High-density Nuclear Equation Of State Research Articles

Systematics on the high-density nuclear equation of state from relativistic Hartree-Fock theory with Brown-Rho scaling

Using the Brown-Rho (BR) scaling law, several new relativistic Hartree-Fock (RHF) models with chiral limit are thoroughly investigated. The high-density nuclear equation of state (EOS) of RHF with the BR scaling become softer than one without the BR scaling. The EOS of RHF with BR scaling is consistent with the constraint extracted from collective flows and kaon production in heavy-ion collisions. It is found that, with a sizable strength parameter of the mass drop $x=0.126$, the symmetry energy is almost flat at density above 3 times the saturation density ${\ensuremath{\rho}}_{0}$, and even decreases slightly. This is caused from the fact that the decline of the potential part of symmetry energy is faster than the increase of the kinetic part of symmetry energy. The decrease of potential part is mainly because the neutron mass ${M}_{n}^{*}$ and the proton mass ${M}_{p}^{*}$ are close to each other when the density gradually approaches the critical density of chiral limit. For a mass drop of $x=0.092$, since the critical density of chiral limit is higher than one of $x=0.126$, the symmetry energy becomes flat at density above $5{\ensuremath{\rho}}_{0}$. While, since the critical density of chiral limit is very high for a small mass drop $x=0.053$, the symmetry energy of RHFs with $x=0.053$ always increases at the entire density domain of this work (below 6 ${\ensuremath{\rho}}_{0}$). The maximum mass of neutron star (NS) obtained with present models can satisfy $M=2.08\ifmmode\pm\else\textpm\fi{}0.07{M}_{\ensuremath{\bigodot}}$. However, the radius of 1.4 ${M}_{\ensuremath{\bigodot}}$ with the mass drop of $x=0.126$ will surpass the upper limit (13.7 km) extracted from the tidal deformability parameter of coalescence of a NS binary system and the radius of $\text{J0030}+0451$ being $12.{71}_{\ensuremath{-}1.19}^{+1.14}$ km. The radius of 1.4 ${M}_{\ensuremath{\bigodot}}$ with the mass drop of $x=0.092$ is 13.6 km, closing to 13.7 km and the radius of $\text{J0030}+0451$ being $12.{71}_{\ensuremath{-}1.19}^{+1.14}$ km. Therefore, the RHF model with BR scaling prefers the mass drop of $x\ensuremath{\lesssim}0.092$.

Chiral Effective Field Theory and the High-Density Nuclear Equation of State

Born in the aftermath of core-collapse supernovae, neutron stars contain matter under extraordinary conditions of density and temperature that are difficult to reproduce in the laboratory. In recent years, neutron star observations have begun to yield novel insights into the nature of strongly interacting matter in the high-density regime where current theoretical models are challenged. At the same time, chiral effective field theory has developed into a powerful framework to study nuclear matter properties with quantified uncertainties in the moderate-density regime for modeling neutron stars. In this article, we review recent developments in chiral effective field theory and focus on many-body perturbation theory as a computationally efficient tool for calculating the properties of hot and dense nuclear matter. We also demonstrate how effective field theory enables statistically meaningful comparisons among nuclear theory predictions, nuclear experiments, and observational constraints on the nuclear equation of state.

The Nuclear Equation of State in Heavy Ion Collisions

We present several possibilities offered by the dynamics of intermediate energy heavy ion collisions to investigate the nuclear matter equation of state (EoS) beyond the ground state. In particular the relation between the reaction dynamics and the high density nuclear EoS is discussed by comparing theoretical results with experiments.

Level inversion in kaonic nuclei and the high-density nuclear equation of state

It is very difficult for any nuclear model to pin down the saturation property and high-density equation of state (EOS) simultaneously because of high nonlinearity of the nuclear many-body problem. In this work, we propose, for the first time, to use the special property of light kaonic nuclei to characterize the relation between saturation property and high-density EOS. With a series of relativistic mean-field models, this special property is found to be the level inversion between orbitals 2S1/2 and 1D5/2 in light kaonic nuclei. This level inversion can serve as a theoretical laboratory to group the incompressibility at saturation density and the EOS at supra-normal densities simultaneously.

