IBS CTPU-CGA 2025 Workshop on Quasi Normal Mode and Black Hole Perturbation

Contribution List

5. Invited Talk: Takahiro Tanaka (Title: Evolution of super-radiant axion clouds)

26/05/2025, 10:00

Title: Evolution of super-radiant axion clouds

2. Invited Talk: Gimmy Tomaselli (Title: Gravitational atoms and black hole binaries)

26/05/2025, 10:45

Title: Gravitational atoms and black hole binaries

Abstract: Various models of physics beyond the Standard Model predict the existence of ultralight bosons. These particles can be produced through superradiant instabilities, which create boson clouds around rotating black holes, forming so-called "gravitational atoms". In this talk, I review a series of papers that study the interaction...

3. Invited Talk: Thomas Spieksma (Title: Black hole superradiance: a gateway to new physics)

26/05/2025, 13:30

Title: Black hole superradiance: a gateway to new physics

Abstract: Black holes in our Universe are not expected to reside in vacuum. Their environments—such as accretion disks or dark matter distributions—can significantly impact black hole physics, whether in isolation or in binary systems. A particularly intriguing environment arises from black hole superradiance: a process through which...

4. Invited Talk: Huiyu ZHU (Title: Survival of the Fittest: Testing Superradiance Termination with Simulated Binary Black Hole Statistics )

26/05/2025, 14:15

Title: Survival of the Fittest: Testing Superradiance Termination with Simulated Binary Black Hole Statistics

Abstract: The superradiance instability of rotating black holes leads to the formation of an ultralight boson cloud with distinctive observational signatures, making black holes an effective probe of ultralight bosons. However, around black holes in a binary system, the...

6. Invited Talk: Swetha Bhagwat (Title: Mode Amplitudes: Linear and Nonlinear Dynamics In Ringdowns)

26/05/2025, 15:30

Title: Mode Amplitudes: Linear and Nonlinear Dynamics In Ringdowns

7. Invited Talk: Yeong-Bok Bae (Title: Ringdown Gravitational-Waves from the Close Scattering of Two Black Holes )

26/05/2025, 16:15

Title: Ringdown Gravitational-Waves from the Close Scattering of Two Black Holes

Abstract: In this talk, we present fully general-relativistic simulations showing that two equal-mass, nonspinning black holes on close-scattering hyperbolic trajectories can emit a clear ringdown gravitational-wave signal without merging. This signal arises purely from the dynamical tidal deformations during...

8. Invited Talk: Emanuele Berti (online)

27/05/2025, 10:00

9. Invited Talk: Huan Yang (Title: Nonlinear black hole ringdowns)

27/05/2025, 10:45

Title: Nonlinear black hole ringdowns

Abstract: In this talk, I will discuss recent progress in characterizing second order quainormal modes of rotating black holes. This includes two independent ways of computing the mode-mode coupling coefficients, which lead to consistent results. A parameter survey shows that multiple 2nd-order order modes may be detectable for 3G ground-based detectors...

10. Invited Talk: Keefe Mitman (Title: Leveraging binary black hole ringdown excitations as probes of astrophysics and tests of GR )

27/05/2025, 13:30

Title: Leveraging binary black hole ringdown excitations as probes of astrophysics and tests of GR

Abstract: With the commencement of the LIGO-Virgo-KAGRA Collaboration's fourth observing run, the field of gravitational wave (GW) physics is uniquely poised to collect even more precise data from compact binary coalescences. Consequently, we will soon be able to perform even more stringent...

11. Invited Talk: Jaime Redondo-Yuste (Title: Nonlinear effects in perturbation theory)

27/05/2025, 14:15

Title: Nonlinear effects in perturbation theory

Abstract:
General relativity is a nonlinear theory, and understanding its nonlinear features is crucial for many physical phenomena. In this talk I will motivate the study of subleading orders in perturbation theory. I will first review some generalities of perturbation theory in symmetric spacetimes, and then focus on black hole...

13. Invited Talk: Vitor Cardoso (online) (Title: The quest for horizons)

27/05/2025, 15:30

Title: The quest for horizons

Abstract: One of the most remarkable possibilities of General Relativity concerns gravitational collapse to black holes. Is the strong field dynamical regime of gravity well described by General Relativity? I will summarize the status of black hole spectroscopy and attempts at probing near horizon physics.

12. Invited Talk: Naritaka Oshita (Title: Excitability, convergence and (in)completeness of quasi-normal modes)

27/05/2025, 16:15

Title: Excitability, convergence and (in)completeness of quasi-normal modes

Abstract: After the merger of a binary black hole system, the remnant black hole undergoes free oscillations, emitting gravitational waves known as the ringdown signal.
These ringdown waveforms contain multiple quasi-normal modes (QNMs), and it is expected that black hole spectroscopy—resolving these modes...

14. Invited Talk: Zihan Zhou (online) (Title: When black hole perturbation theory meets scattering amplitudes and conformal field theory )

28/05/2025, 10:00

Title: When black hole perturbation theory meets scattering amplitudes and conformal field theory

Abstract:
The study of black hole perturbation theory has seen a resurgence in recent years after the observation of the gravitational waves generated by the coalescence of binary black holes. In this talk, I will summarize some of the recent progress in understanding black hole perturbation...

15. Invited Talk: Yasuyuki Hatsuda (Title: Heun connection formulae and quasinormal modes)

28/05/2025, 10:45

Title: Heun connection formulae and quasinormal modes

Abstract:
Recently, analytic formulae of connection coefficients in Heun's differential equation were conjectured. In this talk, I will explain how to use them to analyze quasinormal mode problems for four-dimensional asymptotically de Sitter black holes.

16. Invited Talk: Masashi Kimura

29/05/2025, 10:00

17. Invited Talk: Pablo Cano (Title: Eikonal quasinormal modes of rotating black holes beyond GR: a window into extremality )

29/05/2025, 10:45

Title: Eikonal quasinormal modes of rotating black holes beyond GR: a window into extremality

Abstract:
The computation of quasinormal modes of rotating black holes in modified theories of gravity has been recently made possible thanks to the development of new techniques, like a modified Teukolsky equation and spectral methods. However, no method so far has been able to peek into the...

18. Invited Talk: Sebastian Völkel (Title: Advances in the Parametrized QNM Framework and New Perspectives from Bound States)

29/05/2025, 13:30

Title: Advances in the Parametrized QNM Framework and New Perspectives from Bound States

Abstract:
Black hole spectroscopy, applied to the ringdown phase of compact binary mergers, is one of the most promising tools to test the nature of black holes. It allows us to quantify whether black holes and their perturbative dynamics are well described by general relativity and, thus, serve as a...

19. Invited Talk: Young-Hawn Hyun

29/05/2025, 14:15

20. Contributed Talk: Miok Park (Title: Hairy Black Holes by Spontaneous Symmetry Breaking in ESGB theory )

29/05/2025, 15:30

Title: Hairy Black Holes by Spontaneous Symmetry Breaking in ESGB theory

Abstract: We study hairy black hole solutions in Einstein-(Maxwell)-scalar-Gauss-Bonnet theory. The scalar coupling function includes quadratic and quartic terms, so the gravitational action has a U(1) symmetry. We argued that when the effective mass of the scalar field is at the critical value, hairy black holes are...

21. Contributed Talk: Theodoros Nakas (Title: Black holes in string-inspired Euler-Heisenberg theory: Doppelgänger black holes)

29/05/2025, 16:15

Title: Black holes in string-inspired Euler-Heisenberg theory: Doppelgänger black holes

27. Invited Talk: Helvi Witek (online)

30/05/2025, 10:00

23. Invited Talk: Francisco Duque

30/05/2025, 10:45

24. Invited Talk: Caio Macedo (Title: Black holes and bosonic fields: modes and binary systems)

30/05/2025, 13:30

Title: Black holes and bosonic fields: modes and binary systems

Abstract
Bosonic fields around rotating black holes can grow exponentially due to superradiant instabilities, producing detectable dynamical signatures in gravitational waves. We explore relativistic configurations of bosonic fields and black holes, analyzing their quasinormal modes and inspiral dynamics. Our findings provide...

25. Contributed Talk: Ao Guo (Title: Common Envelope Evolution of Ultralight Boson Clouds )

30/05/2025, 14:15

Title: Common Envelope Evolution of Ultralight Boson Clouds

Abstract: Ultralight bosons, as potential dark matter candidates, can form dense clouds around black holes via superradiant instabilities. In binary black hole systems, these clouds evolve under mutual tidal interactions, and form a shared structure that envelopes the entire binary—termed a gravitational molecule —as orbital...

26. Contributed Talk: Ziyu Tang (Title: A photon cloud induced from an axion cloud )

30/05/2025, 15:30

Title: A photon cloud induced from an axion cloud

Abstract: It is known that the coupling between axions (m a = µ ℏ) and photons can lead to a superradiant growth and cause electromagnetic (EM) bursts with frequency µ /2 when the coupling constant ka multiplied with the amplitude of the axion clould ϕ 0 larger than a critical value. In the first-order of the coupling constant, we studied...

22. Invited Talk: Giada Santoro

30/05/2025, 16:15

1. Invited Talk: Takahiro Tanaka

Superradiance & QNM

28. Opening