Séminaire

Astrophysical background of gravitational waves: anisotropies, polarization and cross-correlations with cosmological observables. 

 

The astrophysical background of gravitational waves (AGWB) is composed by the incoherent superposition of gravita

Neutrinos have played a key role in astrophysics, from the characterization of nuclear fusion processes in the Sun to the observation of supernova SN1987A and multiple extragalactic events. The Super-Kamiokande experiment has played a major part in past in these astrophysical studies by investigating low energy O(10)~MeV neutrinos, and currently exhibits the best sensitivity to the diffuse neutrino background from distant supernovae.

Slow-roll single-field inflation constitutes the main paradigm of the
Early Universe.

The standard cosmological model determined from the accurate cosmic microwave background measurements made by the Planck satellite implies a value of the Hubble constant H0 that is 4.4 standard deviations lower than the one determined from Type Ia supernovae. The Planck best fit model also predicts lower values of the matter density fraction Om and clustering amplitude S8 compared to those obtained from the Dark Energy Survey Year 1 data.

The KATRIN (Karlsruhe Tritium Neutrino) experiment investigates the energetic endpoint of the tritium beta-decay spectrum to determine the effective mass of the electron anti-neutrino. The collaboration reported its first neutrino mass result in fall 2019. Its unprecedented tritium source luminosity and spectroscopic quality make it a unique instrument to also search for physics beyond the standard model such as eV or keV sterile neutrinos.

The idea that low energy fields such as Gravitons or Axions can be 
thought of as composite particles has been entertained since a long 
time. We revisit this idea motivated by the AdS/CFT correspondence. We 
focus in the case of axions and show that hidden sectors coupled to SM 
fields may provide an emergent axionic field that is a composite of the 
hidden fields (instanton density). This is a more general phenomenon 
beyond holographic theories. We study the general properties of such an 
"emergent axion", without a PQ symmetry.