http://arxiv.org/abs/2304.10315
We propose a new probe of inflationary gravitational waves (IGWs): the cross-correlation of the lensing of inflationary $B$-mode polarization with a large-scale structure (LSS) tracer, which can also be a CMB lensing map. This is equivalent to measuring a three-point function of two CMB $B$-modes and an LSS tracer. We forecast expected $1\,\sigma$ constraints on the tensor-to-scalar ratio, $r$, albeit with a simplistic foreground treatment, and find constraints of $\sigma_r \simeq 7 \times 10^{-3}$ from the correlation of CMB-S4-Deep $B$-mode lensing and LSST galaxies, $\sigma_r \simeq 5 \times 10^{-3}$ from the correlation of CMB-S4-Deep $B$-mode lensing and CMB-S4-Deep CMB lensing, and $\sigma_r \simeq 10^{-2}$ from the correlation of LiteBIRD $B$-mode lensing and CMB-S4-Wide lensing. Because this probe is inherently non-Gaussian, simple Gaussian foregrounds will not produce any biases to the measurement of $r$. While a detailed investigation of non-Gaussian foreground contamination for different cross-correlations will be essential, this observable has the potential to be a powerful probe of IGWs, complementary to standard methods for constraining $r$.
T. Namikawa and B. Sherwin
Fri, 21 Apr 23
28/60
Comments: 7 pages, 1 figure