knowledge of nuclear experiments and astrophysical observations via theoretical frameworks. A matter in neutron stars is neutron rich, and may further accommodate non-nucleonic degrees of freedom such as hyperons and quarks. The structure and composition of neutron stars are determined by equations of state of matter, which are the primary subject in this chapter. In case of supernovae, the time evolution includes several dynamical stages whose descriptions require equations of state at finite temperature and various lepton fractions. Equations of state also play essential roles in neutron star mergers which allow us to explore new conditions of matter not achievable in static neutron stars and supernovae. Several types of hadron-to-quark transitions, from first order transitions to crossover, are reviewed, and their characteristics are summarized.

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K. Sumiyoshi, T. Kojo and S. Furusawa
Mon, 4 Jul 22
61/62

Comments: 53 pages, 24 figures, Contribution to the “Handbook of Nuclear Physics”, Springer, 2022, edited by I. Tanihata, H. Toki and T. Kajino

Relativistic Mean Field Study of Neutron Stars and Hyperon Stars [CL]

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http://arxiv.org/abs/2206.02202


This thesis focuses on a variety of active research topics, such as nuclear matter, neutron stars, and phase transition within the framework of the RMF model. We use the previously successful effective field theory-driven Relativistic Mean Field (RMF) and density-dependent RMF (DD-RMF)formalisms for analyzing hadron matter to examine the infinite nuclear matter and neutron stars. The presence of exotic phases such as quarks has been investigated using the MIT Bag model and its variants, such as the vBag model, at various bag constants. The other exotic phases, such as hyperons, have also been studied under the influence of a strong magnetic field.

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I. Rather
Tue, 7 Jun 22
15/70

Comments: PhD Thesis

Do we need equation of state in curved spacetime for neutron stars? [CL]

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http://arxiv.org/abs/2206.02106


Neutron star (NS) is regarded as the natural laboratory for nuclear physics. The equation of state (EoS) extracted in flat spacetime is used chronically as an input to the Tolman-Oppenheimer-Volkoff (TOV) equation to constrain the structure of NS. However, using such EoS to characterize the NS with obvious gravitational effect seems controversial. In our work, we demonstrate the EoS of the same nuclear matter, either on earth or inside NS, ought to be in the same form due to the relativity principle. Gravity only enhances the temperature and the chemical potential, known as Tolman’s law and Klein’s law. We also clarify the self-consistency of the TOV equation, i.e., the equilibrium thermodynamics and gravity are included uniformly. The reason for conclusions in JCAP 02, 026 (2021) and Phys. Rev. D 104, 123005 (2021) is that the equilibrium thermodynamic relations protected by the equivalence principle in local spacetime are not taken into account.

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J. Li, T. Guo, J. Zhao, et. al.
Tue, 7 Jun 22
48/70

Comments: 15 pages, 5 figures, 4 tables

An Improved Method for Coupling Hydrodynamics with Astrophysical Reaction Networks [IMA]

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http://arxiv.org/abs/2206.01285


Reacting astrophysical flows can be challenging to model because of the difficulty in accurately coupling hydrodynamics and reactions. This can be particularly acute during explosive burning or at high temperatures where nuclear statistical equilibrium is established. We develop a new approach based on the ideas of spectral deferred corrections (SDC) coupling of explicit hydrodynamics and stiff reaction sources as an alternative to operator splitting that is simpler than the more comprehensive SDC approach we demonstrated previously. We apply the new method to a double detonation problem with a moderately-sized astrophysical nuclear reaction network and explore the timestep size and reaction network tolerances to show that the simplified-SDC approach provides improved coupling with decreased computational expense compared to traditional Strang operator splitting. This is all done in the framework of the Castro hydrodynamics code, and all algorithm implementations are freely available.

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M. Zingale, M. Katz, A. Nonaka, et. al.
Mon, 6 Jun 22
20/41

Comments: submitted to ApJ. Castro is available at this https URL — all code for the results here is in the github repo

Axion effects in the stability of hybrid stars [CL]

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http://arxiv.org/abs/2206.01631


We investigate the effects of including strong charge-parity (CP) violating effects through axion fields in the description of massive hybrid stars. We assume that their cores contain deconfined quark matter and include the effects of axions via an effective ‘t Hooft determinant interaction. The hadronic crusts are described using different approaches in order to make our results more general. We find that the presence of axions stabilizes massive hybrid stars against gravitational collapse by weakening the deconfinement phase transition and bringing it to lower densities. This allows to reproduce hybrid stars in agreement with modern astrophysical constraints.

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B. Lopes, R. Farias, V. Dexheimer, et. al.
Mon, 6 Jun 22
37/41

Comments: 6 pages, 2 figures

Spin symmetry energy and equation of state of spin-polarized neutron star matter [CL]

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http://arxiv.org/abs/2206.00218


Equation of states (EOS) of the spin-polarized nuclear matter (NM) is studied within the Hartree-Fock (HF) formalism using the realistic density dependent nucleon-nucleon interaction. With a nonzero fraction $\Delta$ of spin-polarized baryons in NM, the spin- and spin-isospin dependent parts of the HF energy density give rise to the \emph{spin symmetry} energy that behaves in about the same manner as the \emph{isospin symmetry} energy, widely discussed in literature as the nuclear symmetry energy. The present HF study shows a strong correlation between the spin symmetry energy and nuclear symmetry energy over the whole range of baryon densities. The important contribution of the spin symmetry energy to the EOS of the spin-polarized NM is found to be comparable with that of the nuclear symmetry energy to the EOS of the isospin-polarized or asymmetric (neutron-rich) NM. Based on the HF energy density, the EOS of the spin-polarized ($\beta$-stable) np$e\mu$ matter is obtained for the determination of the macroscopic properties of neutron star (NS). A realistic density dependence of the spin-polarized fraction $\Delta$ have been suggested to explore the impact of the spin symmetry energy to the gravitational mass $M$ and radius $R$, as well as the tidal deformability of NS. Given the empirical constrains inferred from a coherent Bayesian analysis of gravitational wave signals of the NS merger GW170817 and the observed masses of the heaviest pulsars, the strong impacts of the spin symmetry energy $W$, nuclear symmetry energy $S$, and nuclear incompressibility $K$ to the EOS of nucleonic matter in magnetar were revealed.

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N. Khoa, N. Tan and D. Khoa
Thu, 2 Jun 22
33/57

Comments: Accepted for publication in Phys. Rev. C. arXiv admin note: text overlap with arXiv:2010.00869

Core-collapse supernovae and neutrino properties [CL]

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http://arxiv.org/abs/2205.13868


We highlight developments in the domain of supernova neutrinos. We discuss the importance of the future observation, by running and upcoming experiments, of the neutrino signals from the next supernova as well as of the diffuse supernova neutrino background.

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M. Volpe
Mon, 30 May 22
29/47

Comments: Proceedings for the plenary talk to the “10th Symposium on Large TPCs for low-energy rare event detection”, 15th-17th December 2021, 9 pages, 10 figures

Quantum design in study of pycnonuclear reactions in compact stars and new quasibound states [CL]

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http://arxiv.org/abs/2205.13895


Pycnonuclear reactions in the compact stars at zero temperatures are studied on quantum mechanical basis in the paper. Formalism of multiple internal reflections is generalized for analysis, that was developed for nuclear decays and captures by nuclei with high precision and tests. For the chosen reaction $^{12}$C + $^{12}$C = $^{24}$Mg, we find the following. A quantum study of the pycnonuclear reaction requires a complete analysis of quantum fluxes in the internal nuclear region. This reduces rate and number of pycnonuclear reactions by 1.8 times. This leads to the appearance of new states (called as quasibound states) where the compound nuclear system is formed with maximal probability. As shown, minimal energy of such a state is a little higher than energy of zero-point vibrations in lattice sites in pycnonuclear reaction, however probability of formation of compound system at the quasibound state is essentially larger than the corresponding probability at state of zero-point vibrations. Hence, there is a sense to tell about reaction rates in such quasibound states as more probable, rather than states of zero-point vibrations. This can lead to the essential changes in estimation of the rates of nuclear reactions in stars.

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S. Maydanyuk and K. Shaulskyi
Mon, 30 May 22
34/47

Comments: 19 pages, 6 figures

Astrophysical implications on hyperon couplings and hyperon star properties with relativistic equations of states [HEAP]

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http://arxiv.org/abs/2205.10631


Hyperons are essential constituents in the neutron star interior. The poorly-known hyperonic interaction is a source of uncertainty for studying laboratory hypernuclei and neutron star observations. In this work, we perform Bayesian inference of phenomenological hyperon-nucleon interactions using the tidal-deformability measurement of the GW170817 binary neutron star merger as detected by LIGO/Virgo and the mass-radius measurements of PSR J0030+0541 and PSR J0740+6620 as detected by NICER. The analysis is based on six relativistic neutron-star-matter equation of states with hyperons from the relativistic mean-field theory, naturally fulfilling the causality requirement and empirical nuclear matter properties. We specifically utilize the strong correlation recently deduced between the scalar and vector meson hyperon couplings, imposed by the measured $\Lambda$ separation energy in single-$\Lambda$ hypernuclei, and perform four different tests with or without the strong correlation. We find that the laboratory hypernuclear constraint ensures a large enough $\Lambda$-scalar-meson coupling to match the large vector coupling in hyperon star matter. When adopting the current most probable intervals of hyperon couplings from the joint analysis of laboratory and astrophysical data, we find the maximum mass of hyperon stars is at most $2.176^{+0.085}{-0.202}M{\odot}$ ($1\sigma$ credible interval) from the chosen set of stiff equation of states. The reduction of the stellar radius due to hyperons is quantified based on our analysis and various hyperon star properties are provided.

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X. Sun, Z. Miao, B. Sun, et. al.
Tue, 24 May 22
28/92

Comments: 13 pages, 7 figures, 2 tables

Effects of pairing gap and band gap on superfluid density in the inner crust of neutron stars [CL]

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http://arxiv.org/abs/2205.10742


Calculations of the superfluid density in the inner crust of neutron stars by different approaches are in strong disagreement, which causes a debate on the accountability of pulsar glitches based on superfluidity. Taking a simple unified model, we study the dependence on approximation of the superfluid density in a periodic potential. In comparison with the Hartree-Fock-Bogoliubov (HF-Bogoliubov) theory which treats the effects of the band gap and the pairing gap on equal footing, we examine the HF-BCS-type approximation in which the former is incorporated in priority, and another approximation in which the latter is incorporated in priority. We find that, when the pairing gap and the band gap are comparable as in the inner crust of neutron stars, they need to be treated on equal footing, and the HF-BCS approximation can considerably underestimate the superfluid density even if the pairing gap is much smaller than the Fermi energy. Our result suggests that the validity of the HF-BCS approximation for evaluating the superfluid density in neutron star crusts is questionable.

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Y. Minami and G. Watanabe
Tue, 24 May 22
83/92

Comments: 8 pages, 4 figures

Relativistic mean-field theories for neutron-star physics based on chiral effective field theory [CL]

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http://arxiv.org/abs/2205.10283


We describe and implement a procedure for determining the couplings of a Relativistic Mean Field Theory (RMFT) that is optimized for application to neutron star phenomenology. In the standard RMFT approach, the couplings are constrained by comparing the theory’s predictions for symmetric matter at saturation density with measured nuclear properties. The theory is then applied to neutron stars which consist of neutron-rich matter at densities ranging up to several times saturation density, which allows for additional astrophysical constraints. In our approach, rather than using the RMFT to extrapolate from symmetric to neutron-rich matter and from finite-sized nuclei to uniform matter we fit the RMFT to properties of uniform pure neutron matter obtained from chiral effective field theory. Chiral effective field theory incorporates the experimental data for nuclei in the framework of a controlled expansion for nuclear forces valid at nuclear densities and enables us to account for theoretical uncertainties when fitting the RMFT. We construct four simple RMFTs that span the uncertainties provided by chiral effective field theory for neutron matter, and are consistent with current astrophysical constraints on the equation of state. Our new RMFTs can be used to model the properties of neutron-rich matter across the vast range of densities and temperatures encountered in simulations of neutron stars and their mergers.

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M. Alford, L. Brodie, A. Haber, et. al.
Mon, 23 May 22
17/50

Comments: V1. 12 pages and 5 figures

Delta baryons in magnetars: exploring the effects of the anomalous magnetic moment in magnetized neutron-star matter [HEAP]

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http://arxiv.org/abs/2205.09827


Strong magnetic fields can modify the microscopic composition of matter with consequences on stellar macroscopic properties. Within this context, we study, for the first time, the possibility of the appearance of spin-3/2 $\Delta$ baryons in magnetars. We make use of two different relativistic models for the equation of state of dense matter under the influence of strong magnetic fields considering the effects of Landau levels and the anomalous magnetic moment (AMM) proportional to the spin of all baryons and leptons. In particular, we analyze the effects of the AMM of $\Delta$ baryons in dense matter for the first time. {We also obtain global properties corresponding to the EoS models numerically and study the corresponding role of the $\Delta$ baryons.} We find that they are favored over hyperons, which causes an increase in isopin asymmetry and a decrease in spin polarization. We also find that, contrary to what generally occurs when new degrees of freedom are introduced, the $\Delta$s do not make the EoS significantly softer and magnetars less massive. Finally, the magnetic field distribution inside a given star is not affected by the presence of $\Delta$s.

