Solving a Crisis in Cosmology
Mary Gerhardinger, University of Pennsylvania
How fast the Universe is expanding today is not an easy question to answer. Broadly, there are two methods for measuring the current expansion rate of the Universe, H0. The two methods, one using local observations and the other global, result in answers that differ by five σ. Assuming both of these experimental techniques are correct, this discrepancy–known as the Hubble tension–indicates the presence of new physics not currently included in the standard model of cosmology. There are many solutions to this so-called crisis in cosmology, the most popular of which is Early Dark Energy (EDE). EDE posits there is extra energy present in the Universe that behaves like a cosmological constant before it turns-on around matter-radiation equality, affects the Universe for a short while during Matter-Radiation Equality, and decays away quickly, thereby altering the global measurement of H0 enough to mitigate the Hubble Tension. In this work, we take the most popular model of EDE and evolve its nonlinear dynamics in a range of cosmological models, in order to understand how its parameters affect observables in our Universe. The goal is to make quantitative predictions about what a Universe with EDE in it would look like today, so that future cosmological observations can constrain solutions to the Hubble tension and probe other aspects of dark energy.