On the effect of non-Gaussian lensing deflections on CMB lensing measurements

TL;DR

This paper demonstrates that assuming Gaussianity in lensing deflections introduces significant biases in CMB lensing power spectrum measurements, especially in temperature data, and emphasizes the importance of accounting for non-Gaussian effects.

Contribution

It provides a detailed analysis of non-Gaussian lensing deflections' impact on CMB lensing measurements using simulations and compares results with analytical predictions.

Findings

Bias in temperature-based measurements due to non-Gaussian deflections.

No significant bias found in polarization-based measurements.

Bias magnitude aligns with analytical models.

Abstract

We investigate the impact of non-Gaussian lensing deflections on measurements of the CMB lensing power spectrum. We find that the false assumption of their Gaussianity significantly biases these measurements in current and future experiments at the percent level. The bias is detected by comparing CMB lensing reconstructions from simulated CMB data lensed with Gaussian deflection fields to reconstructions from simulations lensed with fully non-Gaussian deflection fields. The non-Gaussian deflections are produced by ray-tracing through snapshots of an N-body simulation and capture both the non-Gaussianity induced by non-linear structure formation and by multiple correlated deflections. We find that the amplitude of the measured bias is in agreement with analytical predictions by B\"ohm et al. 2016. The bias is largest in temperature-based measurements and we do not find evidence for it in measurements from a combination of polarization fields ($EB,EB$). We argue that the non-Gaussian bias should be even more important for measurements of cross-correlations of CMB lensing with low-redshift tracers of large-scale structure.