Séminaire

The H0 tension and non-minimal couplings to gravity

Theoretical models that aim to solve the tension between local measurements of the Hubble constant H0 and its inference from CMB data  have to include a modification to the standard LCDM model around the time of matter-radiation equality. I propose that such an early-time modification consists in a scalar field non-minimally coupled to the Ricci scalar, which behaves effectively like a dark radiation component and induces a time evolution of the Newton constant G.

Reconstruction of neutrino events in the MicroBooNE detector 

MicroBooNE is a Liquid Argon Time Projection Chamber (LArTPC) neutrino experiment on the Booster Neutrino Beamline at the Fermi National Accelerator Laboratory, with an 85-tonne active mass.
One of MicroBooNE’s primary physics goals is to investigate the excess of electron neutrino events seen by MiniBooNE in the [200-600] MeV range.
MicroBooNE will constrain the intrinsic electron neutrino component of the beam by measuring the muon neutrino spectrum.
Our low-energy excess analysis makes use of deep learning algorithms applied to the high-resolution images provided by the MicroBooNE LAr

Vainshtein screening for slowly rotating stars 

We study the Vainshtein mechanism in the context of slowly rotating stars in scalar-tensor theories.
While the Vainshtein screening is well established for spherically symmetric spacetimes, we introduce a slow rotation of the source and examine its validity in the axi-symmetric case.
We solve for the frame-dragging function accounting for the slow rotation and show that the deviations from the general relativity (GR) solution are screened in the weak-field approximation, meaning the solution for the frame-dragging function is the same as GR to leading order.
This suggests that the Vainsh

The power of probe combination : cosmology with LSS and CMB data

Through weak lensing and galaxy clustering measurements, the next generation of large-scale surveys (Euclid, LSST, ...) will provide unprecedented observations and constraints on the late Universe, and thus shed light on dark matter and dark energy. On the other hand, high-quality CMB observations (current and planned) can -- and already do -- put tight constraints on the early Universe and its content.

General relativistic weak-field limit and Newtonian N-body simulations

Future galaxy surveys such as Euclid, LSST and SKA will cover larger and larger scales where general relativistic effects become important. On the other hand, our study of large scale structure still relies on Newtonian N-body simulations. I show how standard Newtonian N-body simulations can be interpreted in terms of the weak-field limit of general relativity. Our framework allows the inclusion of radiation perturbations and the non-linear evolution of matter. I show how to construct the weak-field metric by combining Newtonian simulations with results from Einstein-Boltzmann codes.

Formation and abundance of primordial black holes

Primordial black holes can form in the early Universe from the collapse of cosmological perturbations after the cosmological horizon crossing. They are possible candidates for the dark matter as well as for the seeds of supermassive black holes observed today in the centre of galaxies. In calculations of spherically symmetric collapse, a Lagrangian relativistic hydrodynamical code is used to follow the non linear evolution. If the perturbation is larger than a threshold depending on the equation of state and on the specific shape of the perturbation, a black hole is formed.
Séminaire