Impact of Instrumental Systematics on the CMB Bispectrum
  We study the effects of instrumental systematics on the estimation of
primordial non-Gaussianity using the cosmic microwave background (CMB)
bispectrum from both the temperature and the polarization anisotropies. For
temperature systematics we consider gain fluctuation and beam distortions. For
polarization we consider effects related to known instrumental systematics:
calibration, pixel rotation, differential gain, pointing, and ellipticity of
the instrument beam. We consider these effects at next to leading order, which
we refer to as non-linear systematic effects. We find that if the instrumental
response is linearly proportional to the received CMB intensity, then only the
shape of the primordial CMB bispectrum, if there is any, will be distorted. We
show that the nonlinear response of the instrument can in general result in
spurious non-Gaussian features on both the CMB temperature and polarization
anisotropies, even if the primordial CMB is completely Gaussian. We determine
the level for both the linear and non-linear systematics parameters for which
they would cause no significant degradation of our ability to constrain the
primordial non-Gaussianity amplitude f_{nl}. We find that the non-linear
systematics are potentially bigger worry for extracting the primordial
non-Gaussianity than the linear systematics. Especially because the current and
near future CMB probes are optimized for CMB power-spectrum measurements which
are not particularly sensitive to the non-linear instrument response. We find
that if instrumental non-linearities are not controlled by dedicated
calibration, the effective local non-Gaussianity can be as large as f_{nl} ~
O(10) before the corresponding non-linearities show up in the CMB dipole
measurements. The higher order multipoles are even less sensitive to
instrumental non-linearities.
