How Well Do We Know The Supernova Equation of State? [CL]

We give an overview about equations of state (EOS) which are currently available for simulations of core-collapse supernovae and neutron star mergers. A few selected important aspects of the EOS, such as the symmetry energy, the maximum mass of neutron stars, and cluster formation, are confronted with constraints from experiments and astrophysical observations. There are just very few models which are compatible even with this very restricted set of constraints. These remaining models illustrate the uncertainty of the uniform nuclear matter EOS at high densities. In addition, at finite temperatures the medium modifications of nuclear clusters represent a conceptual challenge. In conclusion, there has been significant development in the recent years, but there is still need for further improved general purpose EOS tables.

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M. Hempel, M. Oertel, S. Typel, et. al.
Mon, 13 Mar 17

Comments: 6 pages, 1 table, 1 figure; proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016)


High-mass twin stars with a multi-polytrope EoS [CL]

We show that in the 3-polytropes model of Hebeler et al. \cite{Hebeler:2013nza} for the neutron star equation of state at supersaturation densities a third family of compact stars can be obtained which confirms the possibility of high-mass twin stars that have coincident masses $M_1=M_2\approx 2~M_\odot$ and significantly different radii $|R_1-R_2|>2-3 $ km. We consider a scenario of a first order phase transition which eliminates one of the three polytropes from the star structure and results in a sharp boundary between a high-density and low-density phase.

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D. Alvarez-Castillo and D. Blaschke
Thu, 9 Mar 17

Comments: 4 pages, 2 figures, 1 table

Quantum Nuclear Pasta and Nuclear Symmetry Energy [CL]

Complex and exotic nuclear geometries are expected to appear naturally in dense nuclear matter found in the crust of neutron stars and supernovae environment collectively referred to as nuclear pasta. The pasta geometries depend on the average baryon density, proton fraction and temperature and are critically important in the determination of many transport properties of matter in supernovae and the crust of neutron stars. Using a set of self-consistent microscopic nuclear energy density functionals we present the first results of large scale quantum simulations of pasta phases at baryon densities $0.03 \leq \rho \leq 0.10$ fm$^{-3}$, proton fractions $0.05 \leq Y_p \leq 0.40$, and zero temperature. The full quantum simulations, in particular, allow us to thoroughly investigate the role and impact of the nuclear symmetry energy on pasta configurations. We use the Sky3D code that solves the Skyrme Hartree-Fock equations on a three-dimensional Cartesian grid. For the nuclear interaction we use the state of the art UNEDF1 parametrization, which was introduced to study largely deformed nuclei, hence is suitable for studies of the nuclear pasta. Density dependence of the nuclear symmetry energy is simulated by tuning two purely isovector observables that are insensitive to the current available experimental data. We find that a minimum total number of nucleons $A=2000$ is necessary to prevent the results from containing spurious shell effects and to minimize finite size effects. We find that a variety of nuclear pasta geometries are present in the neutron star crust and the result strongly depends on the nuclear symmetry energy. The impact of the nuclear symmetry energy is less pronounced as the proton fractions increase. Quantum nuclear pasta calculations at $T=0$ MeV are shown to get easily trapped in meta-stable states, and possible remedies to avoid meta-stable solutions are discussed.

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F. Fattoyev, C. Horowitz and B. Schuetrumpf
Tue, 7 Mar 17

Comments: 23 pages, 18 figures, 8 tables

Pinning down the superfluid and nuclear equation of state and measuring neutron star mass using pulsar glitches [HEAP]

Pulsars are rotating neutron stars that are renowned for their timing precision, although glitches can interrupt the regular timing behavior when these stars are young. Glitches are thought to be caused by interactions between normal and superfluid matter in the star. We update our recent work on a new technique using pulsar glitch data to constrain superfluid and nuclear equation of state models, demonstrating how current and future astronomy telescopes can probe fundamental physics such as superfluidity near nuclear saturation and matter at supranuclear densities. Unlike traditional methods of measuring a star’s mass by its gravitational effect on another object, our technique relies on nuclear physics knowledge and therefore allows measurement of the mass of pulsars which are in isolation.

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W. Ho, C. Espinoza, D. Antonopoulou, et. al.
Mon, 6 Mar 17

Comments: 4 pages, 4 figures; proceedings of Nuclei in the Cosmos 2016 in Niigata, Japan, S. Kubono (ed.)

Constructing a neutron star in G2-QCD [HEAP]

The inner structure of neutron stars is still an open question. To make progress and understand the qualitative impact of gauge interactions on the neutron star structure we study neutron stars in a modified version of QCD. In this modification the gauge group of QCD is replaced by the exceptional Lie group G$_2$, which has neutrons and is accessible at finite density in lattice calculations. Using an equation of state constructed from lattice calculations we determine the mass-radius-relation for a neutron star in this theory using the Tolman-Oppenheimer-Volkoff equation. The results exhibit an influence of the non-trivial interactions on the mass-radius relation. However, the masses of the quarks are found to have little influence. We also give density profiles and the phase structure inside the neutron star. If the results carry over to full QCD, much of the internal structure of neutron stars could already be inferred from a precise measurement of the mass-radius relation.

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O. Hajizadeh and A. Maas
Wed, 1 Mar 17

Comments: (19 pages, 9 figures)

Neutrino Emission from Supernovae [HEAP]

Supernovae are the most powerful cosmic sources of MeV neutrinos. These elementary particles play a crucial role when the evolution of a massive star is terminated by the collapse of its core to a neutron star or a black hole and the star explodes as supernova. The release of electron neutrinos, which are abundantly produced by electron captures, accelerates the catastrophic infall and causes a gradual neutronization of the stellar plasma by converting protons to neutrons as dominant constituents of neutron star matter. The emission of neutrinos and antineutrinos of all flavors carries away the gravitational binding energy of the compact remnant and drives its evolution from the hot initial to the cold final state. The absorption of electron neutrinos and antineutrinos in the surroundings of the newly formed neutron star can power the supernova explosion and determines the conditions in the innermost supernova ejecta, making them an interesting site for the nucleosynthesis of iron-group elements and trans-iron nuclei. In this Chapter the basic neutrino physics in supernova cores and nascent neutron stars will be discussed. This includes the most relevant neutrino production, absorption, and scattering processes, elementary aspects of neutrino transport in dense environments, the characteristic neutrino emission phases with their typical signal features, and the perspectives connected to a measurement of the neutrino signal from a future galactic supernova.

