4th Paris Primordial Cosmology Meeting

mardi 3 mars 2020, 09:30 → 17:00 Europe/Paris

Amphithéâtre Pierre Gilles de Gennes (APC Paris)

09:30 Welcoming coffee

1 New Early Dark Energy

Orateur: Prof. Martin Sloth (CP³-Origin)

2 The Trouble with Hubble: signs of new physics?

The value of the Hubble constant as measured using the classical distance ladder method is 4 to 6sigma higher than the value inferred from a ΛCDM fit to the cosmic microwave background (CMB). While the possibility that unaccounted for systematic effect are responsible for this discrepancy, none are currently universally accepted. Moreover, we now have several independent local probes of the Hubble constant (supernovae, strongly lensed quasars), such that none of the suggested systematics could simultaneously explain all measurements. Consequently, increasing attention is given to the possibility that this “Hubble tension” indicates new physics beyond ΛCDM. In this talk, I would like to review promising solutions to this tension and argue that this discrepancy should be interpreted as a tension between our understanding of the early and late universe cosmology, rather than a tension between a few datasets. In particular, I will entertain the idea that these observations might indicate that our Universe has undergone anomalous expansion due to the presence of an early dark energy (EDE) at redshift z ~ 3500. Such idea, if confirmed, could have far-reaching implications for our understanding of the current epoch of dark energy domination. While undetectable for Planck, future CMB experiment should be able to unambiguously tell us about the presence of the EDE.

Orateur: Dr Vivian Poulin (LUPM Montpellier)

12:30 Lunch break

3 String compactifications & non-perturvative effects

Recent conjectures of the Swampland program challenge the possibility of having 4 dimensional de Sitter vacua or even purely 4 dimensional fully stable Anti de Sitter compactifications. In this talk I will first explain how in compactifications with only classical ingredients one finds support for the previous claims. Then, I will argue that non-perturbative effects such as gaugino condensates on stacks of Dp-branes can provide the key to evade this classical intuition.

Orateur: Dr Ander Retolaza (IPhT Saclay)

4 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. Fluxes of energy, angular momentum and octupole super-angular momentum arise at 2.5PN, fluxes of quadrupole supermomentum arise at 3PN and fluxes of momentum, center-of-mass and octupole super-center-of-mass arise at 3.5PN. If time permits, we argue how each BMS flux-balance law can be thought of as a constraint on the source evolution.

Orateur: Dr Roberto Oliveri (CEICO Prague)