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K. Marquez, M. Pelicer, S. Ghosh, et. al.
Mon, 23 May 22
23/50

Comments: 11 pages, 9 figures, 2 tables

Nuclear Weak Rates and Nuclear Weak Processes in Stars [CL]

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http://arxiv.org/abs/2205.09262


Nuclear weak rates in stellar environments are obtained by shell-model calculations including Gamow-Teller (GT) and spin-dipole transitions, and applied to nuclear weak processes in stars. The important roles of accurate weak rates for the study of astrophysical processes are pointed out. The weak rates in $sd$-shell are used to study the evolution of ONeMg cores in stars with 8-10 M$_{\odot}$. Cooling of the core by nuclear Urca processes, and the heating by double e-captures on $^{20}$Ne are studied. Especially, the e-capture rates for a second-forbidden transition in $^{20}$Ne are evaluated with the multipole expansion method of Walecka and Behrens-B$\ddot{\mbox{u}}$hring, and the final fate of the cores, core-collapse or thermonuclear explosion, are discussed. The weak rates in $pf$-shell are applied to nucleosynthesis of iron-group elements in Type Ia supernovae. The over-production problem of neutron-rich iron isotopes compared with the solar abundances is now reduced to be within a factor of two. The weak rates for nuclear Urca pair with $A$=31 in the island of inversion are evaluated with the effective interaction obtained by the extended Kuo-Krenciglowa method. The transition strengths and e-capture rates in $^{78}$Ni, important for core-collapse processes, are evaluated with the $pf$-$sdg$ shell, and compared with those obtained by the random-phase-approximation and an effective rate formula. $\beta$-decay rates of $N$ =126 isotones are evaluated with both the GT and first-forbidden transitions. The half-lives are found to be shorter than those obtained by standard models. Neutrino-nucleus reaction cross sections on $^{13}$C, $^{16}$O and $^{40}$Ar are obtained with new shell-model Hamiltonians. Implications on nucleosynthesis, neutrino detection, neutrino oscillations and neutrino mass hierarchy are discussed.

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T. Suzuki
Fri, 20 May 22
28/65

Comments: N/A

Feasibility of studying astrophysically important charged-particle emission with the variable energy $γ$-ray system at the Extreme Light Infrastructure — Nuclear Physics facility [CL]

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http://arxiv.org/abs/2205.09599


In the environment of a hot plasma, as achieved in stellar explosions, capture and photodisintegration reactions proceeding on excited states in the nucleus can considerably contribute to the astrophysical reaction rate. Such reaction rates including the excited-state contribution are obtained from theoretical calculations as the direct experimental determination of these astrophysical rates is currently unfeasible. In the present study, ($\gamma$,p) and ($\gamma$,$\alpha$) reactions in the mass and energy range relevant to the astrophysical $p$ process are considered and the feasibility of measuring them with the ELISSA detector system at the future Variable Energy $\gamma$-ray (VEGA) facility at ELI-NP is investigated. The simulation results reveal that, for the ($\gamma$,p) reaction on twelve targets of $^{29}$Si, $^{56}$Fe, $^{74}$Se, $^{84}$Sr, $^{91}$Zr, $^{96,98}$Ru, $^{102}$Pd, $^{106}$Cd, and $^{115, 117, 119}$Sn, and the ($\gamma$,$\alpha$) reaction on five targets of $^{50}$V, $^{87}$Sr, $^{123,125}$Te, and $^{149}$Sm, the yields of the reaction channels with the transitions to the excited states in the residual nucleus are relevant and even dominant. It is further found that for each considered reaction, the total yields of the charged-particle $X$ may be dominantly contributed from one, two or three ($\gamma$,$X_{i}$) channels within a specific, narrow energy range of the incident $\gamma$-beam. Furthermore, the energy spectra of the ($\gamma$,$X_{i}$) channels with $0\leq i\leq 10$ are simulated for each considered reaction, with the incident $\gamma$-beam energies in the respective energy range as derived before. It becomes evident that measurements of the photon-induced reactions with charged-particle emissions considered in this work are feasible with the VEGA+ELISSA system and will provide knowledge useful for nuclear astrophysics.

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H. Lan, W. Luo, Y. Xu, et. al.
Fri, 20 May 22
46/65

Comments: 11 figures, 17 pages

Oscillating Magnetized Color Superconducting Quark Stars [HEAP]

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http://arxiv.org/abs/2205.07928


The main objective of this work is to study the structure, composition, and oscillation modes of color superconducting quark stars with intense magnetic fields. We adopted the MIT bag model within the color superconductivity CFL framework, and we included the effects of strong magnetic fields to construct the equation of state of stable quark matter. We calculated observable quantities, such as the mass, radius, frequency, and damping time of the oscillation fundamental $f$ mode of quark stars, taking into account current astrophysical constraints. The results obtained show that color superconducting magnetized quark stars satisfy the constraints imposed by the observations of massive pulsars and gravitational wave events. Furthermore, the quantities associated with the oscillation $f$ mode of these objects fit the universal relationships for compact objects. In the context of the new multi-messenger gravitational wave astronomy era and the future asteroseismology of neutron stars, we hope that our results contribute to the understanding of the behavior of dense matter and compact objects.

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M. Celi, M. Mariani, M. Orsaria, et. al.
Wed, 18 May 22
11/66

Comments: N/A

Horizons: Nuclear Astrophysics in the 2020s and Beyond [CL]

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http://arxiv.org/abs/2205.07996


Nuclear Astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated. We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities.

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H. Schatz, A. Reyes, A. Best, et. al.
Wed, 18 May 22
15/66

Comments: 96 pages. Submitted to Journal of Physics G

NMMA: A nuclear-physics and multi-messenger astrophysics framework to analyze binary neutron star mergers [HEAP]

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http://arxiv.org/abs/2205.08513


The multi-messenger detection of the gravitational-wave signal GW170817, the corresponding kilonova AT2017gfo and the short gamma-ray burst GRB170817A, as well as the observed afterglow has delivered a scientific breakthrough. For an accurate interpretation of all these different messengers, one requires robust theoretical models that describe the emitted gravitational-wave, the electromagnetic emission, and dense matter reliably. In addition, one needs efficient and accurate computational tools to ensure a correct cross-correlation between the models and the observational data. For this purpose, we have developed the NMMA (Nuclear-physics and Multi-Messenger Astrophysics) framework. The code allows incorporation of nuclear-physics constraints at low densities as well as X-ray and radio observations of isolated neutron stars. It also enables us to classify electromagnetic observations, e.g., to distinguish between supernovae and kilonovae. In previous works, the NMMA code has allowed us to constrain the equation of state of supranuclear dense matter, to measure the Hubble constant, and to compare dense-matter physics probed in neutron-star mergers and in heavy-ion collisions. The extension of the NMMA code presented here is the first attempt of analysing the gravitational-wave signal, the kilonovae, and the GRB afterglow simultaneously, which reduces the uncertainty of our constraints. Incorporating all available information, we estimate the radius of a 1.4 solar mass neutron star to be $R=11.98^{+0.35}_{-0.40}$ km.

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P. T.H.Pang, T. Dietrich, M. W.Coughlin, et. al.
Wed, 18 May 22
46/66

Comments: code available at this https URL

In-medium polarization tensor in strong magnetic fields (II): Axial Ward identity at finite temperature and density [CL]

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http://arxiv.org/abs/2205.06411


We investigate the axial Ward identity (AWI) for massive fermions in strong magnetic fields. The divergence of the axial-vector current is computed at finite temperature and/or density with the help of a relation between the polarization and anomaly diagrams in the effective (1+1) dimensions realized in the lowest Landau level (LLL). We discuss delicate interplay between the vacuum and medium contributions that determines patterns of the spectral flow in the adiabatic limit and, more generally, the diabatic chirality production rate. We also establish an explicit relation between the AWIs from the LLL approximation and from the familiar triangle diagrams in the naive perturbative series with respect to the coupling constant.

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K. Hattori and K. Itakura
Mon, 16 May 22
26/42

Comments: N/A

Quark formation and phenomenology in binary neutron-star mergers using V-QCD [CL]

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http://arxiv.org/abs/2205.05691


Using full 3+1 dimensional general-relativistic hydrodynamic simulations of equal- and unequal-mass neutron-star binaries with properties that are consistent with those inferred from the inspiral of GW170817, we perform a detailed study of the quark-formation processes that could take place after merger. We use three equations of state consistent with current pulsar observations derived from a novel finite-temperature framework based on V-QCD, a non-perturbative gauge/gravity model for Quantum Chromodynamics. In this way, we identify three different post-merger stages at which mixed baryonic and quark matter, as well as pure quark matter, are generated. A phase transition triggered collapse already $\lesssim 10\,\rm{ms}$ after the merger reveals that the softest version of our equations of state is actually inconsistent with the expected second-long post-merger lifetime of GW170817. Our results underline the impact that multi-messenger observations of binary neutron-star mergers can have in constraining the equation of state of nuclear matter, especially in its most extreme regimes.

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S. Tootle, C. Ecker, K. Topolski, et. al.
Fri, 13 May 22
27/64

Comments: 11 pages, 5 figures, 3 appendices

A new class of hybrid EoS with multiple critical endpoints for simulations of supernovae, neutron stars and their mergers [CL]

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http://arxiv.org/abs/2205.03455


We introduce a family of equations of state (EoS) for hybrid neutron star (NS) matter that is obtained by a two-zone parabolic interpolation between a soft hadronic EoS at low densities and a stiff quark matter EoS with color superconductivity at high densities within a finite region of baryonic chemical potentials $\mu_B^h < \mu_B < \mu_B^q$. We consider two scenarios corresponding to a cross-over and a strong first-order transition between quark and hadron phases considered at finite and zero temperatures. This allows us to analyze the effects of finite entropy on the EoS and mass-radius relation of NS. We demonstrate that the formation of a color superconducting state of quark matter drives the evolution of matter in supernovae explosions under the condition of entropy conservation to higher temperatures than in the case of deconfinement to normal quark matter. Within the presented hybrid EoS scenario, regions of the QCD phase diagram may be accessible to supernovae and NS mergers that can be reached also in terrestrial experiments with relativistic heavy ion collisions.

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O. Ivanytskyi and D. Blaschke
Tue, 10 May 22
25/70

Comments: 10 pages, 6 figures

Gravitational Wave Signal for Quark Matter with Realistic Phase Transition [HEAP]

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http://arxiv.org/abs/2205.03882


The cores of neutron stars (NSs) near the maximum mass realize the most highly compressed matter in the universe where quark degrees of freedom may be liberated. Such a state of dense matter is hypothesized as quark matter (QM) and its presence has awaited to be confirmed for decades in nuclear physics. Gravitational waves from binary NS mergers are expected to convey useful information called the equation of state (EOS). However, the signature for QM with realistic EOS is not yet established. Here, we show that the gravitational wave in the post-merger stage can distinguish the theory scenarios with and without a transition to QM. Instead of adopting specific EOSs as studied previously, we compile reliable EOS constraints from the ab initio approaches. We demonstrate that early collapse to a black hole after NS merger signifies softening of the EOS associated with the onset of QM in accord with ab initio constraints. Nature of hadron-quark phase transition can be further constrained by the condition that electromagnetic counterparts need to be energized by the material left outside the remnant black hole.

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Y. Fujimoto, K. Fukushima, K. Hotokezaka, et. al.
Tue, 10 May 22
26/70

Comments: 20 pages, 5 figures

In-medium polarization tensor in strong magnetic fields (I): Magneto-birefringence at finite temperature and density [CL]

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http://arxiv.org/abs/2205.04312


We investigate in-medium polarization effects of the fermion and antifermion pairs at finite temperature and density in strong magnetic fields within the lowest Landau level approximation. Inspecting the integral representation of the polarization tensor by analytic and numerical methods, we provide both the real and imaginary parts of the polarization tensor obtained after delicate interplay between the vacuum and medium contributions essentially due to the Pauli-blocking effect. Especially, we provide a complete analytic form of the polarization tensor at zero temperature and finite density that exhibits an exact cancellation and associated relocation of the singular threshold behaviors for a single photon decay to a fermion and antifermion pair. As a physical application of the in-medium polarization tensor, we discuss the magneto-birefringence that is polarization-dependent dispersion relations of photons induced by the strong magnetic fields.

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K. Hattori and K. Itakura
Tue, 10 May 22
57/70

Comments: N/A

Nonparametric Representation of Neutron Star Equation of State Using Variational Auto-Encoder [HEAP]

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http://arxiv.org/abs/2205.03855


We introduce a new nonparametric representation of the neutron star (NS) equation of state (EoS) by using the variational auto-encoder (VAE). As a deep neural network, the VAE is widely used for dimensionality reduction since it can compress input data to a low dimensional latent space using the encoder component and then reconstruct the data using the decoder component. Once a VAE is trained one can take the decoder of the VAE as a generator. We employ 100,000 EoSs generated with the nonparametric representation method in \citet{2021ApJ…919…11H} as the training set and try different settings of the neural network, then get an EoS generator (trained VAE’s decoder) with 4 parameters. We use the mass\textendash{}tidal-deformability data of binary neutron star (BNS) merger event GW170817, and the mass\textendash{}radius data of PSR J0030+0451, PSR J0740-6620, PSR J0437-4715, and 4U 1702-429 to perform the joint Bayesian inference. We find out that $R_{1.4}=12.66^{+0.71}{-0.54}\,\rm km$, $\Lambda{1.4}=484^{+118}{-90}$, and $M{\rm max}=2.30^{+0.30}{-0.21}\,\rm M\odot$ ($90\%$ credible levels), where $R_{1.4}$/$\Lambda_{1.4}$ are the radius/tidal-deformability of a canonical $1.4\,\rm M_\odot$ NS, and $M_{\rm max}$ is the maximum mass of a non-rotating NS.

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M. Han, S. Tang and Y. Fan
Tue, 10 May 22
64/70

Comments: 9 pages, 4 figures, and 1 table

Equations of state for hot neutron stars — II. The role of exotic particle degrees of freedom [CL]

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http://arxiv.org/abs/2205.03177


Explosive astrophysical systems – such as supernovae or compact star binary mergers – provide conditions where exotic degrees of freedom can be populated. Within the covariant density functional theory of nuclear matter we build several general purpose equations of state which, in addition to the baryonic octet, account for $\Delta(1232)$ resonance states. The thermodynamic stability of $\Delta$-admixed nuclear matter is investigated in the limiting case of vanishing temperature for charge fractions $Y_Q=0.01$ and $Y_Q=0.5$ and wide ranges of the coupling constants to the scalar and vector mesonic fields. General purpose equation of state models with exotica presently available on the \textsc{CompOSE} database are further reviewed; for a selection of them we then investigate thermal properties for thermodynamic conditions relevant for core-collapse supernovae and binary neutron star mergers. Modifications induced by hyperons, $\Delta(1232)$, $K^-$, pions and quarks are discussed.

