Recent PN/PM Analytic Results in the Gravitational Two-Body System

• Donato Bini (IAC, CNR, Rome)

Room: Centre de conférences Marilyn et James Simons Some recent results (up to the 3.5PN accuracy level) concerning the waveform, the radiation losses, the scattering angle etc., in a gravitational two-body system are discussed, with special attention to theoretical bottlenecks for future improvements.

Feynman Integrals and EFT Approach to Gravitational Interactions: 6 Loops for 6 PN

• Pierpaolo Mastrolia (University of Padova)

Room: Centre de conférences Marilyn et James Simons I discuss the diagrammatic approach to the conservative dynamics of coalescing binary systems within the effective field theory (EFT) framework applied to General Relativity (GR). In this setting, the Post-Newtonian (PN) expansion of the interaction potential can be systematically computed using techniques familiar from quantum field theory. Focusing on the static sector, I present the evaluation of the sixth-order PN correction, which requires the computation of six-loop two-point Feynman integrals. I review the main ingredients of the calculation and outline how the structure of the contributing diagrams enables a controlled organization of the computation. I will also discuss how a factorization theorem for the static potential can be exploited to extend the analysis to higher PN orders. Finally, I comment on general structural properties of Feynman integrals arising in GR-context, including their vector-space structure and their relations to D-modules theory.

De Sitter, anti De Sitter and All That

• Ugo Moschella (Insubria U., Como & INFN, Milano)

Room: Centre de conférences Marilyn et James Simons I will outline a general approach to quantum field theory in de Sitter and anti-de Sitter spaces, developed primarily at IHES in Bures-sur-Yvette over the past 30 years in collaboration with Jacques Bros and Henri Epstein, whose memory I wish to honour and to keep alive as long as I am able. I will also discuss my most recent results on a plane wave expansion of the **anti** de Sitter two-point Wightman function, along with some of its applications.

Cool Surprises Near Cool Horizons - REMOTE

• Jorge Santos (University of Cambridge)

Room: Centre de conférences Marilyn et James Simons We will explain why near-extremal black holes can be used as probes of new physics. Our journey starts by exploring near-extremal black holes with anti-de Sitter boundary conditions in Einstein-Maxwell theory. We show that, in almost all cases, tidal forces diverge as one crosses the horizon, and this singularity is stronger for larger black holes. In particular, this applies to generic nonspherical black holes, such as those satisfying inhomogeneous boundary conditions. Nevertheless, all scalar curvature invariants remain finite. Moreover, we show that nonextremal black holes have tidal forces that diverge in the extremal limit. Next, we will discuss how the same mechanism generates large tidal forces for near-extremal black holes with asymptotically flat boundary conditions due to the presence of generic higher-curvature terms in the gravitational action generated by quantum corrections to general relativity.

Thermodynamics of Near-Extreme Black Holes

• Chiara Toldo (Université Libre de Bruxelles)

Room: Centre de conférences Marilyn et James Simons From the perspective of classical gravity, a black hole is the simplest object we know of. At the same time, it possesses huge entropy, hinting at an incredibly complex microstructure: understanding this fact falls in the realm of quantum gravity. In this talk I will review recent results concerning the microscopics and the thermodynamics of black holes close to extremality. In the first part, I will describe how recently developed techniques allow to compute the quantum corrections to the entropy of near-extremal Kerr black holes, both by making use of an effective near-horizon theory (Jackiw-Teitelboim gravity) and by regularizing certain zero-modes appearing in the gravitational path integral in the near horizon geometry. I then will show that the quantum-corrected near-extremal entropy exhibits 3/2logT behavior characteristic of the Schwarzian model, and predicts the lifting of the ground state degeneracy for the extremal Kerr black hole. I will then show the computation for the density of states for AdS4 black holes which admit a supersymmetric limit, and near extremal de Sitter ones.

The Third Law of Black Hole Mechanics

• Harvey Reall (University of Cambridge)

Room: Centre de conférences Marilyn et James Simons The third law of black hole mechanics asserts that it is impossible for a non-extremal black hole to become extremal in finite time (in classical General Relativity). Counterexamples were found recently: gravitational collapse of a massless charged scalar field can produce an exactly extremal Reissner-Nordstrom black hole in finite time, passing through an intermediate phase in which the solution is exactly Schwarzschild at the horizon. These examples involve matter with a large charge to mass ratio. I will describe how if the charge to mass ratio of matter is suitably bounded then one cannot form an extremal Reissner-Nordstrom black hole in finite time. It is conjectured that one can form an extremal rotating black hole via gravitational collapse of gravitational waves. I will describe recent work showing that this conjecture is true in five spacetime dimensions.

