Effective field theory post-Newtonian approach to the two-body inspiral dynamics

• Stefano Foffa (U. Geneva)

Room: E51, HIT building Over the past two decades, ideas and techniques originating from particle physics—and more broadly from quantum and classical field theory—have been increasingly and successfully applied to the study of compact binaries in general relativity. Non-Relativistic General Relativity is one of the precursors of this trend; in this talk I will describe its contributions to the field from the simplest cases to the latest developments.

Overview of QFT methods in GR

• Radu Roiban (Pennsylvania State University)

Room: E51, HIT building Abstract TBA

Black hole modes

• Laura Sberna (Nottingham U.)

Room: E51, HIT building I will discuss black hole modes (quasinormal and quasibound/superradiant), their properties (orthogonality and (in)completeness) and their application in modelling the black hole ringdown and scalar clouds.

Black hole perturbation theory: from Love numbers to ringdown

• Lam Hui (Columbia U.)

Room: E51, HIT building A time honored way to study black holes is to perturb them. We will give an overview of several recent developments, including the tidal deformability of black holes (characterized by their Love numbers), and their ringdown after a binary merger. We will go over the surprising symmetries governing black hole perturbatioins, and discuss the latest progress into the nonlinear regime.

Static Quadratic Love Numbers

• Filippo Vernizzi (U. Paris-Saclay)

Room: E51, HIT building 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 orbits of an inspiral and are tightly connected to the microphysics of the compact object. I will present a framework for computing tidal Love numbers beyond linear order by matching relativistic perturbation theory of compact objects (Schwarzschild black holes and neutron stars) with the worldline effective field theory approach used to define their tidal deformability.

Nonlinear Tails in Black Hole Ringdown

• Alex Kehagias (Natl. Tech. U. Athens)

Room: E51, HIT building Black holes relax toward stationarity through gravitational‐wave ringdown, followed at fixed radius by late–time power-law tails. Recent work suggests that nonlinear tails sourced by quadratic self-couplings can outshine the familiar linear tails. In this talk I present a compact derivation of these nonlinear tails using the near-horizon AdS2×S2 perspective. The method treats the late-time waveform as a response of the AdS2 scalar sector to an effective quadratic source and maps the tail amplitude to horizon data. In particular, I show that the overall normalization of the dominant nonlinear tail is controlled by Aretakis constants, providing a direct link between conserved horizon charges and observable late-time decay.

Dynamical Tidal Response of Schwarzschild Black Holes

• Luca Santoni (APC, U. Paris-Cité)

Room: E51, HIT building The tidal deformability of a gravitating object is characterized by a set of coefficients that quantify its response to an external field perturbation. 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, the dissipative and conservative response coefficients become nonzero, capturing, respectively, absorption across the horizon and frequency-dependent corrections to the tidal Love numbers. Using the framework of the 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.

Naturalness of vanishing black-hole tides

• Alessandro Podo (IHES Paris)

Room: E51, HIT building I will present a symmetry argument for the vanishing and non-renormalization of static Love numbers for spherically symmetric black holes at nonlinear order, in D=4 classical General Relativity. The symmetry is realized both in full GR and in the worldline EFT, allowing for a unified treatment. This clarifies the naturalness of vanishing static Love numbers in the worldline EFT when including non-linearities, and extends previous vanishing results to all nonlinear static tides. When extended to higher dimensional gravity, this also explains the pattern of vanishing and running static Love numbers of electric and tensor type, and predicts new results at the nonlinear order. Based on joint work with Julio Parra-Martinez.

Nonlinear gravitational memory from scattering amplitudes

• Carlo Heissenberg (IPhT Saclay)

Room: E51, HIT building Scattering amplitudes offer a convenient tool to recast gravitational-wave observables in terms of gauge-invariant building blocks. Amplitude methods are particularly relevant in the the post-Minkowskian (PM) regime, in which sources are far apart and interact weakly. A complementary approach is provided by soft theorems, which apply for small frequencies while retaining exact information on the hard dynamics. In this talk, I will discuss recent progress achieved by combining these two methods to calculate the waveform sourced by the scattering of two compact objects. In particular, I will show how the nonlinear memory effect emerges from amplitudes in the NNLO PM waveform, to leading order in the soft limit, and illustrate how its explicit calculation can be reduced to cut two-loop integrals.

Positivity in Renormalization: from BSM to Love Numbers

• Chia-Hsien Shen (NTU Taiwan)

Room: E51, HIT building Renormalization group (RG) evolution is a fundamental feature of quantum field theory, playing a pivotal role in both its formal structures and phenomenological applications in particle physics and beyond. While the framework for calculating RG flows is well established, unexpected patterns continue to emerge. In this talk, I will leverage fundamental principles—unitarity and analyticity—to constrain a large sector of RG evolution in effective field theory. This result can be understood as an infrared avatar of positivity bounds. For phenomenological applications, I will discuss examples in the context of the SMEFT. For the second half of the talk, I will discuss the analogous cases of Love numbers renormalization for classical black holes and neutron stars. In both quantum and classical EFTs, the RG evolution exhibits an interesting positive direction.

Gravitational memory and soft theorems for equal-time correlators

• Justin Khoury (U. Pennsylvania)

Room: E51, HIT building Gravitational memory describes the lasting change in the separation and relative velocity of freely-falling detectors after the passage of gravitational waves. The phenomenon is intimately related to Weinberg's soft graviton theorems and BMS symmetries at future null infinity. In this talk, I will elucidate the relation between BMS transformations and the description of gravitational memory in synchronous coordinates, commonly used in gravitational wave detectors like LISA. I will show that gravitational memory corresponds to large residual diffeomorphisms in this gauge, such as volume-preserving spatial rescalings. I will then derive the associated soft theorems for equal-time correlation functions. These turn out to be the flat space analogues of the well-known inflationary consistency relations.

Is Love positive?

• Paolo Creminelli (ICTP Trieste)

Room: E51, HIT building I will show that in the regime of weak gravity, all electric Love numbers are strictly positive. The statement is based on a Kramers-Kronig dispersion relation and it requires some assumptions that I will discuss with several examples.

Asymptotic Causality

• Enrico Trincherini (SNS Pisa)

Room: E51, HIT building

Towards claiming a detection of gravitational memory

• Jann Zosso (NBI Copenhagen)

Room: E51, HIT building After offering an introduction into the topic of gravitational memory, I will present the ongoing research of the LISA fundamental physics working group towards a first single event detection of the phenomenon: This includes an assessment of the proper theoretical modeling of the gravitational memory signal, a study of the LISA response to memory, as well as continuing efforts towards a realistic estimate of the detectability from supermassive black hole mergers.