A new probe of Axion-Like Particles: CMB polarization distortions due to cluster magnetic fields

TL;DR

This paper proposes using future CMB experiments to detect axion-like particles through polarization distortions caused by their interaction with magnetic fields in galaxy clusters, offering a new method to probe ALPs.

Contribution

It introduces a novel approach to detect ALPs via polarization distortions in the CMB caused by cluster magnetic fields, improving sensitivity over current bounds.

Findings

Potential to probe photon-ALP coupling over specific mass range.

Estimates of signal measurability with upcoming CMB experiments.

Distinct spectral shape allows separation from other distortions.

Abstract

We propose using the upcoming Cosmic Microwave Background (CMB) ground based experiments to detect the signal of ALPs (Axion like particles) interacting with magnetic fields in galaxy clusters. The conversion between CMB photons and ALPs in the presence of the cluster magnetic field can cause a polarized spectral distortion in the CMB around a galaxy cluster. The strength of the signal depends upon the redshift of the galaxy cluster and will exhibit a distinctive spatial profile around it depending upon the structure of electron density and magnetic field. This distortion produces a different shape from the other known spectral distortions like $y$-type and $\mu$-type and hence are separable from the multi-frequency CMB observation. The spectrum is close to kinematic Sunyaev-Zeldovich (kSZ) signal but can be separated from it using the polarization information. For the future ground-based CMB experiments such as Simons Observatory and CMB-S4, we estimate the measurability of this signal in the presence of foreground contamination, instrument noise and CMB anisotropies. This new avenue can probe the photon-ALP coupling over the ALP mass range from $10^{-13}$ eV to $10^{-12}$ eV with two orders of magnitude better accuracy from CMB-S4 than the current existing bounds.