Theoretical Challenges in Gravitational Wave Astronomy

• Alessandra Buonanno (Max-Planck Institute, Potsdam)

Room: Centre de conférences Marilyn et James Simons

News From the LIGO-Virgo-KAGRA Collaboration: Results and Perspectives

• Marie-Anne Bizouard (ARTEMIS, Nice)

Room: Centre de conférences Marilyn et James Simons The LIGO-Virgo-KAGRA collaboration has completed its fourth observation run in 2025. These data have led to unprecedented studies on gravity, which I will summarize in this presentation.

Waveform Modeling Within the Effective-One-Body Approach: Status and New Perspectives From PM/PN Approaches and the Confluent Heun Equation

• Alessandro Nagar (INFN, Torino)

Room: Centre de conférences Marilyn et James Simons The effective-one-body (EOB) approach is a powerful analytical formalism apted ad describing the dynamics and waveform from coalescing compact binaries in full generality, from the quasi-adiabatic inspiral to plunge, merger and ringdown.EOB waveform are key for the analysis of gravitational wave data. In the first part of the talk I will briefly review the basic elements of the formalism and its use in the construction of the two currently widely used waveform model, SEOB and TEOB. Then I will streamline new theoretical perspective for: (i) the joint use of post-Minkowskian and post-Newtonian analytical results within the new Lagrange-EOB (LEOB) approach to describe the conservative part of the dynamics and (ii) a new use of black hole perturbation theory based on the mapping of the Teukolsky equation into the confluent Heun equation that allows us to identify new analytical, closed-form, structures that look promising to construct more accurate resummations for the EOB waveform and radiation reaction force.

Exploring Tests of General Relativity with Recent Gravitational Wave Observations

• Simon Maenaut (Niels Bohr Institute, Copenhagen)

Room: Centre de conférences Marilyn et James Simons Six months ago, a new gravitational-wave transient catalogue was released by the LIGO, Virgo and KAGRA collaborations. As the worldwide network of gravitational-wave detectors continues to increase in sensitivity, the quantity and quality of the detected signals from compact binary coalescences also increases. In this presentation I will briefly explore various tests applied in the analysis of recent gravitational-wave observations, to see how well these match the predictions from General Relativity. First are consistency tests between the observed signal and theoretical predictions that describe the strong-field dynamics of spacetime present during binary mergers. These are followed by a set of tests that examine the nature of gravitational waves and the propagation characteristics of these signals. Finally, a suite of tests are discussed that probe the fundamental properties of the coalescence remnants with the observed gravitational waves.

Advances in Numerical Relativity: Null Infinity, BMS, and Precision Gravitational-Wave Astronomy

• Keefe Mitman (Cornell University)

Room: Centre de conférences Marilyn et James Simons In recent years, numerical relativity has seen a surge of development, with new codes coming online and catalogs of simulations expanding to new parts of parameter space. However, the looming accuracy demands of next-generation detectors are also becoming ever more prevalent. In this talk, I will review some of the recent advancements that have been made in numerical relativity simulations of binary black holes, including improved waveform extraction, a more careful treatment of the BMS gauge freedom, and the resolution of subtle physical effects such as memory and tails. Following this, I will also discuss what we can expect from numerical relativity in the future and what is required from waveform models to be able to maximize the scientific return from future gravitational-wave observations.

What the Black Holes High Energy Collision Kicks Teach Us? - REMOTE

• Carlos Lousto (Rochester Inst. Tech.)

Room: Centre de conférences Marilyn et James Simons The collision of black holes at ultra-relativistic speeds represents one of the most extreme physical regimes accessible to theoretical study, offering a unique testing ground for General Relativity, the Cosmic Censorship Conjecture, and high-energy astrophysics. Based on extensive numerical simulations detailed in recent studies (Healy et al., 2023, 2025), this essay explores the fundamental upper bounds of these cataclysmic events. We synthesize findings on the maximum possible gravitational recoil—approaching 10% of the speed of light—and the maximum radiated gravitational energy, estimated at 32% of the system's total mass. Expanding on the related bibliography cited within these works, we contextualize these results against historical limits derived from head-on collisions and discuss their profound implications for the gauge-gravity duality, holography, and the dynamics of primordial black holes in the early Universe.

