Nuclear Equation Of State Research Articles

Impact of the stiffness of equation of state on saturation properties of asymmetric nuclear matter and Urca cooling in neutron stars

Abstract We consider nuclear equation of state (EOS) based on the semi-realistic M3Y-Paris and M3Y-Reid effective nucleon-nucleon (NN) interactions to assess the influence of the stiffness of the isospinasymmetric nuclear matter (ANM) on its isoscalar and isovector saturation properties, and on the β-stable proton fraction in neutron star (NS) matter. Two parameterizations schemes of the CDM3Y isovector density dependence of the NN interaction are adopted, one is scaled to the isoscalar density dependence and the other (IVF1) is developed independently of it. We found that the stiffer EOS yields larger binding saturation density that decreases with the isospin asymmetry (I), and slightly decreases the maximum asymmetry (Imax) reached for bound ANM. The density-slope (L) of the symmetry energy is found to correlate directly with the stiffness of ANM, meanwhile the symmetryenergy curvature (Ksym) and the quadratic isovector incompressibility coefficient (Kτ ) are found to correlate with it inversely. We found also that the stiffer EOS indicates larger neutron-rich npeμ NS matter under β-equilibrium. Only the CDM3Y-Paris EOSs of isoscalar incompressibility K0 up to 270 MeV and that of CDM3Y-Reid with K0 = 200 MeV indicate allowed direct URCA (DU) cooling process in β-stable NS matter, at densities greater than 3.5 ρ0, based on the IVF1 density dependence. The stiffer EOS proposes a narrower density range for DU process in NS. According to the considered Paris (Reid) forces, muons can emerge in cold β-stable npe matter at ρ ≥ 0.85 ρ0 (0.79 ρ0), which slightly decreases both the neutron richness at NS core and the DU threshold density.

Dependence of the reconstructed core-collapse supernova gravitational wave high-frequency feature on the nuclear equation of state in real interferometric data

Dependence of the reconstructed core-collapse supernova gravitational wave high-frequency feature on the nuclear equation of state in real interferometric data

MURCA driven bulk viscosity in neutrino trapped baryonic matter

We examine bulk viscosity, taking into account trapped neutrinos in baryonic matter, in the context of binary neutron star mergers. Following the merging event, the binary star can yield a remnant compact object with densities up to 5 nuclear saturation density and temperature up to 50 MeV resulting in the retention of neutrinos. We employ two relativistic mean field models, NL3 and DDME2, to describe the neutrino-trapped baryonic matter. The dissipation coefficient is determined by evaluating the Modified URCA interaction rate in the dense baryonic medium, and accounting for perturbations caused by density oscillations. We observe the resonant behavior of bulk viscosity as it varies with the temperature of the medium. The bulk viscosity peak remains within the temperature range of ∼13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 13$$\\end{document}–50 MeV, depending upon the underlying equation of states and lepton fractions. This temperature range corresponds to the relevant domain of binary neutron star mergers. We also note that in presence of neutrinos in the medium the bulk viscosity peak shifts towards higher temperature and the peak value of bulk viscosity also changes. The time scale of viscous dissipation is dictated by the beta-off-equilibrium susceptibilities derived from the nuclear equation of state. The resulting viscous decay time scale ranges from 32–100 ms, which aligns with the order of magnitude of the post-merger object’s survival time in some specific scenarios.

Cautionary Tales on Heating-rate Prescriptions in Kilonovae

A major ingredient for kilonova lightcurves is the radioactive heating rate and its dependence on the electron fraction and velocity of the ejecta and, in principle, on the nuclear mass formula. Heating-rate formulae commonly used as the basis for kilonova models previously employed in the literature produce substantially different outputs for high electron fractions (Y e ≳ 0.3) and at late times (t ≳ 1 day) compared to newer prescriptions. Here, we employ standard semianalytical models for kilonovae with better heating rate prescriptions valid for the full parameter space of kilonova velocities and electron fractions to explore the impact of the heating rate on kilonova lightcurves. We show the dangers of using inappropriate heating rate estimates by simulating realistic observations and inferring the kilonova parameters via a misspecified heating-rate prescription. While providing great fits to the photometry, an incorrect heating-rate prescription fails to recover the input ejecta masses with a bias significantly larger than the typical statistical uncertainty. This bias from an incorrect prescription has significant consequences for interpreting kilonovae, their use as additional components in gamma-ray burst afterglows, and understanding their role in cosmic chemical evolution or for multimessenger constraints on the nuclear equation of state. We showcase a framework and tool to better determine the impact of different modeling assumptions and uncertainties on inferences into kilonova properties.

