The nuclear symmetry energy determines the birth of neutron stars and the elementary nucleosynthesis in the universe. To constrain the nuclear symmetry energy, besides the studies in astrophysics, many terrestrial nuclear experiments are being carried out using a wide variety of advanced new facilities. In this paper, by cross-checking two unrelated experimental measurements using the newly updated transport model, we obtained a slightly soft symmetry energy at supra-saturation nuclear densities. While extrapolating to low nuclear densities, this result is compatible with the recent finding by comparing the available data on the electric dipole polarizability with the theoretical predictions. Our finding is expected to push the studies of nuclear physics and astrophysics forward.
The density dependence of the nuclear symmetry energy governs important aspects of very neutron rich systems such as heavy nuclei and their collisions, neutron stars and their mergers. Many analyses of experimental data have generated constraints on the symmetry energy and its first derivative at saturation density, rho_0 ~ 2.7xE14 g/cm3. We show that each analysis does not accurately constrain the symmetry energy at rho_0, but rather at a lower density, rho_s, that is most sensitively probed by that analysis. Using published constraints on the symmetry energy and its first derivative at rho_0…
Within the framework of BCS theory and Skyrme-Hartree-Fock model, we employ various microscopic pairing gaps and effective pairing interactions to study pairing effects on the equation of state (EOS) of neutron matter and the symmetry energy at subsaturation densities. We find pairing effects may have considerable contributions to the EOS of neutron matter at very low densities ($\lesssim 0.02~\rm{fm}^{-3}$), while only have a small impact on the symmetry energy at subsatruation densities. In addition, the reliability of the parabolic approximation for the isospin asymmetry dependence of nucle…
By simultaneously describing the data of isospin sensitive nucleonic flow and pion observables, such as $v_2^n/v_2^{ch}$ and $π^-/π^+$, with ultra-relativistic quantum molecular dynamics (UrQMD) model, we got the symmetry energy at flow and pion characteristic densities which are $S(1.2ρ_0)=34\pm 4$ MeV and $S(1.5ρ_0)=36\pm 8$ MeV. Within the uncertainties, the constraints of symmetry energy at characteristic densities are consistent with the previous constraints by using other transport models. The consistency suggests that the reliable constraints on symmetry energy should be presented at th…
By directly inverting several neutron star observables in the three-dimensional parameter space for the Equation of State of super-dense neutron-rich nuclear matter, we show that the lower radius limit for PSR J0740+6620 of mass $2.08\pm 0.07~M_{\odot}$ from Neutron Star Interior Composition Explorer (NICER)'s very recent observation sets a much tighter lower boundary than previously known for nuclear symmetry energy in the density range of $(1.0\sim 3.0)$ times the saturation density $ρ_0$ of nuclear matter. The super-soft symmetry energy leading to the formation of proton polarons in this de…
Using relativistic Hartree-Fock (RHF) approximation, we study the effect of Fock terms on the nuclear properties not only around the saturation density, $ρ_{0}$, but also at higher densities. In particular, we investigate how the momentum dependence due to the exchange contribution affects the nuclear symmetry energy and its slope parameter, using the Lorentz-covariant decomposition of nucleon self-energies in an extended version of the RHF model, in which the exchange terms are adjusted so as to reproduce the single-nucleon potential at $ρ_{0}$. We find that the Fock contribution suppresses t…
We study the implications of isospin symmetry in nuclear systems on two-body distributions and derive relations between different densities or momentum distributions of a given nucleus or of different nuclei in the same isospin multiplet. A connection between neutrinoless double beta decay transition of mirror nuclei and two-body densities is also obtained. The relations are numerically verified by means of quantum Monte Carlo calculations. We discuss the relevance of these results to the analysis of nuclear short-range correlations and also show that isospin symmetry allows us to extract info…
A sensitive correlation between the ground-state properties of light kaonic nuclei and the symmetry energy at high densities is constructed under the framework of relativistic mean-field theory. Taking oxygen isotopes as an example, we see that a high-density core is produced in kaonic oxygen nuclei, due to the strongly attractive antikaon-nucleon interaction. It is found that the $1S_{1/2}$ state energy in the high-density core of kaonic nuclei can directly probe the variation of the symmetry energy at supranormal nuclear density, and a sensitive correlation between the neutron skin thickness…
