Axion absorption and the spin temperature of primordial hydrogen

Adrien Auriol (1) , Sacha Davidson (1) , Georg Raffelt

1 LUPM - Laboratoire Univers et Particules de Montpellier

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.

Domaines: Physique des Hautes Energies - Phénoménologie [hep-ph]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]

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