Primordial black holes, gravitational wave beats, and the nuclear equation of state

Primordial black holes, gravitational wave beats, and the nuclear equation of state

Nuclear Charge Radii of Silicon Isotopes.

The nuclear charge radius of ^{32}Si was determined using collinear laser spectroscopy. The experimental result was confronted with abinitio nuclear lattice effective field theory, valence-space in-medium similarity renormalization group, and mean field calculations, highlighting important achievements and challenges of modern many-body methods. The charge radius of ^{32}Si completes the radii of the mirror pair ^{32}Ar-^{32}Si, whose difference was correlated to the slope L of the symmetry energy in the nuclear equation of state. Our result suggests L≤60 MeV, which agrees with complementary observables.

Implications on Skyrme equations of state from neutron skin measurements

Abstract The recent measurements on neutron skins via parity violation in electron scattering have extracted an abnormal thick neutron skin for $^{208}$Pb, which has significant consequences in nuclear equation of state (EoS) and neutron star observations. This work performs optimizations of extended Skyrme forces in a consistent manner by including neutron skin thicknesses from PREX-II and CREX experiments
and investigates nuclear EoS and neutron stars in the GW170817 event. By varying the fitting weights of neutron skins, several new Skyrme parameterizations are obtained. Our results show the competition in the fitting procedure to simultaneously describe neutron skins, other properties of finite nuclei and neutron star observations. The prospects in resolving the neutron skin issues are also discussed.

First order event plane correlated directed and triangular flow in Au+Au collisions from BES-II at STAR

In heavy-ion collisions, the measurements of anisotropic flow coefficients (vn) offer insights into collective hydrodynamic expansion and transport properties of the produced medium at higher collision energies, while also being sensitive to the compressibility of the nuclear matter and nuclear equation of state at lower collision energies. In this contribution, we present the measurement of charged particle v1 over ten units of pseudorapidity (η) in Au+Au collisions at √SNN = 27 and 19.6 GeV and compare it with multiple model calculations. Only UrQMD was able to reproduce a sizable v1 at the forward pseudorapidity as observed in the experiment. We also present the results of v1 and v3 at √SNN = 3 - 3.9 GeV for identified hadrons and light nuclei with respect to Ψ1. The results are compared with theoretical models to identify the source of nonzero v3{Ψ1} and to demonstrate its vital connection to the equation of state.

Effects of nuclear matter properties in neutron star mergers

ABSTRACT The dynamics in mergers of binary neutron star (BNS) systems depend sensitively on the equation of state (EOS) of dense matter. This has profound implications on the emission of gravitational waves (GWs) and the ejection of matter in the merger and post-merger phases and is thus of high interest for multimessenger astronomy. Today, a variety of nuclear EOSs are available with various underlying microphysical models. This calls for a study to focus on EOS effects from different physical nuclear matter properties and their influence on BNS mergers. We perform simulations of equal-mass BNS mergers with a set of nine different EOSs based on Skyrme density functionals. In the models, we systematically vary the effective nucleon mass, incompressibility, and symmetry energy at saturation density. This allows us to investigate the influence of specific nuclear matter properties on the dynamics of BNS mergers. We analyse the impact of these properties on the merger dynamics, the fate of the remnant, disc formation, ejection of matter, and GW emission. Our results indicate that some aspects of the merger, such as the frequencies of the post-merger GW spectrum and the shock-heated ejecta mass, are sensitive to the EOS around saturation density while others, such as the contraction of the remnant and the tidal ejecta mass, are sensitive to the behaviour towards higher densities, e.g. characterized by the slope of the pressure versus density. The detailed density dependence of the EOS thus needs to be taken into account to describe its influence on BNS mergers.

Nuclear Equation of State and many-body phase-space correlations in the Constrained Molecular Dynamics

Many-body correlations characterizing the Constrained Molecular Dynamics (CoMD) are analyzed in the case of finite and zero-range effective microscopic interactions. The study begins by analyzing the case of infinite nuclear matter at zero temperature. A comparison with the predictions in the mean-field (MF) limit corresponding to different effective masses, highlights non-negligible differences regarding the produced Equation of State (EoS). A procedure is illustrated to determine the necessary corrections of the effective interaction parameters in the CoMD model so to reproduce the chosen EoS. The specific model calculations, the general feature of the discussed correlations gives a wider meaning to the resulting differences, which are in fact strongly related both to the Pauli principle constraint and to the localization effects related to wave-packets dynamics. Moving on to finite systems, preliminary results are shown in relation to the reaction mechanisms in the N64i+48Ca system described by the CoMD model. Therefore, the topic covered illustrates the effects produced by the correlations of the CoMD dynamics on the EoS and on some observables commonly studied in heavy ion collisions.

Preface

XLIV Symposium on Nuclear Physics Hacienda Cocoyoc, Morelos, Mexico January 9-12, 2023The 44th Symposium on Nuclear Physics was celebrated from January 9th to 12th, 2023 at the Hacienda Cocoyoc, Morelos, Mexico. This Symposium has been held every year since its inauguration in 1978 until 2020 despite earth quakes, last minute cancelations by the venue and economic crises. The COVID-19 crisis presented too much of a challenge and the Symposium had to be postponed for two years in a row.In this 2023, the Symposium is back! We had a tremendous response from the international community of nuclear physics which led to a very successful and lively meeting. The program consisted of 32 plenary talks and 20 posters over a broad range of hot topics, such as nuclear structure and reactions, instrumentation, relativistic heavy ions, nuclear astrophysics, fundamental symmetries and hadron physics.This proceedings contain 20 articles of exciting new results and developments in progress of amazing instrumentation that were presented at the meeting.At the meeting there were representatives of several international collaborations to report on the most recent research progress and the most recent developments in laboratories like FRIBS, ORNL, INFN-LNS, INFN-LNL, INFN-LUNA, ININ and the Texas A&M, Notre Dame University and IF-UNAM facilities. During the presentations, recent data from NUMEN, AGATA, SUGAR@LNL, NNBAR, nEDM@SNS and the NOPTREX collaborations were shown. Many apparatus were as well presented, either as recent developments or showing their recent results; such as the K600 spectrometer, LHASA, SUGAR, AGATA, MUGAST, VAMOS, TriSol, FRAISE, FARCOS, CHIMERA and PROSPECT-I.Regarding the theoretical studies, interesting new developments involving different topics were presented on this edition, such as Shell Model, QCD, QED, Abinitio, baryons and pentaquarks, Nuclear Equation of State, Artificial Intelligence Approaches, nuclear clusters, R-matrix, nuclear dynamics and neutrino physics. The high quality of the talks and posters, the expertise of the speakers and the broad spectrum of subjects covered in the meeting, shows that nuclear physics continued working hard despite the Pandemic restrictions, being a very active area at the frontier of scientific research which establishes bridges between many different disciplines, putting together theoretical and experimental researchers and having an extension to the instrumentation developments and applications.Unfortunately, during the last three years we had to say goodbye to four distinguished colleagues who made pioneering contributions to nuclear physics in Mexico and were very instrumental in the success of this series of symposia. María Esther Ortiz (1936-2021) was the last surviving member of the organizing committee of the first symposium in 1978, Jorge Flores (1941-2020) and Pier Mello (1939-2022) were among the first graduate students in nuclear theory in Mexico, and Alfonso Mondragón (1941-2020) was a regular participant in the Symposium for some 35 years. All four were members of the Instituto de Física of the UNAM. The 44th Symposium is dedicated to their memory in celebration of their distinguished careers and in recognition of their important contributions to the development of nuclear physics in Mexico. Some local colleagues presented part of the history of these distinguish researchers at the beginning of the Symposium. In the following lines, some words coming from this homage:List of Editors, International Advisory Committee, Organizing Committee, Sponsors, Photograph of the event are available in this pdf.

