Taylor Hoyt (University of Chicago) “Using Astrophysical Distance Indicators to Test Standard Cosmology”

Abstract:
Measurements of the universe’s present-day expansion rate, or the Hubble constant (H0), that use a Cepheid variable star calibration of Type Ia supernovae (SNe Ia) are in >4σ disagreement with values predicted by the standard, Lambda cold dark matter (LCDM) model of the universe. In this talk, I will review the evidence for this “Hubble Tension” and discuss in particular my work on an alternative calibration of the SNe Ia using the Tip of the Red Giant Branch (TRGB), a standard candle that can return distances precise to 2% when observed in ancient populations of stars. Anchored by the TRGB, we derived in the Carnegie Chicago Hubble Program a SN value of H0 that is significantly less in tension with base LCDM (<2σ) than the Cepheid-calibrated SN H0, which raises the question of underestimated uncertainties and softens evidence for new physics. I will identify likely causes of this Cepheid-TRGB divergence, present paths to a potential resolution, and highlight how the astrophysical distance scale can converge on a self-consistent, 1% determ
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