Motivated by the historical detection of gravitational waves from GW170817, the neutron star and the neutron drop, i.e., a certain number of neutrons confined in an external field, are systematically investigated by ab initio calculations as well as the nonrelativistic and relativistic state-of-art density functional theories. Strong correlations are found among the neutron star tidal deformability, the neutron star radius, the root-mean-square radii of neutron drops, and the symmetry energies of nuclear matter at supra-saturation densities. From these correlations and the upper limit on the t…
The cooling process of a protoneutron star is investigated with focus on its sensitivity to properties of hot and dense matter. An equation of state, which includes the nucleon effective mass and nuclear symmetry energy at twice the saturation density as control parameters, is constructed for systematic studies. The numerical code utilized in this study follows a quasi-static evolution of a protoneutron star solving the general-relativistic stellar structure with neutrino diffusion. The cooling timescale evaluated from the neutrino light curve is found to be longer for the models with larger e…
The correlation between neutron skin-thickness of a neutron-rich nucleus and slope parameter of symmetry energy is assessed as a function of density using relativistic mean field models containing non-linear couplings among different mesons. Models with larger skin were found to probe the slope parameter even at suprasaturation densities, whereas models with smaller skin were observed to be sensitive only at specific subsaturation density, connected to the average density of nuclei. Possible reasons behind this density dependence are explored systematically. These results might be model specif…
There is an ongoing quest to improve on the spectroscopic quality of nuclear energy density functionals (EDFs) of the Skyrme type through extensions of its traditional form. One direction for such activities is the inclusion of terms of higher order in gradients in the EDF. We report on exploratory symmetry-breaking calculations performed for an extension of the Skyrme EDF that includes central terms with four gradients at next-to-next-to-leading order (N2LO) and for which the high-quality parametrization SN2LO1 has been constructed recently [P. Becker et al, Phys. Rev. C 96, 044330 (2017)]. U…
Nuclear symmetry energy $E_{\rm{sym}}(ρ)$ at density $ρ$ is normally expanded or simply parameterized as a function of $χ=(ρ-ρ_0)/3ρ_0$ in the form of $E_{\rm{sym}}(ρ)\approx S+Lχ+2^{-1}K_{\rm{sym}}χ^2+6^{-1}J_{\rm{sym}}χ^3+\cdots$ using its magnitude $S$, slope $L $, curvature $K_{\rm{sym}}$ and skewness $J_{\rm{sym}}$ at the saturation density $ρ_0$ of nuclear matter. Much progress has been made in recent years in constraining especially the $S$ and $L$ parameters using various terrestrial experiments and astrophysical observations. However, such kind of expansions/parameterizations do not c…
We investigate the structure attained by neutron star matter with proton to neutron ratios ranging from x=0.1 to 0.5, densities in the range of 0.02 fm-3 to 0.085 fm-3, and temperatures T<4 MeV. In particular we study the pasta shapes and the phase changes previously observed in nuclear matter, as well as the behavior of the symmetry energy. We corroborate the existence of homogeneous to non-homogeneous phase transitions, and the different values of the symmetry energy at different densities and temperatures.
Equation of state of isospin-asymmetric nuclear matter in relativistic mean-field models with chiral limits
利用高密度下手征对称性恢复引起的Brown-Rho标度下的介质中强子性质，并考虑到耦合常数的自然性，我们新构造了几个具有手征极限的相对论平均场拉格朗日量.调整模型参数，使所得的状态方程在超常密度的对称部分是一致的，所需的集体流数据从高能量重离子反应，而所得的密度依赖性的对称能在亚饱和密度同意从最近的中能重离子反应的同位旋扩散数据提取。所得的状态方程具有在中等密度下软而在高密度下自然硬的特点。利用这些约束状态方程，我们发现1.4 $M_\odot$正则中子星的半径在11.9 km $\leq$ R $\leq$ 13.1 km的范围内，中子星的最大质量在2.0 $M_\odot$左右，与最近的观测结果接近.
The large imbalance in the neutron and proton densities in very neutron rich systems increases the nuclear symmetry energy so that it governs many aspects of neutron stars and their mergers. Extracting the density dependence of the symmetry energy therefore constitutes an important scientific objective. Many analyses have been limited to extracting values for the symmetry energy, $S_0$, and its ``derivative'', $L$, at saturation density $ρ_0 \approx 2.6 \times 10^{14}~\mathrm{g/cm^3}$ $\approx 0.16~\mathrm{nucleons/fm^{3}}$, resulting in constraints that appear contradictory. We show that most…
Low density nuclear matter with light clusters in a generalized nonlinear relativistic mean-field model
利用广义非线性相对论平均场（gNL-RMF）模型，系统地研究了低密度、有限温度下轻团簇的均匀核物质的热力学性质，其中光聚集达到$α$（$1 \le A \le 4$）作为显式自由度包括在内，并作为点处理。相似粒子与它们的相互作用由介子交换描述，介质对团簇结合能的影响由密度和温度描述，通过拟合实验团簇Mott密度得到的参数，依赖的能量移动。我们发现，轻团簇的低密度核物质的组成基本上是由团簇结合能位移的密度和温度依赖性决定的。与传统的二阶对称能、对称自由能和对称熵值相比，它们的四阶值在低密度（$ρ\sim 10^{-3}$ fm $^{-3}$）和低温（$T \lesssim 3$ MeV）下是显著的，表明经验抛物线定律对这些核物质性质的同位旋非对称性依赖性是无效的.结果表明，在$ρ\gtrsim 0.02$ fm $^{-3}$的密度区，团簇效应变得不明显，核物质主要由核子自由度决定.此外，我们还将gNL-RMF模型对低密度和有限温度下重离子碰撞的对称能和对称自由能的预测结果与相应的实验数据进行了比较，发现两者符合较好.
