2017/10/31 by Vedran Brdar, Joachim Kopp, Jia Liu +1 · 1 citation
Physics and Astronomy · #Annihilation #Astrophysics #Cosmology #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #Dark energy #Dark matter #Dark photon #Fermion #Galaxy #Light dark matter #Line (geometry) #Parameter space #Particle physics #Particle physics theoretical and experimental studies #Photon #Physics #Quantum mechanics #Scalar field dark matter #Warm dark matter #astro-ph.HE #hep-ph
paper · pdf · doi:10.1103/physrevlett.120.061301
published as Phys. Rev. Lett. 120, 061301 (2018) · 8 pages, 3 figures. v2: reference added, version matched to journal
openalex publication_date 2018/02/05 · arxiv created 2018/02/06 · arxiv updated 2018/02/07 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In 2014, several groups reported hints for a yet unidentified line in astrophysical x-ray signals from galaxies and galaxy clusters at an energy of 3.5 keV. While it is not unlikely that this line is simply a reflection of imperfectly modeled atomic transitions, it has renewed the community's interest in models of keV-scale dark matter, whose decay would lead to such a line. The alternative possibility of dark matter annihilation into monochromatic photons is far less explored, a lapse that we strive to amend in this Letter. More precisely, we introduce a novel model of fermionic dark matter χ with O(keV) mass, annihilating to a scalar state ϕ which in turn decays to photons, for instance via loops of heavy vectorlike fermions. The resulting photon spectrum is box shaped, but if χ and ϕ are nearly degenerate in mass, it can also resemble a narrow line. We discuss dark matter production via two different mechanisms-misalignment and freeze-in-which both turn out to be viable in vast regions of parameter space. We constrain the model using astrophysical x-ray data, and we demonstrate that, thanks to the velocity dependence of the annihilation cross section, it has the potential to reconcile the various observations of the 3.5 keV line. We finally argue that the model can easily avoid structure formation constraints on keV-scale dark matter.