Séminaire

Evolution of magnetic fields in the early Universe

Magnetic fields are observed on virtually all astrophysical scales of the modern Universe, from planets and stars to galaxies and galaxy clusters. Observations of blazars suggest that even the intergalactic medium is permeated by magnetic fields. Such large-scale fields were most likely generated very shortly after the Big Bang and therefore are a unique window into the physics of the very early Universe.

Euclidean Wormholes and Holography

Wormholes are exotic solutions of General Relativity that still challenge our physical intuition. In this talk I will first review and distinguish various types of wormholes along with their expected physical properties. I will then focus on asymptotically AdS wormhole solutions in the context of holography. I will explain how to compute correlation functions of local operators as well as non local observables such as correlation functions of Wilson loops on the distinct boundaries and discuss their behavior.

The European Low Frequency Survey: observing the radio sky to understand the beginning of the Universe

Nowadays the leading contender to understand the initial conditions of the Big Bang is inflation, which predicts the existence of a primordial background of gravitational waves that must have left its imprint in the CMB polarization: the so-called ​ B-modes. The main difficulty in measuring the ​ B-modes comes not just from its sheer faintness but from the fact that many other objects in the universe also emit polarized microwaves.

Free falling with a pulsar in a triple system 

Universality of free fall, famously depicted by Galileo's letting down various masses from the top of Pisa's tower, is a cornerstone of General Relativity to the extent that any alternative theory of gravity would almost certainly break that principle. This is why it is being tested by ever more sensitive experiments in the Solar system, such as the recent Microscope satellite.

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.
Séminaire