Séminaire

Black holes and the integrability of extended body dynamics

In general relativity, freely-falling test objects follow geodesics of the background spacetime in which they live. In a sense, this feature is a mere rephrasing of Einstein’s equivalence principle. In 1968, Brandon Carter showed that the geodesic motion of objects orbiting a Kerr black hole was integrable, in the sense of Hamiltonian mechanics, by discovering a fourth constant of motion that now bears his name. This “universality” of geodesic free fall is, however, but an approximation: In general, two different bodies will follow two distinct paths, depending on how they spin and deform.

Spectroscopic surveys: DESI, DESI-2, Spec-S5

The DESI experiment will put tight constraints on the dark energy with the observation of more than 40 million spectroscopic redshifts, mostly at z < 2. It started its Main Survey in May, 2021, making it the first Stage-IV cosmological experiment to go on-sky. Cosmological analysis of the Y1 data acquisition were made public in Apr. 2024, and the Y3 data acquisition is done. I will present the DESI survey current status, along with the proposed extension of operations. I will then present the DESI-2 and Spec-S5 experiments.

Latest Results of the Diffuse Supernova Neutrino Background Search in Gadolinium-loaded Super-Kamiokande

The Diffuse Supernova Neutrino Background (DSNB) is the collection of neutrinos emitted from all past core-collapse supernovae, and it has yet to be detected experimentally. An observation of the DSNB can probe the star formation history of the universe, the fraction of black hole-forming supernovae, and even novel neutrino physics phenomena. At present, the Super-Kamiokande (SK) water Cherenkov detector is the most sensitive experiment to detect the DSNB.

Analytic Inversion of the M-R relation

The structure of neutron stars is determined by the so-called TOV equations of general relativity. Knowledge of the pressure-energy density relation is sufficient to determine the neutron star mass-radius (M-R) relation. Recent observations from X-ray telescopes, radio timing of pulsars, and gravitational wave observations, have provided several constraints on the masses and radii of neutron stars.

Late-time signal from binary black hole coalescences

Recently, studies on numerical evolutions of eccentric binary inspirals found a several orders of magnitude enhancement of the post-ringdown tail amplitude. This characteristic might render the tail a phenomenon of observational interest, opening the way to experimental verification of this general relativistic prediction in the near future. I will present an analytical perturbative model that accurately predicts the numerically observed tail evolution.

A Big Telescope and a Big Computer: How HPC and AI Will Enable Next Breakthroughs in Our Understanding of the Universe

The upcoming mega-telescopes, such as European Space Agency’s recently launched Euclid satellite, and the upcoming radio Square Kilometer Array (SKA), will provide images of our universe over 10 billion years of cosmic history, and enable us to study its evolution with unprecedented level of detail. In the framework of simulations-based inference, the big telescopes deliver a throve of high-resolution observations and big computers provide the feature-rich numerical theory prediction.

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