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H. Janka
Wed, 1 Mar 17

Comments: Author version of chapter for ‘Handbook of Supernovae,’ edited by A. Alsabti and P. Murdin, Springer. 30 pages, 9 figures

Hybrid Quark Stars With Strong Magnetic Field [HEAP]

Discovery of huge magnetic field in magnetars has stimulated a renewed interest about the magnetic field and physics of compact stars, where microphysics such as QED or QCD may play active parts.
Here we discuss the equation of state (EOS) of quark matter in the core of compact stars by taking into account the strong magnetic field. We show that quark EOS becomes very stiff in the presence of the strong magnetic field, and becomes stiffest under the causality condition beyond the threshold strength of $B_c\sim O(10^{19})$ G. This is because quarks make the Landau levels in the presence of the magnetic field and thereby only the lowest Landau level is occupied in the extreme case beyond $B_c$. Thus quarks can freely move along the magnetic field with localization in the perpendicular plane, which resembles the quasi-one dimensional systems and gives rise to a stiff EOS. Consequently, we may easily produce high-mass stars beyond two solar mass.
As another interesting possibility, we discuss the appearance of the third family of compact stars, succeeding white dwarfs and neutron stars, before collapsing into black holes. We demonstrate an example, which is specified by a discontinuous increase of the adiabatic index at the hadron-quark phase transition. Such new family may affect the supernova explosions or the gravitational wave emitted from the neutron star mergers.

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T. Tatsumi and H. Sotani
Tue, 28 Feb 17

Comments: 8pages,5figures, Proc.of INPC 2016

Enforcing causality in nonrelativistic equations of state at finite temperature [HEAP]

We present a thermodynamically consistent method by which equations of state based on nonrelativistic potential models can be modified so that they respect causality at high densities, both at zero and finite temperature (entropy). We illustrate the application of the method using the high density phase parametrization of the well known APR model in its pure neutron matter configuration as an example. We also show that, for models with only contact interactions, the adiabatic speed of sound is independent of the temperature in the limit of very large temperature. This feature is approximately valid for models with finite-range interactions as well, insofar as the temperature dependence they introduce to the Landau effective mass is weak. In addition, our study reveals that in first principle nonrelativistic models of hot and dense matter, contributions from higher than two-body interactions must be screened at high density to preserve causality.

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C. Constantinou and M. Prakash
Fri, 24 Feb 17

Comments: 12 pages, 12 figures

The effect upon neutrinos of core-collapse supernova accretion phase turbulence [HEAP]

During the accretion phase of a core-collapse supernovae, large amplitude turbulence is generated by the combination of the standing accretion shock instability and convection driven by neutrino heating. The turbulence directly affects the dynamics of the explosion, but there is also the possibility of an additional, indirect, feedback mechanism due to the effect turbulence can have upon neutrino flavor evolution and thus the neutrino heating. In this paper we consider the effect of turbulence during the accretion phase upon neutrino evolution, both numerically and analytically. Adopting representative supernova profiles taken from the accretion phase of a supernova simulation, we find the numerical calculations exhibit no effect from turbulence. We explain this absence using two analytic descriptions: the Stimulated Transition model and the Distorted Phase Effect model. In the Stimulated Transition model turbulence effects depend upon six different lengthscales, and three criteria must be satisfied between them if one is to observe a change in the flavor evolution due to Stimulated Transition. We further demonstrate that the Distorted Phase Effect depends upon the presence of multiple semi-adiabatic MSW resonances or discontinuities that also can be expressed as a relationship between three of the same lengthscales. When we examine the supernova profiles used in the numerical calculations we find the three Stimulated Transition criteria cannot be satisfied, independent of the form of the turbulence power spectrum, and that the same supernova profiles lack the multiple semi-adiabatic MSW resonances or discontinuities necessary to produce a Distorted Phase Effect. Thus we conclude that even though large amplitude turbulence is present in supernova during the accretion phase, it has no effect upon neutrino flavor evolution.

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J. Kneller and M. Reyes
Fri, 24 Feb 17

Comments: N/A

The Core-Collapse Supernova Explosion Mechanism [SSA]

The explosion mechanism of core-collapse supernovae is a long-standing problem in stellar astrophysics. We briefly outline the main contenders for a solution and review recent efforts to model core-collapse supernova explosions by means of multi-dimensional simulations. We discuss several suggestions for solving the problem of missing or delayed neutrino-driven explosions in three-dimensional supernova models, including — among others — variations in the microphysics and large seed perturbations in convective burning shells. Focusing on the neutrino-driven mechanism, we summarise currents efforts to predict supernova explosion and remnant properties based on first-principle models and on more phenomenological approaches.

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B. Muller
Thu, 23 Feb 17

Comments: Invited review to appear in the International Astronomical Union Proceedings Serie (IAU Symposium 329, “The Lives and Death Throes of Massive Stars”). 8 pages, 2 figures

Quark-hadron Phase Transition in Proto-Neutron Stars Cores based on a Non-local NJL Model [HEAP]

We study the QCD phase diagram using a non-local SU(3) NJL model with vector interactions among quarks. We analyze several thermodynamic quantities such as entropy and specific heat, and study the influence of vector interactions on the thermodynamic properties of quark matter. Upon imposing electric charge neutrality and baryon number conservation on the field equations, we compute models for the equation of state of the inner cores of proto-neutron stars providing a non-local treatment of quark matter for astrophysics.

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G. Malfatti, G. Contrera, M. Orsaria, et. al.
Tue, 21 Feb 17

Comments: 4 pages, 2 figures. Contribution to the Proceedings of the VII International Workshop on Astronomy and Relativistic Astrophysics – IWARA 2016

Hot magnetized nuclear matter: Thermodynamic and Saturation Properties [CL]

We have used a realistic nuclear potential, AV18, and a many body technique, the lowest order constraint variational (LOCV) approach, to calculate the properties of hot magnetized nuclear matter. By investigating the free energy, spin polarization parameter, and symmetry energy, we have studied the temperature and magnetic field dependence of the saturation properties of magnetized nuclear matter. In addition, we have calculated the equation of state of magnetized nuclear matter at different temperatures and magnetic fields. It was found that the flashing temperature of nuclear matter decreases by increasing the magnetic field. In addition, we have studied the effect of the magnetic field on liquid gas phase transition of nuclear matter. The liquid gas coexistence curves, the order parameter of the liquid gas phase transition, and the properties of critical point at different magnetic fields have been calculated.

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Z. Rezaei and G. Bordbar
Tue, 21 Feb 17

Comments: 30 pages, 13 figures, 2 tables. Accepted for publication in European Physical Journal A

Highly magnetized neutron stars in a many-body forces formalism [CL]

In this work, we study the effects of different magnetic field configurations in neutron stars described by a many-body forces formalism (MBF model). The MBF model is a relativistic mean field formalism that takes into account many-body forces by means of a meson field dependence of the nuclear interaction coupling constants. We choose the best parametrization of the model that reproduces nuclear matter properties at saturation and also describes massive neutron stars. We assume matter to be in beta-equilibrium, charge neutral and at zero temperature. Magnetic fields are taken into account both in the equation of state and in the structure of the stars by the self-consistent solution of the Einstein-Maxwell equations. We assume a poloidal magnetic field distribution and calculate its effects on neutron stars, showing its influence on the gravitational mass and deformation of the stars.