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A. Raduta
Mon, 9 May 22
30/63

Comments: 25 pages; 22 figures; contribution to the EPJ A Topical Issue “CompOSE: a repository for Neutron Star Equations of State and Transport Properties”

Bayesian Inference of Phenomenologycal EoS of Neutron Stars with Recent Observations [CL]

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http://arxiv.org/abs/2205.01174


The description of stellar interiors remains as a big challenge for the nuclear astrophysics community. The consolidated knowledge is restricted to density regions around the saturation of hadronic matter $\rho {0} = 2.8\times 10^{14} {\rm\ g\ cm^{-3}}$, regimes where our nuclear models are successfully applied. As one moves towards higher densities and extreme conditions up to five to twenty times $\rho{0}$, little can be said about the microphysics of such objects. Here, we employ a Markov Chain Monte Carlo (MCMC) strategy in order to access the variability of polytropic three-pircewised models for neutron star equation of states. With a fixed description of the hadronic matter, we explore a variety of models for the high density regimes leading to stellar masses up to 2.5 $M_{\odot}$. In addition, we also discuss the use of a Bayesian power regression model with heteroscedastic error. The set of EoS from LIGO was used as inputs and treated as data set for testing case.

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E. Chimanski, R. Lobato, A. Goncalves, et. al.
Wed, 4 May 22
19/48

Comments: N/A

Hybrid Equations of State for Neutron Stars with Hyperons and Deltas [HEAP]

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http://arxiv.org/abs/2205.00559


In this contribution, we describe new chemically-equilibrated charge-neutral hybrid equations of state for neutron stars. They present a first-order phase transition to quark matter and differentiate by the particle population considered and how these particles interact. While some equations of state contain just nucleons and up, down-quarks, others also contain hyperons, Delta baryons, and strange quarks. The hybrid equations of state, together with corresponding hadronic ones, are available on the CompOSE repository and can be used for different astrophysical applications.

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A. Clevinger, J. Corkish, K. Aryal, et. al.
Tue, 3 May 22
43/82

Comments: Invited contribution to Special Issue on “CompOSE: a repository for Neutron Star Equations of State and Transport Properties”

Investigating Possible Existence of Hyper-Heavy Nuclei in Neutron Star Environment [CL]

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http://arxiv.org/abs/2205.00478


The synthesis of hyper-heavy elements is investigated under conditions simulating neutron star environment. The Constrained Molecular Dynamics (CoMD) approach is used to simulate low energy collisions of extremely n-rich nuclei. A new type of the fusion barrier due to a “neutron wind” is observed when the effect of neutron star environment (screening of Coulomb interaction) is introduced implicitly. When introducing also a background of surrounding nuclei, the nuclear fusion becomes possible down to temperatures of 10$^{8}$ K and synthesis of extremely heavy and n-rich nuclei appears feasible. A possible existence of hyper-heavy nuclei in a neutron star environment could provide a mechanism of extra coherent neutrino scattering or an additional mechanism, resulting in X-ray burst or a gravitational wave signal and, thus, becoming another crucial process adding new information to the suggested models on neutron star evolution.

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M. Veselsky, V. Petousis, C. Moustakidis, et. al.
Tue, 3 May 22
74/82

Comments: 10 pages, 5 figures

Nuclear equation of state for arbitrary proton fraction and temperature based on chiral effective field theory and a Gaussian process emulator [CL]

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http://arxiv.org/abs/2204.14016


We calculate the equation of state of asymmetric nuclear matter at finite temperature based on chiral effective field theory interactions to next-to-next-to-next-to-leading order. Our results assess the theoretical uncertainties from the many-body calculation and the chiral expansion. Using a Gaussian process emulator for the free energy, we derive the thermodynamic properties of matter through consistent derivatives and use the Gaussian process to access arbitrary proton fraction and temperature. This enables a first nonparametric calculation of the equation of state in beta equilibrium, and of the speed of sound and the symmetry energy at finite temperature. Moreover, our results show that the thermal part of the pressure decreases with increasing densities.

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J. Keller, K. Hebeler and A. Schwenk
Mon, 2 May 22
12/52

Comments: 6 pages, 5 figures

Radiative transfer in stars by feebly interacting bosons [SSA]

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http://arxiv.org/abs/2204.11862


Starting from first principles, we study radiative transfer by new feebly-interacting bosons (FIBs) such as axions, axion-like particles (ALPs), dark photons, and others. Our key simplification is to include only boson emission or absorption (including decay), but not scattering between different modes of the radiation field. Based on a given distribution of temperature and FIB absorption rate in a star, we derive explicit volume-integral expressions for the boson luminosity, reaching from the free-streaming to the strong-trapping limit. The latter is seen explicitly to correspond to quasi-thermal emission from a “FIB sphere” according to the Stefan-Boltzmann law. Our results supersede expressions and approximations found in the recent literature on FIB emission from a supernova core and, for radiatively unstable FIBs, provide explicit expressions for the nonlocal (“ballistic”) transfer of energy recently discussed in horizontal-branch stars.

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A. Caputo, G. Raffelt and E. Vitagliano
Wed, 27 Apr 22
46/68

Comments: 30 pages, 13 figures

Ab-initio QCD calculations impact the inference of the neutron-star-matter equation of state [CL]

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http://arxiv.org/abs/2204.11877


We demonstrate that ab-initio calculations in QCD at high densities offer significant and nontrivial information about the equation of state of matter in the cores of neutron stars, going beyond that which is obtainable from current astrophysical observations. We do so by extrapolating the equation of state to neutron-star densities using a Gaussian process and conditioning it sequentially with astrophysical observations and QCD input. Using our recent work, imposing the latter does not require an extrapolation to asymptotically high density. We find the QCD input to be complementary to the astrophysical observations, offering strong additional constraints at the highest densities reached in the cores of neutron stars; with the QCD input, the equation of state is no longer prior dominated at any density. The QCD input reduces the pressure and speed of sound at high densities, and it predicts that binary collisions of equal-mass neutron stars will produce a black hole with greater than $95\%$ ($68\%$) credence for masses $M \geq 1.38 M_\odot$ ($M \geq 1.25 M_\odot$). We provide a Python implementation of the QCD likelihood function so that it can be conveniently used within other inference setups.

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T. Gorda, O. Komoltsev and A. Kurkela
Wed, 27 Apr 22
67/68

Comments: 10 pages, 8 figures

The Role of the Hadron-Quark Phase Transition in Core-Collapse Supernovae [HEAP]

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http://arxiv.org/abs/2204.10397


The hadron-quark phase transition in quantum chromodyanmics has been suggested as an alternative explosion mechanism for core-collapse supernovae. We study the impact of three different hadron-quark equations of state (EoS) with first-order (DD2F, STOF-B145) and second-order (CMF) phase transitions on supernova dynamics by performing 97 simulations for solar- and zero-metallicity progenitors in the range of $14\texttt{-}100\,\text{M}\odot$. We find explosions only for two low-compactness models ($14 \text{M}\odot$ and $16\,\text{M}\odot$) with the DD2F EoS, both with low explosion energies of $\mathord{\sim}10^{50}\,\mathrm{erg}$. These weak explosions are characterised by a neutrino signal with several mini-bursts in the explosion phase due to complex reverse shock dynamics, in addition to the typical second neutrino burst for phase-transition driven explosions. The nucleosynthesis shows significant overproduction of nuclei such as $^{90}\mathrm{Zr}$ for the $14\,\text{M}\odot$ zero-metallicity model and $^{94}\mathrm{Zr}$ for the $16\,\text{M}\odot$ solar-metallicity model, but the overproduction factors are not large enough to place constraints on the occurrence of such explosions. Several other low-compactness models using the DD2F EoS and two high-compactness models using the STOS EoS end up as failed explosions and emit a second neutrino burst. For the CMF EoS, the phase transition never leads to a second bounce and explosion. For all three EoS, inverted convection occurs deep in the core of the proto-compact star due to anomalous behaviour of thermodynamic derivatives in the mixed phase, which heats the core to entropies up to $4k\text{B}/\text{baryon}$ and may have a distinctive gravitational wave signature, also for a second-order phase transition.

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P. Jakobus, B. Mueller, A. Heger, et. al.
Mon, 25 Apr 22
14/36

Comments: Submitted to MNRAS

Constraining the equation of state of neutron stars using multimessenger observations [HEAP]

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http://arxiv.org/abs/2204.08555


Neutron stars are the densest objects known in our visible universe. Properties of matter inside a neutron star are encoded in its equation of state, which has wide-ranging uncertainty from a theoretical perspective. With the current understanding of quantum chromodynamics, it is hard to determine the interactions of neutron star matter at such high densities. Also performing many body calculations is computationally intractable. Besides the constitution of the neutron star core is highly speculative — it is not ruled out that it contains exotic matter like strange baryons, meson condensates, quark matter, etc. Although the matter inside the neutron star is extremely dense, but the temperature of this object is very cold in most of its life span. We cannot produce such dense but rather cold material in our laboratory. Since probing the physics of neutron star matter is inaccessible by our earth based experiments, we look for astrophysical observations of neutron stars. This thesis deals with the theoretical and computational techniques required to translate neutron star observables from astrophysical observations to its equation of state.

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B. Biswas
Wed, 20 Apr 22
12/62

Comments: PhD thesis

Neutron star radii, deformabilities, and moments of inertia from experimental and ab initio theory constraints on the 208Pb neutron skin thickness [CL]

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http://arxiv.org/abs/2204.09000


Recent experimental and ab initio theory investigations of the 208Pb neutron skin thickness are sufficiently precise to inform the neutron star equation of state. In particular, the strong correlation between the 208Pb neutron skin thickness and the pressure of neutron matter at normal nuclear densities leads to modified predictions for the radii, tidal deformabilities, and moments of inertia of typical 1.4 solar-mass neutron stars. In the present work, we study the relative impact of these recent analyses of the 208Pb neutron skin thickness on bulk properties of neutron stars within a Bayesian statistical analysis. Two models for the equation of state prior are employed in order to study the role of the highly uncertain high-density equation of state. From our combined Bayesian analysis of nuclear theory, nuclear experiment, and observational constraints on the dense matter equation of state, we find at the 90% credibility level $R_{1.4}=12.36^{+0.38}{-0.73}$ km for the radius of a 1.4 solar-mass neutron star, $R{2.0}=11.96^{+0.94}{-0.71}$ km for the radius of a 2.0 solar-mass neutron star, $\Lambda{1.4}=440^{+103}{-144}$ for the tidal deformability of a 1.4 solar-mass neutron star, and $I{1.338}=1.425^{+0.074}_{-0.146}\, \times 10^{45}\,\rm{g\,cm}^{2}$ for the moment of inertia of PSR J0737-3039A whose mass is 1.338 solar masses.

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Y. Lim and J. Holt
Wed, 20 Apr 22
44/62

Comments: 13 pages, 6 figures. Submitted to Galaxies special issue “Neutron Stars and Hadrons in the Era of Gravitational Wave Astrophysics”

Structure and pulse profiles of dark matter admixed neutron stars [HEAP]

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http://arxiv.org/abs/2204.05560


Neutron stars (NSs) could efficiently capture dark matter (DM) due to their extreme densities and are considered sensitive probes of the presence and the properties of DM. The distribution of the DM in DM-admixed NSs (DANSs) is supposed to be either a dense dark core or an extended dark halo, which is subject to the DM fraction of DANS ($f_{\chi}$) and the DM properties, such as the mass ($m_{\chi}$) and the strength of the self-interaction ($y$). In this paper, we perform an in-depth analysis of the formation criterion for dark core/dark halo and point out that the relative distribution of these two components is essentially determined by the ratio of the central enthalpy of the DM component to that of the baryonic matter component inside DANSs. For the critical case where the radii of DM and baryonic matter are the same, we further derive an analytical formula to describe the dependence of $f^{\rm crit}{\chi}$ on $m{\chi}$ and $y$ for given DANS mass. The relative distribution of the two components in DANSs can lead to different observational effects on NSs. We here focus on the modification of the pulsar pulse profile due to the extra light-bending effect in the case of a dark-halo existence and conduct the first investigation of the dark-halo effects on NS pulse profiles. We find that the peak flux deviation is strongly dependent on the ratio of the halo mass to the radius of the DM component. Lastly, we perform Bayesian parameter estimation on the DM particle properties based on the recent X-ray observations of PSR J0030+0451 and PSR J0740+6620 by the Neutron Star Interior Composition Explorer.

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Z. Miao, Y. Zhu, A. Li, et. al.
Wed, 13 Apr 22
38/73

Comments: 12 pages, 10 figures, 1 table

Long-term 3D-MHD Simulations of Black Hole Accretion Disks formed in Neutron Star Mergers [HEAP]

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http://arxiv.org/abs/2204.03005


We examine the long-term evolution of accretion tori around black hole (BH) remnants of compact object mergers involving at least one neutron star, to better understand their contribution to kilonovae and the synthesis of r-process elements. To this end, we modify the unsplit magnetohydrodynamic (MHD) solver in FLASH4.5 to work in non-uniform three-dimensional spherical coordinates, enabling more efficient coverage of a large dynamic range in length scales while exploiting symmetries in the system. This modified code is used to perform BH accretion disk simulations that vary the initial magnetic field geometry and disk compactness, utilizing a physical equation of state, a neutrino leakage scheme for emission and absorption, and modeling the BH’s gravity with a pseudo-Newtonian potential. Simulations run for long enough to achieve a radiatively-inefficient state in the disk. We find robust mass ejection with both poloidal and toroidal initial field geometries, and suppressed outflow at high disk compactness. With the included physics, we obtain bimodal velocity distributions that trace back to mass ejection by magnetic stresses at early times, and to thermal processes in the radiatively-inefficient state at late times. The electron fraction distribution of the disk outflow is broad in all models, and the ejecta geometry follows a characteristic hourglass shape. We test the effect of removing neutrino absorption or nuclear recombination with axisymmetric models, finding $\sim 50\%$ less mass ejection and more neutron-rich composition without neutrino absorption, and a subdominant contribution from nuclear recombination. Tests of the MHD and neutrino leakage implementations are included.

