Opening remarks

• Valerio De Luca

Room: 205

Tests of General Relativity with ground-based detectors - A status report

• Joachim Pomper

Room: 205 We are living in a remarkable era for gravitational-wave astronomy. With an ever-growing catalog of compact binary mergers observed by ground-based detectors, we can now test General Relativity in the strong-field, highly dynamical regime with unprecedented precision. In this talk, I will review the current status of tests of General Relativity with ground-based gravitational-wave observatories, ten years after the dawn of gravitational-wave astronomy. I will focus primarily on inspiral and black-hole ringdown tests, highlighting several results obtained over the past year, some of which I actively contributed to during my PhD.

Wave-Optics Gravitational Lensing with Gravitational Waves

• Alice Garoffolo

Room: 205 The growing observational prospects for gravitational waves make wave-optics effects in gravitational lensing increasingly relevant. In this talk, I will first show that the standard diffraction integral relies on approximations that can be systematically understood and extended using scattering theory. This provides a way to go beyond the usual wave-optics treatment of lensing. I will then discuss a first example in modified gravity, where some curvature couplings produce signatures that are visible only in the wave-optics regime. The main point is that gravitational-wave lensing can be used not only to study compact lenses, but also to probe aspects of gravitational propagation that are hidden in geometric optics.

Probing astrophysical environment of stellar mass black hole binaries through LISA stochastic signal

• Rohit Chandramouli

Room: 205 The LISA stochastic signal from stellar mass black holes may be detectable. These binaries can be significantly affected by an astrophysical environment in their early inspiral. In this talk, I will describe how the presence of an astrophysical environment can be inferred from the stochastic signal produced by unresolved stellar mass black holes in the LISA band. I will first provide an overview of some environmental effects and then focus on gas-induced dynamical friction and accretion. Additionally, I will discuss how eccentricity affects the spectrum and can be used as an indirect probe of the astrophysical formation of such binaries. Further, when using vacuum quasi-circular models for the stochastic signal, there can be significant biases in the parameter estimation, which motivates the need to parametrically model these effects.

Discussions/Collaborations Room: 205

Dynamical Tidal Response of Compact Objects

• Luca Santoni

Room: 205 The tidal deformability of a gravitating object is characterized by a set of coefficients that quantify its response to external tidal perturbations. It is well known that the zero-frequency response coefficients—also known as the static tidal Love numbers—of Schwarzschild black holes vanish identically in four-dimensional general relativity. At subleading order in the adiabatic expansion, dissipative and conservative contributions become nonzero, capturing, respectively, horizon absorption and frequency-dependent corrections to the tidal Love numbers. Using the framework of point-particle effective field theory, I will present the calculation of the dynamical Love numbers of Schwarzschild black holes up to second order in frequency. In addition to the previously known logarithmic renormalization-group running, I will derive the scheme-dependent finite terms. Finally, I will discuss how this framework for dynamical tidal response extends to neutron stars.

Static Quadratic Love Numbers

• Filippo Vernizzi

Room: 205 Tidal Love numbers quantify the deformability of compact objects under external tidal fields. They are key quantities in gravitational‑wave astronomy for accurately modeling waveforms during the final stage of an inspiral and carry information about the microphysics of the object. I will present a framework for computing tidal Love numbers beyond linear order by matching relativistic perturbation theory of compact objects with the worldline effective field theory approach used to define their tidal deformability.

Impact of sky localization uncertainty on ringdown inference

• Kallol Dey

Room: 205 As gravitational-wave ringdown signals grow louder, quasinormal-mode inference depends increasingly on the treatment of extrinsic parameters. Standard analyses fix sky localization - and sometimes also polarization and inclination - to point estimates from a prior inspiral-merger-ringdown analysis, artificially breaking degeneracies and underestimating the true uncertainty of mode-amplitude values. We test two alternatives: uninformative priors on the extrinsic parameters, sampled jointly with the remnant mass, spin, mode amplitudes, and phases; and informed priors on sky position from the full signal posterior. The former yields wider marginal constraints on amplitude posteriors, and both avoid potential bias introduced by fixing the sky localization. In contrast, mode amplitude ratios remain consistent across approaches, making them a robust observable for Kerr spectroscopy. Our publicly available pipeline enables fast ringdown analyses capable of sampling all parameters, requiring tens of minutes on a laptop for a full inference. Applied to GW250114 and GW190521, our methods confirm the robust detection of the (2,2,1) overtone in GW250114, and, for GW190521, find only mild evidence for the (3,3,0) mode.

Discussions/Collaborations Room: 205

Green's function of Black Holes

• Adrien Kuntz

Room: 205 I will present recent progress regarding the exact solution for the Green function of Schwarzschild black holes. Building on a toy-model based on the Poschl-Teller potential, I will show how the Green function can be decomposed in a prompt response and a QNM part by appropriate complex contour deformation. The prompt response itself involves new modes, the Matsubara frequencies. I will introduce the bounce radius, which separate the region of convergence of the QNM and Matsubara mode sums, and I will comment on the existence of redshift modes in the waveform.

