# PHYSICS PHD DISSERTATION DEFENSE: Jae Hwan Kang

Ph.D. Candidate:  Jae Hwan Kang

Date: Wednesday, August 21, 2019

Time: 3:00 pm

Location: Varian 355

Title: Measurement of the Polarization of the Cosmic Microwave Background with BICEP3 and the Keck Array Telescopes

Abstract:

The Cosmic Microwave Background (CMB) shows the afterglow image of the Big Bang, providing a window to probe the very early Universe. The CMB encodes the information in the temperature and polarization fluctuations. BICEP3 and the Keck Array telescopes are small aperture refracting telescopes at the South Pole to measure the B-mode polarization of the CMB at the degree angular scales, which holds a key to probe inflation theory. This talk will present the progress of the BICEP/Keck Array telescopes on measuring the B modes and the recent test of low elevation observation with BICEP3 to expand the sky coverage at the South Pole.

The BICEP/Keck Array telescopes produced the tightest constraint to the power of primordial B-modes, parametrized by the tensor-to-scalar ratio r, to be less than 0.07 at 95% confidence using polarization data up to 2015 observing season. BICEP3 was fully deployed for 2016 observing season and has been operating since. Together with the Keck Array telescopes operating at higher frequencies, we expect to achieve the uncertainty $\sigma(r)\approx0.01$ from data up to 2018 observing season.

During the austral summer of 2018-19, we tested the feasibility of using BICEP3 to observe the CMB at low elevation. Due to operational constraints, we had to use a flat mirror to direct the beams to the low elevation range and obtained five weeks of observing time at various elevation settings. We present the temperature and polarization maps from this data set, which clearly shows the detection of the E mode polarization. This potentially opens an opportunity to cover extended patch of the sky at the South Pole. If the primordial B-mode is detected at the main observing field, probing larger area will reduce sample variance. Larger observing field is also important to study the non-Gaussianity and decorrelation of the foregrounds. An interesting patch in this extended region is the CMB Cold Spot centered at declination of -19.58 deg. The possibility of testing polarization anomaly deviating from the standard Gaussian fluctuation around the Cold Spot is discussed.

August 21, 2019 - 3:00pm
Varian 355