Kavli Affiliate: Toshiya Namikawa
| First 5 Authors: Toshiya Namikawa, Irene Abril-Cabezas, Blake D. Sherwin, ,
| Summary:
We present a follow-up study to the method recently proposed by Namikawa &
Sherwin (2023) to probe gravitational waves using cross-correlations between
two CMB $B$-modes and a large-scale structure tracer. We first improve on the
previous forecast by including the impact of CMB component separation and find
that we can achieve $sigma_rsimeq3.5times10^{-3}$ by combining upcoming
experiments, i.e., LiteBIRD, CMB-S4 and the Advanced Simons Observatory. With a
more futuristic experiment, we can achieve even tighter constraints on $r$ if
improved delensing can be realized. Using a simulated analysis pipeline, we
also explore possible biases from higher-order terms in the lensing potential,
which were previously not examined in detail. We find that these bias terms are
negligible compared to a detectable signal from inflationary gravitational
waves. Our simulated results confirm that this new method is capable of
obtaining powerful constraints on $r$. The method is immune to Gaussian
Galactic foregrounds and has a different response to non-Gaussian Galactic
foregrounds than the $B$-mode power spectrum, offering an independent
cross-check of $r$ constraints from the standard power spectrum analysis.
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