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S. Fahlman and R. Fernández
Fri, 8 Apr 22
18/65

Comments: N/A

Density functional approach to quark matter with confinement and color superconductivity [CL]

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http://arxiv.org/abs/2204.03611


We present a novel relativistic density-functional approach to modeling quark matter with a mechanism to mimic confinement. The quasiparticle treatment of quarks provides their suppression due to a large quark selfenergy already at the mean-field level. We demonstrate that our approach is equivalent to a chiral quark model with medium-dependent couplings. The dynamical restoration of the chiral symmetry is ensured by construction of the density functional. Supplemented with the vector repulsion and diquark pairing the model is applied to construct a hybrid quark-hadron EoS of cold compact-star matter. We study the connection of such a hybrid EoS with the stellar mass-radius relation and tidal deformability. The model results are compared to various observational constraints including the NICER radius measurement of PSR J0740+6620 and the tidal deformability constraint from GW170817. The model is shown to be consistent with the constraints, still allowing for further improvement by adjusting the vector repulsion and diquark pairing couplings.

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O. Ivanytskyi and D. Blaschke
Fri, 8 Apr 22
46/65

Comments: 14 pages, 9 figures

Universal Relations for Neutron Star F-Mode and G-Mode Oscillations [HEAP]

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http://arxiv.org/abs/2204.03037


Among the various oscillation modes of neutron stars, f- and g- modes are the most likely to be ultimately observed in binary neutron star mergers. The f-mode is known to correlate in normal neutron stars with their tidal deformability, moment of inertia and quadrupole moment. Using a piecewise polytropic parameterization scheme to model the uncertain hadronic high-density EOS and a constant sound-speed scheme to model pure quark matter, we refine this correlation and show that these universal relations also apply to both self-bound stars and hybrid stars containing phase transitions. We identify a novel 1-node branch of the f-mode that occurs in low-mass hybrid stars in a narrow mass range just beyond the critical mass necessary for a phase transition to appear. This 1-node branch shows the largest, but still small, deviations from the universal correlation we have found. The g-mode frequency only exists in matter with a non-barotropic equation of state involving temperature, chemical potential or composition, or a phase transition in barotropic matter. The g-mode therefore could serve as a probe for studying phase transitions in hybrid stars. In contrast with the f-mode, discontinuity g-mode frequencies depend strongly on properties of the transition (the density and the magnitude of the discontinuity) at the transition. Imposing causality and maximum mass constraints, the g-mode frequency in hybrid stars is found to have an upper bound of about 1.25 kHz. However, if the sound speed c_s in the inner core at densities above the phase transition density is restricted to c_s^2 < c^2/3, the g-mode frequencies can only reach about 0.8 kHz, which are significantly lower than f-mode frequencies, 1.3-2.8 kHz. Also, g-mode gravitational wave damping times are extremely long, >10^4 s (10^2 s) in the inner core with c_s^2< c^{2/3} (c^2), in comparison with the f-mode damping time, 0.1-1 s.

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T. Zhao and J. Lattimer
Fri, 8 Apr 22
56/65

Comments: 44 pages, 16 figures

Quasi-stationary sequences of hyper massive neutron stars with exotic equations of state [HEAP]

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http://arxiv.org/abs/2204.01778


In this work, we study the effect of differential rotation, finite temperature and strangeness on the quasi stationary sequences of hyper massive neutron stars (HMNS). We generate constant rest mass sequences of differentially rotating and uniformly rotating stars. The nucleonic matter relevant to the star interior is described within the framework of the relativistic mean field model with the DD2 parameter set. We also consider the strange $\Lambda$ hyperons using the BHB$\Lambda\phi$ equation of state (EoS). Additionally, we probe the behaviour of neutron stars (NS) with these compositions at different temperatures. We report that the addition of hyperons to the EoS produces a significant boost to the spin-up phenomenon. Moreover, increasing the temperature can make the spin-up more robust. We also study the impact of strangeness and thermal effects on the T/W instability. Finally, we analyse equilibrium sequences of a NS following a stable transition from differential rotation to uniform rotation. The decrease in frequency relative to angular momentum loss during this transition is significantly smaller for EoS containing hyperons, compared to nucleonic EoS.

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S. Khadkikar, C. Mangat and S. Banik
Wed, 6 Apr 22
2/68

Comments: Accepted for publication in the Journal of Astrophysics and Astronomy

Role of nucleon effective mass and symmetry energy on the neutrino mean free path in neutron star [CL]

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http://arxiv.org/abs/2204.02061


The Korea-IBS-Daegu-SKKU energy density functional (KIDS-EDF) models, derived from the universal Skyrme functional, have been successfully and widely applied in describing the properties of finite nuclei and infinite nuclear matter. In the present work, we extend the applications of the KIDS-EDF models to investigate the implications of the nucleon effective mass and nuclear symmetry energy obtained from the KIDS-EDF models on the properties of neutron star (NS) and neutrino interaction with the NS constituents matter in the linear response approximation (LRA). We then analyze the total differential cross-section of neutrino, neutrino mean free path (NMFP), and the NS mass-radius (M-R) relations. We find that the NS M-R relations predictions for all KIDS-EDF models are in excellent agreement with the recent observations as well as the NICER result. Remarkable prediction results on the NMFPs are given by the KIDS0-m77 and KIDS0-m99 models with $M_n^* /M \lesssim 1$ which are quite higher in comparison with those obtained for the KIDS0, KIDS-A, and KIDS-B models with $M_n^/M \gtrsim 1$. For the KIDS0, KIDS-A, and KIDS-B models, we obtain the $\lambda \lesssim R_{\textrm{NS}}$, indicating that these models support the slow NS cooling and neutrino trapping in NS. On the contrary, both KIDS0-m77 and KIDS0-m*99 models support faster NS cooling and a small possibility of neutrino trapping within NS, predicting $\lambda \gtrsim R_{\textrm{NS}}$. More interestingly the NMFP decreases as the density and neutrino energy increase, which is consistent with those obtained in the Brussels-Montreal Skyrme (BSk17 and BSk18) models at saturation density.

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P. Hutauruk, H. Gil, S. Nam, et. al.
Wed, 6 Apr 22
6/68

Comments: 24 pages, 2 tables, 22 figures

Calculations of $p(n,γ)d$ reaction in chiral effective field theory [CL]

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http://arxiv.org/abs/2204.01865


We present a calculation of the radiative capture cross section $p(n,\gamma )d$ in the low-energy range, where the $M1$ reaction channel dominates. Employing the LENPIC nucleon-nucleon interaction up to the fifth order (N4LO) that is regularized by the semi-local coordinate space regulators, we obtain the initial and final state wave functions, and evaluate the phase shifts of the scattering state and deuteron properties. We derive the transition operator from the chiral effective field theory up to the next-to-next-to leading order (N2LO), where we also regularize the transition operator using regulators consistent with those of the interactions. We compute the capture cross sections and the results show a converging pattern with the chiral-order expansion of the nucleon-nucleon interaction, where the regulator dependence of the results is weak when higher-order nucleon-nucleon interactions are employed. We quantify the uncertainties of the cross-section results due to the chiral-order truncation. The chirally complete and consistent cross-section results are performed up to N2LO and they compare well with the experiments and other theoretical predictions.

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W. Du, S. Pal, M. Sharaf, et. al.
Wed, 6 Apr 22
29/68

Comments: 12 pages, 3 tables, 1 figure

Heavy baryons in hot stellar matter with light nuclei and hypernuclei [CL]

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http://arxiv.org/abs/2204.02260


The production of light nuclei and hypernuclei together with heavy baryons, both hyperons and $\Delta$-baryons, in low density matter as found in stellar environments such as supernova or binary mergers is studied within relativistic mean-field models. Five light nuclei were considered together with three light hypernuclei. The presence of both hyperons and $\Delta$-baryons shift the dissolution of clusters to larger densities and increase the abundance of clusters. This effect is larger the smaller the charge fraction and the higher the temperature. The couplings of the $\Delta$-baryons were chosen imposing that the nucleon effective mass remains finite inside neutron stars.

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T. Custódio, H. Pais and C. Providência
Wed, 6 Apr 22
60/68

Comments: 11 pages, 8 figures, submitted to Phys. Rev. C

Effects of a strong phase transition on supernova explosions, compact stars and their mergers [CL]

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http://arxiv.org/abs/2203.17188


We outline a theoretical approach supporting strong phase transitions from normal nuclear matter to the deconfined quark-gluon plasma, in the equation of state (EOS) for compact star matter. Implications of this hypothesis are discussed for astrophysical applications. Special emphasis is devoted to potentially detectable signatures, which can be directly related with the occurrence of a sufficiently strong phase transition. Therefore, simulations of core-collapse supernovae and binary compact star mergers are considered, including the subsequent emission of gravitational waves and, in the case of supernova, in addition the neutrinos play the role of messengers.

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A. Bauswein, D. Blaschke and T. Fischer
Fri, 1 Apr 22
17/85

Comments: 39 pages, 13 figures, contribution submitted on 20.02.2022 to the Book “Astrophysics in the XXI Century with Compact Stars”, edited by Cesar Augusto Zen Vasconcellos and Fridolin Weber, World Scientific

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

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http://arxiv.org/abs/2203.16827


We study the properties of pasta structures and their influence on the neutron star observables employing the effective relativistic mean-field theory (E-RMF). The compressible liquid drop model is used to incorporate the finite size effects, considering the possibility of non-spherical structures in the inner crust. The unified equation of state are constructed for several E-RMF parameters to study various properties such as pasta mass and thickness in the neutron star’s crust. The majority of the pasta properties are sensitive to the symmetry energy in the subsaturation density region. Using the results from Monte Carlo simulations, we estimate the shear modulus of the crust in context of quasiperiodic oscillations from soft gamma-ray repeaters and calculate the frequency of fundamental torsional oscillation mode in the inner crust. Global properties of the neutron star such as mass-radius profile, the moment of inertia, crustal mass, crustal thickness and fractional crustal moment of inertia are worked out. The results are consistent with various observational and theoretical constraints.

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V. Parmar, H. Das, A. Kumar, et. al.
Fri, 1 Apr 22
45/85

Comments: 15 pages, 10 figures, 3 tables, comments welcome. The unified equation of states including pasta phases are available on GitHub (this https URL)

On the Sound Speed in Neutron Stars [HEAP]

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http://arxiv.org/abs/2203.14974


Determining the sound speed $c_s$ in compact stars is an important open question with numerous implications on the behaviour of matter at large densities and hence on gravitational-wave emission from neutron stars. To this scope, we construct more than $10^7$ equations of state (EOSs) with continuous sound speed and build more than $10^8$ nonrotating stellar models consistent not only with nuclear theory and perturbative QCD, but also with astronomical observations. In this way, we find that EOSs with sub-conformal sound speeds, i.e. with $c^2_s < 1/3$ within the stars, are possible in principle but very unlikely in practice, being only $0.03\%$ of our sample. Hence, it is natural to expect that $c^2_s > 1/3$ somewhere in the stellar interior. Using our large sample, we obtain estimates at $95\%$ credibility of neutron-star radii for representative stars with $1.4$ and $2.0$ solar masses, $R_{1.4}=12.42^{+0.52}{-0.99}\,{\rm km}$, $R{2.0}=12.12^{+1.11}{-1.23}\,{\rm km}$, and for the binary tidal deformability of the GW170817 event, $\tilde\Lambda{1.186}=485^{+225}_{-211}$. Interestingly, our lower-bounds on the radii are in very good agreement with the prediction derived from very different arguments, namely, the threshold mass. Finally, we provide simple analytic expressions to determine the minimum and maximum values of $\tilde\Lambda$ as a function of the chirp mass.

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S. Altiparmak, C. Ecker and L. Rezzolla
Wed, 30 Mar 22
72/77

Comments: 7 pages + Supplemental Material, 5 figures, comments welcome

Constraining the parameterized neutron star equation of state with astronomical observations [CL]

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http://arxiv.org/abs/2203.14722


We utilise the phenomenologically parameterized piecewise polytropic equations of state to study various neutron star properties. We investigate the compliance of these equations of state with several astronomical observations. We also demonstrate that the theoretical estimates of the fractional moment of inertia cannot explain all the pulsar glitches observed. We model the crust as a solid spheroidal shell to calculate the fractional moment of inertia of fast-spinning neutron stars. We also show that the braking index obtained in a simple magnetic dipole radiation model with a varying moment of inertia deviates significantly from the observed data. Future developments in both theory and observations may allow us to use the fractional moment of inertia and braking index as observational constraints for neutron star equation of state.

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J. Singha, S. Vaneshwar and A. Kumar
Tue, 29 Mar 22
12/73

Comments: Accepted for publication in Research in Astronomy nd Astrophysics (RAA) journal. 12 pgs, 6 figures

Astrophysical reaction rates with realistic nuclear level densities [CL]

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http://arxiv.org/abs/2203.14220


Realistic nuclear level densities (NLDs) obtained within the spectral distribution method (SDM) are employed to study nuclear processes of astrophysical interest. The merit of SDM lies in the fact that the NLDs corresponding to many body shell model Hamiltonian consisting of residual interaction can be obtained for the full configurational space without recourse to the exact diagnolization of huge matrices. We calculate NLDs and s-wave neutron resonance spacings which agree reasonably well with the available experimental data. By employing these NLDs, we compute reaction cross-sections and astrophysical reaction rates for radiative neutron capture in few Fe-group nuclei, and compare them with experimental data as well as with those obtained with NLDs from phenomenological and microscopic mean-field models. The results obtained for the NLDs from SDM are able to explain the experimental data quite well. These results are of particular importance since the configuration mixing through the residual interaction naturally accounts for the collective excitations. In the mean-field models, the collective effects are included through the vibrational and rotational enhancement factors and their NLDs are further normalized at low energies with neutron resonance data.

