Axion-Induced Patchy Screening of the Cosmic Microwave Background

TL;DR

This paper investigates how axion-photon interactions in large-scale structures cause patchy screening of the CMB, leading to observable anisotropies that can be used to constrain axion properties with current and future surveys.

Contribution

It introduces a model for axion-induced patchy screening effects on the CMB and forecasts the sensitivity of upcoming surveys to axion-photon couplings within a specific mass range.

Findings

Planck and unWISE data could probe couplings down to 3×10^{-12} GeV^{-1}.

Future CMB-S4 observations could improve sensitivity by nearly an order of magnitude.

The study provides a new method to search for axions using CMB anisotropies correlated with large-scale structure.

Abstract

Cosmic Microwave Background (CMB) photons can undergo resonant conversion into axions in the presence of magnetized plasma distributed inside non-linear large-scale structure (LSS). This process leads to axion-induced patchy screening: secondary temperature and polarization anisotropies with a characteristic non-blackbody frequency dependence that are strongly correlated with the distribution of LSS along our past light cone. We compute the axion-induced patchy screening contribution to two- and three- point correlation functions that include CMB anisotropies and tracers of LSS within the halo model. We use these results to forecast the sensitivity of existing and future surveys to photon-axion couplings for axion masses between $2\times 10^{-13}$ eV and $3\times 10^{-12}$ eV, using a combination of empirical estimates from Planck data of the contribution from instrumental noise and foregrounds as well as modeled contributions on angular scales only accessible with future datasets. We demonstrate that an analysis using Planck and the unWISE galaxy catalogue would be complementary to the most sensitive existing astrophysical axion searches, probing couplings as small as $3\times 10^{-12} \, {\rm GeV}^{-1}$, while observations from a future survey such as CMB-S4 could extend this reach by almost an additional order of magnitude.