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Axion absorption and the spin temperature of primordial hydrogen

Abstract : An absorption dip in the spectrum of the cosmic microwave background observed by the EDGES experiment suggests an unexplained reduction of the hydrogen spin temperature at cosmic redshift z ~ 17. The mass of dark-matter axions could correspond to the hyperfine splitting of 5.9 micro-eV, between the triplet (H1) and singlet (H0) state. However, the rate for a+ H0 <-> H1 is extremely small and on balance actually heats the spin temperature. Therefore, axions in this mass range are not ruled in or out by the EDGES result.
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Submitted on : Thursday, August 30, 2018 - 9:35:24 AM
Last modification on : Wednesday, May 1, 2019 - 6:25:46 AM

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Adrien Auriol, Sacha Davidson, Georg Raffelt. Axion absorption and the spin temperature of primordial hydrogen. Physical Review D, American Physical Society, 2019, 99 (2), pp.023013. ⟨10.1103/PhysRevD.99.023013⟩. ⟨hal-01864506⟩



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