CMB lensing and Ly\alpha\ forest cross bispectrum from DESI's first-year quasar sample

TL;DR

This paper reports a significant detection of the cross bispectrum between CMB lensing and the Lyα forest using DESI data, providing new constraints on cosmological parameters and validating theoretical models.

Contribution

First measurement of the CMB lensing and Lyα forest cross bispectrum at high significance using DESI data, testing theoretical predictions and addressing contamination effects.

Findings

Detected the cross bispectrum with 4.8σ significance.

Found reasonable agreement with perturbation theory models.

Demonstrated robustness against foreground contamination.

Abstract

The squeezed cross-bispectrum \bispeconed\ between the gravitational lensing in the Cosmic Microwave Background and the 1D \lya\ forest power spectrum can constrain bias parameters and break degeneracies between $\sigma_8$ and other cosmological parameters. We detect \bispeconed\ with $4.8\sigma$ significance at an effective redshift $z_\mathrm{eff}=2.4$ using Planck PR3 lensing map and over 280,000 quasar spectra from the Dark Energy Spectroscopic Instrument's first-year data. We test our measurement against metal contamination and foregrounds such as Galactic extinction and clusters of galaxies by deprojecting the thermal Sunyaev-Zeldovich effect. We compare our results to a tree-level perturbation theory calculation and find reasonable agreement between the model and measurement.