CMB Lensing Trispectrum as a Probe of Parity Violation in LSS

TL;DR

This paper demonstrates that the CMB lensing trispectrum can detect parity violation in large-scale structures, providing a new observational tool for future experiments to explore fundamental physics.

Contribution

It introduces a general expression for the CMB lensing trispectrum sensitive to parity violation and presents the first explicit calculation of a parity-odd lensing trispectrum.

Findings

Derived a compact formula for the lensing trispectrum with parity violation

Computed the parity-odd lensing trispectrum for a toy model

Estimated the signal-to-noise ratio for detecting parity violation

Abstract

We show that the Cosmic Microwave Background (CMB) lensing trispectrum is sensitive to parity violation in Large-Scale Structure (LSS). We obtain a compact expression for the reduced lensing trispectrum that is general for any input matter trispectrum. We then present as an example a simple parity-violating toy model for the latter, and explicitly compute the parity-odd lensing trispectrum, including an estimate of the Signal-to-Noise Ratio (SNR). This work serves as a proof of principle, demonstrating how future studies of more physically motivated models can be conducted. It also provides an intuitive physical explanation of why CMB lensing is sensitive to parity. Our work is the first to point out that secondary CMB anisotropies can be used to probe parity in LSS, and will be important in enabling upcoming experiments such as Simons Observatory and CMB-S4 to contribute maximal power on parity violation.