标题： 高分辨率磁流体动力学湍流中的自相似宇宙射线输运 显示英文标题

标题： Self-Similar Cosmic-Ray Transport in High-Resolution Magnetohydrodynamic Turbulence

摘要： 我们研究宇宙射线（CRs）在磁流体动力学（MHD）湍流中的传播，该模拟达到了前所未有的分辨率$10{,}240^3$。我们驱动的湍流是亚音速且超阿尔芬的，其特征为$\delta B_{\rm rms}/B_0=2$。高分辨率使得惯性范围扩展，使得阿尔芬尺度$l_A$，其中$\delta B (l_A)\approx B_0$，得到了很好的解析。这使我们能够正确捕捉级联如何从大尺度上的大振幅过渡到小尺度上的小振幅。我们发现，即使在小尺度上，磁场的急剧弯曲也是粒子传输的关键媒介，通过共振曲率散射实现。我们进一步发现，湍流中的粒子散射表现出自相似性的强烈迹象：(1) 在几乎两个数量级的粒子能量范围内，扩散的能源依赖性较弱；(2) 粒子的随机行走表现出碰撞时间的广泛幂律分布，使得扩散主要由最罕见的长距离运动主导。我们的结果表明，大振幅MHD湍流可以在广泛的CR能量范围内提供有效的散射，并可能有助于解释高于$\sim$TeV 的许多CR观测结果：B/C谱的平坦化、CR原初谱的硬化以及到达各向异性对CR能量的弱依赖性。 显示英文摘要

摘要： We study the propagation of cosmic rays (CRs) through a simulation of magnetohydrodynamic (MHD) turbulence at unprecedented resolution of $10{,}240^3$. We drive turbulence that is subsonic and super-Alfv\'enic, characterized by $\delta B_{\rm rms}/B_0=2$. The high resolution enables an extended inertial range such that the Alfv\'en scale $l_A$, where $\delta B (l_A)\approx B_0$, is well resolved. This allows us to properly capture how the cascade transitions from large amplitudes on large scales to small amplitudes on small scales. We find that sharp bends in the magnetic field are key mediators of particle transport even on small scales via resonant curvature scattering. We further find that particle scattering in the turbulence shows strong hints of self-similarity: (1) the diffusion has weak energy dependence over almost two decades in particle energy and (2) the particles' random walk exhibits a broad power-law distribution of collision times such that the diffusion is dominated by the rarest, long-distance excursions. Our results suggest that large-amplitude MHD turbulence can provide efficient scattering over a wide range of CR energies and may help explain many CR observations above a $\sim$TeV: the flattening of the B/C spectrum, the hardening of CR primary spectra and the weak dependence of arrival anisotropy on CR energy.