Role of equation of state and clusterization algorithms on nuclear vaporization

By using the Quantum Molecular Dynamics (QMD) model, a study on the nuclear vaporization in [Formula: see text] collision is presented for different nuclear equations of state along with a systematic comparison of different clusterization methods based on simple spatial correlations, spatial-momentum correlations, mass dependent binding energy cuts and Simulated Annealing Clusterization Algorithm (SACA). The effect of different nuclear equations of state i.e., Soft, Hard and Soft with Momentum Dependent (SMD) interactions on the energy of onset of vaporization for [Formula: see text] collisions is predicted by investigating gas/liquid content and probability of vaporization versus incident energy behavior. These two observables probe the critical point of nuclear vaporization very well. Further outcome of different clusterization algorithms on the energy of onset of nuclear vaporization is also probed and a comparison of calculations with the experimental data for [Formula: see text] and [Formula: see text] collisions is carried out for different clusterization algorithms.

Gravitational Wave Eigenfrequencies from Neutrino-driven Core-collapse Supernovae

Core-collapse supernovae (CCSNe) are predicted to produce gravitational waves (GWs) that may be detectable by Advanced LIGO/Virgo. These GW signals carry information from the heart of these cataclysmic events, where matter reaches nuclear densities. Recent studies have shown that it may be possible to infer the properties of the proto-neutron star (PNS) via GWs generated by hydrodynamic perturbations of the PNS. However, we lack a comprehensive understanding of how these relationships may change with the properties of CCSNe. In this work, we build a self-consistent suite of over 1000 exploding CCSNe from a grid of progenitor masses and metallicities combined with six different nuclear equations of state (EOS). Performing a linear perturbation analysis on each model, we compute the resonant GW frequencies of the PNS, and we motivate a time-agnostic method for identifying characteristic frequencies of the dominant GW emission. From this, we identify two characteristic frequencies, of the early- and late-time signal, that measure the surface gravity of the cold remnant neutron star, and simultaneously constrain the hot nuclear EOS. However, we find that the details of the CCSN model, such as the treatment of gravity or the neutrino transport, and whether it explodes, noticeably change the magnitude and evolution of the PNS eigenfrequencies.

Nuclear physics inputs for dense-matter modelling in neutron stars. The nuclear equation of state

In this contribution, we briefly present the equation-of-state modelling for application to neutron stars and discuss current constraints coming from nuclear physics theory and experiments. To assess the impact of model uncertainties, we employ a nucleonic meta-modelling approach and perform a Bayesian analysis to generate posterior distributions for the equation of state with filters accounting for both our present low-density nuclear physics knowledge and high-density neutron-star physics constraints. The global structure of neutron stars thus predicted is discussed in connection with recent astrophysical observations.

Diffuse Neutrino Flux Based on the Rates of Core-collapse Supernovae and Black Hole Formation Deduced from a Novel Galactic Chemical Evolution Model

Fluxes of the diffuse supernova neutrino background (DSNB) are calculated based on a new modeling of galactic chemical evolution, where a variable stellar initial mass function (IMF), depending on the galaxy type, is introduced and black hole (BH) formation from the failed supernova is considered for progenitors heavier than 18M ⊙. The flux calculations are performed for different combinations of the star formation rate, nuclear equation of state, and neutrino mass hierarchy, to examine the systematic effects from these factors. In any case, our new model predicts the enhanced DSNB flux at E ν ≳ 30 MeV and E ν ≲ 10 MeV, due to more frequent BH formation and a larger core-collapse rate at high redshifts in early-type galaxies, respectively. Event rate spectra of the DSNB at a detector from the new model are shown, and the detectability at water-based Cherenkov detectors, Super-Kamiokande with a gadolinium dissolution and Hyper-Kamiokande, is discussed. In order to investigate the impacts of the assumptions in the new model, we prepare alternative models, based on different IMF forms and treatments of BH formation, and estimate the discrimination capabilities between the new and alternative models at these detectors.

The Interrelated Roles of Correlations in the Nuclear Equation of State and in Response Functions: Application to a Chiral Confining Theory

We study the role of short-range correlations, as well as pion and rho loops governing long-range RPA correlations, in nuclear matter properties and response functions. We use an adapted formulation of the Brueckner G-matrix approach to generate a pair correlation function satisfying the Beg–Agassi–Gal theorem, providing a natural cutoff to the loop integrals. We present results for the case of a relativistic chiral theory, including the effects of quark confinement and of the chirally broken vacuum in a version where parameters are directly connected to QCD observables or constrained by well-established hadron phenomenology. This provides a unified and coherent view of the nuclear matter equation of state and the effect of correlations on neutrino–nucleus scattering.

