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Hubble speed from first principles

Fabrizio Renzi
Lorentz Center, Leiden University

The Hubble parameter, H0, is arguably the most fundamental constant of our Universe. It provides its current expansion rate, an indication of its age and an overall scale for distances. After almost a century of increasingly precise determinations, two leading experiments nowadays report values of H0 in tension at more than 4 standard deviation : H0 = 74.03 pm 1.42 Km/s/Mpc at 68% C.L. from Type Ia supernovae (SNIa) within the SH0ES collaboration and H0 = 67.4 pm 0.5 Km/s/Mpc 68% C.L. inferred by Planck from the Cosmic Microwave Background (CMB), within the standard cosmological model LCDM. Some yet unaccounted for systematics in the data or a modification of the standard cosmological model could reconcile these measurements, however no compelling resolution in neither direction has been found yet. In this talk I will discuss a novel way of measuring H0 from a combination of independent geometrical datasets, with no need of calibration nor of the choice of a cosmological model. This method builds on the distance duality relation which sets the ratio of the luminosity and angular diameter distance to a fixed scaling in redshift for any metric theory of gravity with standard photon propagation. We find H0 = 69.5 pm 1.7 Km/s/Mpc at 68% C.L. and uncover some features that hint at a twofold solution of the Hubble tension. Our result shows unmistakably that the Hubble constant can be constrained at percent level independently of the cosmological model, and pave the way for a resolution of the Hubble tension.

2020 December 07, 15:30

Online broadcast (Zoom)

Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia