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.

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. 

Phenomenology and theory of galactic cosmic-ray propagation

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.

Simulating gravitational wave production during a vacuum phase transition

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.

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.


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