Studies of Systematic Uncertainties for Simons Observatory: Polarization
  Modulator Related Effects
  The Simons Observatory (SO) will observe the temperature and polarization
anisotropies of the cosmic microwave background (CMB) over a wide range of
frequencies (27 to 270 GHz) and angular scales by using both small (0.5 m) and
large (6 m) aperture telescopes. The SO small aperture telescopes will target
degree angular scales where the primordial B-mode polarization signal is
expected to peak. The incoming polarization signal of the small aperture
telescopes will be modulated by a cryogenic, continuously-rotating half-wave
plate (CRHWP) to mitigate systematic effects arising from slowly varying noise
and detector pair-differencing. In this paper, we present an assessment of some
systematic effects arising from using a CRHWP in the SO small aperture systems.
We focus on systematic effects associated with structural properties of the HWP
and effects arising when operating a HWP, including the amplitude of the HWP
synchronous signal (HWPSS), and I -> P (intensity to polarization) leakage that
arises from detector non-linearity in the presence of a large HWPSS. We
demonstrate our ability to simulate the impact of the aforementioned systematic
effects in the time domain. This important step will inform mitigation
strategies and design decisions to ensure that SO will meet its science goals.
