Recently, it has been proposed that the black hole greybody factors can be important to model ringdown spectral amplitudes. We study the stability of greybody factors against a small-bump correction in the perturbation equation. We find (I) that the greybody factor is stable in the frequency region relevant to ringdown and (II) that it is destabilized at higher frequencies, especially for a sharper bump correction. This behavior is similar to the case of higher overtones, which is also very sensitive to a small correction. We clarify this (in)stability with the WKB analysis. As the greybody factor is stable at the frequency region relevant to the main part of ringdown, we conclude that the greybody factor is suitable to model ringdown amplitude. In order to investigate a bump correction in a self-consistent manner, we consider the small-bump correction that can be realized in the general framework of effective field theory of black hole perturbations.
Ringdown and greybody signatures of rational regular black holes in non-polynomial gravity
Kimyo International University in Tashkent（塔什干化学国际大学）；Tashkent State Technical University（塔什干国立技术大学）；School of Physics, Harbin Institute of Technology（哈尔滨工业大学物理学院）；University of Tashkent for Applied Sciences（塔什干应用科学大学）；Institute of Theoretical Physics, National University of Uzbekistan（乌兹别克斯坦国立大学理论物理研究所）；Samarkand State Pedagogical Institute（撒马尔罕国立师范学院）；New Uzbekistan University（新乌兹别克斯坦大学）；Research Institute of Irrigation and Water Problems（灌溉与水资源问题研究所）；Tashkent International University（塔什干国际大学）
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）
Parity violating spectral dynamics of black holes in dynamical Chern-Simons gravity
Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Department of Physics, Yantai University（烟台大学物理系）；School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences（中国科学院大学杭州高等研究院基础科学与数学学院）