Strange particle production and hypernucleus formation in medium and high energy heavy-ion collisions

The nuclear matter at supra-saturation densities might be created in medium and high energy heavy-ion collisions. The strangeness ingredient in dense nuclear matter impacts the equation of state and maybe exists in the neutron stars. On the other hand, heavy-ion collisions provide a unique way for producing the neutron-rich hypernuclides. In this article, the new progress on strangeness physics in heavy-ion collisions is reviewed. Possible experiments at the high-intensity heavy-ion accelerator facility (HIAF) are to be discussed, in particular on the topics of the high-density nuclear equation of state and hypernuclide in the neutron-rich domain. Within the framework of the Lanzhou quantum molecular dynamics (LQMD) model, the strangeness production and high-density nuclear equation of state in heavy-ion collisions near threshold energies has been investigated, i.e., for the reactions of $^{58}$Ni+$^{58}$Ni and $^{197}$Au+$^{197}$Au. The formation mechanism of $\Lambda$-hyperfragments in heavy-ion collisions is to be investigated. A coalescence approach is developed for constructing the primary fragments in phase space. The secondary decay process of the fragments is described by the well-known statistical code. The impacts of nuclear equation of state on the hyperfragment formation are discussed. The mass, charge and kinetic energy spectra of hypernuclides produced in heavy-ion collisions are thoroughly analyzed. It is found that the kaon yields in the high kinetic energy domain are useful for extracting the high-density nuclear equation of state. The $K^{+}$ yields are strongly suppressed with a hard equation of state. However, the hyperon production is weakly influenced by the incompressibility of nuclear matter. The $\Lambda$-nucleon potential impacts the hypernuclide formation, i.e., the attractive potential enhancing the hypernuclide yields. The heavy-ion collisions are available to produce the light mass neutron-rich hypernuclides and the mid-central collisions are favorable for the medium mass hypernuclide formation. Free hyperons are captured by nucleonic fragments to form hypernuclides in the domain of lower kinetic energies and narrower rapidities. A soft equation of state is available for producing the hyperfragments. The results are very valuable for the forthcoming hypernuclide physics at HIAF.

Strangeness to increase the density of finite nuclear systems in constraining the high-density nuclear equation of state

As the high-density nuclear equation of state (EOS) is not very well constrained, we suggest that the structural properties from the finite systems can be used to extract a more accurate constraint. By including the strangeness degrees of freedom, the hyperon or anti-kaon, the finite systems can then have a rather high-density core which is relevant to the nuclear EOS at high densities directly. It is found that the density dependence of the symmetry energy is sensitive to the properties of multi-\(\Lambda \) hypernuclei, while the high-density EOS of symmetric matter correlates sensitively to the properties of kaonic nuclei.

Neutron star structure with hyperons and quarks

The high-density nuclear equation of state within the Brueckner-Hartree-Fock approach is discussed. Particular attention is paid to the effects of nucleonic three-body forces, the presence of hyperons, the joining with an eventual quark matter phase, and the extension to finite temperature. The resulting properties of neutron stars, in particular the mass-radius relation, are determined. It turns out that in this approach stars heavier than about 1.4 solar masses contain necessarily quark matter.

Brueckner-Hartree-Fock Approach to Neutron Star Structure

The high-density nuclear equation of state within the Brueckner-Hartree-Fock approach is discussed. Particular attention is paid to the effects of nucleonic three-body forces, the presence of hyperons, and the joining with an eventual quark matter phase. The resulting properties of neutron stars, in particular the mass-radius relation, are determined. It turns out that in this approach the maximum mass is about 1.8 solar masses and that stars heavier than about 1.4 solar masses contain necessarily quark matter. During the last decades the increasing interest for the equation of state (EOS) of nuclear matter has stimulated a lot of theoretical activity. The properties of nuclear matter at high density and large isospin asymmetry are relevant for astrophysical objects, i.e., supernovae and neutron stars. In particular, the structure of a neutron star is very sensitive to the compressibility and the symmetry energy. The neutron star mass, measured in binary systems, has been proposed as a constraint for the

Neutron star structure with modern nucleonic three-body forces

We provide convenient parametrizations of the high-density nuclear equation of state obtained within the Brueckner-Hartree-Fock approach using different modern nucleon-nucleon potentials together with compatible microscopic nuclear three-body forces. The corresponding neutron star mass-radius relations are also presented.

