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arXiv 2407.20131gr-qchep-th
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黑洞的谱不稳定性:关联频域与时域

Spectral instability of black holes: relating the frequency domain to the time domain

Yiqiu Yang, Zhan-Feng Mai, Run-Qiu Yang, Lijing Shao, Emanuele Berti

AI总结:

本文通过散射分析解释黑洞准正模频域强不稳定与早期时域铃振波形变化微弱之间的关系,识别影响 Schwarzschild 和 Kerr 黑洞的 II 型不稳定性,并证明早期波形偏差在 $ε\lesssim10^{-2}$ 时正比于 $ε$。

摘要:

近期研究表明,在径向势受到量级为 $ε$ 的小微扰时,黑洞的准正模谱并不稳定,而早期时域铃振波形仅受到轻微影响。本文通过分析该问题的散射性质,进一步揭示频域描述与时域描述之间这种表面张力的内在原因。在频域中,我们解析地研究了与受扰势对应的解。我们证明存在两类性质不同的不稳定性,并且 Schwarzschild 黑洞与 Kerr 黑洞都会受到我们所称的“II 型”不稳定性影响:当扰动“鼓包”从未受扰势的峰值处移开时,模频率会以指数方式偏离其未受扰值。在时域中,我们利用 Green 函数的因果结构阐明了谱不稳定性的效应。通过一个等价的散射问题,我们以解析方式确认(并以数值方式展示):当 $ε\lesssim10^{-2}$ 时,早期铃振阶段中波形相对于未受扰波形的偏离与 $ε$ 成正比。

英文摘要:

Recent work has shown that the quasinormal mode spectrum of black holes is unstable under small perturbations (of order $ε$) of the radial potential, while the early time-domain ringdown waveform is only marginally affected. In this paper we provide further insight into the apparent tension between the frequency-domain and the time-domain descriptions by analyzing the scattering properties of the problem. In the frequency domain, we study analytically the solutions corresponding to the perturbed potential. We show that there are two qualitatively different classes of instabilities, and that both Schwarzschild and Kerr black holes are affected by what we call a "Type II" instability, i.e., an exponential migration of the mode frequencies away from their unperturbed value as the perturbing "bump" moves away from the peak of the unperturbed potential. In the time domain, we elucidate the effect of the spectral instability in terms of the causal structure of the Green's function. By using an equivalent scattering problem we confirm analytically (and show numerically) that the deviation from the unperturbed waveform in the early ringdown stage is proportional to $ε$ when $ε\lesssim10^{-2}$.

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