K. S. Arnold | Searcharxiv

arXiv2022

Improved upper limit on degree-scale CMB B-mode polarization power from the 670 square-degree POLARBEAR survey

We report an improved measurement of the degree-scale cosmic microwave background $B$-mode angular-power spectrum over 670 square-degree sky area at 150 GHz with POLARBEAR. In the original analysis of the data, errors in the angle measurement of the continuously rotating half-wave plate, a polarization modulator, caused significant data loss. By introducing an angle-correction algorithm, the data volume is increased by a factor of 1.8. We report a new analysis using the larger data set. We find the measured $B$-mode spectrum is consistent with the $Λ$CDM model with Galactic dust foregrounds. We estimate the contamination of the foreground by cross-correlating our data and Planck 143, 217, and 353 GHz measurements, where its spectrum is modeled as a power law in angular scale and a modified blackbody in frequency. We place an upper limit on the tensor-to-scalar ratio $r$ < 0.33 at 95% confidence level after marginalizing over the foreground parameters.

astro-ph.CO↗

arXiv2018

Design and characterization of a ground-based absolute polarization calibrator for use with polarization sensitive CMB experiments

We present the design and characterization of a ground-based absolute polarization angle calibrator accurate to better than 0.1 degrees for use with polarization sensitive cosmic microwave background (CMB) experiments. The calibrator's accuracy requirement is driven by the need to reduce upper limits on cosmic polarization rotation, which is expected to be zero in a large class of cosmological models. Cosmic polarization effects such as cosmic birefringence and primordial magnetic fields can generate spurious B-modes that result in non-zero CMB TB and EB correlations that are degenerate with a misalignment of detector orientation. Common polarized astrophysical sources used for absolute polarization angle calibration have not been characterized to better than 0.5 degrees. Higher accuracy can be achieved through self-calibration methods, however these are subject to astrophysical foreground contamination and inherently assume the absence of effects like cosmic polarization rotation. The deficiencies in these two calibration methods highlight the need for a well characterized polarized source. The calibrator we present utilizes a 76 GHz Gunn oscillator coupled to a frequency doubler, pyramidal horn antenna, and co-rotating wire-grid polarizer. We use an accurate bubble level in combination with four precision-grade aluminum planes located within the enclosure to calibrate the source's linear polarization plane with respect to the local gravity vector to better than the 0.1 degree goal. In 2017 the calibrator was deployed for an engineering test run on the POLARBEAR CMB experiment located in Chile's Atacama Desert and is being upgraded for calibration of the POLARBEAR-2b receiver in 2018. In the following work we present a detailed overview of the calibrator design, systematic control, characterization, deployment, and plans for future CMB experiment absolute polarization calibration.

astro-ph.IM↗