Séminaire

The Diffuse Supernova Neutrino Background in Super-Kamiokande 

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.

Cosmology as a CFT1

Over the last decades, the emergence of conformal symmetry in gravitational systems has provided a powerful tool to investigate new aspects in classical, semi-classical and quantum general relativity.

Relieving the Hubble tension with primordial magnetic fields 

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.

Seminar Thibaut Houdy: KATRIN, from neutrino mass to Dark Matter

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.

Composite and holographic axions 

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.

Inflation and Geometry

Inflation, an era of accelerated expansion of the universe prior to the radiation phase, constitutes the paradigm of primordial cosmology. Within this paradigm, the simplest single-field slow-roll models economically explain all curent data. However, the sensitivity of inflation to Planck scale physics, and the fact that ultraviolet completions of inflation invariably involve extra fields coupled to the inflaton, indicate that these models constitute at best a phenomenological description that emerges from a more realistic physical framework.

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.

Séminaire