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S. Sangeeta, T. Ghosh, B. Maheshwari, et. al.
Tue, 29 Mar 22
21/73

Comments: Accepted in Physical Review C (2022)

Embedding short-range correlations in relativistic density functionals through quasi-deuterons [CL]

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http://arxiv.org/abs/2203.14635


The formation of clusters at sub-saturation densities constitutes an essential feature for a reliable modelization of the nuclear matter equation of state (EoS). Phenomenological models that make use of energy density functionals (EDFs) offer a convenient approach to account for the presence of these bound states of nucleons when introduced as additional degrees of freedom. However, in these models clusters dissolve, by construction, when the nuclear saturation density is approached from below, revealing inconsistencies with recent findings that evidence the existence of short-range correlations (SRCs) even at larger densities.
In this work, within the EDF framework, a novel approach is proposed to embed SRCs within a relativistic mean-field model with density dependent couplings. This is realized through the introduction of suitable in-medium modifications of the cluster binding energy shifts, which are responsible for describing the cluster dissolution. As a first exploratory step, the example of a quasi-deuteron within the generalized relativistic density functional approach is investigated.
For the first time, suitable parameterizations of the cluster mass shift at zero temperature are derived for all baryon densities. They are constrained by experimental results for the effective deuteron fraction in nuclear matter near saturation and by microscopic many-body calculations in the low-density limit. The strength of the deuteron-meson couplings is assessed to be of crucial importance. The findings of the present study represent a first step to improve the description of nuclear matter and its EoS at supra-saturation densities in EDFs by considering correlations in an effective way. Novel effects on some thermodynamic quantities, such as the matter incompressibility, the symmetry energy and its slope, are finally discerned and discussed.

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S. Burrello and S. Typel
Tue, 29 Mar 22
26/73

Comments: 28 pages, 12 figures

Phase transitions and resilience of the MDCDW phase at finite temperature and density [CL]

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http://arxiv.org/abs/2203.14209


We study the phase transitions of the magnetic dual chiral density wave (MDCDW). This spatially inhomogeneous phase emerges in cold, dense QCD in the presence of a strong magnetic field. Starting from the generalized GL expansion of the free energy, we derive several analytical formulas that enable fast numerical computation of the expansion coefficients to arbitrary order, allowing high levels of precision in the determination of the physical dynamical parameters, as well as in the transition curves in the temperature vs. chemical potential plane at different magnetic fields. At magnetic fields and temperatures compatible with neutron star (NS) conditions, the MDCDW remains favored over the symmetric ground state at all densities. The phase’s “resilience” manifests in (1) a region of small but nonzero remnant mass and significant modulation at intermediate densities, originating in part from the nontrivial topology of the lowest Landau level, and (2) a region of increasing condensate parameters at high densities. Our analysis suggests the MDCDW condensate remains energetically favored at densities and temperatures much higher than previously considered, opening the possibility for this phase to be a viable candidate for the matter structure of even young neutron stars produced by NS mergers.

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W. Gyory and V. Incera
Tue, 29 Mar 22
39/73

Comments: N/A

Partially accreted crusts of neutron stars [HEAP]

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http://arxiv.org/abs/2203.14735


Neutron stars in low-mass binary systems are subject to accretion. The common assumption in studying the properties of the neutron star crust is the fully accreted crust approximation. However, observations of some X-ray transient sources indicate that the original crust has not been completely replaced by accreted material, but is partly composed of the compressed original crust. A two-part (or hybrid) crust made of the original crust that is compressed and of the accreted material crashing onto it was reconstructed as a function of the accretion stage. The differences in the composition and energy sources for the fully accreted and hybrid crusts influence the cooling and transport properties. A simple semi-empirical formula of a compressible liquid drop was used. We compared the nuclear reactions triggered by compression in the original crust and in the accreted matter part of the hybrid crust. We discuss another crust compression astrophysical phenomenon related to spinning neutron stars. The compression of the originally catalyzed outer crust triggers exothermic reactions (electron captures and pycnonuclear fusions) that deposit heat in the crust. The heat sources are cataloged as a function of the compression until the fully accreted crust approximation is reached. The pressure at which neutron drip occurs is a nonmonotonic function of the depth, leading to a temporary neutron drip anomaly. The additional potential source of energy for partially accreted crusts is the occurrence of a density inversion phenomenon between some compressed layers. The original crust of a neutron star cannot be neglected when the original crust is not fully replaced by the accreted matter. The amount of heat associated with the compression of the original crust is on the same order of magnitude as that from the sources acting in the accreted part of the hybrid crust.

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L. Suleiman, J. Zdunik, P. Haensel, et. al.
Tue, 29 Mar 22
46/73

Comments: 17 pages, 10 figures, 4 files in Ancillary (2 movies, 2 .res files)

Comprehensive Analyses of the Neutrino-Process in the Core-collapsing Supernova [CL]

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http://arxiv.org/abs/2203.13365


We investigate the effects of the neutrino flavor change by the neutrino self-interaction, the shock effect and the matter effect on the neutrino-process of the core-collapsing supernova (CCSN). For the hydrodynamics, we compare the results of a simple thermal bomb and a specified hydrodynamic model for SN1987A. As a pre-supernova model, we take an updated model adjusted to explain the SN1987A employing recent development of the $(n,\gamma)$ reaction rates calculated for nuclei near the stability line $(A \sim 100)$. As for the neutrino luminosity, we adopt two different models: equivalent neutrino luminosity and non-equivalent luminosity models. The latter is taken from the synthetic analysis of the CCSN simulation data which compared quantitatively the results obtained by various neutrino transport models. Relevant neutrino-induced reaction rates are calculated by a shell model for light nuclei and a quasi-particle random phase approximation model for heavy nuclei. For each model, we present and discuss abundances of the light nuclei ($^7$Li, $^7$Be, $^{11}$B and $^{11}$C) and heavy nuclei ($^{92}$Nb, $^{98}$Tc, $^{138}$La and $^{180}$Ta). The light nuclei are known to be sensitive to the Mikheyev-Smirnov-Wolfenstein region around O-Ne-Mg region. Through the detailed analysis of the numerical abundances, we find that neutrino self-interaction becomes a key ingredient in addition to the MSW effect for understanding the neutrino-process and the relevant nuclear abundances. However, the whole results are shown to depend on the adopted neutrino luminosity scheme. Detailed analyses of the nuclear abundances for the two possible neutrino mass hierarchies are also performed with the data from the meteorite analyses. The normal mass hierarchy is shown to be more compatible with the meteoritic data.

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H. Ko, D. Jang, M. Cheoun, et. al.
Mon, 28 Mar 22
40/50

Comments: N/A

Deciphering Effects of Relativistic Kinematics, Dimensionality, Interactions and Short-Range Correlations on the Ratio of Quartic over Quadratic Nuclear Symmetry Energies [CL]

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http://arxiv.org/abs/2203.12773


While ample evidence for the so-called empirical parabolic law of the Equation of State (EOS) of isospin asymmetric nuclear matter (ANM) has been obtained in many studies within both non-relativistic and relativistic nuclear many-body theories using various interactions, it has been unclear if there is any fundamental physics reason for the small quartic symmetry energy compared to the quadratic one even as the ANM approaches pure neutron matter. Within both relativistic and non-relativistic Free Fermi Gas (FFG) models in coordinate spaces of arbitrary dimension $d$ with and without considering Short-Range Correlations (SRC) as well as non-linear Relativistic Mean Field (RMF) models, we study effects of relativistic kinematics, dimensionality, interactions and SRC on the ratio $\Psi(\rho)$ of quartic over quadratic symmetry energies in ANM EOSs. We found that the ratio $\Psi(\rho)$ in the FFG model depends strongly on the dimension $d$. While it is very small already in the normal 3D space, it could be even smaller in spaces with reduced dimensions for sub-systems of particles in heavy-ion reactions and/or whole neutron stars due to constraints, collectivities and/or symmetries. We also found that the ratio $\Psi(\rho)$ could theoretically become very large only at the ultra-relativistic limit far above the density reachable in neutron stars. On the other hand, nuclear interaction directly and/or indirectly through SRC-induced high-momentum nucleons affect significantly the density dependence of $\Psi(\rho)$ compared to the relativistic FFG model prediction. The SRC affects significantly not only the kinetic energy of symmetric nuclear matter but also the ratio $\Psi(\rho)$ while the relativistic corrections are found negligible. The results may help better understand the EOS of dense neutron-rich matter.

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B. Cai and B. Li
Fri, 25 Mar 22
29/46

Comments: 11 pages with 3 figures

Confronting a set of Skyrme and $χ_{EFT}$ predictions for the crust of neutron stars [CL]

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http://arxiv.org/abs/2203.11645


With the improved accuracy of neutron star observational data, it is necessary to derive new equation of state where the crust and the core are consistently calculated within a unified approach. For this purpose we describe non-uniform matter in the crust of neutron stars employing a compressible liquid-drop model, where the bulk and the neutron fluid terms are given from the same model as the one describing uniform matter present in the core. We then generate a set of fifteen unified equations of state for cold catalyzed neutron stars built on realistic modelings of the nuclear interaction, which belongs to two main groups: the first one derives from the phenomenological Skyrme interaction and the second one from $\chi_{EFT}$ Hamiltonians. The confrontation of these model predictions allows us to investigate the model dependence for the crust properties, and in particular the effect of neutron matter at low density. The new set of unified equations of state is available at the CompOSE repository.

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G. Grams, J. Margueron, R. Somasundaram, et. al.
Wed, 23 Mar 22
4/76

Comments: N/A

Simultaneous Inference of Neutron Star Equation of State and Hubble Constant with a Population of Merging Neutron Stars [CEA]

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http://arxiv.org/abs/2203.11756


We develop a method for implementing a proposal on utilizing knowledge of neutron star (NS) equation of state (EoS) for inferring the Hubble constant from a population of binary neutron star (BNS) mergers. This method is useful in exploiting BNSs as standard sirens when their redshifts are unavailable. Gravitational wave (GW) signals from compact object binaries provide a direct measurement of their luminosity distances, but not the redshifts. Unlike in the past, we employ a realistic EoS parameterization in a Bayesian framework to simultaneously measure the Hubble constant and refine the constraints on the EoS parameters. The uncertainty in the redshift depends on the uncertainty in EoS and mass parameters estimated from GW data. Combining the inferred BNS redshifts with the corresponding luminosity distances, one constructs a redshift-distance relationship and deduces the Hubble constant from it. Here, we show that in the Cosmic Explorer era, one can measure the Hubble constant to a precision of $\sim 3\%$ (with a $90\%$ credible interval) with a realistic distribution of thousand BNSs, while allowing for uncertainties in their EoS parameters. The methodology implemented in this work demonstrates a comprehensive algorithm to infer NS EoS and the Hubble constant by simultaneously combining GW observations from merging NSs, choosing a simple population model of NS masses and keeping the merger rate of NSs constant. This method can be immediately extended to incorporate merger rate, population properties, and different cosmological parameters.

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T. Ghosh, B. Biswas and S. Bose
Wed, 23 Mar 22
64/76

Comments: N/A

Hybrid stars and QCD phase transition with a NJL-like model [CL]

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http://arxiv.org/abs/2203.11791


In this paper, we introduce a self-consistent mean field approximation to study the QCD phase transition and the structure of hybrid stars within the framework of NJL model. In our practice, a phenomenological parameter $\alpha$ is introduced, which reflects the weights of “direct” channel and “exchange” channel under a finite chemical potential. The mass-radius relation is obtained by solving the Tolman-Oppenheimer-Volkoff equation using a crossover equation of state (EOS). We calculate the density distribution in a two solar-mass hybrid star to show the effects of different parameters. We also calculate the tidal Love number $k_2$ and the deformability $(\Lambda)$. It is found that the stiffness of the EOS increases with $\alpha $, which allows us to obtain a hybrid star with a maximum mass of 2.40 solar-mass through our model. The observation of over 2.06 solar-mass neutron stars may indicates that the chiral transition may be a crossover on the whole $T-\mu$ plane.

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B. Zuo, Y. Huang and H. Feng
Wed, 23 Mar 22
76/76

Comments: N/A

Physically Interpretable Machine Learning for nuclear masses [CL]

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http://arxiv.org/abs/2203.10594


We present a novel approach to modeling the ground state mass of atomic nuclei based directly on a probabilistic neural network constrained by relevant physics. Our Physically Interpretable Machine Learning (PIML) approach incorporates knowledge of physics by using a physically motivated feature space in addition to a soft physics constraint that is implemented as a penalty to the loss function. We train our PIML model on a random set of $\sim$20\% of the Atomic Mass Evaluation (AME) and predict the remaining $\sim$80\%. The success of our methodology is exhibited by the unprecedented $\sigma_\textrm{RMS}\sim186$ keV match to data for the training set and $\sigma_\textrm{RMS}\sim316$ keV for the entire AME with $Z \geq 20$. We show that our general methodology can be interpreted using feature importance.

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M. Mumpower, T. Sprouse, A. Lovell, et. al.
Tue, 22 Mar 22
32/82

Comments: 5 pages, 3 figures, comments welcome

Neutron star mass formula with nuclear saturation parameters [CL]

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http://arxiv.org/abs/2203.09004


We derive the empirical formulas for the neutron star mass and gravitational redshift as a function of the central density and specific combination of the nuclear saturation parameters, which are applicable to the stellar models constructed with the central density up to threefold nuclear saturation density. Combining the both empirical formulas, one also estimates the neutron star radius. In practice, we find that the neutron star mass (radius) can be estimated within $\sim 10\%$ (a few percent) accuracy by comparing the mass and radius evaluated with our empirical formulas to those determined with the specific equation of state. Since our empirical formulas directly connect the neutron star mass and radius to the nuclear saturation parameters, one can discuss the neutron star properties with the specific values of nuclear saturation parameters constrained via nuclear experiments.

