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

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 cos-mic 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 3H0 <= ma <= 3Hcmb. 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 ma, ALP-photon coupling A oc ga1,7fa, the domain wall number Ndw, 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.

Automated summary

Axion-like particles (ALPs) can form a network of cosmic strings and domain walls, leading to anisotropic birefringence of the cosmic microwave background (CMB). However, measurements of CMB birefringence from several telescopes show no evidence for axion-defect-induced anisotropic birefringence.