The equation of state for neutron star matter has been obtained through Bayesian inference utilizing a relativistic mean field model with a non-linear mesonic interaction.

The equation of state for matter in neutron stars has been obtained through Bayesian inference utilizing a relativistic mean field model with a non-linear mesonic interaction. ----------------------------<br> Dr. Tuhin Malik<br> Department of Physics, University of Coimbra<br> [e-mail]<br> Date: 22 Apr 2023<br> -----------------------------<br> The high density behavior of nuclear matter is analyzed within a relativistic mean field description with non-linear meson interactions. To assess the model parameters and their output, a Bayesian inference technique is used. The Bayesian setup is limited only by a few nuclear saturation properties, the neutron star maximum mass larger than 2 M$_\odot$, and the low-density pure neutron matter equation of state (EOS) produced by an accurate N$^3$LO calculation in chiral effective field theory. Depending on the strength of the non-linear scalar vector field contribution, we have found three distinct classes of EOSs, each one correlated to different star properties distributions. If the non-linear vector field contribution is absent, the gravitational maximum mass and the sound velocity at high densities are the greatest. However, it also gives the smallest speed of sound at densities below three times saturation density. On the other hand, models with the strongest non-linear vector field contribution, predict the largest radii and tidal deformabilities for 1.4 M$_\odot$ stars, together with the smallest mass for the onset of the nucleonic direct Urca processes and the smallest central baryonic densities for the maximum mass configuration. {These models have the largest speed of sound below three times saturation density, but the smallest at high densities, in particular, above four times saturation density the speed of sound decreases approaching approximately $\sqrt{0.4}c$ at the center of the maximum mass star. On the contrary, a weak non-linear vector contribution gives a monotonically increasing speed of sound.} {A 2.75 M$_\odot$ NS maximum mass was obtained in the tail of the posterior with a weak non-linear vector field interaction. This indicates that the secondary object in GW190814 could also be an NS. {The possible onset of hyperons and the compatibility of the different sets of models with pQCD are discussed. It is shown that pQCD favors models with a large contribution from the non-linear vector field term or which include hyperons.}} The article e-Print: 2301.08169 We release model parameters, its nuclear saturation properties, equation of state, and TOV solutions derived from Bayesian Inference with Prior Set 0, 1, 2, and 3. We also share Set 0 with Hyperon. <br> <br> For every Set, our data release packet contains four CSV files, namely "set{X}_prop.csv", "set{X}_eos.csv", "set{X}_tov.csv", and "set{X}_cs2.csv", where X in [0,1,2,3 and 0_hyp].