Constraints on the high-density nuclear equation of state from the phenomenology of compact stars and heavy-ion collisions

A new scheme for testing nuclear matter equations of state (EoSs) at high densities using constraints from neutron star (NS) phenomenology and a flow data analysis of heavy-ion collisions is suggested. An acceptable EoS shall not allow the direct Urca process to occur in NSs with masses below 1.5M� , and also shall not contradict flow and kaon production data of heavy-ion collisions. Compact star constraints include the mass

Shock Breakout in Core‐Collapse Supernovae and Its Neutrino Signature

(Abridged) We present results from dynamical models of core-collapse supernovae in one spatial dimension, employing a newly-developed Boltzmann neutrino radiation transport algorithm, coupled to Lagrangean hydrodynamics and a consistent high-density nuclear equation of state. We focus on shock breakout and its neutrino signature and follow the dynamical evolution of the cores of 11 M_sun, 15 M_sun, and 20 M_sun progenitors through collapse and the first 250 milliseconds after bounce. We examine the effects on the emergent neutrino spectra, light curves, and mix of species of artificial opacity changes, the number of energy groups, the weak magnetism/recoil corrections, nucleon-nucleon bremsstrahlung, neutrino-electron scattering, and the compressibility of nuclear matter. Furthermore, we present the first high-resolution look at the angular distribution of the neutrino radiation field both in the semi-transparent regime and at large radii and explore the accuracy with which our tangent-ray method tracks the free propagation of a pulse of radiation in a near vacuum. Finally, we fold the emergent neutrino spectra with the efficiencies and detection processes for a selection of modern underground neutrino observatories and argue that the prompt electron-neutrino breakout burst from the next galactic supernova is in principle observable and usefully diagnostic of fundamental collapse/supernova behavior. Though we are not in this study focusing on the supernova mechanism per se, our simulations support the theoretical conclusion (already reached by others) that spherical (1D) supernovae do not explode when good physics and transport methods are employed.

Relativistic mean-field theory and the high-density nuclear equation of state

The properties of high-density nuclear and neutron matter are studied using a relativistic mean-field approximation to the nuclear matter energy functional. Based on ideas of effective field theory, nonlinear interactions between the fields are introduced to parametrize the density dependence of the energy functional. Various types of nonlinearities involving scalar-isoscalar ($\sigma$), vector-isoscalar ($\omega$), and vector-isovector ($\rho$) fields are studied. After calibrating the model parameters at equilibrium nuclear matter density, the model and parameter dependence of the resulting equation of state is examined in the neutron-rich and high-density regime. It is possible to build different models that reproduce the same observed properties at normal nuclear densities, but which yield maximum neutron star masses that differ by more than one solar mass. Implications for the existence of kaon condensates or quark cores in neutron stars are discussed.

The relativistic two-nucleon problem in nuclear matter

A new covariant formalism is developed for studying two-baryon correlations in infinite nuclear matter. The formalism is based on renormalizable, relativistic quantum field theories of mesons and baryons (quantum hadrodynamics) and involves a self-consistent summation of the relativistic ladder diagrams using a quasipotential approximation. Self-consistency modifies both the singleparticle spectrum and wave functions and introduces important density dependence into matrix elements of the one-boson-exchange (ladder) interaction. Results are obtained for the Walecka model, which describes the nucleon-nucleon interaction through neutral scalar and vector meson exchange. The mean-field theory (MFT) values of the large scalar and vector components of the baryon self-energy (“single-particle potential”) are modified only slightly by correlations, yielding a baryon effective mass M ∗ that decreases rapidly with increasing density. Moreover, correlations have a small effect on the high-density nuclear equation of state, which is quite stiff due to the small value of M ∗ and is given accurately by the MFT. In contrast, due to cancellations near equilibrium density, correlations produce significant corrections to the MFT binding energy. Calculated saturation properties are sensitive to the choice of quasipotential and the introduction of meson-baryon form factors. Finally, modifications from the shifted baryon mass in negative-energy states are included in a mean-field approximation. These corrections are significant in calculations of the binding energy.