Cosmic String Interpretation of NANOGrav Pulsar Timing Data and its impact on Cosmic Archaeology with Gravitational Waves

The NANOGrav Collaboration has recently reported strong evidence for a stochastic common-spectrum process, which we interpret as a SGWB in the framework of cosmic strings. The possible NANOGrav signal would correspond to a string tension Gμ∈(4×10^{−11},10^{−10}) at the 68% confidence level, with a different frequency dependence from supermassive black hole mergers.

Dark Holograms and Gravitational Waves

First order cosmological phase transitions in beyond the Standard Model theories may trigger the

A numerical approach to stochastic inflation and primordial black holes

Primordial black holes are a dark matter candidate, which may originate from strong perturbations created during inflation. These perturbations can be studied using the formalism of stochastic inflation. I present a numerical approach to this problem, where the stochastic dynamics is solved by generating a large number of random realizations. This makes it possible to go beyond analytical approximations and take into account additional effects such as backreaction between the perturbations and the background.

From pulsars to supermassive black holes and gravitational waves in between

Pulsar Timing Arrays (PTAs) aim to detect nHz gravitational waves (GWs) from supermassive black hole binaries (SMBHBs). This is done by looking for correlated variations of the Time of Arrivals (TOA) across an array of ultra-stable millisecond pulsars. Comparing the predicted TOAs from our timing model against the measured TOAs gives us the residuals. These contain the imprint of GWs, but also other effects and sources of noise processes.

Catalogue and background description of a population of GW sources: features, complementarities and caveats.

There are two possible approaches to describe a population of astrophysical gravitational wave (GW) sources: one can focus on high signal-to-noise sources that can be detected individually, and build a catalogue.

Detecting quantum entanglement in the sky

Although inflation is broadly accepted to be the standard paradigm for early universe cosmology, many of its quantum properties remain unknown. For instance, the crowning glory of inflation lies in explaining late-time macroscopic inhomogeneities as arising from tiny quantum fluctuations; however, most of the established literature ignores the crucial role that entanglement between the modes of the fluctuating field plays in its observable predictions.

Stochastic Gravitational Wave Backgrounds (SGWB) characterization with LISA

In this seminar I will discuss Stochastic Gravitational Wave Backgrounds (SGWB) characterization with LISA. After a general introduction on SGWB detection, I will explain the peculiar features of LISA with a focus on the response function and on the noise spectrum. The core of my talk will be the presentation of two different methods for model independent SGWB frequency reconstruction:
- The so-called ``binning method'' (1906.09244, 2009.11845) based on the idea of approximating the signal with a piecewise-defined function where each sub-function is a power law.

Primordial black holes from metric preheating: mass fraction in the excursion-set approach

We calculate the mass distribution of Primordial Black Holes (PBHs) produced during metric preheating. After inflation, the oscillations of the inflaton at the bottom of its potential source a parametric resonant instability for small-scale scalar perturbations, that may collapse into black holes. After reviewing in a pedagogical way different techniques that have been developed in the literature to compute mass distributions of PBHs, we focus on the excursion-set approach.

Wash-in leptogenesis

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

New gravitational degrees of freedom as a solution to the dark matter problem

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.

LABORATOIRE

ASTROPARTICULE & COSMOLOGIE

Théorie