Black hole spectroscopy is the program to measure the complex gravitational-wave frequencies of merger remnants, and to quantify their agreement with the characteristic frequencies of black holes computed at linear order in black hole perturbation theory. In a "weaker" (non-agnostic) version of this test, one assumes that the frequencies depend on the mass and spin of the final Kerr black hole as predicted in perturbation theory. Linear perturbation theory is expected to be a good approximation only at late times, when the remnant is close enough to a stationary Kerr black hole. However, it has been claimed that a superposition of overtones with frequencies fixed at their asymptotic values in linear perturbation theory can reproduce the waveform strain even at the peak. Is this overfitting, or are the overtones physically present in the signal? To answer this question, we fit toy models of increasing complexity, waveforms produced within linear perturbation theory, and full numerical relativity waveforms using both agnostic and non-agnostic ringdown models. We find that higher overtones are unphysical: their role is mainly to "fit away" features such as initial data effects, power-law tails, and (when present) nonlinearities. We then identify physical quasinormal modes by fitting numerical waveforms in the original, agnostic spirit of the no-hair test. We find that a physically meaningful ringdown model requires the inclusion of higher multipoles, quasinormal mode frequencies induced by spherical-spheroidal mode mixing, and nonlinear quasinormal modes. Even in this "infinite signal-to-noise ratio" version of the original spectroscopy test, there is convincing evidence for the first overtone of the dominant multipole only well after the peak of the radiation.
Gravitational waves in massive gravity: Waveforms generated by a particle plunging into a black hole and the excitation of quasinormal modes and quasibound states
Repeated faint quasinormal bursts in extreme-mass-ratio inspiral waveforms: Evidence from frequency-domain scalar self-force calculations on generic Kerr orbits
我们报告的代码来计算标量带电粒子上的克尔时空中的一般束缚轨道运动的标量自作用力的发展。标量自作用力模型允许快速发展的计算技术相关的通用引力极值质量比的inspirals（EMRI）。我们的频域计算是用\textsc{Mathematica}编写的任意数值精度代码进行的。我们扩展光谱源集成技术的克尔时空，提高计算效率。我们模拟轨道几乎任意倾角$0\leqι<π/2$和偏心率高达$e \lesssim 0.8$。这一努力扩展了沃伯顿和巴拉克早期的工作，其中运动被限制在赤道平面或倾斜的球形轨道。与Thornburg和Wardell \cite{ThorWard17}在时域计算中的最新发现相一致，我们观察到在围绕快速旋转的黑洞的高偏心轨道的径向向外部分期间的自作用力振荡。如前所述，这些振荡反映了在近心通过期间激发的准正规模式耦合到自作用力中。我们的研究结果证实了频域代码的效果。\emph{More importantly, we find that quasinormal bursts (QNBs) appear directly in the waveform following each periastron passage.}这些微弱的猝发被示出为最小阻尼泛音的叠加（即，基本）的至少四个（$l=m \le 4$）准正规模。我们的研究结果表明，QNB应该出现在引力波形，从而提供规范不变…
Quasinormal modes and their excitation beyond general relativity. II: isospectrality loss in gravitational waveforms
The Grainger College of Engineering, University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校格兰杰工程学院）；Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））；ETH Zürich（苏黎世联邦理工学院）；Universidad de Murcia（穆尔西亚大学）；University of Tübingen（蒂宾根大学）；University of Virginia（弗吉尼亚大学）
Exceptional Points in Quasinormal Spectra of Hairy Black Holes
College of Physics, Sichuan University（四川大学物理学院）；School of Data Science, Shanghai University of Finance and Economics Zhejiang College（上海财经大学浙江学院数据科学学院）
Asymptotics and Universality in Black Holes: from the quasinormal Weyl's law to the binary merger waveform
Radboud University（拉德堡德大学）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究学院）；Niels Bohr Institute（尼尔斯·玻尔研究所）；University of Southampton（南安普顿大学）
Excitation factors for horizonless compact objects: long-lived modes, echoes, and greybody factors
Dipartimento di Fisica, Sapienza Università di Roma（罗马大学物理系）；INFN, Sezione di Roma（意大利国家核物理研究所罗马分部）；Indian Institute of Technology, Gandhinagar（印度理工学院甘地纳加尔分校）；School of Physical Sciences, Indian Association for the Cultivation of Science（印度科学培养协会物理科学学院）
Scalaron Quasinormal and Quasi-Bound Modes of Schwarzschild Black Holes in the Bondi-Sachs Formulation of Metric $f(R)$ Gravity
University of Cape Town（开普敦大学）；Botswana International University of Science and Technology（博茨瓦纳国际科学与技术大学）；University of South Africa（南非大学）；University of Oslo（奥斯陆大学）
Searching for a waveform-agnostic gravitational wave signal in pulsar timing arrays
Columbia University（哥伦比亚大学）；University of Birmingham（伯明翰大学）；Monash University（蒙纳士大学）；Montana State University（蒙大拿州立大学）；Oregon State University（俄勒冈州立大学）
Quantum gravitational corrections at third-order curvature, acoustic analog black holes and their quasinormal modes
Dipartimento di Fisica e Astronomia, Università di Bologna（博洛尼亚大学物理与天文学系）；I.N.F.N., Sezione di Bologna, I.S. FLAG（意大利国家核物理研究所博洛尼亚分部 FLAG 研究所）；Center for Natural and Human Sciences, Federal University of ABC（ABC 联邦大学自然与人类科学中心）；Center of Mathematics, Federal University of ABC（ABC 联邦大学数学中心）
Niels Bohr Institute（尼尔斯·玻尔研究所）；CENTRA, Departamento de Fisica, Instituto Superior Técnico – IST, Universidade de Lisboa – UL（科英布拉天体物理与中心研究中心，物理学系，高等技术学院，里斯本大学）；University of Birmingham（伯明翰大学）；University of Nottingham（诺丁汉大学）
