Séminaire

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.

Beyond the Standard Models with Cosmic Strings

Cosmic strings (CS) are topological defects formed after spontaneous breaking of a U(1) symmetry. Remarkably, thanks to the scaling regime, CS loops constitute a long-standing source of Gravitational Waves (GW) and produce a flat GW spectrum during radiation domination, spanning many orders of magnitude in frequency.

Séminaire Gravitation - Giulia Cusin, Astrophysical background of gravitational waves: anisotropies, polarization and cross-correlations with cosmological observables.

Le groupe Gravitation organise le séminaire suivant le lundi 24 février à 11h, par Giulia Cusin, dans la salle 631B de l’APC.
 
Astrophysical background of gravitational waves: anisotropies, polarization and cross-correlations with cosmological observables. 
 
The astrophysical background of gravitational waves (AGWB) is composed by the incoherent superposition of gravita
Séminaire