New Probe of Inflationary Gravitational Waves: Cross-Correlations of Lensed Primary CMB <math display="inline"><mi>B</mi></math>-Modes with Large-Scale Structure

-mode polarization with a large-scale structure (LSS) tracer, which can also be a cosmic microwave background (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 σ

constraints on the tensor-to-scalar ratio

r

, albeit with a simplistic foreground treatment, and find constraints of

σ_{r} ≃ 7 \times 10^{- 3}

from the correlation of CMB-S4-Deep

B

-mode lensing and LSST galaxies,

σ_{r} ≃ 5 \times 10^{- 3}

from the correlation of CMB-S4-Deep

B

-mode lensing and CMB-S4-Deep CMB lensing, and

σ_{r} ≃ 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 useful probe of IGWs, which, due to different sensitivity to many potential sources of systematic errors, can be complementary to standard methods for constraining

r

.

Note:

6 pages, 1 figure, accepted for publication in Physical Review Letters

cosmic background radiation: B-mode
n-point function: 3
gravitation: lens
inflation
correlation function
gravitational radiation
non-Gaussianity
structure
polarization
LiteBIRD

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