12:00–1:00 pm Zoom
Host: Vikram Dwarkadas
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Abigail Lee (UChicago) "Using Carbon Stars as Standard Candles: Establishing the Foundations for an Independent Measurement of the Hubble Constant"
In the past several years, a distinct 5-sigma tension has arisen between measurements of the Hubble constant (Ho) determined via the local Type Ia supernova distance ladder based on Cepheids and from measurements of the cosmic microwave background fluctuations, assuming the standard Lambda Cold Dark Matter (LCDM) model. This discrepancy points to either yet-to-be discovered systematic errors in the local distance scale or a necessary revision of the LCDM model, which would indicate new physics of the universe. I will present an independent route to measuring Ho based on a new standard candle that capitalizes on the stable intrinsic luminosities of carbon-rich asymptotic giant branch (AGB) stars. These carbon stars, completely independent of Cepheids and the TRGB, can provide valuable cross-checks and may shed light on currently hidden systematic errors in the local distance scale. These stars are a magnitude brighter than the TRGB and 10-day Cepheids in the near infrared, and thereby capable of calibrating a much larger sample of SNe Ia. I will discuss the advantages and current uncertainties of this new standard candle, and its future with JWST.
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David Zegeye (UChicago) "The Square Kilometer Array as a Cosmic Microwave Background experiment"
Measuring primordial gravitational waves and the primordial bispectrum would provide knowledge of the energy scale and dynamics of inflation. The Cosmic Microwave Background - Stage IV (CMB-S4) experiment aims to constrain both, respectively parameterized by r and fnl, down to \sigma(r) ~ 0.001 and \sigma(fnl) ~ 1. In order for future CMB experiments to improve on these constraints, signal-to-noise of B-modes would need to greatly improve and bispectrum measurements would need to go beyond cosmic-variance limits of the primary CMB. In this talk we suggest using the upcoming Square Kilometer Array (SKA) to improve measurements of the B-modes power spectrum, and constrain the squeezed-limit bispectrum through anisotropies of mu-distortions generated from diffusion damping of the CMB. Under current assumptions, SKA has the potential to improve constraints on r and fnl.
