Dark energy after gravitational wave observations

The observed accelerated expansion of the Universe opens up
the possibility that general relativity is modified on cosmological
scales. While this has motivated the theoretical study of many
alternative theories that will be tested by the next generation of
cosmic large-scale structure surveys, I will show that the recent
observations of gravitational waves by LIGO/Virgo has dramatic
consequences on these theories.

Horndeski and the Sirens

Mergers of compact objects, such as black holes and neutron stars, have been nicknamed standard sirens, by analogy with electromagnetic standard candles, because their waveform directly gives access to their distance. When an electromagnetic counterpart is observed, such sources thus allow us to construct a Hubble diagram, just as supernovae. Recently, the gravitational-wave Hubble diagram has been argued to be a key probe of alternative theories of gravity, such as Horndeski models.

BMS flux-balance laws

Asymptotically flat spacetimes admit both supertranslations and Lorentz transformations as asymptotic symmetries known as BMS symmetries. Furthermore, they admit super-Lorentz transformations, namely superrotations and superboosts, as outer symmetries associated with super angular momentum and super-center-of-mass charges. In this talk, we present the flux-balance laws for all such (extended) BMS charges in terms of radiative multipole moments at future null infinity.

Vacuum stability without Supersymmetry: Brane dynamics, bubbles and holography

n this talk I will present some recent results on instabilities of anti-de Sitter flux compactifications in effective field theories arising from non-supersymmetric string models, namely the USp(32) and U(32) orientifold models and the SO(16) x SO(16) heterotic string. We focus on non-perturbative instabilities, framing the vacua in terms of brane stacks, analyzing their back-reacted geometry and reproducing AdS its near-horizon limit.

D-brane model building and phenomenology

I will present a review on D-brane realizations of the Standard Model and their phenomenological consequences.

First, I will provide the basic ingredients of D-brane (open string) models which are useful for model building.

Next, I will use them in order to embed the Standard Model in open string vacua.

Finally, I will discuss new gauge fields and new matter particles which are predictions of the D-brane realizations of the Standard Model described above.

Neutrino properties from atmospheric neutrinos from a KM3NeT/ORCA near-future perspective

Atmospheric neutrino experiments measure the oscillations of neutrinos produced in the atmosphere by default assuming unitary mixing of electron-, muon-, and tau-neutrinos. The task-list for the upcoming years involves: (a) Measure the atmospheric mixing parameters with increased precision. (b) Determine the known unknowns in the framework of three neutrino flavours: ordering of neutrino masses and CP-violation.

Singularity avoidance, clocks and primordial power spectrum

There are ways to cure the singularity problem in cosmology
by means of quantum effects. In the process, one encounters
the question of time, which can for instance be addressed by
using an internal degree of freedom. Applying such a method
to an anisotropic Bianchi I model where the shear serves as a
clock, I show that some generic features can be obtained for
the trajectory of the average scale factor, all avoiding the
singularity and reaching similar asymptotic states, deemed
semi-classical. Using a trajectory approach yields similar

TBA

Stochastic inflation in the phase space

Inflation is currently the leading paradigm describing the physical conditions that prevail in the very early universe. During this epoch, quantum fluctuations are extracted out of the vacuum and amplified to cosmological perturbations at astronomical scales, later seeded CMB anisotropies and large-scale structures. As inflation proceeds, this inflow of super-horizon perturbations may impact on the large-scale dynamics of the universe, potentially perturbing the inflationary trajectory.

LABORATOIRE

ASTROPARTICULE & COSMOLOGIE

Séminaire