Detecting Axion-like particles using Cosmic Variance Cancellation with CMB and Radio surveys

TL;DR

This paper proposes a novel method using cosmic variance cancellation with multi-frequency CMB and radio surveys to improve constraints on axion-like particles (ALPs), leveraging spectral signatures across different wavelengths and galaxy cluster observations.

Contribution

It introduces a new approach combining CMB and radio data with cosmic variance cancellation to enhance ALP detection sensitivity and constrain ALP parameters more effectively.

Findings

CVC significantly improves ALP signal ratio constraints.

Method enhances detection sensitivity for low-mass ALPs.

Auto-only spectra yield a standard deviation of 0.059, improved to 0.01 with CVC.

Abstract

Axions and axion-like particles (ALPs) arise naturally in many extensions of the Standard Model and are among the well-motivated candidates for dark matter. In the presence of magnetic fields of galaxy clusters, Cosmic Microwave Background (CMB) photons can convert to ALPs, with the efficiency of the process governed by the cluster electron density and magnetic field profiles, the photon--ALP coupling strength ($g_{a\gamma}$), as well as the frequency ($\nu$) of the photon at the redshift of the cluster. The CMB blackbody spectrum suggests that this resonant conversion also takes place at radio wavelengths, following the spectral behaviour of the ALP distortion signal. This opens a new window to search for ALPs using cosmic variance cancellation (CVC), with multi-frequency tracers of the same phenomenon in CMB photon--ALP resonant conversion. The constraints on the ALP signal ratios from different combinations of microwave and radio bands of the Simons Observatory (SO) and the Square Kilometre Array (SKA) can be significantly improved using CVC compared to the case of using auto-only spectra from the two experiments. With the large number of galaxy clusters that will be observed by SO and SKA, we will be able to obtain much more information using CVC, especially for low-mass ALPs with stronger signals. Using the auto-only spectra from galaxy clusters up to redshift $z = 1$ for inference of the normalized ratio parameter, we obtain a standard deviation of $5.9 \times 10^{-2}$ for an ALP mass $m_a = 10^{-14} \, \mathrm{eV}$, which improves to $1 \times 10^{-2}$ using CVC. This method provides a universal probe of the ALP distortion signal using its spectral dependence and can also invalidate false detections of the ALP signal based on its frequency behaviour in different bands.