12:00–1:00 pm ERC 501
Host: Vikram Dwarkadas
Christoph Welling "Finding UHE neutrinos with the Radio Neutrino Observatory Greenland"
The Radio Neutrino Observatory Greenland (RNO-G) is aiming for the first detection of astrophysical neutrinos in the EeV energy range. It does so by detecting radio signals that are emitted by showers produced through neutrino interactions in the ice sheet near Summit Station, Greenland. Thanks to the large attenuation lengths of radio signals in ice, these particle showers can be detected over distances up to several kilometers, allowing us to instrument a large volume with relatively few antennas. I will talk about how this detection technique works and, once we have found a neutrino, what the radio signal can tell us about its properties, such as its energy or direction.
Joshua Frieman "How Many Angels Dancing on the Head of a Pin does it Take to Solve the Hubble Tension?"
Measurements of the Cosmic Microwave Background and the large-scale structure of the Universe consistently yield estimates of the Hubble parameter (~67 km/sec/Mpc) that are in conflict with local measurements from Cepheids and type Ia supernovae (~73 km/sec/Mpc). While local measurements based on the Tip of the Red Giant Branch suggest a middle value, the Hubble tension has motivated a number of theoretical extensions of the Lambda-CDM cosmology that aim to reconcile CMB/LSS measurements with larger H_0. An interesting example is the recent model of Cyr-Racine, etal, that invokes a mirror dark sector to realize a scaling symmetry, but it requires a primordial Helium abundance at odds with observation. I describe work with UC undergraduate John Zhang that improves upon this model, restoring Helium concordance, by invoking an ultra-light scalar field coupled to electromagnetism. In this model, alpha, the fine-structure constant of electromagnetism, prior to and during photon decoupling is smaller than the current value by 2x10^{-5}, and the post-decoupling evolution of the field makes alpha(z) consistent with observational constraints from QSO absorption lines, abundance ratios in meteorites, and the Oklo natural reactor.
