Théorie

I will present a new leptogenesis mechanism based on the
standard type-I seesaw model that successfully operates at
right-handed-neutrino masses as low as a few 100 TeV. This mechanism,
which we dub wash-in leptogenesis, does not require any $CP$ violation
in the neutrino sector and can be implemented even in the regime of
strong washout. The key idea behind wash-in leptogenesis is to
generalize standard freeze-out leptogenesis to a nonminimal cosmological
background in which the chemical potentials of all particles not in

Cosmological and astronomical observations indicate that the majority of mass and energy density of fields in the universe are in a form which interacts extremely weakly, if at all, with light. The standard interpretation is the existence of dark matter, commonly thought to be in the form of particles not part of the standard model of particle physics. At present a firm detection of such a particle is lacking, and moreover, all these observations concern a mismatch between the observed dynamics of visible matter with its gravitational influence.

In the primordial Universe, neutrino decoupling occurs only slightly before electron-positron annihilations. This leads to an increased neutrino energy density with order 1% spectral distortions compared to the standard instantaneous decoupling approximation. A precise calculation of neutrino evolution is needed to assess its consequences on BBN, structure formation or on the CMB, and requires to take into account multiple effects such as neutrino oscillations, which represents a genuine numerical challenge. 

Understanding the cosmic-ray (CR) transport in the Milky Way magnetic field is fundamental to unveil their galactic factories. While we know now that they can be created in supernovas, there may be other sources available for CR acceleration. To trace back CR origins we can look at what they are made of. By weighing the different isotopes of elements that hit CR detectors, we can infer global properties as the galactic grammage and escape time.

In this talk I will discuss cosmological first-order phase transitions. These phase transitions which proceed through the nucleation and merger of bubbles on the new phase are known to source gravitational waves. If one of these events occurred in the early universe then upcoming space based gravitational wave detectors like LISA may be able to detect the resulting gravitational wave background that remains today. In this talk I will focus on transitions in which the bubble wall accelerates until collision.

I will start with the overview of principles used in detecting gravitational waves with millisecond pulsars, then
describe the main challenges. Finally, I will review the current status of the search focusing on the latest
results by NanoGrav and EPTA collaborations.

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.

Understanding gravity in the framework of quantum mechanics is one of the great challenges in modern physics. Along this line, a prime question is to find whether gravity is a quantum entity subject to the rules of quantum mechanics. It is fair to say that there are no feasible ideas yet to test the quantum coherent behaviour of gravity directly in a laboratory experiment. Here, I will introduce an idea for such a test based on the principle that two objects cannot be entangled without a quantum mediator.

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.