Abstract
LiteBIRD is a planned JAXA-led CMB B-mode satellite experiment aiming for
launch in the late 2020s, with a primary goal of detecting the imprint of
primordial inflationary gravitational waves. Its current baseline focal-plane
configuration includes 15 frequency bands between 40 and 402 GHz, fulfilling
the mission requirements to detect the amplitude of gravitational waves with
the total uncertainty on the tensor-to-scalar ratio, $r$, down to
$r<0.001$. A key aspect of this performance is accurate astrophysical
component separation, and the ability to remove polarized thermal dust emission
is particularly important. In this paper we note that the CMB frequency
spectrum falls off nearly exponentially above 300 GHz relative to the thermal
dust SED, and a relatively minor high frequency extension can therefore result
in even lower uncertainties and better model reconstructions. Specifically, we
compare the baseline design with five extended configurations, while varying
the underlying dust modeling, in each of which the HFT (High-Frequency
Telescope) frequency range is shifted logarithmically towards higher
frequencies, with an upper cutoff ranging between 400 and 600 GHz. In each
case, we measure the tensor-to-scalar ratio $r$ uncertainty and bias using both
parametric and minimum-variance component-separation algorithms. When the
thermal dust sky model includes a spatially varying spectral index and
temperature, we find that the statistical uncertainty on $r$ after foreground
cleaning may be reduced by as much as 30--50 % by extending the upper limit of
the frequency range from 400 to 600 GHz, with most of the improvement already
gained at 500 GHz. We also note that a broader frequency range leads to better
ability to discriminate between models through higher $\chi^2$ sensitivity.
(abridged)
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