CMB, LSS and the distance ladder: cosmic discordance? [Remote talk]

par Vivian Poulin (LUPM (CNRS & U. de Montpellier))

jeudi 12 mai 2022, 11:00 → 12:00 Europe/Paris

Auditorium (LAPTh)

The Lambda-cold-dark-matter (LCDM) model has established itself as a fantastic (yet parametric)  concordance model able to adjust a wide variety of cosmological observables — CMB, BBN, Large Scale Structure (LSS) & SN1a most notably.  However as the precision of the data has increased over the past few years, a number of predictions of the LCDM model are challenged by recent observations.

First and foremost, the infamous 'Hubble tension’ is a strong mismatch between the value of the Hubble constant measured using the classical distance ladder method and that inferred from the ΛCDM model. Second, the ‘S8 tension’ is a longstanding discrepancy between the determination of the amplitude of matter fluctuations on a 8 Mpc/h scale by galaxy (weak lensing) surveys and its prediction within the LCDM model.  

After a brief review of the various measurements (and some potential short-comings), I will discuss potential implications that such measurements could have. I will argue that current data favor the possibility that our Universe has undergone anomalous expansion just before recombination and present an overview of the most promising models (early dark energy, additional dark radiation component and new neutrino properties), and their current limitations. I will present guidelines to resolve these tensions simultaneously and suggest what it might take to establish a new `concordance model’ beyond LCDM.