Detection of the CMB lensing -- galaxy bispectrum

TL;DR

This paper reports the first detection of the galaxy-galaxy-CMB lensing bispectrum with high significance, providing a new tool for cosmological analysis and bias parameter constraints.

Contribution

It introduces a novel measurement of the CMB lensing galaxy bispectrum using a compressed estimator and validates its cosmological origin with consistency tests.

Findings

Significant detection of the bispectrum at 26σ and 22σ.

Reasonable agreement with halo model predictions on large scales.

Potential for constraining higher-order galaxy bias parameters.

Abstract

We present a first measurement of the galaxy-galaxy-CMB lensing bispectrum. The signal is detected at $26\sigma$ and $22\sigma$ significance using two samples from the unWISE galaxy catalog at mean redshifts $\bar{z}=0.6$ and $1.1$ and lensing reconstructions from Planck PR4. We employ a compressed bispectrum estimator based on the cross-correlation between the square of the galaxy overdensity field and CMB lensing reconstructions. We present a series of consistency tests to ensure the cosmological origin of our signal and rule out potential foreground contamination. We compare our results to model predictions from a halo model previously fit to only two-point spectra, finding reasonable agreement when restricting our analysis to large scales. Such measurements of the CMB lensing galaxy bispectrum will have several important cosmological applications, including constraining the uncertain higher-order bias parameters that currently limit lensing cross-correlation analyses.