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H. Sotani and H. Togashi
Fri, 18 Mar 22
56/66

Comments: N/A

Nearly model independent constraints on dense matter equation of state in a Bayesian approach [CL]

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http://arxiv.org/abs/2203.08521


We apply Bayesian approach to construct a large number of minimally constrained equations of state (EoSs) and study their correlations with a few selected properties of neutron star (NS). Our set of minimal constraints includes a few basic properties of saturated nuclear matter and low density pure neutron matter EoS which is obtained from a precise next-to-next-to-next-to-leading order (N$^{3}$LO) calculation in chiral effective field theory. The tidal deformability and radius of NS with mass $1$-$2M_\odot$ are found to be strongly correlated with the pressure of $\beta$-equilibrated matter as well as with the symmetry energy at densities higher than the saturation density ($\rho_0 = 0.16$ fm$^{-3}$) in a nearly model independent manner. These correlations are employed to parametrize the pressure for $\beta$-equilibrated matter, around 2$\rho_0$, as a function of neutron star mass and the corresponding tidal deformability. The maximum mass of neutron star is also strongly correlated with the pressure of symmetric and $\beta$-equilibrated matter at densities $\sim$ 4.5$\rho_0$.

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N. Patra, S. Imam, B. Agrawal, et. al.
Thu, 17 Mar 22
8/66

Comments: 19 pages, 7 figures, submitted to Symmetry Journal

Cold Quark-Gluon Plasma EOS Applied to a Magnetically Deformed Quark Star with an Anomalous Magnetic Moment [CL]

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http://arxiv.org/abs/2203.08241


We consider a QCD cold plasma motivated Equation of State (EOS) to examine the impact of an Anomalous Magnetic Moment (AMM) coupling and small shape deformations for static oblate and prolate core shapes of quark stars. Using the Foga\c{c}a QCD motivated EOS which shifts from the high temperature low chemical potential quark gluon plasma environment to the low temperature high chemical potential quark stellar core environment we consider the impact of an AMM coupling with a metric induced shape deformation parameter in the TOV equations. The EOS is developed using a hard gluon and soft gluon decomposition of the gluon field tensor using a mean field effective mass for the gluons. The AMM is considered using the Dirac spin tensor coupled to the EM field tensor with quark flavor based magnetic moments. The shape parameter is introduced in a metric ansatz that represents oblate and prolate static stellar cores for modified TOV equations. These equations are numerically solved for the final mass and radius states representing the core collapse of a massive star with a phase transition leading to an unbound quark-gluon plasma. We find that the combined shape parameter and AMM effects can alter the coupled EOS-TOV equations resulting in an increase in the final mass and a decrease in the final equatorial radius without collapsing the core into a black hole and without violating causality constraints, we find maximum mass values in the range: 2.3 Solar Masses < M < 2.7 Solar Masses. These states are consistent with some astrophysical high mass magnetar/pulsar and gravity wave systems which may provide evidence for a core that has undergone a quark-gluon phase transition such as PSR 0943+10 and the secondary from the GW 190814 event.

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K. Andrew, E. Steinfelds and K. Andrew
Thu, 17 Mar 22
39/66

Comments: 12 pages, 6 figures

$^1$S$_0$ pairing gaps, chemical potential and entrainment matrix in superfluid neutron-star cores for the Brussels-Montreal functionals [CL]

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http://arxiv.org/abs/2203.08778


Temperature and velocity-dependent $^1$S$_0$ pairing gaps, chemical potentials and entrainment matrix in dense homogeneous neutron-proton superfluid mixtures constituting the outer core of neutron stars, are determined fully self-consistently by solving numerically the time-dependent Hartree-Fock-Bogoliubov equations over the whole range of temperatures and flow velocities for which superfluidity can exist. Calculations have been made for $npe\mu$ in beta-equilibrium using the Brussels-Montreal functional BSk24. The accuracy of various approximations is assessed and the physical meaning of the different velocities and momentum densities appearing in the theory is clarified. Together with the unified equation of state published earlier, the present results provide consistent microscopic inputs for modeling superfluid neutron-star cores.

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V. Allard and N. Chamel
Thu, 17 Mar 22
51/66

Comments: 36 pages, 19 figures. Numerical results for pairing gaps are available on the CompOSE database, see this https URL

Mapping topology of skyrmions and fractional quantum Hall droplets to nuclear EFT for ultra-dense baryonic matter [CL]

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http://arxiv.org/abs/2203.06998


We describe the mapping at high density of topological structure of baryonic matter to a nuclear effective field theory that implements hidden symmetries emergent from strong nuclear correlations. The theory so constructed is found to be consistent with no conflicts with the presently available observations in both normal nuclear matter and compact-star matter. The hidden symmetries involved are “local flavor symmetry” of the vector mesons identified to be (Seiberg-)dual to the gluons of QCD and hidden “quantum scale symmetry” with an IR fixed point with a “genuine dilaton (GD)” characterized by non-vanishing pion and dilaton decay constants. Both the skyrmion topology for $N_f \geq 2$ baryons and the fractional quantum Hall (FQH) droplet topology for $N_f=1$ baryons are unified in the “homogeneous/hidden” Wess-Zumino term in the hidden local symmetry (HLS) Lagrangian. The possible indispensable role of the FQH droplets in going beyond the density regime of compact stars approaching scale-chiral restoration is explored by moving toward the limit where both the dilaton and the pion go massless.

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M. Rho
Tue, 15 Mar 22
30/108

Comments: 18 pages, 1 figure, e-prints: 2004.09082, 2103.01860, 2109.10059 combined for contribution to Special Issue of MDPI “Symmetries and Ultra Dense Matter of Compact Stars”

New constraints on the neutron-star mass and radius relation from the terrestrial nuclear experiments [CL]

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http://arxiv.org/abs/2203.05410


The study of the equation of state (EOS) for nuclear matter has been still a challenging problem, although the EOS is essential for determining the properties of neutron stars. In order to constrain the EOS, several studies have been based on astronomical observations with the X-ray and gravitational waves, which mainly cover the higher density of neutron star matter. In this study, focusing on the relatively lower density region, we show an allowed area in the neutron-star mass and radius relation by using the constraints on the density-dependence of the nuclear symmetry energy obtained via the recent nuclear experiments with different projects (i.e., S$\pi$RIT and PREX-II) together with the experiment at RCNP. Each region predicted by these experiments is still consistent with the area in the higher density allowed by the various astronomical observations. Our results show that terrestrial nuclear experiments must provide further constraints on the EOS for neutron stars, complementing astronomical observations.

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H. Sotani, N. Nishimura and T. Naito
Fri, 11 Mar 22
53/59

Comments: 10 pages, 2 figures, submitted

Merger and post-merger of binary neutron stars with a quark-hadron crossover equation of state [HEAP]

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http://arxiv.org/abs/2203.04528


Fully general-relativistic binary-neutron-star (BNS) merger simulations with quark-hadron crossover (QHC) equations of state (EOSs) are studied for the first time. In contrast to EOSs with purely hadronic matter or with a first-order quark-hadron transition, in the transition region QHC EOSs show a peak in sound speed, and thus a stiffening. We study the effects of such stiffening in the merger and post-merger gravitational (GW) signals. Through simulations in the binary-mass range $2.5 < M/M_{\odot} < 2.75$, characteristic differences due to different EOSs appear in the frequency of the main peak of the post-merger GW spectrum ($f_2$), extracted through Bayesian inference. In particular, we found that (i) for lower-mass binaries, since the maximum baryon number density ($n_{\rm max}$) after the merger stays below $3-4$ times the nuclear-matter density ($n_0$), the characteristic stiffening of the QHC models in that density range results in a lower $f_2$ than that computed for the underlying hadronic EOS and thus also than that for EOSs with a first-order phase transition, and (ii) for higher-mass binaries, where $n_{\rm max}$ may exceed $4-5 n_0$ depending on the EOS model, whether $f_2$ in QHC models is higher or lower than that in the underlying hadronic model depends on the height of the sound-speed peak. Comparing the values of $f_2$ for different EOSs and BNS masses gives important clues on how to discriminate different types of quark dynamics in the high-density end of EOSs and is relevant to future kHz GW observations with third-generation GW detectors.

Read this paper on arXiv…

Y. Huang, L. Baiotti, T. Kojo, et. al.
Thu, 10 Mar 22
8/60

Comments: 6+6 pages, 5+4 figures

Interacting $ud$ and $uds$ quark matter at finite densities and quark stars [CL]

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http://arxiv.org/abs/2203.04798


The stability and equation of state of quark matter are studied within both two-flavor and (2+1)-flavor Nambu-Jona-Lasinio (NJL) models including the vector interactions. With a free parameter $\alpha$, the Lagrangian is constructed by two parts, the original NJL Lagrangian and the Fierz transformation of it, as $L=(1-\alpha) L_{\rm{NJL}}+\alpha L_{\rm{Fierz}}$. We find that there is a possibility for both $ud$ nonstrange and $uds$ strange matter being absolute stable, depending on the interplay of the confinement with quark vector interaction and the exchange interaction channels. The calculated quark star properties can reconcile with the recently measured masses and radii of PSR J0030+0451 and PSR J0740+6620, as well as the tidal deformability of GW170817. Furthermore, the more strongly-interacting quark matter in the nonstrange stars allows a stiffer equation of state and consequently a higher maximum mass ($\sim2.7\, M_{\odot}$) than the strange ones ($\sim2.1\, M_{\odot}$). The sound velocities in strange and nonstrange quark star matter are briefly discussed compared to those of neutron star matter.

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W. Yuan, A. Li, Z. Miao, et. al.
Thu, 10 Mar 22
54/60

Comments: 13 pages, 9 figures, 2 tables

Status of deep subbarrier $\mathbf{{}^{12}{\rm C}+{}^{12}{\rm C}}$ fusion and advancing the Trojan horse method [CL]

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http://arxiv.org/abs/2203.04094


In this paper, I will update the current status of the carbon-carbon fusion research taking into account that after the latest analysis [Beck {\it et al.} Eur. Phys. J. A {\bf 56}, 97 (2020), Letter to the Editor] new important experimental and theoretical results had been published and will discuss how to advance new THM measurements to extract the low-energy astrophysical $S$-factors.

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A. Mukhamedzhanov
Wed, 9 Mar 22
63/68

Comments: 13 pages, 7 figures

General relativistic treatment of $f$-mode oscillations of hyperonic stars [HEAP]

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http://arxiv.org/abs/2203.03141


We present a systematic study of $f$-mode oscillations in neutron stars containing hyperons, extending recent results obtained within the Cowling approximation to linearized General Relativity. Employing a relativistic mean field model, we find that the Cowling approximation can overestimate the quadrupolar $f$-mode frequency of neutron stars by up to 30\% compared to the frequency obtained in the linearized general relativistic formalism. Imposing current astrophysical constraints, we derive updated empirical relations for gravitational wave asteroseismology. The frequency and damping time of quadrupole $f$-mode oscillations of hyperonic stars are found to be in the range of 1.47 – 2.45kHz and 0.13 – 0.51 sec respectively. Our correlation studies demonstrate that among the various parameters of the nucleonic and hyperonic sectors of the model, the nucleon effective mass shows the strongest correlation with mode characteristics and neutron star observables. Estimates for the detectability of $f$-modes in a transient burst of gravitational waves from isolated hyperonic stars is also provided.

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B. Pradhan, D. Chatterjee, M. Lanoye, et. al.
Tue, 8 Mar 22
21/100

Comments: 16 pages, 13 figures

CompOSE Reference Manual [HEAP]

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http://arxiv.org/abs/2203.03209


CompOSE (CompStar Online Supernovae Equations of State) is an online repository of equations of state (EoS) for use in nuclear physics and astrophysics, e.g., in the description of compact stars or the simulation of core-collapse supernovae and neutron-star mergers, see this http URL The main services, offered via the website, are: a collection of data tables in a flexible and easily extendable data format for different EoS types and related physical quantities with extensive documentation and referencing; software for download to extract and to interpolate these data and to calculate additional quantities; webtools to generate EoS tables that are customized to the needs of the users and to illustrate dependencies of various EoS quantities in graphical form. This manual is an update of previous versions that are available on the CompOSE website, at arXiv:1307.5715 [astro-ph.SR], and that was originally published in the journal “Physics of Particles and Nuclei” with doi:10.1134/S1063779615040061. It contains a detailed description of the service, containing a general introduction as well as instructions for potential contributors and for users. Short versions of the manual for EoS users and providers will also be available as separate publications.

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S. Typel, M. Oertel, T. Klähn, et. al.
Tue, 8 Mar 22
26/100

Comments: 91 pages, 20 tables. This manual is an update of arXiv:1307.571

Neutron stars and phase diagram in a hard-wall AdS/QCD model [CL]

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http://arxiv.org/abs/2202.12845


We study the phase diagram of (large-$N_c$) QCD using a simplistic holographic hard-wall model with a dynamical scalar field and a homogeneous Ansatz representing a smeared instanton/baryon density. The resulting phase diagram is qualitatively consistent with expectations, including a mesonic, baryonic, quarkyonic, and quark-gluon plasma phase. As in other holographic models, we also find a baryonic popcorn transition, which appears at large chemical potential as a crossover. We then evaluate the nuclear matter equation of state, which turns out to be rather stiff with a large peaked sound velocity above the conformal limit, construct corresponding neutron stars using the TOV equations, and finally use a full numerical gravity/hydrodynamics computation to extract the gravitational wave signal of neutron star mergers.

