Forecasting the Ly-𝛼 forest × CMB lensing bispectrum from ACT, SO, S4, and DESI

Posta, Adrien La [Univ. of Oxford (United Kingdom); Université Paris-Saclay, Orsay (France); Centre National de la Recherche Scientifique (CNRS) (France)] (ORCID:0000000226132445); Schaan, Emmanuel [Kavli Institute for Particle Astrophysics and Cosmology, Stanford, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000246198927)

doi:10.1103/9x9x-pqqm

DOE OSTI · 2998760

Forecasting the Ly-𝛼 forest × CMB lensing bispectrum from ACT, SO, S4, and DESI

Posta, Adrien La [Univ. of Oxford (United Kingdom); Université Paris-Saclay, Orsay (France); Centre National de la Recherche Scientifique (CNRS) (France)] (ORCID:0000000226132445)·Schaan, Emmanuel [Kavli Institute for Particle Astrophysics and Cosmology, Stanford, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000246198927)

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Abstract

We forecast the sensitivity of future correlations between cosmic microwave background (CMB) lensing and the Lyman-𝛼 forest power spectrum. This squeezed-limit bispectrum probes the connection between the Lyman-𝛼 transmission and the underlying large-scale matter density field. We recover the measured signal-to-noise (SNR) ratio obtained with Planck × BOSS, and forecast a SNR of 10.3, 14.8 and 20.2 for DESI combined with ACT, SO, and CMB-S4, respectively. For DESI and SO/CMB-S4, the correlation should be detectable at SNR ≥ 5 in 5 redshift bins, useful for distinguishing our signal from several contaminants. Indeed, our forecast is affected by large theoretical uncertainties in the current modeling of the signal and its contaminants, such as continuum misestimation bias or damped-Lyman-𝛼 absorbers. Quantifying these more accurately will be crucial to enable a reliable cosmological interpretation of this observable in future measurements. We attempt to enumerate the features required in future Lyman-𝛼 forest simulations required to do so.

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Posta, Adrien La [Univ. of Oxford (United Kingdom); Université Paris-Saclay, Orsay (France); Centre National de la Recherche Scientifique (CNRS) (France)] (ORCID:0000000226132445), Schaan, Emmanuel [Kavli Institute for Particle Astrophysics and Cosmology, Stanford, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000246198927). 2025-09-16. Forecasting the Ly-𝛼 forest × CMB lensing bispectrum from ACT, SO, S4, and DESI. https://doi.org/10.1103/9x9x-pqqm

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