非球形坍缩在早期物质主导时期引力波辐射的N体模拟研究
Gravitational wave emission from nonspherical collapse in an early matter-dominated era using N-body simulations
AI总结：
研究通过N体模拟探讨早期物质主导时期非球形过密区域坍缩的动力学及引力波产生，发现非线性坍缩需全数值处理，峰值分布显示BBKS结果更小，引力波谱可映射至不同探测器灵敏度范围。
摘要：
我们利用开发的半相对论N体框架，研究早期物质主导时期非球形过密区域坍缩的动力学及关联的引力波（GW）产生。坍缩区域通过Zel'dovich变形初始化，并在Einstein-de Sitter背景中演化，而发射信号直接通过数值四极子演化计算。我们证明可靠预测信号需要全数值处理非线性坍缩动力学。特别是，基于拟合的程序和Zel'dovich估计无法捕捉壳交叉后演化，并可能高估或低估GW发射功率。在平均过现实现，加权Doroshkevich和BBKS（峰值理论）分布后，发现两种谱形相似，峰值幅度在同一数量级，尽管BBKS结果系统更小。主导贡献来自相对较低高度的峰值，约ν≈3，而较大方差显著增强信号。最后，通过改变视界质量和再加热温度，我们将现时GW谱映射到不同探测器类别的灵敏度带。这样，信号可在脉冲星定时阵列到极高频实验的广泛频率范围内出现，表明非球形坍缩的GW可探测预BBN热史。
英文摘要：
We study the dynamics of the collapse of a nonspherical overdense patch during an early matter-dominated era and the associated production of gravitational waves (GWs) using a semirelativistic N-body framework that we develop. The collapsing patch is initialized through a Zel'dovich deformation of a homogeneous sphere and evolved in an Einstein--de Sitter background, while the emitted signal is computed directly from the numerical quadrupole evolution. We show that a reliable prediction of the signal requires a fully numerical treatment of the nonlinear collapse dynamics. In particular, fitting-based procedures and Zel'dovich-based estimates fail to capture the post-shell-crossing evolution and can over/under-estimate the emitted power of the GWs. After averaging over realizations weighted by the Doroshkevich and BBKS (peak theory) distributions, we find that the two spectra have similar shapes and remain within the same overall order of magnitude at the peak amplitude, although the BBKS result is systematically smaller. The dominant contribution arises from peaks of relatively modest height, around $ν\simeq 3$, while a larger variance significantly enhances the signal. Finally, by varying the horizon mass and reheating temperature, we map the present-day GW spectra to the sensitivity bands of different classes of detectors. In this way, the signal can populate a broad range of frequencies, from pulsar timing arrays to very high-frequency experiments, showing that GWs from nonspherical collapse can provide a probe of the pre-BBN thermal history.
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