Time: 5:30 PM, Apr 20th (Wed) 2022

Venue: Room 204, Natural Science Building #5

Speaker: Donghui Jeong (Department of Astronomy and Astrophysics, Pennsylvania State University)

Title: Gravitational Wave, CMB Polarization, and Hubble Tension

Abstract: The discrepancy between the Hubble parameter inferred from local measurements and that from the cosmic microwave background (CMB) has motivated careful scrutiny of the assumptions that enter both analyses. Here we point out that the location of the recombination peak in the CMB B-mode power spectrum is determined by the light horizon at the surface of last scattering and thus provides an alternative early-Universe standard ruler. It can thus be used as a cross-check for standard ruler inferred from the acoustic peaks in the CMB temperature power spectrum and to test various explanations for the Hubble tension. The measurement can potentially be carried out with a precision <= 2% with state-IV B-mode experiments. The measurement can also be used to measure the propagation speed of gravitational waves in the early Universe.