AI 中文总结
研究差分旋转中子星中MRI的输运性质，通过GRMHD模拟测量相关输运系数及与平均流参数的相关性，发现饱和时相关量与预期有偏差且高度间歇性，混合长度与密度无关，强调完全解析模拟对定量预测的必要性。
AI 中文摘要
我们对差分旋转中子星中的磁旋转不稳定性（MRI）进行了三维、高分辨率、广义相对论磁流体动力学（GRMHD）模拟。考虑了高质量模型（因角动量向外传输失去旋转支撑而迅速坍缩）和低质量模型（即使达到刚体旋转仍保持稳定）。测量了湍流的有效输运系数，如剪切粘度αvis、混合长度ℓmix和平均场发电机αDYN参数及其与平均流参数的相关性。结果显示，饱和时ℓmix和αDYN分别与λMRI和vA相关，但与基于这些相关性预测的值有数量级偏差，且在时空上高度间歇性。混合长度在很大程度上与密度无关。结果表明，虽然采用量纲分析选择输运系数的模拟可能定性再现MRI诱导湍流的影响，但要进行定量预测需要完全解析的GRMHD模拟。
英文摘要
We perform three-dimensional, high-resolution, general-relativistic magnetohydrodynamics (GRMHD) simulations of the magnetorotational instability (MRI) in differentially rotating neutron stars. We consider both high-mass models which collapse either promptly, or due to the outward transport of angular momentum removing rotational support, and lower-mass models, which remain stable even after solid-body rotation has been achieved. We measure effective transport coefficients of the resulting turbulent flow, shear-viscosity $α_{\rm vis}$, mixing-length $\ell_{\rm mix}$, and mean-field dynamo $α_{\rm DYN}$-parameter, and their correlations with mean-flow parameters, such as rest-mass density $ρ$, characteristic wavelength of the MRI $λ_{\rm MRI}$, and vertical Alfvén velocity $v_A$. At saturation, $\ell_{\rm mix}$ and $α_{\rm DYN}$ correlate with $λ_{\rm MRI}$ and $v_A$ respectively, as expected from dimensional analysis. However, both quantities show deviations of roughly an order of magnitude from the values predicted on the basis of these correlations. They are also highly intermittent in space and time. The mixing length is found to be largely independent of density, calling into question the $\ell_{\rm mix}(ρ)$ ansatz used in many general-relativistic large-eddy simulations. Our results show that, while the effects of MRI-induced turbulence might be qualitatively reproduced by simulations that employ transport coefficients chosen using dimensional-analysis considerations, fully-resolved GRMHD simulations are needed to make quantitative predictions.