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R. Gomes, B. Franzon, V. Dexheimer, et. al.
Tue, 21 Feb 17

Comments: Contribution to the Proceedings of the VII International Workshop on Astronomy and Relativistic Astrophysics – IWARA 2016

The population of highly magnetized neutron stars [CL]

In this work, we study the effects of strong magnetic field configurations on the population of neutron stars. The stellar matter is described within a relativistic mean field formalism which considers many-body force contributions in the scalar couplings. We choose the parametrization of the model that reproduces nuclear matter properties at saturation and also describes massive hyperon stars. Hadronic matter is modeled at zero temperature, in beta-equilibrium, charge neutral and populated by the baryonic octet, electrons and muons. Magnetic effects are taken into account in the structure of stars by the solution of the Einstein-Maxwell equations with the assumption of a poloidal magnetic field distribution. Our results show that magnetic neutron stars are populated essencialy by nucleons and leptons, due to the fact that strong magnetic fields decrease the central density of stars and, hence, supress the appearance of exotic particles.

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R. Gomes, V. Dexheimer, B. Franzon, et. al.
Tue, 21 Feb 17

Comments: Prepared for Conference “Compact Stars in the QCD phase diagram V” 23-27 May 2016 GSSI and LNGS (L’Aquila, Italy)

Rotation-driven phase transitions in the cores of pulsars [HEAP]

In this paper, we discuss the impact of rotation on the particle composition of rotating neutron stars (pulsars). Particular emphasis is put on the formation of quark matter during stellar spin-down, driven by continuous gravitational compression. Our study is based on modern models for the nuclear equation of state whose parameters are tightly constrained by nuclear data, neutron star masses, and the latest estimates of neutron star radii.

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R. Mellinger, F. Weber, W. Spinella, et. al.
Tue, 21 Feb 17

Comments: 7 pages, 5 figures; Paper presented at the 7th International Workshop on Astronomy and Relativistic Astrophysics, Gramado, Rio Grande do Sul, Brazil, October 9 – 13, 2016

Nuclear equation of state for core-collapse supernova simulations with realistic nuclear forces [CL]

A new table of the nuclear equation of state (EOS) based on realistic nuclear potentials is constructed for core-collapse supernova numerical simulations. Adopting the EOS of uniform nuclear matter constructed by two of the present authors with the cluster variational method starting from the Argonne v18 and Urbana IX nuclear potentials, the Thomas-Fermi calculation is performed to obtain the minimized free energy of a Wigner-Seitz cell in non-uniform nuclear matter. As a preparation for the Thomas-Fermi calculation, the EOS of uniform nuclear matter is modified so as to remove the effects of deuteron cluster formation in uniform matter at low densities. Mixing of alpha particles is also taken into account following the procedure used by Shen et al. (1998, 2011). The critical densities with respect to the phase transition from non-uniform to uniform phase with the present EOS are slightly higher than those with the Shen EOS at small proton fractions. The critical temperature with respect to the liquid-gas phase transition decreases with the proton fraction in a more gradual manner than in the Shen EOS. Furthermore, the mass and proton numbers of nuclides appearing in non-uniform nuclear matter with small proton fractions are larger than those of the Shen EOS. These results are consequences of the fact that the density derivative coefficient of the symmetry energy of our EOS is smaller than that of the Shen EOS.

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H. Togashi, K. Nakazato, Y. Takehara, et. al.
Mon, 20 Feb 17

Comments: 40 pages, 15 figures, accepted for publication in Nuclear Physics A. The EOS table constructed in this study is available on the Web at this http URL

Ab initio calculations of the isotopic dependence of nuclear clustering [CL]

Nuclear clustering describes the appearance of structures resembling smaller nuclei such as alpha particles (4He nuclei) within the interior of a larger nucleus. While clustering is important for several well-known examples, little is known about the general nature of clustering in nuclei. In this letter we present lattice Monte Carlo calculations based on chiral effective field theory for the ground states of helium, beryllium, carbon, and oxygen isotopes. By computing model-independent measures that probe three- and four-nucleon correlations at short distances, we determine the effective number of alpha clusters in any nucleus as well as their shape compared to alpha particles in vacuum. We also introduce a new computational approach called the pinhole algorithm, which solves a long-standing deficiency of auxiliary-field Monte Carlo simulations in computing density correlations relative to the center of mass. We use the pinhole algorithm to determine the proton and neutron density distributions and the geometry of cluster correlations in 12C, 14C, and 16C. The structural similarities among the carbon isotopes suggest that 14C and 16C have excitations analogous to the well-known Hoyle state resonance in 12C.

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S. Elhatisari, E. Epelbaum, H. Krebs, et. al.
Mon, 20 Feb 17

Comments: 5 + 9 pages (main + supplemental materials), 4 + 6 figures (main + supplemental materials)

The cosmological CP odd axion field as the coherent Berry's phase of the Universe [CL]

We study a testable dark matter (DM) model outside of the standard WIMP paradigm. The model is unique in a sense that the observed ratio $\Omega_{\rm dark} \simeq \Omega_{\rm visible}$ for visible and dark matter densities finds its natural explanation as a result of their common QCD origin when both types of matter (DM and visible) are formed during the QCD transition and both are proportional to single dimensional parameter of the system, $\Lambda_{\rm QCD}$. The focus of the present work is the detail study of the dynamics of the $\cal{CP}$-odd coherent axion field $a(x)$ just before the QCD transition. We argue that the baryon charge separation effect on the largest possible scales inevitably occurs as a result of merely existence of the coherent axion field in early Universe. It leads to preferential formation of one species of nuggets on the scales of the visible Universe where the axion field $a(x)$ is coherent. A natural outcome of this preferential evolution is that only one type of the visible baryons (not anti- baryons) remains in the system after the nuggets complete their formation. This represents a specific mechanism on how the baryon charge separation mechanism (when the Universe is neutral, but visible part of matter consists the baryons and not anti-baryons) replaces the conventional “baryogenesis” proposals.
The rare events of annihilation of the anti-nuggets with visible matter lead to a number of observable effects, which are consistent with all known astrophysical, cosmological, satellite and ground based constraints. Furthermore, there is a number of frequency bands where some excess of emission was observed, and this model may explain some portion, or even entire excess of the observed radiation in these frequency bands. We also comment on implications of these studies for the axion search experiments.

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S. Ge, X. Liang and A. Zhitnitsky
Thu, 16 Feb 17

Comments: 23 pages, 4 figures

Transport coefficients of two-flavor quark matter from the Kubo formalism [CL]

The transport coefficients of quark matter at non-zero chemical potential and temperature are computed within the two-flavor Nambu–Jona-Lasinio model. We apply the Kubo formalism to obtain the thermal ($\kappa$) and electrical ($\sigma$) conductivities as well as an update of the shear viscosity ($\eta$) by evaluating the corresponding equilibrium two-point correlation functions to leading order in the $1/N_c$ expansion. The Dirac structure of the self-energies and spectral functions is taken into account as these are evaluated from the meson-exchange Fock diagrams for on-mass-shell quarks. We find that the thermal and electrical conductivities are decreasing functions of temperature and density above the Mott temperature $T_{\rm M}$ of dissolution of mesons into quarks, the main contributions being generated by the temporal and vector components of the spectral functions. The coefficients show a universal dependence on the ratio $T/T_{\rm M}$ for different densities, i.e., the results differ by a chemical-potential dependent constant. We also show that the Wiedemann-Franz law for the ratio $\sigma/\kappa$ does not hold. The ratio $\eta/s $, where $s$ is the entropy density, is of order of unity (or larger) close to the Mott temperature and, as the temperature increases, approaches the AdS/CFT bound $1/4\pi$. It is also conjectured that the ratio $\kappa T/c_V $, with $c_V$ being the specific heat, is bounded from below by $1/18$.

