The H0 puzzle: early vs. late time resolutions

Bhuvnesh Jain (University of Pennsylvania)

November 21, 2019

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Abstract: The expansion rate H0 measured directly is significantly higher than inferred from cosmic microwave background measurements at high redshift. Possible resolutions to this puzzle generally involve new physics in the pre-recombination era. I will describe a low redshift resolution based on the cepheid calibration of Supernova distances. Fifth forces due to unscreened scalar fields can modify the period-luminosity relation of cepheids and alleviate the H0 tension. I will conclude by discussing prospects for empirical progress on the H0 and sigma8 tensions.