能量-动量平方引力中的中子星：结构、稳定性与多信使约束
Neutron Stars in Energy--Momentum Squared Gravity: Structure, Stability, and Multimessenger Constraints
AI总结：
该研究在能量-动量平方引力框架下，利用四种强子物态方程构建非旋转中子星模型，结合多信使观测约束分析其结构稳定性，发现耦合参数影响高密度分支偏移且部分模型声速存在超光速问题。
AI中文摘要：
我们研究能量-动量平方引力（EMSG）中的非旋转中子星。恒星模型由修正的托尔曼-奥本海默-沃尔科夫（Tolman-Oppenheimer-Volkoff）方程，以及WFF1、SLy4、APR4和MPA1这四种原始表格形式的强子物态方程得到。我们采用耦合参数集α∈{-20,-10,0,+5,+7.5} km²，构建质量-半径序列与质量-中心密度序列，并将这些序列与2倍太阳质量（2 M☉）的质量要求、NICER对PSR J0030+0451和PSR J0740+6620的测量结果，以及GW170817推断出的区域进行比较。在所采样的耦合参数范围内，计算得到的转向前分支与这四个基准仍兼容。α的负值通常会使高密度分支向更大质量偏移，正值则产生相反方向的较小偏移。在WFF1和SLy4的表格中，微观声速在高密度下变为超光速，而APR4和MPA1在其表格范围内仍满足因果性。对于WFF1，因果边界处于表格的粗粒段内，因此在现有密度分辨率下无法确定其与2 M☉要求的兼容性。当α=-20 km²时，WFF1、SLy4和APR4的有效流体声速诊断会出现奇点，而显式修正的TOV系统中不存在该奇点。所有计算得到的序列均低于标准布赫达尔（Buchdahl）参考值的致密性和表面红移。
英文摘要：
We study nonrotating neutron stars in energy--momentum squared gravity (EMSG). The stellar models are obtained from the modified Tolman--Oppenheimer--Volkoff equations and four original tabulated hadronic equations of state: WFF1, SLy4, APR4, and MPA1. We use the common coupling set $α\in\{-20,-10,0,+5,+7.5\}\,\mathrm{km}^{2}$ and construct mass--radius and mass--central-density sequences. We compare these sequences with the $2\,M_\odot$ mass requirement, the NICER measurements of PSR J0030+0451 and PSR J0740+6620, and the region inferred from GW170817. Within the sampled coupling range, the computed pre-turning-point branches remain compatible with these four benchmarks. Negative values of $α$ generally shift the high-density branches toward larger masses. Positive values produce smaller shifts in the opposite direction. The microscopic sound speed becomes superluminal at high density in the WFF1 and SLy4 tables, whereas APR4 and MPA1 remain causal over their tabulated ranges. For WFF1, the causal boundary falls within a coarse table segment. Its compatibility with the $2\,M_\odot$ requirement therefore cannot be decided at the available density resolution. At $α=-20\,\mathrm{km}^{2}$, the effective-fluid sound-speed diagnostic becomes singular for WFF1, SLy4, and APR4. This singularity is absent from the explicit modified TOV system. All computed sequences remain below the standard Buchdahl reference values for compactness and surface redshift.
