Conference timetable and talk details.
Chair: Morning and afternoon — Cristofoli
| Time | Speaker / Activity |
|---|---|
| 09:00 - 10:00 | Registration |
| 10:00 - 10:15 | Opening remarks |
| 10:15 - 11:15 | Thibault DamourHigh-Precision Dynamics and Waveform in Two-Body Gravitational Scattering |
| 11:15 - 11:45 | Coffee break |
| 11:45 - 12:45 | Fei TengOn-shell Approaches for Gravitational Wave Physics: waveform and beyond |
| 12:45 - 14:15 | Lunch |
| 14:15 - 15:15 | Donal O'ConnellSupertranslations are Soft Dressings |
| 15:15 - 15:45 | Coffee break |
| 15:45 - 16:05 | Hyun Jeong (contributed talk)Gravitational Memory in Black Hole Mergers from Scattering Amplitudes |
| 16:05 - 16:25 | Kaho Yoshimura (contributed talk)From On-shell amplitudes to Hawking radiation |
| 16:25 - 16:45 | Hajime Kobayashi (contributed talk)Dynamical Tidal Response of Non-rotating Black Holes: Connecting the MST Formalism and Worldline EFT |
Chairs: Morning — Mukohyama; Afternoon — Teng
| Time | Speaker / Activity |
|---|---|
| 10:00 - 11:00 | Vitor CardosoLight by Light |
| 11:00 - 11:30 | Coffee break |
| 11:30 - 12:30 | Maximiliano IsiBlack hole ringdown observations: a status update |
| 12:30 - 14:00 | Lunch |
| 14:00 - 15:00 | Hui-Yu ZhuDark Matter-Independent Orbital Decay Bounds on Ultralight Bosons from OJ287 |
| 15:00 - 15:30 | Coffee break |
| 15:30 - 15:50 | Jaime Redondo-Yuste (contributed talk)Nonlinear Dynamics in General Relativity |
| 15:50 - 16:10 | Yuto Suichi (contributed talk)Pole Structure of Kerr Black Hole Perturbations |
| 16:10 - 18:00 | Poster session |
Chair: Morning — Oshita
| Time | Speaker / Activity |
|---|---|
| 10:00 - 11:00 | Takahiro TanakaEvolution of axion clouds with self-interaction |
| 11:00 - 11:30 | Coffee break |
| 11:30 - 12:30 | Maarten van de MeentEccentric eccentricities |
| 12:30 - 14:00 | Lunch |
| 14:00 onward | Free discussion session |
| 18:00 | Conference dinner / banquet |
Chairs: Morning — Aoki; Afternoon — Furugori
| Time | Speaker / Activity |
|---|---|
| 10:00 - 11:00 | Lucile CangemiKerr Geometry from Worldlines, Higher-Spin QFT, and Scattering Amplitudes |
| 11:00 - 11:30 | Coffee break |
| 11:30 - 12:30 | Zvi BernProgress at the Fifth Post-Minkowskian Order |
| 12:30 - 14:00 | Lunch |
| 14:00 - 15:00 | Teruaki SuyamaKramers–Kronig Relations in Gravitational-Wave Lensing |
| 15:00 - 15:30 | Coffee break |
| 15:30 - 16:30 | Toshifumi NoumiOpen EFT for Cosmology & Gravity |
| 16:30 - 16:50 | Panagiotis Marinellis (contributed talk)Spinning binaries in scalar-tensor EFTs and their UV consistency from Scattering Amplitudes |
| 16:50 - 17:10 | Taiga Miyachi (contributed talk)Path to an exact WKB analysis of black hole quasinormal modes |
| 17:10 - 17:30 | Motoki Suzuki (contributed talk)Ringdown Analysis Using Orthonormal Modes |
Chairs: Morning — Takeda; Afternoon — Cristofoli
| Time | Speaker / Activity |
|---|---|
| 10:00 - 11:00 | Yanbei ChenFrom Quantum Noise Reduction to Tests of Classical and Quantum Gravity |
| 11:00 - 11:30 | Coffee break |
| 11:30 - 12:30 | Daniel CarneyQuantum Mechanics of Gravitational Waves |
| 12:30 - 14:00 | Lunch |
| 14:00 - 15:00 | Elisa MaggioRingdown tests of the black-hole paradigm |
| 15:00 | Closing remarks |
Title: High-Precision Dynamics and Waveform in Two-Body Gravitational Scattering
Abstract: One will present results concerning the dynamics and the radiation of gravitationally scattering systems recently obtained by combining information from various analytical approximation methods (Post-Newtonian, Post-Minkowskian, Multipolar Post-Minkowskian, Effective-One-Body, Tutti Frutti) as well as from Numerical Relativity.
Title: On-shell Approaches for Gravitational Wave Physics: waveform and beyond
Abstract: The detection of gravitational waves has created a pressing need for high-precision theoretical models for binary systems. In this talk, I will review recent progress in the analytic computation of physical observables for binary black hole and neutron star systems using modern on-shell methods. I will focus on how the on-shell methods, which focus directly on gauge-invariant observables, not only offer significant simplifications over traditional formalisms, but also provide new insights into the structure of classical general relativity. As an illustration, I will present a newly identified violation of the peeling behavior in the asymptotic metric
Title: Supertranslations are Soft Dressings
Abstract: In quantum field theories without a mass gap, the definition of a single-particle state is ambiguous. I will discuss how this ambiguity for a single massive particle, in the regime where the classical approximation is valid, is intimately connected to large gauge transformations of classical theories. In particular, I will describe general BMS supertranslations from this point of view, together with implications for classical observables.
Title: Gravitational Memory in Black Hole Mergers from Scattering Amplitudes
Abstract: We study gravitational memory in the waveform from the merger phase of black hole coalescence using the modern technique of scattering amplitudes. Working up to NLO, we estimate the non-linear and tail memory contributions and clarify their origin within the amplitude framework.
Title: From On-shell amplitudes to Hawking radiation
Abstract: Black holes are widely understood as thermal systems in a macroscopic sense. Various observables in black hole scattering, including Hawking radiation, have been studied using on-shell methods, where the black hole is treated as a quantum particle state. In this talk, we present a complementary on-shell perspective on Hawking radiation. We analyze absorption and emission channels and show that, even for spinning states, CPT invariance together with spherical symmetry requires both processes to be governed by the same coupling constant. The difference between them is thus reduced entirely to state counting. By matching this difference to the classical greybody factor, and assuming that the spectral density is determined by the black hole entropy, we reproduce the Hawking radiation spectrum. This formulation suggests a framework that is not tied to particular black hole geometries and may extend more generally to thermal systems.
Title: Dynamical Tidal Response of Non-rotating Black Holes: Connecting the MST Formalism and Worldline EFT
Abstract: The response of a black hole (BH) to tidal forces encodes key information about the underlying gravitational theory and affects the waveform of gravitational waves emitted during binary inspiral processes. In this paper, we analyze the dynamical tidal response of static and spherically symmetric BHs in a low-frequency regime within general relativity (GR), based on a matching between the Mano-Suzuki-Takasugi (MST) methods for an analytical approach to BH perturbations and the worldline effective field theory (EFT) for an efficient and unified computation of the binary dynamics within the post-Newtonian regime. We show that the renormalized tidal response function is subject to inevitable ambiguities associated with the choice of renormalization scheme and with the initial condition of the renormalization flow equation. Once these ambiguities are fixed, we obtain scheme-dependent dynamical tidal Love numbers. We also discuss possible extensions of our formalism, including generic non-rotating compact objects (e.g., neutron stars) in GR and BHs in theories beyond GR. This talk is based on arXiv:2511.12580 [gr-qc].
Title: Light by Light
Abstract: At very high energies, particle collisions are dominated by gravity, and short-distance physics becomes irrelevant. I will overview some of the main results in gravity-driven collisions and describe ongoing efforts to understand gravitational collapse sourced by electromagnetic radiation.
Title: Black hole ringdown observations: a status update
Abstract: The LIGO-Virgo-KAGRA Collaborations have recently released their fifth gravitational-wave catalog, GWTC-5. This includes multiple signals from black hole coalescences with resolvable power after the merger, allowing for studies of the ringdown radiation from the remnant in full isolation of the preceding inspiral. In this talk, I will summarize the status of their observations, including notable systems like GW250114 and GW231123, which have yielded exciting results for tests of gravity and astrophysics. I will conclude by outlining some open questions and challenges ahead.
Title: Dark Matter-Independent Orbital Decay Bounds on Ultralight Bosons from OJ287
Abstract: Ultralight bosons, predicted in scenarios beyond the Standard Model and viable dark matter (DM) candidates, can form superradiant clouds around spinning black holes influencing their dynamics. Using the century-long monitored OJ287 supermassive black-hole binary, we set the first DM-independent, dynamical constraints on boson masses μ = (8.5-22) × 10⁻²² eV. These constraints, driven by boson-cloud friction, are robust against DM-model uncertainties and offer a novel probe of ultralight bosons. We further show that analogous superradiant dynamics across the cosmic population of supermassive black-hole systems could help resolve the final-parsec stalling problem and imprint a detectable suppression and break in the gravitational-wave background.
Title: Nonlinear Dynamics in General Relativity
Abstract: Black holes and gravitational waves are consequences of the nonlinear character of the Einstein equations. Yet, the remarkable properties of General Relativity point to the existence of other effects. In this talk I discuss the nonlinear interaction of gravitational waves in black hole spacetimes, as well as of scalar fields in near-critical solutions, to demonstrate the existence of higher harmonic generation, spectral broadening, and focusing effects. I conclude by relating these features to the apparent simplicity of merger waveforms at infinity.
Title: Pole Structure of Kerr Black Hole Perturbations
Abstract: Black hole perturbations can be analyzed using Green’s function methods, and their time-domain response is well known to be described by quasi-normal modes and power-law tails. These features are directly related to the pole and branch cut structure of the Green’s function in the frequency domain. In recent years, within the framework of mode decomposition in non-rotating black holes, it has been pointed out that the prompt response is closely associated with the pole structure in the frequency domain, and significant progress has been made in its analysis. Motivated by these developments, in this work we analyze the pole structure of the Green’s function for Kerr black hole perturbations in the frequency domain.
Title: Evolution of axion clouds with self-interaction
Abstract: In this talk, I'll discuss the time evolution of axion clouds formed around a rotating black hole in various situations, mainly focusing on the effects of self-interaction. I will also briefly explain how the phenomena of superradiance is described quantum-mechanically.
Title: Eccentric eccentricities
Abstract: In this talk, I will discuss a number of lessons learned from studying highly eccentric small mass-ratio binaries in the strong field regime that go against the "standard lore" formed from quasicircular intuition.
Title: Kerr Geometry from Worldlines, Higher-Spin QFT, and Scattering Amplitudes
Abstract: The Kerr solution plays a central role in modelling isolated rotating astrophysical black holes and provides a natural arena for effective-field-theory and scattering-amplitude descriptions of spin. In this talk I will compare how Kerr spin-induced multipoles are encoded and computed in several related frameworks: as Wilson coefficients in worldline EFT, through interactions in massive higher-spin QFT, and in the classical limit of on-shell amplitudes. I will also discuss how this picture changes in higher dimensions, where the correspondence between amplitudes and geometry becomes richer and additional spin structures are required to reproduce Myers–Perry black-hole multipoles.
Title: Progress at the Fifth Post-Minkowskian Order
Abstract: I will describe the scattering amplitudes approach to the post-Minkowskian expansion and describe progress and challenges at the 5th post-Minkowskian order.
