Theory HEP Seminar

Early dark energy, quantum gravity, and cosmic tensions

Michael Toomey

Brown University

We are now in the era of precision cosmology and have reached the point where there is no longer cosmological concordance in the ΛCDM model between data sets spanning cosmic history. Nowhere is this best exemplified than in the discrepancy between the expansion rate today, the so-called “Hubble constant” H0, as directly measured by late-Universe probes and that inferred from the early-Universe using the standard model. With recent measurements putting that tension in excess of 5σ and other growing tensions, including the large-scale structure tension, there is now a strong impetus to improve on the most promising extensions of ΛCDM and consider new, well-motivated models. In the first part of the talk we will discuss the state of a popular extension of ΛCDM to address the Hubble tension inspired by axions, early dark energy (EDE). We will discuss the successes and shortcomings of the original proposal and present a promising alternative form of EDE inspired by string theory. In the next part of the talk we will consider the cosmology of a model of quantum gravity that has dynamics triggered by the onset of dark energy domination and results in the suppression of the growth of large-scale structure in the late-Universe. We will show that this model may have the right dynamics to modify structure growth to be consistent with data and may have the machinery necessary to address other cosmic tensions.