Dynamical perspective on black hole ringdown

• Marina De Amicis

Room: 205 Current waveform models of binary black hole mergers incorporate a large amount of analytical information during the inspiral phase. In contrast, post-merger descriptions typically rely on phenomenological ansätze informed by numerical relativity, with the quasi-normal mode frequencies providing the only direct analytical input. I will present a first-principles framework to study the dynamical excitation of quasi-normal modes during the plunge–merger–ringdown stages in EMRI systems, and discuss its implications for ringdown modeling. In this description, the QNMs amplitudes gain a non-trivial time dependence, and a new redshifted component appears in the signal at intermediate times. I will conclude by discussing novel insights into the analytical modelling of the prompt response.

Astrophysical Environmental Effects

• Johan Samsing

Room: 205 How and where do black hole mergers form? Understanding how different astrophysical environments leave imprints in the observed gravitational wave (GW) signal is likely the key to probe the underlying formation of GW sources. Many environmental toy models have been proposed recently; however, I will show how one is linked directly 1:1 to the merger rate and merger properties with essential no uncertainty. This particular environment can therefore serve as a benchmark in future observational searches.

Purely Imaginary Quasinormal Modes of Vaidya Spacetime from Heun Functions

• Thomas Lovo

Room: 205

Discussions/Collaborations Room: 205

Nonlinear QNMs from Penrose Limits and Large-D GR

• David Pereniguez

Room: 205 At high frequencies, black hole dynamics can be described by Penrose-limit plane waves adapted to the photon ring. I will show that, in this limit, gravitational electric–magnetic duality is restored on shell, leading to QNM isospectrality in GR as well as a specific class of EFT extensions. I will then explain how this high-frequency perspective can be used to construct exact nonlinear QNM solutions. If time allows, I will briefly discuss a second, unrelated regime in which ringdown nonlinearities are also exactly tractable: the large-D limit of GR.

Perspectives on black hole ringdown

• Sebastian Volkel

Room: 205 The ringdown of black holes provides a rich arena for exploring complementary perspectives on gravity, from classical general relativity to effective descriptions, numerical simulations, and analog systems. In this overview talk, I will discuss several recent developments in black hole ringdown physics, including the mapping between bound states and quasi-normal modes, progress in parametrized quasi-normal mode frameworks, and semi-analytic approaches to ringdown modeling. I will also review advances in black hole spectroscopy using non-linear simulations, with particular attention to non-vacuum environments and possible systematic effects. Finally, I will discuss how simulation-based inference may offer a powerful route to parameter estimation in analog-gravity quantum simulators of black holes.

Post-Minkowskian, Numerical Relativity and Effective-one-body formalism

• Tamanna Jain

Room: 205 In this talk, I will present our recent work on post-Minkowskian EFT for scalar-tensor theories and boson stars. We first derive the analytical expressions of the scattering angle using PM-EFT techniques for both the cases, and in particular provide the first analytical treatment of boson stars as a two-body problem. We then derive the effective-one-body description of these systems. We then compare analytic results to the scattering angle extracted from sequences of numerical-relativity simulations at fixed energy, varying impact parameter, and coupling strength. We find excellent agreement for both the cases.

Discussions/Collaborations Room: 205

Gravitational-wave memory effects from binary-black-hole mergers

• David Nichols

Room: 205 The gravitational-wave (GW) memory effect is characterized by a persistent offset in the GW strain, which is closely related to the infrared physics of asymptotically flat spacetimes. There are ongoing searches for the memory effect from the mergers of binary black holes, which have been observed by the LIGO-Virgo-KAGRA collaboration. I will discuss how these detectors search for the memory effect and what aspects of the memory effect can be probed by them. The memory effect is just the leading-order persistent GW effect in a hierarchy of "higher GW memory effects" that are related to multiple time integrals of the news tensor (the radiative degrees of freedom in asymptotically flat spacetimes). The next order contains the spin and center-of-mass memory effects (collectively, the drift memory); one order higher are the ballistic memory effects. I also will discuss the definitions of these higher memory effects, the features of the GW strain related to these effects in binary black hole mergers, and their detection prospects.

GW Memory Detection and Beyond

• Silvia Gasparotto

Room: 205 Gravitational-wave (GW) memory is a non-oscillatory component of GW signals that leaves a permanent displacement in spacetime after the wave has passed. It is a generic prediction of General Relativity, arising at second order from the nonlinear dynamics of gravity, yet it has not been detected so far. In this talk, I will present recent results on the detectability of GW memory with future detectors such as LISA and discuss its impact on parameter estimation. I will then show how GW memory can serve as a probe of new physics. First, I will present memory predictions from numerical-relativity waveforms in modified gravity theories, including Einstein-scalar-Gauss-Bonnet gravity and its Ricci-coupled extension, where additional polarization modes modify the memory signal. Finally, I will discuss how the low-frequency nature of GW memory can be exploited in multiband searches to access mergers beyond the nominal frequency range of a detector, with applications to populations of light Primordial Black Holes. This highlights GW memory not only as a fundamental prediction of gravity, but also as a powerful tool for testing new physics.

Closing remarks Room: 205