Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Axion-like Dark Matter Constraints from CMB Birefringence   Axion-like particles are dark matter candidates motivated by the Peccei-Quinn
mechanism and also occur in effective field theories where their masses and
photon couplings are independent. We estimate the dispersion of circularly
polarized photons in a background of oscillating axion-like particles (ALPs)
with the standard $g_{a\gamma}\,a\,F_{\mu\nu}\tilde F^{\mu\nu}/4$ coupling to
photons. This leads to birefringence or rotation of linear polarization by ALP
dark matter. Cosmic microwave background (CMB) birefringence limits $\Delta
\alpha \lesssim (1.0)^\circ$ enable us to constrain the axion-photon coupling
$g_{a\gamma} \lesssim 10^{-17}-10^{-12}\,{\rm GeV}^{-1}$, for ultra-light ALP
masses $m_a \sim 10^{-27} - 10^{-24}$ eV. This improves upon previous
axion-photon coupling limits by up to four orders of magnitude. Future CMB
observations could tighten limits by another one to two orders.

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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: math-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math
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The categories of this paper are: physics
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The categories of this paper are: econ
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The categories of this paper are: acc-phys
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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The categories of this paper are: nlin
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The categories of this paper are: gr-qc
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas