Séminaire

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.

Astronomie multi-messager, croisez les sources

Qu’est-ce que l’astronomie multi-messager ? Quels types de signaux prend-elle en compte ? Comment ces signaux sont-ils associés pour observer sous plusieurs angles un même évènement cosmique ? Quelles sont les principales réussites de cette astronomie, et comment va-t-elle évoluer ?

On peut observer l’univers de multiples façons. Allongé dans l’herbe, la tête dans les étoiles. Avec un télescope, petit ou grand, pour observer la lumière visible.

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

Exotic compact objects and their gravitational waves by Alexandre Toubiana

This week we have the pleasure of welcoming our very own Alexandre Toubiana for the next Gravitation group seminar. He will present his recent work on exotic compact objects and their gravitational waves, abstract below.

The virtual seminar will take place this Friday, 27th November at 11am. The zoom coordinates are also below.

Abstract:

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.

Seminar of Philosophy of Science: Replicability in cosmology: lessons to be drawn from the Hubble constant so called 'crisis'

Seminar of Philosophy of Science

Title: Replicability in cosmology: lessons to be drawn from the Hubble constant so called 'crisis'

Speaker: Dr Marie Gueguen, Center for the Philosophy of Science, University of Pittsburg

Date:
Friday the 20th of November, 11:00

Location:
Zoom: link communicated via e-mail

Details:
We are organising a cycle of seminars of philosophy of science this semester at the APC.

A precision calculation of neutrino decoupling

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. 
Séminaire