<br> <br> set{X}_prop.csv:<br> The file contains the parameters for the RMF model, as well as a few NS properties and nuclear saturation properties. It has the following columns:<br> model name,gs,gv,gr,B,C,xi,lam,rho0,e0,k0,q0,z0,jsym0,lsym0,<br> ksym0,qsym0,zsym0,m_max,r_max,r14,lam14,cs2_max, ec,rhoc,rho_durca.<br> It is to be noted that the parameter B and C are the 10^3*b and 10^3 c (see article for details). <br> <br> set{X}_eos.csv:<br> For those models in set{X}_prop.csv, it is the NS matter EOS file. It has the following columns: model name, baryon number density, energy density and pressure. The units for baryon number density is fm-3 and MeV/fm3 is for both energy density and pressure. The EOS is for the core only. The crust is not added. <br> <br> set{X}_tov.csv:<br> For those models in set{X}_prop.csv, it is the TOV solution. It has the following columns: model name, ns radius (km), ns mass (msun), and dimensionless tidal deformability lambda. set{X}_cs2.csv:<br> For those models in set{X}_prop.csv, it is the square of the speed of sound over density. It has the following columns: model name, number density fm-3, and square of the speed of sound c2. <br> -------------------------------------------------------------------------本研究通过采用带有非线性介子相互作用（non-linear mesonic interaction）的相对论平均场模型（relativistic mean field model），结合贝叶斯推断（Bayesian inference），得到了中子星物质的物态方程（equation of state, EOS）。<br>----------------------------<br>图欣·马利克博士<br>科英布拉大学物理系<br>[e-mail]<br>日期：2023年4月22日<br>-----------------------------<br>核物质的高密度行为通过带有非线性介子相互作用的相对论平均场框架进行分析。为评估模型参数及其输出结果，本研究采用了贝叶斯推断技术。该贝叶斯框架仅受限于少数核饱和性质、中子星最大质量大于2M☉，以及通过精确的N³LO计算在手征有效场论（chiral effective field theory）中得到的低密纯中子物质物态方程。<br><br>根据非线性标量-矢量场贡献的强度，本研究得到了三类截然不同的物态方程，每一类均对应不同的中子星性质分布。若不存在非线性矢量场贡献，则引力最大质量与高密度下的声速均为最大，但此时三倍饱和密度以下的声速却最小。另一方面，非线性矢量场贡献最强的模型则预言，1.4M☉中子星的半径与潮汐形变能力均为最大，同时核子直接乌尔卡过程（direct Urca processes）的触发质量最小，且最大质量构型的中心重子密度最低。{这类模型在三倍饱和密度以下的声速最大，但在高密度下声速最小；具体而言，在四倍饱和密度以上时，最大质量中子星中心的声速会下降至接近√0.4 c。与之相反，非线性矢量场贡献较弱的模型的声速呈单调递增趋势。}<br><br>{在非线性矢量场相互作用较弱的后验分布尾部中，得到了2.75M☉的中子星最大质量，这表明GW190814事件中的次级天体也可能是一颗中子星。{本文还讨论了超子（hyperons）的可能触发条件，以及不同模型集合与微扰量子色动力学（perturbative Quantum Chromodynamics, pQCD）的兼容性。研究表明，pQCD更青睐非线性矢量场项贡献较大或包含超子的模型。}}<br><br>本文预印本编号：2301.08169。本数据集发布了基于先验集合0、1、2、3的贝叶斯推断得到的模型参数、核饱和性质、物态方程以及托尔曼-奥本海默-沃尔科夫（Tolman-Oppenheimer-Volkoff, TOV）解，同时还提供了包含超子的先验集合0的相关数据。<br><br>针对每一个先验集合，本数据集发布包均包含四个CSV文件，分别为`set{X}_prop.csv`、`set{X}_eos.csv`、`set{X}_tov.csv`与`set{X}_cs2.csv`，其中X的取值为0、1、2、3以及0_hyp。<br><br>`set{X}_prop.csv`：<br>该文件包含相对论平均场（relativistic mean field, RMF）模型的参数，以及若干中子星性质与核饱和性质。其列名依次为：模型名称、gs、gv、gr、B、C、xi、lam、rho0、e0、k0、q0、z0、jsym0、lsym0、ksym0、qsym0、zsym0、m_max、r_max、r14、lam14、cs2_max、ec、rhoc、rho_durca。<br>需注意，参数B与C分别对应10³·b与10³·c（详细说明请参见原文）。<br><br>`set{X}_eos.csv`：<br>对应`set{X}_prop.csv`中的模型，该文件为中子星物质物态方程文件。其列名依次为：模型名称、重子数密度、能量密度与压强。重子数密度的单位为fm⁻³，能量密度与压强的单位均为MeV/fm³。本物态方程仅适用于中子星核心区域，未包含外壳部分。<br><br>`set{X}_tov.csv`：<br>对应`set{X}_prop.csv`中的模型，该文件为托尔曼-奥本海默-沃尔科夫（TOV）解。其列名依次为：模型名称、中子星半径（km）、中子星质量（M☉）以及无量纲潮汐形变参数lambda。<br><br>`set{X}_cs2.csv`：<br>对应`set{X}_prop.csv`中的模型，该文件为声速平方随密度的变化关系。其列名依次为：模型名称、数密度（fm⁻³）以及声速平方c²。<br>-------------------------------------------------------------------------