Séminaire

We construct static and axially symmetric magnetically charged hairy black holes in the gravity-coupled 
Weinberg-Salam theory.  Large black holes merge with the Reissner-Nordstr\"om (RN) family, 
while the small ones are extremal and support a hair in the form of a ring-shaped electroweak condensate 
carrying superconducting W-currents and up to $22\%$ of the total magnetic charge. 
The extremal solutions are asymptotically  RN with a  mass {\it below} the total charge, $M<|Q|$,  due to 

Hořava-Lifshitz gravity is  perturbatively renormalizable quantum gravity model candidate with an anisotropic UV-scaling between space and time. I would like to present a cosmological background analysis of the minimal projectable formulations of the theory, with particular focus on the running of the parameter λ with energy.

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.

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.

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.

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.

The statistics of primordial scalar perturbations play a crucial role in providing phenomenological constraints for new inflationary models. In particular, the probability of unlikely large scalar perturbations (leading to primordial black hole formation) and the concurrent GW backgrounds are very sensitive to the tail of the PDF of primordial curvature perturbations. We analyse such tails in inflationary models featuring an ultra-slow roll phase, known to enhance both the amplitude and non-Gaussianity of curvature perturbations at small scales.