Title: Kramers–Kronig Relations in Gravitational-Wave Lensing
Abstract: The Kramers–Kronig (KK) relations, rooted in causality, establish a fundamental link between the real and imaginary parts of a causal response function. In this presentation, I will show that a KK relation exists in gravitational-wave lensing, which is satisfied by the amplification factor which is the fundamental observable of this phenomenon. Furthermore, we discuss how this relation may be utilized as a powerful, model-independent tool to identify lensing signals and perform consistency checks in GW data analysis.
Title: Open EFT for Cosmology & Gravity
Abstract: Many phenomena in cosmology and gravity involve open-system dynamics, where the degrees of freedom of interest interact with an environment and exhibit dissipation and noise. I will review the Schwinger-Keldysh EFT framework for such systems and explain how to incorporate dynamical gravity, with possible applications to cosmic inflation and black-hole physics.
Title: Spinning binaries in scalar-tensor EFTs and their UV consistency from Scattering Amplitudes
Abstract: The detection of gravitational waves by the LIGO-VIRGO collaboration has marked a transformative era in astronomy, providing groundbreaking insights into the cosmos and creating new pathways for exploration. At the same time, advancements in the classical limit of quantum scattering amplitudes, particularly through the KMOC formalism, have enriched our understanding of compact binary systems. In this talk, we apply these techniques to scalar-tensor EFTs of gravity, where long-range interactions are mediated by a massless scalar in addition to the graviton, including the phenomenologically relevant Einstein-scalar-Gauss-Bonnet and dynamical Chern-Simons theories. We first provide an overview of how amplitude techniques are used to derive predictions for gravitational waves from binary systems of black holes and neutron stars. We then proceed to give a purely on-shell description of arbitrarily spinning bodies with and without scalar hair, an effect that can lead to important modifications in the gravitational wave signal. Using spinor-helicity and on-shell techniques, we show how all required amplitudes are calculated straightforwardly and used to directly compute waveforms for spinning binary systems. In the second part of the talk, we turn to examine UV completions of these scalar-tensor EFTs. We consider weakly coupled UV theories with massive particles of spin 0, 1/2, and 1 minimally coupled to gravity and interacting with the scalar. Integrating them out at one loop generates the leading scalar-curvature operators. Using the same on-shell amplitude methods, we perform the matching between the UV theory and the IR EFT, expressing Wilson coefficients in terms of heavy-state masses and couplings, and discuss how UV symmetries are reflected at low energies. Together, this provides a unified amplitude-based framework connecting UV consistency to gravitational-wave predictions.
Title: Path to an exact WKB analysis of black hole quasinormal modes
Abstract: In this talk, we discuss the analysis of black hole quasinormal modes using exact WKB analysis. Exact WKB analysis provides a method to determine the global behavior of solutions to ordinary differential equations without approximation, and is particularly powerful for deriving the quantization conditions that eigenvalues must satisfy. We present our framework for applying exact WKB analysis to black hole quasinormal modes and review recent developments based on this method.
Title: Ringdown Analysis Using Orthonormal Modes
Abstract: Gravitational waves (GWs) are ripples in spacetime that propagate at the speed of light. They were first detected by LIGO in 2015, and to date, more than 300 GW events have been observed by the LIGO-Virgo-KAGRA (LVK) Collaboration. The vast majority of these events are consistent with compact binary coalescences, such as binary black holes (BHs) or neutron stars. The GW signal from these systems can be divided into three phases: inspiral, merger, and ringdown. The ringdown is the post-peak phase during which the remnant BH settles into a stationary Kerr BH while emitting GWs. The ringdown waveform can be modeled as a superposition of damped sinusoids, known as quasinormal modes (QNMs). By detecting multiple QNMs in the observed data, we can perform clean tests of general relativity using only the ringdown signal, a technique known as black hole spectroscopy. The more QNMs are detected, the more accurately we can test general relativity. This is a main motivation for detecting multiple QNMs. However, ringdown analyses with multiple QNMs face several challenges. First, QNMs are not orthogonal and exhibit similar oscillatory behavior. This leads to strong parameter correlations and reduces parameter estimation accuracy. Second, the increased number of parameters results in higher computational costs. To address these challenges, we developed a semi-analytic method based on orthonormalized QNMs. This method enables analytic marginalization over mode amplitudes and reduces parameter correlations. The details of the method are presented in [1]. In this work, we apply our method to real gravitational-wave data from the LVK collaboration, as well as to simulated waveforms designed to mimic resonant excitation that have recently attracted attention. We validate the effectiveness of our approach in terms of computational efficiency and robustness of parameter estimation. [1] Soichiro Morisaki, Hayato Motohashi, Motoki Suzuki, and Daiki Watarai, Phys. Rev. D 112, 124083 (2025), arXiv:2507.12376 [gr-qc].
Title: From Quantum Noise Reduction to Tests of Classical and Quantum Gravity
Abstract: Frequency-dependent squeezing has recently pushed gravitational-wave detectors beyond the standard quantum limit, where the tradeoff between sensing noise and radiation-pressure back-action noise becomes unavoidable. In this regime, the test masses can no longer be regarded as merely classical objects monitored by quantum light: the measurement builds quantum correlations between the optical field and the macroscopic motion of the mirrors. I will briefly discuss this regime, including recent work quantifying entanglement between light and test-mass motion, and then describe future directions for quantum-noise reduction. Within the Gaussian regime, the goal is to use squeezed vacuum and quantum correlations in ways that are robust against optical loss, while improving both sensitivity and bandwidth. Beyond the Gaussian regime, photon counting and related non-Gaussian measurements may offer enhanced sensitivity to selected signal classes; related photodetection ideas are also being pursued in GQuEST to search for Verlinde-Zurek-type fluctuations. I will then turn to precision optomechanical probes of classical versus quantum gravity. First, I will discuss Schrödinger-Newton-type models. Although such models have often been viewed with suspicion because of concerns about nonlinearity, acausality, and interpretation dependence, causal formulations can be constructed in which gravity is sourced only by classical information available from quantum measurements in the causal past. This operational viewpoint makes the phenomenology causal and independent of any particular interpretation of quantum measurement, while still allowing effective self-gravity effects in macroscopic objects, especially in solids where mass is localized near lattice sites. I will also discuss monitoring-feedback models of classical gravity, building on a long line of work in which classical gravitational forces are represented through measurement and feedback. In these models, auxiliary degrees of freedom continuously monitor massive objects and feed the resulting classical records back as Newtonian sources. While such models can reproduce Newtonian force transfer functions, they necessarily introduce classical-gravity noise. I will describe a new phenomenological hierarchy based on the correlation structure of the input noise of monitoring channels, which organizes non-entangling classical-record models, collapse-inspired or universal-monitoring models, effectively entangling models, and genuinely quantum-mediated gravity within a common framework.
Title: Quantum Mechanics of Gravitational Waves
Abstract: Is the gravitational field quantized into gravitons? Theoretically, there is no obstacle to this proposal; ultimately, it is an experimental question. I will give an overview of the very active discussion over the past few years on whether gravitational-wave observations can test this hypothesis.
Title: Ringdown tests of the black-hole paradigm
Abstract: Gravitational waves offer the promising prospect of testing one of the main predictions of general relativity, namely the presence of black holes beyond which nothing can escape. The ringdown is the final stage of a compact binary coalescence when the remnant settles down to a stationary configuration. It is modelled as a superposition of exponentially damped sinusoids whose frequencies and damping times are related to the remnant’s oscillation frequencies, the so-called quasinormal modes. In this talk, I will describe how parametrised tests of general relativity can test the black-hole paradigm by constraining deviations in the frequency and damping time of the quasinormal modes. I will also describe how false violations of general relativity can arise in the data due to missing physics in the waveform models or poorly understood noise artefacts.