CMB birefringence from ultra-light axion string networks

Abstract

The polarization of Cosmic Microwave Background (CMB) photons is rotated as they pass through (ultralight-) axion string loops. Studying this birefringence can reveal valuable information about the axion-photon coupling and the structure of the string network. We develop an approximate analytic formalism and identify a kernel function that can be used to calculate the two-point correlation function for CMB birefringence induced by an arbitrary axion string network. Using this formalism, we evaluate the birefringence signal for some simple loop distributions (including scaling and network collapse). We find that the angular correlation function has a characteristic angular scale set by ${\theta }_{\min }$, which corresponds to the angular extent of the loops at the time of recombination. This results in a peak in the birefringence power spectrum around ${\ell }_p\sim 1/{\theta }_{\min }$. An additional scale, controlled by the axion's mass, is introduced if the network collapses before today.

31 pages + appendices; 9 figures. v2: updated towards the version published in JCAP (added limits from ACTPol n SPTPol in power spectrum figures; added more references)

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Cited by in corpus (24)

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• Cosmic Birefringence from Monodromic Axion Dark Energy
• Searching for axion-like particles through CMB birefringence from string-wall networks
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• Detecting Axion Dark Matter with Black Hole Polarimetry
• Probing cosmic strings by reconstructing polarization rotation of the cosmic microwave background
• Detecting Cosmic Strings with Lensed Fast Radio Bursts
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• Probing Axions via Light Circular Polarization and Event Horizon Telescope
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• Testing charge quantization with axion string-induced cosmic birefringence
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• Constraining Ultralight Axions with Galaxy Surveys
• Berry phase in axion physics, SM global structure, and generalized symmetries