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A. Harutyunyan, D. Rischke and A. Sedrakian
Wed, 15 Feb 17

Comments: 24 pages, 19 figures, RevTeX format

Cooling of neutron stars with stiff stellar matter [HEAP]

Recent evidence for high masses ($\sim 2~ M_\odot$) pulsars PSR J1614-2230 and PSR J0348-0432 requires neutron star matter to have a stiff equation of state (EoS). The thermal evolution of compact stars (CS) with stiff hadronic EoS necessitates the application of the “nuclear medium cooling” scenario with a selection of appropriate proton gap profiles together with in-medium effects (like pion softening) on cooling mechanisms in order to achieve a satisfactory explanation of all existing observational data for the temperature-age relation of CS. Here we focus on two examples from \cite{Grigorian:2016leu} for a stiff hadronic EoS without (DD2 EoS) and with (DD2vex) excluded volume correction.

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H. Grigorian, D. Voskresensky and D. Blaschke
Tue, 7 Feb 17

Comments: 7 pages, 4 Figures, Contribution to the Proceedings of the International Conference on Critical Point and Onset of Deconfinement (CPOD’2016), Wroclaw, Poland, May 29 – June 5, 2016. arXiv admin note: text overlap with arXiv:1603.02634

Concurrent application of ANC and THM to assess the $^{13}{\rm C}(α,n)^{16}{\rm O}$ absolute cross section at astrophysical energies and possible consequences for neutron production in low-mass AGB stars [SSA]

The $^{13}{\rm C}(\alpha,n)^{16}{\rm O}$ reaction is considered to be the main neutron source responsible for the production of heavy nuclides (from ${\rm Sr}$ to ${\rm Bi}$) through slow $n$-capture nucleosynthesis ($s$-process) at low temperatures during the asymptotic giant branch (AGB) phase of low mass stars ($\lesssim 3-4\;{\rm M}_{\odot}$, or LMSs). In recent years, several direct and indirect measurements have been carried out to determine the cross section at the energies of astrophysical interest (around $190\pm40\;{\rm keV}$). However, they yield inconsistent results causing a highly uncertain reaction rate and affecting the neutron release in LMSs. In this work we have combined two indirect approaches, the asymptotic normalization coefficient (or ANC) and the Trojan Horse Method (THM), to unambiguously determine the absolute value of the $^{13}{\rm C}(\alpha,n)^{16}{\rm O}$ astrophysical factor. Therefore, we have determined a very accurate reaction rate to be introduced into astrophysical models of $s$-process nucleosynthesis in LMSs. Calculations using such recommended rate have shown limited variations in the production of those neutron-rich nuclei (with $86\leq A\leq 209$) receiving contribution only by slow neutron captures.

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O. Trippella and M. Cognata
Tue, 7 Feb 17

Comments: N/A

Bayesian analysis for a new class of hybrid EoS models using mass and radius data of compact stars [HEAP]

We present a Bayesian analysis for a new class of realistic models of two-phase equations of state (EoS) for hybrid stars and demonstrate that the observation of a pair of high-mass twin stars would have a sufficient discriminating power to favor hybrid EoS with a strong first order phase transition over alternative EoS. Such a measurement would provide evidence for the existence of a critical endpoint in the QCD phase diagram.

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A. Ayriyan, D. Alvarez-Castillo, S. Benic, et. al.
Mon, 6 Feb 17

Comments: 6 pages, 2 figures, 1 scheme, contribution to the Proceedings of the International Conference on Critical Point and Onset of Deconfinement (CPOD’2016), Wroclaw, Poland, May 29 – June 5, 2016

A self-consistent study of magnetic field effects on hybrid stars [HEAP]

It is understood that strong magnetic fields affect the structure of neutron stars. Nevertheless, many calculations for magnetized neutron stars are still being performed using symmetric solutions of Einstein’s equations. In this conference proceeding, we review why this is not the correct procedure and we also discuss the effects of magnetic fields on the stellar population and temperature profiles.

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V. Dexheimer, B. Franzon and S. Schramm
Thu, 2 Feb 17

Comments: Prepared for Conference “Compact Stars in the QCD phase diagram V” 23-27 May 2016 GSSI and LNGS (L’Aquila, Italy)

The stifness of the supranuclear equation of state (once again) [CL]

We revisit the present status of the stiffness of the supranuclear equations of state, particularly the solutions that increase the stiffness in the presence of hyperons, the putative transition to a quark matter phase and the robustness of massive compact star observations.

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J. Horvath and R. Souza
Thu, 2 Feb 17

Comments: 6 pages, 5 figures. Prepared for the Proceedings of the Conference “Compact Stars in the QCD phase diagram V”, 23-27 May 2016 GSSI and LNGS, L’Aquila, Italy

Dependence of Weak Interaction Rates on Nuclear Composition during Stellar Core Collapse [HEAP]

We investigate the influences of the nuclear composition on the weak interaction rates of heavy nuclei during the core collapse of massive stars. The nuclear abundances in nuclear statistical equilibrium (NSE) are calculated by some equation of state (EOS) models including in-medium effects on nuclear masses. We systematically examine the sensitivities of electron capture and neutrino-nucleus scattering on heavy nuclei to the nuclear shell effects and the single nucleus approximation. We find that the washout of shell effects at high temperatures brings significant change to weak rates by smoothing the nuclear abundance distribution: the electron capture rate decreases by $\sim$ 20$\%$ in early phase and increases by $\sim$ 40$\%$ in late phase at most, while the cross section for neutrino-nucleus scattering is reduced by $\sim$ 15$\%$. This is because the open-shell nuclei become abundant instead of those with closed neutron shells as the shell effects disappear. We also find that the single-nucleus description based on the average values leads to underestimations of weak rates. Electron captures and neutrino coherent scattering on heavy nuclei are reduced by $\sim$ 80$\%$ in early phase and by $\sim$ 5$\%$ in the late phase, respectively. These results indicate that the NSE like EOS accounting for shell washout is indispensable for the reliable estimation of weak interaction rates in simulations of core-collapse supernovae.

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S. Furusawa, H. Nagakura, K. Sumiyoshi, et. al.
Tue, 31 Jan 17

Comments: 28 pages 14 figures, accepted for publication in Phys. Rev. C

Strangeon and Strangeon Star [HEAP]

The nature of pulsar-like compact stars is essentially a central question of the fundamental strong interaction (explained in quantum chromo-dynamics) at low energy scale, the solution of which still remains a challenge though tremendous efforts have been tried. This kind of compact objects could actually be strange quark stars if strange quark matter in bulk may constitute the true ground state of the strong-interaction matter rather than Fe^56 (the so-called Witten’s conjecture). From astrophysical points of view, however, it is proposed that strange cluster matter could be absolutely stable and thus those compact stars could be strange cluster stars in fact. This proposal could be regarded as a general Witten’s conjecture: strange matter in bulk could be absolutely stable, in which quarks are either free (for strange quark matter) or localized (for strange cluster matter). Strange cluster with three-light-flavor symmetry is renamed strangeon, being coined by combining “strange nucleon” for the sake of simplicity. A strangeon star can then be thought as a 3-flavored gigantic nucleus, and strangeons are its constituent as an analogy of nucleons which are the constituent of a normal (micro) nucleus. The observational consequences of strangeon stars show that different manifestations of pulsar-like compact stars could be understood in the regime of strangeon stars.

