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Title: X-Ray Lines from Dark Matter Annihilation at the keV Scale

Abstract

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. Furthermore, 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 variousmore » observations of the 3.5 keV line. We finally argue that the model can easily avoid structure formation constraints on keV-scale dark matter.« less

Authors:
 [1];  [2];  [3];  [4]
  1. Johannes Gutenberg-Univ. Mainz, Mainz (Germany); Max-Planck-Institut für Kernphysik, Heidelberg (Germany)
  2. Johannes Gutenberg-Univ. Mainz, Mainz (Germany)
  3. Johannes Gutenberg-Univ. Mainz, Mainz (Germany); Univ. of Chicago, Chicago, IL (United States)
  4. Johannes Gutenberg-Univ. Mainz, Mainz (Germany); Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
European Union, Horizon 2020 Research and Innovation Programme; German Research Foundation (DFG); USDOE
OSTI Identifier:
1484229
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 120; Journal Issue: 6; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Brdar, Vedran, Kopp, Joachim, Liu, Jia, and Wang, Xiao -Ping. X-Ray Lines from Dark Matter Annihilation at the keV Scale. United States: N. p., 2018. Web. doi:10.1103/PhysRevLett.120.061301.
Brdar, Vedran, Kopp, Joachim, Liu, Jia, & Wang, Xiao -Ping. X-Ray Lines from Dark Matter Annihilation at the keV Scale. United States. doi:10.1103/PhysRevLett.120.061301.
Brdar, Vedran, Kopp, Joachim, Liu, Jia, and Wang, Xiao -Ping. Mon . "X-Ray Lines from Dark Matter Annihilation at the keV Scale". United States. doi:10.1103/PhysRevLett.120.061301. https://www.osti.gov/servlets/purl/1484229.
@article{osti_1484229,
title = {X-Ray Lines from Dark Matter Annihilation at the keV Scale},
author = {Brdar, Vedran and Kopp, Joachim and Liu, Jia and Wang, Xiao -Ping},
abstractNote = {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. Furthermore, 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.},
doi = {10.1103/PhysRevLett.120.061301},
journal = {Physical Review Letters},
number = 6,
volume = 120,
place = {United States},
year = {2018},
month = {2}
}

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