The post-Newtonian approximation to general relativity plays a paramount role in the discovery of gravitational waves by LIGO and Virgo. In this talk, we highlight the seminal contributions from Thibault and review the latest developments concerning the definition of accurate PN templates for gravitational waves.

After reviewing my adventures in gravitation at IHES in 1997-1999, and the original motivations that led to the development of the effective-one-body formalism, I will discuss the path that guided the development of highly accurate waveform models for LIGO-Virgo's searches and inference studies, including the synergistic interplay between analytical and numerical relativity. I will conclude...

The spectacular observation of a wide variety of gravitational-wave sources by Virgo and LIGO has established the field of gravitational-wave astronomy both stand-alone and as an element in multi-messenger astrophysics. There is, however, the clear motivation from the perspective of observational science and also evident paths technically to make significant steps forward in the extent of...

Ground-based gravitational-wave observations of binary neutron stars (BNS) can, in principle, uncover the entire coalescence process spanning from the low-frequencies (few Hz, low-velocities) inspiral motion to the high-frequencies merger and remnant dynamics (in the kiloHertz regime). These observations hold the promise to deliver unprecedent insights on fundamental aspects of physics and...

I will discuss toy models of turbulence which allow to clarify this concept, find a non-Gaussian probability distribution, and establish connections between turbulence, anomalies, and general covariance

In attempts to formulate a unified theory of quantum gravity and the fundamental interactions of the maximal rank, hyperbolic Kac-Moody algebra E10 plays a distinguished role. In this talk, I will touch on selected aspects of recent work in this direction (much of which has been advanced and inspired by Thibault) and review some of the outstanding issues.

Einstein's theory admits interesting limits with different causal structures obtained by letting the speed of light go to infinity (Galilean or "non-relativistic" limit) or to zero (Carrollian, or "ultrarelativistic" limit). In the latter case, instead of the hyperbolic partial differential equations of general relativity and the elliptic differential equations of Newton’s theory, the...

In this talk, I will discuss whether the black hole metric remains to be a solution of gravitational equations provided the classical gravitational action is modified by the generally non-local terms after integrating out the quantum matter. The story appears to be dramatically different for the Hartle-Hawking state and for the Boulware state. The discussion will be based on the analysis of...

We assume that the points in volumes smaller than an elementary volume (which may have a Planck size) are indistinguishable in any physical experiment. This naturally leads to a picture of a discrete space with a finite number of degrees of freedom per elementary volume. In such discrete spaces, each elementary cell is completely characterized by displacement operators connecting a cell to the...

Gravitational waves transport information from faraway regions of the Universe. Studies of gravitational waves have been devoted mostly to sources such as binary black hole mergers or neutron star mergers, or generally sources that are stationary outside of a compact set. These systems are described by asymptotically-flat manifolds solving the Einstein equations with sufficiently fast decay of...

At the end of 2018, a result by Bern et al. on gravitational scattering at order G^3 raised an intriguing puzzle that got more and more embarrassing for about 20 months. Its eventual resolution made everyone, and particularly Thibault, happy. I will give a brief account of that amusing story.

A large cosmic string loop captured by a much smaller black hole oscillates on a nearly periodic orbit. The orbit slowly evolves due to energy and angular momentum exchange between the loop and the black hole. For a non-rotating black hole, the loop gradually loses its energy due to the friction of the moving string against the horizon. But for a spinning black hole, the loop energy can...

Microbial communities, from plankton to the human microbiome, present similar community structures. They are for instance composed of many rare species and a few abundant ones. How a large number of species can coexist in those complex communities and why they are dominated by rare species is still not fully understood. Those communities also present similar dynamical behavior. To study the...

For a variety of reasons, it seems necessary to consider complex saddle points in the "Euclidean'' approach to black hole thermodynamics. But what class of complex saddle points is physically sensible? That will be the subject of this talk.

I will present the role of Thibault Damour (‘D’ in ‘DJS’) and his colleagues (‘S’ and ‘J’ in ‘DJS’) in initiating, at the turn of the millennium, calculations of higher-order Post-Newtonian (PN) corrections to the equations of motion of compact binary systems. DJS derived for the first time complete and error-free dynamics of compact binary systems in the 3PN and 4PN orders, and to achieve...

The talk is a personal recall of my involvement in projects related to gravitational waves from inspiraling compact binaries with colleagues in France. In particular, a summary of aspects related to eccentric binaries pursued in my group.

All inflationary models, in spite of locally approaching the de Sitter space-time inside the Hubble radius, have scalar and tensor ‘hair’ – spatial inhomogeneity - outside it. This inhomogeneity does not disappear with time. Just the opposite, its amplitude at a given comoving scale typically remains constant not only during inflation but a long time after its end up to the moment of the...

Damour has been one of the first to suggest that the dynamics of a black hole's horizon could be interpreted as the motion of a fluid, thus inspiring what became known as the membrane paradigm. I will review his seminal contribution and the more modern developments, originating from the holographic duality, that have led to a more systematic understanding of the connections between gravity and...

We address the physical origin of the ultra-relativistic prompt emission (UPE) phase of GRB 190114C and GRB 180720B. We assume that during the UPE phase, the “inner engine” of the GRB, composed of a Kerr black hole (BH) and a uniform test magnetic field B_0, aligned with the BH rotation axis, a Wald - Papapetrou solution operates in an overcritical field |E| ≥ E_c, where E_c = m^2_ec^3 / (e ħ...

We experience a golden era in testing and exploring relativistic gravity using gravitational wave detectors, satellites, lab experiments, and also radio astronomical observations. Here, especially binary pulsars provide us with complementary insight. Having provided the first evidence for gravitational waves, pulsars continue to allow probing relativistic strong-field effects - within a...

It has been proposed that a small enough black hole in string theory would transition into a hot oscillating string. We explore whether this transition can happen smoothly in classical string theory. We find evidence that this is the case in the heterotic string theory, but not in the type II string theory.

The talk is based on a recent paper by Yiming Chen, JM, and Edward Witten:...

I will give a status report on the stability of Kerr conjecture and focus on my recent results with J. Szeftel and E. Giorgi concerning the case of small angular momentum.

One century ago, Einstein revealed his theory of gravity which shook the foundations of physics. General Relativity (GR) is a revolutionary concept that is not very intuitive for most people. As a pillar of the GR, the weak equivalence principle (WEP) leads to the universality of free-fall historically attached to Galileo Galilei. Because the WEP is a cornerstone of the GR, its test was...

Gravitational self-force theory provides a natural method of modeling binaries with small mass ratios. By expanding the binary's metric around the background metric of the larger body, this approach greatly simplifies the binary problem while remaining accurate in the highly relativistic regime. In this talk, I summarize the foundations of self-force theory, how it leads to an elegant...

In a visionary 2010 paper, T. Damour identified the potential of self-force calculations to inform the construction of a strong-field two-body Hamiltonian in general relativity.

The paper, in a way, foretells much of the history of self-force work in the decade that followed. Six self-force calculations were proposed, each providing a handle on a distinct aspect of the strong-field...