Velocity distributions of forward moving fragments in heavy-ion collisions at Fermi energies

Heavy-ion-induced projectile fragmentation reactions at Fermi energies are of interest to investigate the properties of nuclei far from the valley of stability, nuclear potentials, to get knew knowledge about nuclear equation of state. Isotopes far from stability line can be useful for various applications. It is therefore of interest to predict relative yields of isotopes and their energies with high precision. Here we treat such reactions in a microscopic approach, which consists of several steps: initialization of ground states of the colliding nuclei, dynamical evolution until the freeze-out point where the primary fragments can be identified, calculation of the excitation energy of the primary fragments, and their de-excitation. For the dynamical evolution we use a Boltzmann–Vlasov type transport equation, and for the de-excitation a statistical multi-fragmentation description. We apply this approach to collisions of projectile nuclei 40Ar on target 9Be at energy 36.5 A MeV, obtain isotope distributions and velocity spectra of the produced isotopes and compare the results of our calculations to experimental data obtained at COMBAS set-up in JINR.

Stability of neutron stars with dark matter core using three crustal types and the impact on mass–radius relations

We investigate the effects of dark matter (DM) on the nuclear equation of state (EoS) and neutron star structure, in the relativistic mean field theory, both in the absence and presence of a crust. The σ−ω model is modified by adding a WIMP-DM component, which interacts with nucleonic matter through the Higgs portal. This model agrees well with previous studies which utilized either a more complicated nuclear model or higher-order terms of the Higgs potential, in that DM softens the EoS, resulting in stars with lower maximum masses. However, instabilities corresponding to negative pressure values in the low-energy density regime of the DM-admixed EoS are present, and this effect becomes more prominent as we increase the DM Fermi momentum. We resolve this by confining DM in the star’s core. The regions of instability were replaced by three types of crust: first by the Friedman-Pandharipande-Skyrme (FPS), Skyrme-Lyon (SLy) and BSk19 EoS from the Brussels-Montreal Group, which can be represented by analytical approximations. For a fixed value of the DM Fermi momentum pFDM, the DM-admixed neutron star does not have significant changes in its mass with the addition of the crusts. However, the entire mass–radius relation of the neutron star is significantly affected, with an observed increase in the radius of the star corresponding to the mass. The effect of DM is to reduce the mass of the star, while the crust does not affect the radius significantly, as the value of the pFDM increases.

GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process Nucleosynthesis and Electromagnetic Signatures of Dynamical Ejecta

Fast neutron-rich material ejected dynamically over ≲10 ms during the merger of a binary neutron star (BNS) can give rise to distinctive electromagnetic counterparts to the system’s gravitational-wave emission that serve as a “smoking gun” to distinguish between a BNS and an NS–black hole merger. We present novel ab initio modeling of the kilonova precursor and kilonova afterglow based on 3D general-relativistic magnetohydrodynamic simulations of BNS mergers with nuclear, tabulated, finite-temperature equations of state (EOSs), weak interactions, and approximate neutrino transport. We analyze dynamical mass ejection from 1.35–1.35 M ⊙ binaries, consistent with properties of the first observed BNS merger GW170817, using three nuclear EOSs that span the range of allowed compactness of 1.35 M ⊙-neutron stars. Nuclear reaction network calculations yield a robust second-to-third-peak r-process. We find few ×10−6 M ⊙ of fast (v > 0.6c) ejecta that give rise to broadband synchrotron emission on ∼years timescales, consistent with tentative evidence for excess X-ray/radio emission following GW170817. We find ≈2 × 10−5 M ⊙ of free neutrons that power a kilonova precursor on ≲ hours timescale. A boost in early UV/optical brightness by a factor of a few due to previously neglected relativistic effects, with enhancements up to ≲10 hr post-merger, is promising for future detection with UV/optical telescopes like Swift or ULTRASAT. We find that a recently predicted opacity boost due to highly ionized lanthanides at ≳70,000 K is unlikely to affect the early kilonova based on the obtained ejecta structures. Azimuthal inhomogeneities in dynamical ejecta composition for soft EOSs found here (“lanthanide/actinide pockets”) may have observable consequences for both early kilonova and late-time nebular emission.

A Bayesian Inference of a Relativistic Mean-field Model of Neutron Star Matter from Observations of NICER and GW170817/AT2017gfo

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