Nuclear Particle Astrophysics (NPA) Seminar: Tom Essinger-Hileman, Johns Hopkins University, “Searching for the Signature Inflation in CMB Polarization: the ABS and CLASS experiments”

The cosmic microwave background (CMB) offers a unique glimpse into the state of the young universe, providing a wealth of information about its structure and constituents. CMB polarization also provides a window onto the first moments after the Big Bang through its sensitivity to inflationary gravitational waves, which leave a distinctive curl (B mode) component in the CMB polarization. I will describe two experiments based in the Atacama Desert of Chile that aim to measure B modes: (1) the Atacama B–‐Mode Search (ABS) operated for three seasons with ongoing data analysis yielding new cosmological constraints soon; and (2) the Cosmology Large Angular Scale Surveyor (CLASS), a multi–‐frequency array of telescopes that is unique in aiming to measure the B mode signal on the largest angular scales from the ground. CLASS will also make cosmic–‐variance–‐limited measurements of large–‐scale E mode polarization, improving constraints on the redshift of reionization and the sum of the neutrino masses. Measuring and characterizing B mode polarization would provide confirmation that inflation occurred, our first evidence of quantum gravitational effects, and a probe of physics at grand–‐unified theory (GUT) energy scales. I will review the observational challenges in making these measurements and prospects for the future.