New Physics and the Hubble Tension

by Fabrizio Rompineve (CERN)

Thursday 30 Sep 2021, 12:00 → 13:00 Europe/Madrid

IFAE Seminar Room (IFAE)

Observations of the early Universe indicate a Universe expanding today at a (Hubble) rate which is significantly slower than what is measured locally via supernovae, if the ΛCDM model is assumed. Furthermore, the amplitude of matter fluctuations at late times measured by cosmic shear surveys is smaller than what is inferred from the same early Universe observations, assuming the ΛCDM model. Barring unaccounted systematics, these may be the first hints of new components beyond the ΛCDM model.

In this talk, after a review of interesting ideas in this context, we present a new phenomenological Dark Sector (DS) model that addresses the tensions above. The scenario features a decaying dark energy fluid which raises the value of H_0 and an ultra-light axion, which suppresses the matter power spectrum. We present results of Monte Carlo Markov Chain searches of the parameter space of this DS model with several early and late Universe datasets. Furthermore, we discuss a possible particle physics realization of this model, with a dark confining gauge sector and its associated axion, highlighting its challenges.