# Calendar

## September 2019

Friday 6 September 14:00-15:00, Amphi 5 du CPT

### Tordre la géométrie riemannienne pour obtenir une signature lorentzienne

#### Pierre Martinetti (Math Dept. University of Genova)

La géométrie noncommutative offre une interprétation géométrique du modèle standard des interactions fondamentales qui fonctionne remarquablement en signature euclidienne,
mais dont la généralisation à une signature pseudo-riemannienne (en particulier lorentzienne) est notoirement difficile. Dans ce séminaire, on verra comment obtenir l’action fermionique lorentzienne
en tordant (au sens de Connes, Moscovici), une géométrie noncommutative de signature euclidienne. On trouvera en particulier les équations de Weyl et Dirac en signature lorentzienne en tordant, respectivement,
le triplet spectral canonique d’une variété riemannienne et le triplet spectral de l’électrodynamique de v. Dungen et v. Suijlekom. Le procédé met en évidence un lien inattendu entre la torsion (au sens cette fois de la géométrie différentielle), et la rotation de Wick.

Thursday 12 September 14:00-15:00, Amphi 5 du CPT

### Novel perspectives from redshift-space distortion data

#### Louis Perenon

The study of cosmic acceleration and understanding its nature is nowadays one of the important branches in the field of cosmology. I would like to present how novel measurements from redshift-space distortion data opens windows to test our gravitational model on cosmological scales. I will discuss perspectives trigged by the release of measurements of the growth rate $f$ and the r.m.s of matter fluctuations separated $\sigma_8,0$ from each other. These have been recently provided by the VIPERS and SDSS collaborations. I will take this opportunity to discuss forecasts for future surveys such as SKA and data reconstructions using Gaussian processes as well.

Friday 13 September 14:00-15:00, Amphi 5 du CPT

### Formation and Abundance of Primordial Black Holes

#### Ilia Musco

Primordial black holes can form in the early Universe from the collapse of cosmological perturbations after the cosmological horizon crossing. They are possible candidates for the dark matter as well as for the seeds of supermassive black holes observed today in the centre of galaxies. If the perturbation is larger than a certain threshold, depending on the equation of state and on the specific shape of the perturbation, a black hole is formed. In this talk I will discuss the dependence of PBH formation from the initial shape of the curvature profile showing the relation between the threshold amplitude and the initial shape of the inflationary power spectrum of cosmological perturbations, taking into account also possible primordial non-Gaussianity. Although the abundance of PBHs could vary by several order of magnitudes depending on the model of inflation, we find that the threshold of PBH formation is rather solid against non linearities.

September 2019 :