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X. Lai and R. Xu
Tue, 31 Jan 17

Comments: Proceedings CSQCD5, 23-27 May 2016 GSSI and LNGS (L’Aquila, Italy)

Surface tension of compressed, superheavy atoms [CL]

Based on the relativistic mean field theory and the Thomas-Fermi approximation, we study the surface properties of compressed, superheavy atoms. By compressed, superheavy atom we mean an atom composed by a superheavy nuclear core (superheavy nucleus) with mass number of the order of $10^4$, and degenerate electrons that neutralize the system. Some electrons penetrate into the superheavy nuclear core and the rest surround it up to a distance that depends upon the compression level. Taking into account the strong, weak, and electromagnetic interactions, we numerically study the structure of compressed, superheavy atoms and calculate the nuclear surface tension and Coulomb energy. We analyze the influence of the electron component and the background matter on the nuclear surface tension and Coulomb energy of compressed, superheavy atoms. We also compare and contrast these results in the case of compressed, superheavy atoms with phenomenological results in nuclear physics and the results of the core-crust interface of neutron stars with global charge neutrality. Based on the numerical results we study the instability against Bohr-Wheeler surface deformations in the case of compressed, superheavy atoms. The results in this article show the possibility of the existence of such compressed, superheavy atoms, and provide the evidence of strong effects of the electromagnetic interaction and electrons on the structure of compressed, superheavy atoms.

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J. Rueda, Y. Wu and S. Xue
Mon, 30 Jan 2017

Comments: 14 pages, 6 figures. arXiv admin note: text overlap with arXiv:1305.1974

Quark Deconfinement in Rotating Neutron Stars [HEAP]

In this paper, we use a three flavor non-local Nambu–Jona-Lasinio (NJL) model, an~improved effective model of Quantum Chromodynamics (QCD) at low energies, to investigate the existence of deconfined quarks in the cores of neutron stars. Particular emphasis is put on the possible existence of quark matter in the cores of rotating neutron stars (pulsars). In contrast to non-rotating neutron stars, whose particle compositions do not change with time (are frozen in), the type and structure of the matter in the cores of rotating neutron stars depends on the spin frequencies of these stars, which opens up a possible new window on the nature of matter deep in the cores of neutron stars. Our study shows that, depending on mass and rotational frequency, up to around 8% of the mass of a massive neutron star may be in the mixed quark-hadron phase, if the phase transition is treated as a Gibbs transition. We also find that the gravitational mass at which quark deconfinement occurs in rotating neutron stars varies quadratically with spin frequency, which can be fitted by a simple formula.

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R. Mellinger, F. Weber, W. Spinella, et. al.
Thu, 26 Jan 17

Comments: 16 pages, 6 figures

Impacts of nuclear-physics uncertainty in stellar temperatures on the s-process nucleosynthesis [SSA]

We evaluated the uncertainty relevant to s-process nucleosynthesis using a Monte-Carlo centred approach. We are based on a realistic and general prescription of temperature dependent uncertainty for the reactions. We considered massive stars for the weak s-process and AGB stars for the main s-process. We found that the adopted uncertainty for (n,$\gamma$) rates, tens of per cent on average, affect the production of s-process nuclei along the $\beta$-stability line, while for $\beta$-decay, for which contributions from excited states enhances the uncertainty, has the strongest impact on branching points.

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N. Nishimura, G. Cescutti, R. Hirschi, et. al.
Wed, 25 Jan 17

Comments: 3 pages, 3 figures, to be published in the Proceedings of “the 14th International Symposium on Nuclei in the Cosmos (NIC-XIV)”; see arXiv:1701.00489, for the completed results

Fast neutrino conversions: Ubiquitous in compact binary merger remnants [HEAP]

The massive neutron star (NS) or black hole (BH) accretion disk resulting from NS-NS or NS-BH mergers is dense in neutrinos. We present the first study on the role of angular distributions in the neutrino flavor conversion above the remnant disk. In particular, we focus on “fast” pairwise conversions whose rate depends on the local angular intensity of the electron lepton number carried by neutrinos. Because of the emission geometry and the flux density of $\bar{\nu}_e$ being larger than that of $\nu_e$, fast conversions prove to be a generic phenomenon in NS-NS and NS-BH mergers for physically motivated disturbances in the mean field of flavor coherence. Our findings could have major consequences on the jet dynamics and on the synthesis of elements above the remnant disk.

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M. Wu and I. Tamborra
Wed, 25 Jan 17

Comments: 7 pages, 6 figures

Probing the possibility of hotspots on the central neutron star in HESS J1731-347 [HEAP]

The X-ray spectra of the neutron stars located in the centers of supernova remnants Cas A and HESS J1731-347 are well fit with carbon atmosphere models. These fits yield plausible neutron star sizes for the known or estimated distances to these supernova remnants. The evidence in favor of the presence of a pure carbon envelope at the neutron star surface is rather indirect and is based on the assumption that the emission is generated uniformly by the entire stellar surface. Although this assumption is supported by the absence of pulsations, the observational upper limit on the pulsed fraction is not very stringent. In an attempt to quantify this evidence, we investigate the possibility that the observed spectrum of the neutron star in HESS J1731-347 is a combination of the spectra produced in a hydrogen atmosphere of the hotspots and of the cooler remaining part of the neutron star surface. The lack of pulsations in this case has to be explained either by a sufficiently small angle between the neutron star spin axis and the line of sight, or by a sufficiently small angular distance between the hotspots and the neutron star rotation poles. As the observed flux from a non-uniformly emitting neutron star depends on the angular distribution of the radiation emerging from the atmosphere, we have computed two new grids of pure carbon and pure hydrogen atmosphere model spectra accounting for Compton scattering. Using new hydrogen models, we have evaluated the probability of a geometry that leads to a pulsed fraction below the observed upper limit to be about 8.2 %. Such a geometry thus seems to be rather improbable but cannot be excluded at this stage.