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L. Bartolini, S. Gudnason, J. Leutgeb, et. al.
Tue, 8 Mar 22
69/100

Comments: LaTeX: 44 pages, 12 figures

Entanglement and correlations in fast collective neutrino flavor oscillations [HEAP]

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http://arxiv.org/abs/2203.02783


Collective neutrino oscillations play a crucial role in transporting lepton flavor in astrophysical settings like supernovae and neutron star binary merger remnants, which are characterized by large neutrino densities. In these settings, simulations in the mean-field approximation show that neutrino-neutrino interactions can overtake vacuum oscillations and give rise to fast collective flavor evolution on time-scales $t\propto\mu^{-1}$, with $\mu$ proportional to the local neutrino density. In this work, we study the full out-of-equilibrium flavor dynamics in simple multi-angle geometries displaying fast oscillations in the mean field linear stability analysis. Focusing on simple initial conditions, we analyze the production of pair correlations and entanglement in the complete many-body-dynamics as a function of the number $N$ of neutrinos in the system, for up to thousands of neutrinos. Similarly to simpler geometries with only two neutrino beams, we identify three regimes: stable configurations with vanishing flavor oscillations, marginally unstable configurations with evolution occurring on long time scales $\tau\approx\mu^{-1}\sqrt{N}$, and unstable configurations showing flavor evolution on short time scales $\tau\approx\mu^{-1}\log(N)$. We present evidence that these fast collective modes are generated by the same dynamical phase transition which leads to the slow bipolar oscillations, establishing a connection between these two phenomena and explaining the difference in their time scales. We conclude by discussing a semi-classical approximation which reproduces the entanglement entropy at short to medium time scales and can be potentially useful in situations with more complicated geometries where classical simulation methods starts to become inefficient.

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A. Roggero, E. Rrapaj and Z. Xiong
Tue, 8 Mar 22
73/100

Comments: N/A

Multi-physics constraints at different densities to probe nuclear symmetry energy in hyperonic neutron stars [HEAP]

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http://arxiv.org/abs/2203.03156


The appearance of strangeness in the form of hyperons within the inner core of neutron stars is expected to affect its detectable properties such as its global structure or gravitational wave emission. In this work, we explore the parameter space of hyperonic stars within the framework of the Relativistic Mean Field model allowed by present uncertainties in state-of-the-art nuclear and hypernuclear experimental data. We impose multi-physics constraints at different density regimes to restrict the parameter space: Chiral effective field theory, heavy-ion collision data as well as multi-messenger astrophysical observations of neutron stars. We investigate possible correlations between empirical nuclear and hypernuclear parameters, particularly the symmetry energy and its slope, with observable properties of neutron stars. We do not find a correlation for the hyperon parameters and the astrophysical data. However, the inclusion of hyperons generates a tension between the astrophysical and heavy ion data constraining considerable the available parameter space.

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S. Ghosh, B. Pradhan, D. Chatterjee, et. al.
Tue, 8 Mar 22
93/100

Comments: 26 pages, 7 figures, Accepted for publication in Frontiers in Astronomy and Space Sciences- Nuclear Physics

Thermal Relaxation of Dark Matter Admixed Neutron Star [HEAP]

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http://arxiv.org/abs/2203.02132


Motivated by the various theoretical studies regarding the efficient capturing of dark matter by neutron stars, we explore the possible indirect effects of captured dark matter on the cooling mechanism of a neutron star. The equation of states for different configurations of dark matter admixed star at finite temperature is obtained using the relativistic mean-field formalism with the IOPB-I parameter set. We show that the variation in the dark matter momentum vastly modifies the neutrino emissivity through specific neutrino generating processes of the star. The specific heat and the thermal conductivity of a dark matter admixed star have also been investigated to explore the propagation of cooling waves in the interior of the star. The dependence of theoretical surface temperature cooling curves on the equation of state and chemical composition of the stellar matter has also been discussed along with the observational data of thermal radiation from various sources. We observed that the dark matter admixed canonical stars with $k_{f}^{DM} > 0.04$ comply with the fast cooling scenario. Further, the metric for internal thermal relaxation epoch has also been calculated with different dark matter momentum and we deduced that increment of dark matter segment amplify the cooling and internal relaxation rates of the star.

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A. Kumar, H. Das and S. Patra
Mon, 7 Mar 22
1/64

Comments: 15 pages, 11 figures, 1 table. Submitted to MNRAS

Direct URCA process in light of PREX-2 [CL]

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http://arxiv.org/abs/2203.02272


We study the implications of the recent development in nuclear symmetry energy constraints from PREX-2 data on dense matter equation of state and its impact on dURCA threshold density. In this work, we construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models and exploring the coupling parameter space of isovector-vector meson to baryons constrained by the isospin asymmetry parameter values deduced from recent PREX-2 data. The modified parameter sets are applied to evaluate the dense matter properties. We find that the updated data suggests the occurrence of dURCA process within neutron star even with mass as low as one solar mass.

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V. Thapa and M. Sinha
Mon, 7 Mar 22
51/64

Comments: 8 pages, 7 figures, 3 tables

Chiral symmetry restoration and the $Δ$ matter formation in neutron stars [CL]

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http://arxiv.org/abs/2203.00269


We analyze the effects of chiral symmetry restoration in hadronic matter, including the lowest-lying baryonic resonance $\Delta$ based on the parity doublet model. We study the role of $\Delta$ and its chiral partner on the equation of state (EoS) of dense matter under neutron star (NS) conditions of $\beta$-equilibrium and charge neutrality. We find that the softening of the EoS driven by the early onset of $\Delta$ matter due to partial restoration of chiral symmetry allows accommodating the modern multi-messenger astrophysical constraints on the mass, radius, and tidal deformability. The softening above the saturation density is accompanied by subsequent stiffening at high densities. We also find that the matter composition in the NS cores may be different upon variations of the repulsive interactions of $\Delta$ baryons in hadronic matter.

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M. Marczenko, K. Redlich and C. Sasaki
Wed, 2 Mar 22
39/54

Comments: arXiv admin note: text overlap with arXiv:2110.11056, arXiv:2004.09566

Non-iterative finite amplitude methods for E1 and M1 giant resonances [CL]

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http://arxiv.org/abs/2202.13214


The finite amplitude method (FAM) is a very efficient approach for solving the fully self-consistent random-phase approximation (RPA) equations. We use FAM to rederive the RPA matrices for general Skyrme-like functionals, calculate the electric dipole (E1) and the magnetic dipole (M1) giant resonances, and compare the results with available experimental and evaluated data. For the E1 transitions in heavy nuclei, the calculations reproduce well the resonance energy of the photoabsorption cross sections. In the case of M1 transitions, we show that the residual interaction does not affect the transition strength of double-magic nuclei, which suggests that the spin terms in the Skyrme force currently neglected in the present computation could improve the agreement between FAM and experimental data.

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H. Sasaki, T. Kawano and I. Stetcu
Tue, 1 Mar 22
58/80

Comments: 15 pages, 6 figures

Unsupervised machine learning correlations in EoS of neutron stars [CL]

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http://arxiv.org/abs/2202.13940


Neutron stars are compact objects of large interest in the nuclear astrophysics community. The extreme conditions present in such systems impose big challenges to our current microscopic models of nuclear structure. Equation of states (EoS) are frequently derived from sophisticated quantum mechanical models, such as: relativistic, non-relativistic and many mean-field approaches. Every single model, in general, contains many parameters such as the NN interaction strength, particle compositions, etc. These are particular features of each model and can be represented by numbers and categories in a machine learning context. Different choices of features will affect EoS properties leading to different macroscopic properties of the star. In this work we analyze a selection of EoS containing a variety of different physics models. One of our objectives is to develop tools that enable a better understanding of the correlations among the different model features and the outcome produced by them when employed to model neutron stars.

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R. Lobato, E. Chimanski and C. Bertulani
Tue, 1 Mar 22
72/80

Comments: Contribution to the XV International Workshop on Hadron Physics (XV Hadron Physics) 13 -17 September 2021, hosted by Instituto Tecnol\’ogico de Aeron\’autica, S\~ao Jos\’e dos Campos, Brazil

Benchmark calculations of infinite neutron matter with realistic two- and three-nucleon potentials [CL]

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http://arxiv.org/abs/2202.10293


We present the equation of state of infinite neutron matter as obtained from highly-realistic Hamiltonians that include nucleon-nucleon and three-nucleon coordinate-space potentials. We benchmark three independent many-body methods: Brueckner-Bethe-Goldstone (BBG), Fermi hypernetted chain/single-operator chain (FHNC/SOC), and auxiliary-field diffusion Monte Carlo (AFDMC). We find them to provide similar equations of state when the Argonne $v_{18}$ and the Argonne $v_{6}^\prime$ nucleon-nucleon potentials are used in combination with the Urbana IX three-body force. Only at densities larger than about 1.5 the nuclear saturation density ($\rho_0 = 0.16\,\rm{fm}^{-3}$) the FHNC/SOC energies are appreciably lower than the other two approaches. The AFDMC calculations carried out with all of the Norfolk potentials fitted to reproduce the experimental trinucleon ground-state energies and $nd$ doublet scattering length yield unphysically bound neutron matter, associated with the formation of neutron droplets. Including tritium $\beta$-decay in the fitting procedure, as in the second family of Norfolk potentials, mitigates but does not completely resolve this problem. An excellent agreement between the BBG and AFDMC results is found for the subset of Norfolk interactions that do not make neutron-matter collapse, while the FHNC/SOC equations of state are moderately softer.

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A. Lovato, I. Bombaci, D. Logoteta, et. al.
Tue, 22 Feb 22
47/77

Comments: 15 pages, 3 figures. arXiv admin note: text overlap with arXiv:1908.04426

Prospects for Distinguishing Supernova Models Using a Future Neutrino Signal [HEAP]

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http://arxiv.org/abs/2202.09975


The next Galactic core-collapse supernova (SN) should yield a large number of observed neutrinos. Using Bayesian techniques, we show that with an SN at a known distance up to 25 kpc, the neutrino events in a water Cherenkov detector similar to Super-Kamiokande (SK) could be used to distinguish between seven one-dimensional neutrino emission models assuming no flavor oscillations or the standard Mikheyev-Smirnov-Wolfenstein effect. Some of these models could still be differentiated with an SN at a known distance of 50 kpc. We also consider just the relative distributions of neutrino energy and arrival time predicted by the models and find that a detector like SK meets the requirement to distinguish between these distributions with an SN at an unknown distance up to $\sim 10$ kpc.

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J. Olsen and Y. Qian
Tue, 22 Feb 22
65/77

Comments: 12 pages, 2 figures

Effects of isoscalar- and isovector-scalar meson mixing on neutron star structure [CL]

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http://arxiv.org/abs/2202.08705


Based on the accurately calibrated interaction FSUGold, we show that including isovector scalar $\delta$ meson and its coupling to isoscalar scalar $\sigma$ meson in the relativistic mean field (RMF) model can soften the symmetry energy $E_{\rm{sym}}(n)$ at intermediate density while stiffen the $E_{\rm{sym}}(n)$ at high densities. We find this new RMF model can be simultaneously compatible with (1) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, (2) the neutron skin thickness of $^{208}$Pb from the PREX-II experiment, (3) the largest mass of neutron star (NS) reported so far from PSR J0740+6620, (4) the limit of $\Lambda_{1.4}\leq580$ for the dimensionless tidal deformability of the canonical 1.4$M_{\odot}$ NS from the gravitational wave signal GW170817, (5) the mass-radius of PSR J0030+0451 and PSR J0740+6620 measured by NICER, and thus remove the tension between PREX-II and GW170817 observed in the conventional RMF model.

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F. Li, B. Cai, Y. Zhou, et. al.
Fri, 18 Feb 22
48/63

Comments: 7 pages, 2 figures, 2 tables

Asymmetric nuclear matter in relativistic mean-field models with isoscalar- and isovector-meson mixing [CL]

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http://arxiv.org/abs/2202.06468


Using the relativistic mean-field model with nonlinear couplings between the isoscalar and isovector mesons, we study the properties of isospin-asymmetric nuclear matter. Not only the vector mixing, $\omega_{\mu}\omega^{\mu}\mathbf{\rho}{\nu}\mathbf{\rho}^{\nu}$, but also the quartic interaction due to the scalar mesons, $\sigma^{2}\mathbf{\delta}^{2}$, is taken into account to investigate the density dependence of nuclear symmetry energy, $E{\rm sym}$, and the neutron-star properties. It is found that the $\delta$ meson increases $E_{\rm sym}$ at high densities, whereas the $\sigma$-$\delta$ mixing makes $E_{\rm sym}$ soft above the saturation density. Furthermore, the $\delta$ meson and its mixing have a large influence on the radius and tidal deformability of a neutron star. In particular, the $\sigma$-$\delta$ mixing reduces the neutron-star radius, and, thus, the present calculation can simultaneously reproduce the dimensionless tidal deformabilities of a canonical $1.4M_{\odot}$ neutron star observed from the binary neutron star merger, GW170817, and from the compact binary coalescence, GW190814.

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T. Miyatsu, M. Cheoun and K. Saito
Tue, 15 Feb 22
68/75

Comments: 11 pages, 14 figures, 2 tables

Pasta phases in neutron stars under strong magnetic fields [CL]

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http://arxiv.org/abs/2202.05595


In the present work, we consider nuclear matter in the innermost crust of neutron stars under the presence of a strong magnetic field within the framework of a relativistic mean-field description. Two models with a different slope of the symmetry energy are considered in order to discuss the density-dependence of the equation of state on the crust structure. The non-homogeneous matter in $\beta$-equilibrium is described within the coexisting phases method, and the effect of including the anomalous magnetic moment is discussed. Five different geometries for the pasta structures are considered. It is shown that strong magnetic fields cause an extension of the inner crust of the neutron stars, with the occurrence of a series of disconnected non-homogeneous matter regions above the one existing for a null magnetic field. Moreover, we observed that in these disconnected regions, for some values of the magnetic field, all five different cluster geometrical shapes occur, and the gas density is close to the cluster density. Also, the pressure at the neutron star crust-core transition much larger than the pressure obtained for a zero magnetic field. Another noticeable effect of the presence of strong magnetic fields is the increase of the proton fraction, favoring the appearance of protons in the gas background.

