Beam me up, SCOTTY! New algorithms for characterizing the beams of next-generation CMB experiments

Will Golay; University of Iowa

The latest cosmological theories predict inflation in the early universe imprinted a signature polarization pattern in the cosmic microwave background (CMB) via primordial gravitational waves. The BICEP/Keck collaboration aims to detect this unique pattern to constrain inflation models. However, precision CMB measurements rely on a thorough understanding of instrumental systematics. Determining the differential beam between pairs of orthogonally polarized detectors is essential to mitigating the effects of temperature-to-polarization leakage. This effect is one of the largest sources of uncertainty in the tensor-to-scalar ratio, the value which quantifies the inflaton field strength. The first step in characterizing the beams is the demodulation of a signal when observing a chopped source on the ground. This talk will summarize the scientific rationale for next-gen CMB experiments, review signal-processing basics, and discuss existing demodulation algorithms and their drawbacks. A new approach called SCOTTY will be introduced to alleviate these effects, and new metrics for quantitatively evaluating demodulator performance will be applied. Finally, a demonstration of promising preliminary results from modifications to the original demodulator will be included.