Thermal and quantum windows into the universe

At first glance our understanding of the universe seems to be solely anchored in classical gravity. Indeed, General Relativity (GR) is a powerful tool that provides a successful geometric description of the cosmos. However, if one scratches beneath the surface, the universe becomes a fascinating playground for thermal and quantum phenomena.

Antinuclei as probe for exotic physics

Antideuteron and antihelium nuclei have been proposed as promising detection channels for dark matter because of the low astrophysical backgrounds expected. After a brief review of the current experimental situation, I discuss some of the various flavors of the coalescence model used to describe the formation of light (anti-) nuclei.

Gravitational Bremsstrahlung in the Post-Minkowskian expansion

I will discuss the scattering of two compact objects interacting via gravity, using the so-called world-line Effective Field Theory approach in the post-Minkowskian expansion (i.e. expanding in the Newton's constant G but not in the velocities). In particular, I will focus on the computation of classical observables such as the total emitted momentum. This is obtained by phase-space integration of the graviton momentum weighted by the modulo squared of the radiation amplitude.

Effective field theory approach to thermal bubble nucleation

The possibility of observing a stochastic gravitational wave background originating from a cosmological first-order phase transition elicits interest in studying the transitions. Currently, a limiting factor in accurately determining the gravitational wave spectrum from an underlying microphysical model is the calculation of the nucleation rate. I will discuss recent work in which we have proposed a new effective field theory (EFT) framework for determining the thermal nucleation rate in high-temperature QFTs.

On the perturbative expansion at high temperature and implications for cosmological phase transitions

A first-order phase transition in the early universe would have given rise to a stochastic gravitational wave background which may be observable today. In this talk, I will focus on the crucial problem of making reliable predictions of the thermodynamics of such phase transitions in the face of infrared Bose enhancements at high temperature. Such enhancements lead to large theoretical uncertainties in perturbation theory at low orders. I will unravel the structure of the perturbative expansion in this context, and of the misalignment between loop and coupling expansions.

Evolution and signatures of primordial magnetic fields

The existence of magnetic fields is ubiquitous on astrophysical (e.g., planets and stars) as well as on cosmological scales (galaxies and galaxy clusters). Low-frequency radio observations are revealing an increasing number of diffuse radio sources in galaxy clusters visible through their synchrotron emission.

Gravitational waves from the early-universe turbulent sources

A space-based laser interferometer, pioneered by NASA's LISA concept and now a ESA cornerstone mission, will enable direct detection of gravitational waves at lower frequencies than LIGO, without being limited by seismic noise. Perhaps the most intriguing source for LISA is the stochastic gravitational wave background produced by turbulent plasma motions in an early-universe, particularly at the electroweak energy scale.

Two recent topics in gravitational-wave cosmology: Binary resonance searches and nonlinear memory from cosmic strings

In the first half of this talk, I will discuss how binary systems can be used as dynamical detectors of gravitational waves (GWs). Since the passage of GWs through a binary perturbs the trajectories of the two bodies, we can infer the presence of a GW signal by searching for changes in the binary's orbital parameters. In the presence of a stochastic GW background (SGWB) these changes accumulate over time, causing the binary orbit to execute a random walk through parameter space.

Multimessenger astroparticle physics

I will present a bit more extended version of the talk that I gave recently at the TAUP2021 conference, with overview of the recent developments in the multi-messenger astronomy.

The astrophysics of black hole binaries in the era of gravitational wave astronomy

Black holes (BHs) cover a wide range of mass: from the stellar BH binaries detected with LIGO / Virgo to the massive BHs residing at the center of galaxies. Both these populations will be detectable in future by LISA at low-frequency. In this talk, I will provide a general overview of the current detections from LIGO / Virgo, describing the current state-of-the-art and I will highlight the potential of the LISA mission.

LABORATOIRE

ASTROPARTICULE & COSMOLOGIE

Théorie