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X. Wang, J. Li, J. Fang, et. al.
Mon, 14 Feb 22
33/55

Comments: 13 pages, 8 figures. Accepted for publication in PRD

Transport coefficients of magnetized neutron star cores [CL]

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http://arxiv.org/abs/2202.05794


We review the calculations of the kinetic coefficients (thermal conductivity, shear viscosity, momentum transfer rates) of the neutron star core matter within the framework of the Landau Fermi-liquid theory. We restrict ourselves to the case of normal (i.e. non-superfluid) matter. As an example we consider simplest $npe\mu$ composition of neutron star core matter. Utilizing the CompOSE database of dense matter equations of state and several microscopic interactions we analyze the uncertainties in calculations of the kinetic coefficients that result from the insufficient knowledge of the properties of the dense nuclear matter and suggest possible approximate treatment. In our study we also take into account non-quantizing magnetic field. The presence of magnetic field makes transport anisotropic leading to the tensor structure of kinetic coefficients. We find that the moderate ($B\lesssim 10^{12}$ G) magnetic field do not affect considerably thermal conductivity of neutron star core matter, since the latter is mainly governed by the electrically neutral neutrons. In contrast, shear viscosity is affected even by the moderate $B\sim 10^8 – 10^{10}$ G. Based on the in-vacuum nucleon interactions we provide practical expressions for calculation of transport coefficients for any equation of state of dense matter.

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P. Shternin and D. Ofengeim
Mon, 14 Feb 22
54/55

Comments: 53 pages, 12 figures; accepted for publication in European Physical Journal A

Quark deconfinement in compact stars through sexaquark condensation [CL]

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http://arxiv.org/abs/2202.05061


In this contribution, we present for the first time a scenario according to which early quark deconfinement in compact stars is triggered by the Bose-Einstein condensation (BEC) of a light sexaquark (S) with a mass $m_S<2054$ MeV, that has been suggested as a candidate particle to explain the baryonic dark matter in the Universe. The onset of S BEC marks the maximum mass of hadronic neutron stars and it occurs when the condition for the baryon chemical potential $\mu=m_S/2$ is fulfilled in the center of the star, corresponding to $M_{\rm onset}\lesssim 0.7~M_\odot$. In the gravitational field of the star the density of the BEC of the S increases until a new state of the matter is attained, where each of the S-states got dissociated into a triplet of color-flavor-locked (CFL) diquark states. These diquarks are the Cooper pairs in the color superconducting CFL phase of quark matter, so that the developed scenario corresponds to a Bose-Einstein condensation – Bardeen-Cooper-Schrieffer (BEC-BCS) transition in strongly interacting matter. For the description of the CFL phase, we develop here for the first time the three-flavor extension of the density-functional formulation of a chirally symmetric Lagrangian model of quark matter where confining properties are encoded in a divergence of the scalar self-energy at low densities and temperatures.

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D. Blaschke, O. Ivanytskyi and M. Shahrbaf
Fri, 11 Feb 22
35/71

Comments: 26 pages, 8 figures, Contribution to the Book “New Phenomena and New States of Matter in the Universe. From Quarks to Cosmos” edited by C. A. Z. Vasconcellos, P. O. Hess and T. Boller

Landau parameters and entrainment matrix of cold stellar matter: effect of the symmetry energy and strong magnetic fields [CL]

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http://arxiv.org/abs/2202.05231


Nuclear matter properties based on a relativistic approach suitable for the description of multi-component systems are calculated. We use a set of nuclear relativistic mean-field models that satisfy acceptable nuclear matter properties and neutron star observations. The effects of the density dependence of the symmetry energy and of the Landau quantization due to the presence of a strong external magnetic field are discussed. Properties such as the proton fraction, the Landau mass, Landau parameters and entrainment matrix, the adiabatic index and speed of sound are calculated for cold $\beta$-equilibrium matter. A large dispersion on the calculated properties is obtained at two to three times saturation density $\rho_0 $. The proton Landau mass can be as low as one third of the vacuum nucleon mass at 2-3$~\rho_0 $. Similar effects are obtained for the Landau parameters, in particular, the ones involving protons, where the relative dispersion of $F^0_{pp}$ and $F^1_{pp}$ is as high as 30\% to 50\% at 2-3$~\rho_0 $. These parameters are particularly sensitive to the symmetry energy. The effect of the magnetic field on the nuclear properties is small for fields as high as 10$^{18}$G except for a small range of densities just above the crust-core transition. Tables with the EoS, and the parameters, are provided in the Supplementary Material section.

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H. Pais, O. Ivanytskyi and C. Providência
Fri, 11 Feb 22
40/71

Comments: 26 pages, 10 figures

Chiral condensates for neutron stars in hadron-quark crossover; from a parity doublet nucleon model to an NJL quark model [CL]

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http://arxiv.org/abs/2202.04873


In this contribution, we summarize our recent studies on the chiral invariant mass and the chiral condensates in neutron star matter. We construct a unified equations of state assuming the crossover phase transition from hadronic matter described by a parity doublet model to quark matter by an Nambu–Jona-Lasinio type quark model. We first show that the chiral invariant mass is constrained to be 600 MeV $\lesssim m_0 \lesssim$ 900 MeV from recent observations of neutron stars. We then determine the density dependence of the chiral condensate in the crossover description, and show that the chiral condensates are actually smoothly connected from the hadronic matter where the change is driven by the positive chiral scalar charge in a nucleon, to the quark matter where the change is by the modification of the quark Dirac sea, reflecting the hadron-quark crossover.

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T. Minamikawa, T. Kojo and M. Harada
Fri, 11 Feb 22
64/71

Comments: N/A

Thermal effects on tidal deformability in the last orbits of an inspiraling binary neutron star system [HEAP]

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http://arxiv.org/abs/2202.01820


The study of binary neutron stars mergers by the detection of the emitted gravitational waves is one of the most promised tools to study the properties of dense nuclear matter at high densities. It is worth claiming that, at the moment, strong evidence that the temperature of the stars is zero during the last orbits before coalescing, does not exist. Nevertheless, theoretical studies suggest that the temperature concerning the inspiral phase, could reach even a few MeV. According to the main theory, tides transfer mechanical energy and angular momentum to the star at the expense of the orbit, where friction within the star converts the mechanical energy into heat. During the inspiral, these effects are potentially detectable. Different treatments have been used to estimate the transfer of the mechanical energy and the size of the tidal friction, leading to different conclusions about the importance of pre-merger tidal effects. The present work is dedicated to the study of the effect of temperature on the tidal deformability of neutron stars during the inspiral of a neutron star system just before the merger. We applied a class of hot equations of state, both isothermal and adiabatic, originated from various nuclear models. We found that even for low values of temperature ($T<1$ MeV), the effects on the basic ingredients of tidal deformability are not negligible. On the other hand, in the case of the adiabatic star, the thermal effects on tidal deformability remain imperceptible, up to the value $S=0.2 \ {\rm k}_{B}$. According to the main finding, the effect of the temperature on the tidal deformability is indistinguishable. The consequences of the above result are discussed and analyzed.

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A. Kanakis-Pegios, P. Koliogiannis and C. Moustakidis
Mon, 7 Feb 22
36/46

Comments: v1: 9 pages, 7 figures, 2 tables

Constraints on the merging binary neutron star mass distribution and equation of state based on the fraction of jets [HEAP]

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http://arxiv.org/abs/2202.01656


A relativistic jet has been produced in the single well-localised binary neutron star (BNS) merger detected to date in gravitational waves (GWs), and the local rates of BNS mergers and short gamma-ray bursts are of the same order of magnitude. This suggests that jet formation is not a rare outcome for BNS mergers, and we show that this intuition can be turned into a quantitative constraint: at least about $1/3$ of GW-detected BNS mergers, and at least about $1/5$ of all BNS mergers, should produce a successful jet (90\% credible level). Whether a jet is launched depends on the properties of the merger remnant and of the surrounding accretion disc, which in turn are a function of the progenitor binary masses and equation of state (EoS). The fraction of jets in the population therefore carries information about the binary component mass distribution and EoS. Under the assumption that a jet can only be produced by a black hole remnant surrounded by a non-negligible accretion disc, we show how the jet fraction can be used to place a joint constraint on the space of BNS component mass distributions and EoS. The result points to a broad mass distribution, with particularly strong support for masses in the $1.3-1.6\,\mathrm{M_\odot}$ range. The constraints on the EoS are shallow, but we show how they will tighten as the knowledge on the jet fraction and mass distribution improve. We also discuss how to extend the method to include future BNS events, with possibly uncertain jet associations.

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O. Salafia, A. Colombo, F. Gabrielli, et. al.
Fri, 4 Feb 22
1/65

Comments: 16 pages, 17 figures, submitted to A&A. Comments and suggestions (inlcuding citation requests) are welcome!

Quasi-normal g-modes of neutron stars with quarks [CL]

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http://arxiv.org/abs/2202.01403


Quasi-normal oscillation modes of neutron stars provide a means to probe their interior composition using gravitational wave astronomy. We compute the frequencies and damping times of composition-dependent core g-modes of neutron stars containing quark matter employing linearized perturbative equations of general relativity. We find that ignoring background metric perturbations due to the oscillating fluid, as in the Cowling approximation, underestimates the g-mode frequency by up to 10% for higher mass stars, depending on the parameters of the nuclear equation of state and how the mixed phase is constructed. The g-mode frequencies are well-described by a linear scaling with the central lepton (or combined lepton and quark) fraction for nucleonic (hybrid) stars. Our findings suggest that neutron stars with and without quarks are manifestly different with regards to their quasi-normal g-mode spectrum, and may thus be distinguished from one another in future observations of gravitational waves from merging neutron stars.

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T. Zhao, C. Constantinou, P. Jaikumar, et. al.
Fri, 4 Feb 22
26/65

Comments: 14 pages, 10 figures

Formulating bulk viscosity for neutron star simulations [HEAP]

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http://arxiv.org/abs/2202.01576


In order to extract the precise physical information encoded in the gravitational and electromagnetic signals from powerful neutron-star merger events, we need to include as much of the relevant physics as possible in our numerical simulations. This presents a severe challenge, given that many of the involved parameters are poorly constrained. In this paper we focus on the role of nuclear reactions. Combining a theoretical discussion with an analysis connecting to state-of-the-art simulations, we outline multiple arguments that lead to a reactive system being described in terms of a bulk viscosity. The results demonstrate that in order to properly account for nuclear reactions, future simulations must be able to handle different regimes where rather different assumptions/approximations are appropriate. We also touch upon the link to models based on the large-eddy-strategy required to capture turbulence.

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T. Celora, I. Hawke, P. Hammond, et. al.
Fri, 4 Feb 22
35/65

Comments: N/A

Neutrino Astronomy with IMB, Kamiokande and Super Kamiokande [HEAP]

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http://arxiv.org/abs/2202.01676


Some of the earliest work on neutrino astronomy was accomplished by a class of underground detectors primarily designed for particle physics goals . These detectors used inexpensive water to obtain the large masses needed to observe the very low interaction rates expected from neutrinos. They exploited the relatively large light attenuation length and the index of refraction of the water to get a very inexpensive cost per thousand tons of detector.
The results obtained from these pioneering neutrino detectors have included real time observation of solar neutrinos, supernova neutrinos, and atmospheric neutrinos. Searches for neutrino point sources, dark matter and primordial magnetic monopoles were also made using them.

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J. LoSecco
Fri, 4 Feb 22
65/65

Comments: To be published in Neutrino Physics and Astrophysics, edited by F. W. Stecker, in the Encyclopedia of Cosmology II, edited by G. G. Fazio, World Scientific Publishing Company, Singapore, 2022. 41 pages, 31 figures

Sexaquark dilemma in neutron stars and its solution by quark deconfinement [CL]

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http://arxiv.org/abs/2202.00652


Following the idea that a stable sexaquark state with quark content (uuddss) would have gone unnoticed by experiment so far and that such a particle would be a good dark matter candidate, we investigate the possible role of a stable sexaquark in the physics of compact stars given the stringent constraints on the equation of state that stem from observations of high mass pulsars and GW170817 bounds on the compactness of intermediate mass stars. We find that there is a “sexaquark dilemma” (analogous to the hyperon dilemma) for which the dissociation of the sexaquark in quark matter is a viable solution fulfilling all present constraints from multi-messenger astronomy. The parameters needed to model the hybrid star including sexaquarks are in line with parameters of pre-existing quark- and hadronic-matter models. We find that current constraints — tidal deformability in accordance with GW170817 and maximum mass above the lower limit from PSR J0740+6620 — can be satisfied two ways: with early quark deconfinement such that neither sexaquarks nor hyperons are present in any NS interiors, or with later deconfinement such that a neutron-sexaquark shell surrounds the inner quark matter core.

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M. Shahrbaf, D. Blaschke, S. Typel, et. al.
Wed, 2 Feb 22
11/60

Comments: 21 pages, 15 figures, 4 tables

Evolutions in first-order viscous hydrodynamics [CL]

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http://arxiv.org/abs/2201.13359


Motivated by the physics of the quark-gluon plasma created in heavy-ion collision experiments, we use holography to study the regime of applicability of various theories of relativistic viscous hydrodynamics. Using the microscopic description provided by holography of a system that relaxes to equilibrium, we obtain initial data with which we perform real-time evolutions in 2+1 dimensional conformal fluids using the first-order viscous relativistic hydrodynamics theory of Bemfica, Disconzi, Noronha and Kovtun (BDNK), BRSSS and ideal hydrodynamics. By initializing the hydrodynamics codes at different times, we can check the constitutive relations and assess the predictive power and accuracy of each of these theories.

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H. Bantilan, Y. Bea and P. Figueras
Tue, 1 Feb 22
5/73

Comments: 6 pages plus appendixes, 8 figures