Virtual Particle Physics in Paris

The H0 tension: experiment and theory

by Wendy Freedman (University of Chicago), Marc Kamionkowski (Johns Hopkins University)


16:00:  Tension in  the Hubble Constant: An Observational Perspective by Wendy Freedman.

I will discuss two of our most precise methods for measuring distances in the local universe: Cepheids and the Tip of the Red Giant Branch (TRGB). I will present new results from the Carnegie-Chicago Hubble Program (CCHP), the goal of which is to independently measure a value of the Hubble constant to a precision and accuracy of 2%. Using the Hubble Space Telescope Advanced Camera for Surveys, the  we are  using the TRGB to calibrate Type Ia supernovae. Our value of the Hubble constant,  Ho = 69.6 +/- 0.8 (statistical) +/- 1.7 (systematic) km/sec/Mpc, falls midway between the value obtained from the Planck Cosmic Microwave Background analysis, and that obtained using Cepheids.  I will address the uncertainties,  discuss the current tension in H0, and whether there is need for additional physics beyond the standard CDM model.

17:30: The Hubble Tension and Early Dark Energy by Marc Kamionkowski.

We’ve known since the late 1920s that the Universe is expanding.  However, the expansion rate currently inferred from measurements of the cosmic microwave background now disagrees with that obtained from supernova measurements.   Over the past few years, theorists have been exploring the possibility that this Hubble tension is explained by some new “early dark energy”: a new component of matter that may have been dynamically important several hundred thousand years after the Big Bang.