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V. Suleimanov, D. Klochkov, J. Poutanen, et. al.
Tue, 24 Jan 17

Comments: 8 pages, 14 figures. Accepted for publication in A&A

(No) neutron star maximum mass constraint from hypernuclei [CL]

(Abridged) The recent measurement of the mass of two $2\, M_\odot$ pulsars has raised the question whether such large masses allow for the existence of exotic degrees of freedom, such as hyperons, inside neutron stars. In the present work we will investigate how the existing hypernuclei properties may constrain the neutron star equation of state and confront the neutron star maximum masses obtained with equations of state calibrated to hypernuclei properties with the astrophysical $2\,M_\odot$ constraint.
The study is performed using a relativistic mean field approach to describe both the hypernuclei and the neutron star equations of state. A set of five models consistent with $2\,M_\odot$ for a purely nucleonic composition are employed. The $\Lambda$-meson couplings are determined for all the models considered. Hyperonic stars with the complete baryonic octet are studied, restricting the coupling of the $\Sigma$ and $\Xi$ hyperons to the $\omega-$, $\rho-$ and $\sigma-$mesons due to the lack of experimental data, and maximum star masses calculated for unified equations of state. We conclude that the currently available hypernuclei experimental data and the lack of constraints on the asymmetric equation of state of nuclear matter at high densities do not allow to further constrain the neutron star matter equation of state using the recent $2\, M_\odot$ observations. It is also shown that the $\Lambda$ potential in symmetric nuclear matter takes a value $\sim 30-32$ MeV at saturation for the $g_{\omega \Lambda}$ coupling given by the SU(6) symmetry, close to values generally used in the literature. However, the $\Lambda$ potential in $\Lambda$ matter varies between -16 and -8 MeV taking for vector mesons couplings the SU(6) values, at variance with generally employed values between $-1$ and $-5$ MeV.

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M. Fortin, S. Avancini, C. Providencia, et. al.
Tue, 24 Jan 17

Comments: N/A

Quark matter with strong magnetic field and possibility of the third family of compact stars [HEAP]

We consider the possibility for the existence of the third family of compact objects, considering the effect of strong magnetic fields inside the hybrid stars. As a result, we demonstrate such new sequences of stable equilibrium configurations for some hadronic equations of state. Through the analysis of the adiabatic index inside stars, we find the conditions for appearing the third family of compact objects, i.e., for hadronic stars without quarks, that the maximum mass should be small, the central density for the maximum mass should be also small, and the radius for the the maximum mass should be large. Even for soft hadronic equations of state, the two solar-mass stars might survive as the third family of compact objects, once quark matter with strong magnetic field, such as $\sim {\cal O}(10^{19} {\rm G})$, is taken into account. It might give a hint to solve the so-called hyperon puzzle in nuclear physics.

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H. Sotani and T. Tatsumi
Tue, 24 Jan 17

Comments: accepted for publication in MNRAS

Effect of nuclear saturation parameters on possible maximum mass of neutron stars [HEAP]

In order to systematically examine the possible maximum mass of neutron stars, which is one of the important properties characterizing the physics in high-density region, I construct neutron star models by adopting phenomenological equations of state with various values of nuclear saturation parameters for low-density region, which are connected to the equation of state for high-density region characterized by the possible maximum sound velocity in medium. I derive an empirical formula for the possible maximum mass of neutron star. If massive neutron stars are observed, it could be possible to get a constraint on the possible maximum sound velocity for high-density region.

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H. Sotani
Mon, 23 Jan 17

Comments: accepted for publication in PRC

Quasi-Particle Quark-Nuclear Hybrid EoS with Excluded Volume Effects [HEAP]

A two-phase description of the quark-nuclear matter hybrid equation of state that takes into account the effect of excluded volume in both the hadronic and the quark-matter phases is introduced.
The nuclear phase manifests a reduction of the available volume as density increases, leading to a stiffening of the matter. The quark-matter phase displays a reduction of the effective string-tension in the confining density-functional from available volume contributions. The nuclear equation of state is based upon the relativistic density functional model DD2 with excluded volume. The quark-matter is based upon a mean-field modification to the free fermi gas and will be discussed in greater detail. The interactions are decomposed into mean scalar and vector components. The scalar interaction is motivated by a string potential between quarks, whereas the vector interaction potential is motivated by higher-order interactions of quarks leading to an increased stiffening at high densities. As an application, we consider matter under compact star constraints of electric neutrality and $\beta$-equilibrium. We obtain mass-radius relations for hybrid stars that form a third family, disconnected from the purely hadronic star branch, and fulfill the $2M_\odot$ constraint.

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M. Kaltenborn, N. Bastian and D. Blaschke
Tue, 17 Jan 17

Comments: 11 pages, 16 figures

Upper limit set by causality on the tidal deformability of a neutron star [CL]

A principal goal of gravitational-wave astronomy is to constrain the neutron star equation of state (EOS) by measuring the tidal deformability of neutron stars. The tidally induced departure of the waveform from that of point-particle (or spinless binary black hole (BBH)) increases with the stiffness of the EOS. We show that causality (the requirement that the speed of sound is less than the speed of light for a perfect fluid satisfying a one-parameter equation of state) places an upper bound on tidal deformability as a function of mass. Like the upper mass limit, the limit on deformabity is obtained by using an EOS with $v_{sound} = c$ for high densities and matching to a low density (candidate) EOS at a matching density of order nuclear saturation density. We use these results and those of [B.D. Lackey et al., Phys. Rev. D 89, 043009 (2014)] to estimate the resulting upper limit on the gravitational-wave phase shift of a black hole-neutron star (BHNS) binary relative to a BBH. Even for assumptions weak enough to allow an maximum mass of $4\ M_\odot$ (a match at nuclear saturation density to an unusually stiff low-density candidate EOS), the upper limit on dimensionless tidal deformability is stringent. It leads to a still more stringent estimated upper limit on the maximum tidally induced phase shift prior to merger. We comment in an appendix on the relation between causality, the condition $v_{sound} < c$, and the condition $dp/d\epsilon < 1$ for the effective EOS governing the equilibrium star.

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E. Oeveren and J. Friedman
Tue, 17 Jan 17

Comments: 24 pages, 10 figures

Rotating NSs/QSs and recent astrophysical observations [HEAP]

Both fast and slow configurations of rotating neutron stars (NSs) are studied with the recently-constructed unified NS EoSs. The calculations for pure quark stars (QSs) and hybrid stars (HSs) are also done, using several updated quark matter EoSs and Gibbs construction for obtaining hadron-quark mixed phase. All three types of EoSs fulfill the recent 2-solar-mass constrain. By confronting the glitch observations with the theoretical calculations for the crustal moment of inertia (MoI), we find that the glitch crisis is still present in Vela-like pulsars. An upcoming accurate MoI measurement (eg., a possible 10\% accuracy for pulsar PSR J0737-3039A) could distinguish QSs from NSs, since the MoIs of QSs are generally $> \sim 1.5 $ times larger than NSs and HSs, no matter the compactness and the mass of the stars. Using tabulated EoSs, we compute stationary and equilibrium sequences of rapidly rotating, relativistic stars in general relativity from the well-tested $rns$ code, assuming the matter comprising the star to be a perfect fluid. All three observed properties of the short gamma-ray bursts (SGRBs) internal plateaus sample are simulated using the rotating configurations of NSs/QSs as basic input. We finally argue that for some characteristic SGRBs, the post-merger products of NS-NS mergers are probably supramassive QSs rather than NSs, and NS-NS mergers are a plausible location for quark deconfinement and the formation of QSs.

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A. Li and J. Dong
Tue, 17 Jan 17

Comments: 8 pages, 6 figures, 3 tables, text slightly overlap with 1610.08770, 1606.02934, 1512.00340, 1503.02739, proceeding prepared for “Compact Stars in the QCD phase diagram V”, 23-27 May 2016 GSSI and LNGS, L’Aquila, Italy

The Sun as a probe of Fundamental Physics and Cosmology [CEA]

The high quality data provided by helioseismology, solar neutrino flux measurements, spectral determination of solar abundances, nuclear reactions rates coefficients among other experimental data, leads to the highly accurate prediction of the internal structure of the present Sun – the standard solar model. In this talk, I have discussed how the standard solar model, the best representation of the real Sun, can be used to study the properties of dark matter, for which two complementary approaches have been developed: – to limit the number of theoretical candidates proposed as the dark matter particles, this analysis complements the experimental search of dark matter, and – as a template for the study of the impact of dark matter in the evolution of stars, which possibly occurs for stellar populations formed in regions of high density of dark matter, such as stars formed in the centre of galaxies and the first generations of stars.

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I. Lopes
Tue, 17 Jan 17

Comments: 11 pages; 6 figures; Nuclear Physics in Astrophysics VI (NPA6)

Millisecond radio pulsars with known masses: parameter values and equation of state models [HEAP]

The recent fast growth of a population of millisecond pulsars with precisely measured mass provides an excellent opportunity to characterize these compact stars at an unprecedented level. This is because the stellar parameter values can be accurately computed for known mass and spin rate and an assumed equation of state (EoS) model. For each of the 16 such pulsars and for a set of EoS models from nucleonic, hyperonic, strange quark matter and hybrid classes, we numerically compute fast spinning stable stellar parameter values considering the full effect of general relativity. This first detailed catalogue of the computed parameter values of observed millisecond pulsars provides a testbed to probe the physics of compact stars, including their formation, evolution and EoS. We estimate uncertainties on these computed values from the uncertainty of the measured mass, which could be useful to quantitatively constrain EoS models. We note that the largest value of the central density $\rho_{\rm c}$ in our catalogue is $\sim 5.8$ times the nuclear saturation density $\rho_{\rm sat}$, which is much less than the expected maximum value $13 \rho_{\rm sat}$. We argue that the $\rho_{\rm c}$-values of at most a small fraction of compact stars could be much larger than $5.8 \rho_{\rm sat}$. Besides, we find that the constraints on EoS models from accurate radius measurements could be significantly biased for some of our pulsars, if stellar $spinning$ configurations are not used to compute the theoretical radius values.

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S. Bhattacharyya, I. Bombaci, D. Bandyopadhyay, et. al.
Mon, 16 Jan 17

Comments: 16 pages, 2 figures, 4 tables, accepted for publication in New Astronomy

Hyperon threshold and stellar radii [CL]

In this work we show how the emergence of a new degree of freedom in the nuclear bulk not only softens the EoS but reduces the radii of stars with high central density. If an enough repulsive channel, as the strange vector $\phi$ meson, is added to the scheme, we are able to simulate very massive and compact stars. Indeed we are able to construct an equation of state (EoS) that predicts a 2.05 $M_\odot$ as maximum mass and a radius of 11.51 km for the canonical 1.4$M_\odot$ in a thermodynamical consistent way. We also link the radii of the canonical stars to a soft EoS for densities not much above the nuclear saturation point. Moreover, comparing our EoS with results obtained from heavy ion collisions, we show that the presence of a new degree of freedom allows a better agreement between theory and experiment.

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L. Lopes and D. Menezes
Fri, 13 Jan 17

Comments: 10 pages, 14 figures

Reduced $E$1 $S$-factor of $^{12}$C($α$,$γ_0$)$^{16}$O [CL]

The astrophysical $S$-factor of $E$1 transition for $^{12}$C($\alpha$,$\gamma_0$)$^{16}$O is discussed in the $R$-matrix theory. The reduced $\alpha$-particle widths of the 1$^-_1$ ($E_x= 7.12$ MeV) and 1$^-_2$ ($E_x= 9.59$ MeV) states are extracted from the result of the potential model. The formal parameters are obtained without the linear approximation to the shift function. The resultant $E$1 $S$-factor is not strongly enhanced by the subthreshold 1$^-_1$ state if the channel radius is 4.75 fm. The calculated $\beta$-delayed $\alpha$-particle spectrum of $^{16}$N and the p-wave phase shift of $\alpha$+$^{12}$C elastic scattering are also found to be consistent with the previous studies. The small channel radius leads to the low penetrability to the Coulomb barrier, and it makes the reduced $E$1 $S$-factor below the barrier. Owing to the large reduced width from the molecular structure, the $R$-matrix pole of the 1$^-_2$ state is shifted in the vicinity of 1$^-_1$. The proximity of the two poles suppresses the interference between the states. The weak coupling feature of the $\alpha$+$^{12}$C system appears to be expressed as the shrinking strong interaction region.

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M. Katsuma
Thu, 12 Jan 17

Comments: 17 pages, 8 figures, 2 tables. Submitted to PTEP

An analytical coalescence formula for particle production in relativistic heavy-ion collisions [CL]

Based on a covariant coalescence model with a blast-wave-like parametrization of the phase-space configuration for constituent particles at freezeout, we derive an approximate analytical formula for the yields of clusters produced in relativistic heavy-ion collisions. Compared to previous existing formulae, the present work additionally considers the longitudinal dimension in momentum space, the relativistic corrections, and the finite size effects of the produced clusters relative to the space distribution of constituent particles at freezeout. The new analytical coalescence formula provides a useful approach to evaluate the yield of produced clusters, such as light nuclei from nucleon coalescence and hadrons from quark coalescence, in heavy-ion collisions. As a first application of the new analytical formula, we explore the strangeness population factor $S_3 = ^3_{\Lambda}$H/($^3$He$\times \Lambda/$p) based on nucleon/$\Lambda$ coalescence as well as the production of exotic hadrons based on quark coalescence in central Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. The results are compared with the prediction from other models.

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K. Sun and L. Chen
Tue, 10 Jan 17

Comments: 12 pages, 0 figures, 3 tables

Identifying the QCD Phase Transitions via the Gravitational Wave Frequency [CL]

We investigate the nonradial oscillations of newly born neutron stars (NSs) and strange quark stars (SQSs). This is done with the relativistic nuclear field theory with hyperon degrees of freedom employed to describe the equation of state for the stellar matter in NSs, and with both the MIT bag model and the Nambu–Jona-Lasinio model adopted to construct the configurations of the SQSs. We find that the gravitational-mode ($g$-mode) eigenfrequencies of newly born SQSs are about one order of magnitude lower than those of NSs, which is independent of models implemented to describe the equation of state for the strange quark matter. Meanwhile the eigenfrequencies of the other modes of nonradial oscillations, e.g., fundamental ($f$)- and pressure ($p$)-modes, are much larger than those of the $g$-mode. In the light of the first direct observation of gravitational waves, it is promising to employ the gravitational waves to identify the QCD phase transition in high density strong interaction matter.

