Searching for axion-like particles through CMB birefringence from string-wall networks

TL;DR

This paper investigates the potential of cosmic string and domain wall networks formed by axion-like particles (ALPs) to produce anisotropic birefringence in the CMB, using observational data to constrain the properties of ALPs and their defect networks.

Contribution

It clarifies how ALP domain walls affect CMB birefringence signals and provides new constraints on ALP parameters based on observational data.

Findings

No evidence for ALP-induced anisotropic birefringence in CMB

Constraints placed on ALP mass and coupling parameters

Difficulty reconciling isotropic birefringence with defect network models

Abstract

Axion-like particles (ALPs) can form a network of cosmic strings and domain walls that survives after recombination and leads to anisotropic birefringence of the cosmic microwave background (CMB). In addition to studying cosmic strings, we clarify and emphasize how the formation of ALP-field domain walls impacts the cosmic birefringence signal; these observations provide a unique way of probing ALPs with masses in the range $3H_0 \lesssim m_a \lesssim 3H_{\rm cmb}$. Using measurements of CMB birefringence from several telescopes, we find no evidence for axion-defect-induced anisotropic birefringence of the CMB. We extract constraints on the model parameters that include the ALP mass $m_a$, ALP-photon coupling $\mathcal{A} \propto g_{a\gamma\gamma} f_a$, the domain wall number $N_{\rm dw}$, and parameters characterizing the abundance and size of defects in the string-wall network. Considering also recent evidence for isotropic CMB birefringence, we find it difficult to accommodate this with the non-detection of anisotropic birefringence under the assumption that the signal is generated by an ALP defect network.