Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session R03: New Approaches to H_0Invited Live
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Sponsoring Units: DAP DGRAV GPMFC Chair: Glennys Farrar, New York University Room: Washington 2 |
Monday, April 20, 2020 1:30PM - 2:06PM Live |
R03.00001: Local Distance Ladder Measurements and Determination of the Hubble Constant Invited Speaker: Wendy Freedman Our ability to measure the current expansion rate of the universe, or Hubble constant, H0, continues to improve with the development of new techniques, instrumentation, and both ground- and space-based telescopes. An early program of the Hubble Space Telescope (HST) was a Key Project to measure H0, using Cepheid variables to calibrate the extragalactic distance scale. In 2001 the Key Project resolved a factor-of-two debate, and yielded a value of H0 = 72 km / sec / Megaparsec with a combined statistical and systematic uncertainty of 10%. The value of the Hubble constant measured using Cepheid variables has remained stable (in the low to mid-70s) for about two decades, but the precision of the measurements (using HST and Spitzer) has increased significantly. A new value of H0 based on the Tip of the Red Giant Branch (TRGB) results in a value of H0 = 70 km / sec / Megaparsec, with an uncertainty of 3%, in good agreement with that obtained using Cepheids. However, a tension has arisen between the value inferred from measurement of the cosmic background radiation (assuming a standard cosmological model with a cosmological constant and cold dark matter), and those measured locally. If the tension is real, it may be signaling new physics beyond the standard model. [Preview Abstract] |
Monday, April 20, 2020 2:06PM - 2:42PM Live |
R03.00002: CMB measurements of $H_0$ Invited Speaker: Suzanne Staggs The cosmic microwave background (CMB) encodes information about the expansion history of the universe both before the radiation decoupled from the matter, and since that decoupling. Deducing the current value of the Hubble parameter from the CMB data amounts to a stringent test of the standard cosmological model. All measurements of $H_0$ require excellent understanding of, and strict control of, systematic effects on the data. The best constraints on $H_0$ from the CMB rely on the Planck data. I will describe an upcoming complementary path to estimating $H_0$ from a combination of ACT and WMAP data, with similar constraining power to the Planck results. [Preview Abstract] |
Monday, April 20, 2020 2:42PM - 3:18PM Live |
R03.00003: An Independent Measurement of H0 from Lensed Quasars Invited Speaker: Kenneth Wong Strong gravitational lens systems with time delays between the multiple images are a powerful probe of cosmology, particularly of the Hubble constant ($H_{0}$) that is key to probing dark energy, neutrino physics, and the spatial curvature of the Universe, as well as discovering new physics. The $H_{0}$ Lenses In COSMOGRAIL’s Wellspring (H0LiCOW) project has measured $H_{0}$ from lensed quasars using deep Hubble Space Telescope and AO imaging, precise time delay measurements from the COSMOGRAIL monitoring project, a measurement of the velocity dispersion of the lens galaxies, and a characterization of the mass distribution along the line of sight. Our latest results from a total of six lenses constrains H0 to be $73.3_{-1.8}^{+1.7}$ km/s/Mpc for a flat Lambda CDM cosmology, which is a measurement to 2.4% precision. These results are consistent with independent determinations of $H_{0}$ using type Ia supernovae calibrated by the distance ladder method, and are in 3.1$\sigma$ tension with the results of Planck CMB measurements. Combined with the latest distance ladder results from the SH0ES project, we find a 5.3$\sigma$ tension between Planck and late-Universe probes, hinting at possible new physics beyond the standard LCDM model and highlighting the importance of this independent probe. [Preview Abstract] |
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