Informing Effective-One-Body Models With Numerical Simulations: From Linear Perturbations to Numerical Relativity

• Simone Albanesi (Friedrich-Schiller University Jena)

Room: Centre de conférences Marilyn et James Simons Gravitational wave modeling increasingly relies on the synergy between analytical frameworks and numerical simulations. In this talk, we explore how information from numerical calculations can be used to inform and improve effective-one-body (EOB) models across different regimes. We begin by focusing on the test-mass limit, where linear perturbation theory provides highly accurate waveforms, allowing us, for example, to probe in detail the merger-ringdown transition in the quasi-circular and eccentric scenarios. We then discuss full numerical relativity simulations of binary black holes, focusing in particular on the transition from unbound to bound motion. Finally, we discuss how to optimally place future simulations in the parameter space in order to maximize improvements for EOB model.

GRMHD Simulations of Spinning Supermassive Black Hole Binaries: Gas Dynamics and Observational Signatures - REMOTE

• Manuela Campanelli (Rochester Inst. Tech.)

Room: Centre de conférences Marilyn et James Simons We investigate the astrophysical environments of supermassive black hole binaries approaching merger using advanced General Relativistic Magnetohydrodynamics (GRMHD). Our simulations focus on the interplay between circumbinary disks and the magnetized accretion flows onto individual spinning black holes. By accurately modeling these relativistic environments, we provide essential data for predicting the electromagnetic counterparts to gravitational wave events. These findings are instrumental for informing observational strategies for upcoming missions, including LISA and other high-cadence astronomical facilities.

Progress at the 5th Post-Minkowskian Order

• Zvi Bern (UCLA)

Room: Centre de conférences Marilyn et James Simons I will describe recent progress at the 5th post-Minkowskian order, including new ideas for dealing with the loop integrals encountered.

Black Hole Scattering at High Precision

• Gustav U. Jakobsen (Humbolt U., Berlin & Max Planck Inst., Potsdam)

Room: Centre de conférences Marilyn et James Simons Analytic results for black hole scattering events may be used to inform gravitational waveform models and resum infinite contributions to the conventional post-Newtonian potential of the binary system. In recent work, we have reached unprecedented precision in the weak-field expansion of these processes, namely fifth order in Newton’s constant and second order in self-force effects. This progress builds on methods originally developed in quantum field theory and collider physics. In this talk, I will present our approach, which models black holes as point-like particles and yields analytic predictions for scattering observables involving remarkable mathematical structures, most notably Calabi–Yau periods. These results capture several physical effects, including radiative energy loss, recoil, and nonlocal tail and memory effects.

The ADM Description of the Bondi-Metzner-Sachs Group of Asymptotically Flat Spaces

• Marc Henneaux (International Solvay Institutes & Collège de France)

Room: Centre de conférences Marilyn et James Simons A review of asymptotic symmetries of gravity in the asymptotically flat context will be given following the Hamiltonian (ADM) approach. General features (such as the form of the symmetry generators and the structure of the algebra) will be explained. The talk will also cover logarithmic supertranslations and explain how they lead to a remarkable simplification of the infinite-dimensional BMS algebra.

From Mirror Symmetry to Black Hole Perturbation Theory - REMOTE

• Alba Grassi (Université de Genève & CERN)

Room: Centre de conférences Marilyn et James Simons

Gravitational Radiation From Hyperbolic Orbits: a Self-Force Perspective

• Niels Warburton (University College, Dublin)

Room: Centre de conférences Marilyn et James Simons In this talk I will review the self-force approach to calculating gravitational radiation and associated quantities for a small compact body moving on a hyperbolic geodesic around a large black hole. I will present the latest gravitational self-force (GSF) calculations and comparisons with post-Minkowskian (PM), post-Newontian and numerical relativity results. I will also discuss how a resummation for PM results can be used to improve the convergence in the strong-field.

Static Quadratic Love Numbers

• Filippo Vernizzi (IPhT, Saclay)

Room: Centre de conférences Marilyn et James Simons 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.

Naturalness of Black-Hole Tides

• Julio Parra-Martinez (IHES)

Room: Centre de conférences Marilyn et James Simons In this talk I will explain how certain aspects of black-hole physics can be understood using ideas from effective field theory. Many of the familiar notions from particle physics will play a role, including the renormalization group, universality and naturalness. In particular, I will explain why black holes naively seem like fine-tuned systems, but they are ultimately not thanks to an accidental symmetry of General Relativity. The talk is based on work in collaboration with Alessandro Podo.