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W. Fu, Z. Bai and Y. Liu
Mon, 9 Jan 17

Comments: 14 pages, 7 figures and 3 tables

From microphysics to dynamics of magnetars [HEAP]

MeV-scale magnetic fields in the interiors of magnetars suppress the pairing of neutrons and protons in the $S$-wave state. In the case of a neutron condensate the suppression is the consequence of the Pauli-paramagnetism of the neutron gas, i.e., the alignment of the neutron spins along the magnetic field. The proton $S$-wave pairing is suppressed because of the Landau diamagnetic currents of protons induced by the field. The Ginzburg-Landau and BCS theories of the critical magnetic fields for unpairing are reviewed. The macrophysical implications of the suppression (unpairing) of the condensates are discussed for the rotational crust-core coupling in magnetars and the neutrino-dominated cooling era of their thermal evolution.

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A. Sedrakian, X. Huang, M. Sinha, et. al.
Thu, 5 Jan 17

Comments: 10 pages, 4 figures, Proceedings of “Compact Stars in the QCD phase diagram V”, 23-27 May 2016 GSSI and LNGS, L’Aquila, Italy

Hybrid Stars in the Framework of different NJL Models [CL]

We compute models for the equation of state (EoS) of the matter in the cores of hybrid stars. Hadronic matter is treated in the non-linear relativistic mean-field approximation, and quark matter is modeled by three-flavor local and non-local Nambu$-$Jona-Lasinio (NJL) models with repulsive vector interactions. The transition from hadronic to quark matter is constructed by considering either a soft phase transition (Gibbs construction) or a sharp phase transition (Maxwell construction). We find that high-mass neutron stars with masses up to $2.1-2.4 M_\odot$ may contain a mixed phase with hadrons and quarks in their cores, if global charge conservation is imposed via the Gibbs conditions. However, if the Maxwell conditions is considered, the appearance of a pure quark matter core either destabilizes the star immediately (commonly for non-local NJL models) or leads to a very short hybrid star branch in the mass-radius relation (generally for local NJL models).

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G. Contrera, M. Orsaria, I. Ranea-Sandoval, et. al.
Tue, 3 Jan 17

Comments: 7 pages, 4 figures. Contribution to the Proceedings of the VII International Workshop on Astronomy and Relativistic Astrophysics – IWARA 2016

Hybrid Stars in the Framework of different NJL Models [CL]

We compute models for the equation of state (EoS) of the matter in the cores of hybrid stars. Hadronic matter is treated in the non-linear relativistic mean-field approximation, and quark matter is modeled by three-flavor local and non-local Nambu$-$Jona-Lasinio (NJL) models with repulsive vector interactions. The transition from hadronic to quark matter is constructed by considering either a soft phase transition (Gibbs construction) or a sharp phase transition (Maxwell construction). We find that high-mass neutron stars with masses up to $2.1-2.4 M_\odot$ may contain a mixed phase with hadrons and quarks in their cores, if global charge conservation is imposed via the Gibbs conditions. However, if the Maxwell conditions is considered, the appearance of a pure quark matter core either destabilizes the star immediately (commonly for non-local NJL models) or leads to a very short hybrid star branch in the mass-radius relation (generally for local NJL models).

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G. Contrera, M. Orsaria, I. Ranea-Sandoval, et. al.
Mon, 2 Jan 17

Comments: 7 pages, 4 figures. Contribution to the Proceedings of the VII International Workshop on Astronomy and Relativistic Astrophysics – IWARA 2016

Nuclear Weak Rates and Detailed Balance in Stellar Conditions [CL]

Detailed balance is often invoked in discussions of nuclear weak transitions in astrophysical environments. Satisfaction of detailed balance is rightly touted as a virtue of some methods of computing nuclear transition strengths, but we argue that it need not necessarily be strictly obeyed, especially when the system is far from weak equilibrium. We present the results of shell model calculations of nuclear weak strengths in both charged current and neutral current channels at astrophysical temperatures. Using these strengths to compute some reaction rates, we find that, despite some violation of detailed balance, our method is robust up to high temperature, and we comment on the relationship between detailed balance and weak equilibrium in astrophysical conditions.

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G. Misch
Mon, 2 Jan 17

Comments: 10 pages, 11 figures

Radiative 3He-alpha reaction in Halo Effective Field Theory [CL]

In this work we study the radiative capture of ${\rm {}^3He}$ on ${\rm {}^4He}$ within the halo effective field theory framework. At leading order the capture amplitude comprises the initial state s-wave strong and Coulomb interactions summed to all orders, and depends on four parameters that can, in principle, be extracted from elastic ${\rm {}^3He}$-$\alpha$ scattering alone. At next-to-leading order, $s$- to p-wave initial state radiation with non-perturbative Coulomb and two-body currents contribute, with two extra parameters from the latter that are fitted to capture data. We perform three different fits of our parameters to available scattering data and most recent capture data. Our astrophysical $S$-factor, $S_{34}\sim 0.60\,{\rm keV\cdot b}$, is slightly above the average in the literature, though consistent within current error bars.

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R. Higa, G. Rupak and A. Vaghani
Fri, 30 Dec 16

Comments: 24 pages, 8 figures

Ab initio nuclear response functions for dark matter searches [CL]

We study the process of dark matter particles scattering off $^{3,4}$He with nuclear wave functions computed using an ab initio many-body framework. We employ realistic nuclear interactions from chiral effective field theory at next-to-next-to-leading order (NNLO) and develop an ab initio scheme to compute a general set of different nuclear response functions. In particular, we then perform an accompanying uncertainty quantification on these quantities and study error propagation to physical observables. We find a rich structure of allowed nuclear responses with significant uncertainties for certain spin-dependent interactions. The approach and results that are presented in this Paper establish a new framework for nuclear structure calculations and uncertainty quantification in the context of direct and (certain) indirect searches for dark matter.

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D. Gazda, R. Catena and C. Forssen
Fri, 30 Dec 16

Comments: 13 pages, 8 figures

Generalized density functional equation of state for astrophysical simulations with 3-body forces and quark gluon plasma [CL]

We present an updated general purpose nuclear equation of state (EoS) for use in simulations of core-collapse supernovae, neutron star mergers and black hole collapse. This EoS is formulated in the context of Density Functional Theory (DFT) and is generalized to include all DFT EoSs consistent with known nuclear and astrophysical constraints. This EoS also allows for the possibility of the formation of material with a net proton excess ($Y_p > 0.5$) and has an improved treatment of the nuclear statistical equilibrium and the transition to heavy nuclei as the density approaches nuclear matter density. We include the effects of pions in the regime above nuclear matter density and incorporate all of the known mesonic and baryonic states at high temperature.
We analyze how a 3-body nuclear force term in the DFT at high densities stiffens the EoS to satisfy the maximum neutron star constraint, however the density dependence of the symmetry anergy and the formation of pions at high temperatures allows for a softening of the central core in supernova collapse calculations leading to a robust explosion. We also add the possibility of a transition to a QCD chiral-symmetry-restoration and deconfinement phase at densities above nuclear matter density. This paper details the physics, and constraints on, this new EoS and presents an illustration of its implementation in both neutron stars and core-collapse supernova simulations. We present the first results from core-collapse supernova simulations with this EoS.

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J. Olson, M. Warren, M. Meixner, et. al.
Fri, 30 Dec 16

Comments: Submitted to Physical Review C. arXiv admin note: substantial text overlap with arXiv:1303.0064