Measuring Ultralight-Axion Coherence with Galaxy Polarization Correlations
Abstract
Ultralight axion-like particles coupled to photons rotate the linear polarization of distant sources. We propose using the three-dimensional two-point correlation of galaxy polarization-rotation angles to measure not only the amplitude of this birefringence field but also its spatial coherence scale. For a nonrelativistic ALP component with an isotropic Gaussian velocity distribution, the equal-time field correlation has an e−1 scale LGphys=√6/(ma va), where va is the three-dimensional rms ALP velocity dispersion. A detected turnover in the galaxy-pair correlation therefore measures the characteristic momentum scale ma va, while the correlation amplitude constrains gaγ√(Ωa/ΩDM). For a fiducial survey with 106 polarized galaxies over a quarter of the sky to z=2 and effective per-galaxy scatter σtot=10∘, we find 5σ sensitivity to sub-degree correlated rotations over ma(10−3c/va)∼10−29--10−27 eV, with σ[log10(ma va)]≲0.1 for detected signals across much of this range. This provides a geometric late-time probe complementary to CMB birefringence and structure-formation constraints.
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BibTeX
@misc{doi2026measuring,
title = {{Measuring Ultralight-Axion Coherence with Galaxy Polarization Correlations}},
author = {Yasuo Doi},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.12446},
eprint = {2607.12446},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.12446},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Measuring Ultralight-Axion Coherence with Galaxy Polarization Correlations
AU - Yasuo Doi
PY - 2026
DA - 2026/10/21
PB - arXiv
DO - 10.48550/arxiv.2607.12446
UR - https://arxiv.org/abs/2607.12446
AB - Ultralight axion-like particles coupled to photons rotate the linear polarization of distant sources. We propose using the three-dimensional two-point correlation of galaxy polarization-rotation angles to measure not only the amplitude of this birefringence field but also its spatial coherence scale. For a nonrelativistic ALP component with an isotropic Gaussian velocity distribution, the equal-time field correlation has an e^−1 scale L_G^phys=√6/(m_a v_a), where v_a is the three-dimensional rms ALP velocity dispersion. A detected turnover in the galaxy-pair correlation therefore measures the characteristic momentum scale m_a v_a, while the correlation amplitude constrains g_aγ√(Ω_a/Ω_DM). For a fiducial survey with 10^6 polarized galaxies over a quarter of the sky to z=2 and effective per-galaxy scatter σ_tot=10^∘, we find 5σ sensitivity to sub-degree correlated rotations over m_a(10^−3c/v_a)∼10^−29--10^−27 eV, with σ[log_10(m_a v_a)]≲0.1 for detected signals across much of this range. This provides a geometric late-time probe complementary to CMB birefringence and structure-formation constraints.
ER -