X-ray Lines from Dark Matter: The Good, The Bad, and The Unlikely

Preprint number: CP3-Origins-2014-7 DNRF90 and DIAS-2014-7
Authors: Mads Frandsen (CP3-Origins & DIAS), Francesco Sannino (CP3-Origins & DIAS), Ian M. Shoemaker (CP3-Origins & DIAS), and Ole Svendsen (CP3-Origins & DIAS)
External link: arXiv.org

We consider three classes of dark matter (DM) models to account for the recently observed 3.5 keV line: metastable excited state DM, annihilating DM, and decaying DM. We study two examples of metastable excited state DM. The first, millicharged composite DM, has both inelasticity and photon emission built in, but with a very constrained parameter space. In the second example, up-scattering and decay come from separate sectors and is thus less constrained. The decay of the excited state can potentially be detectable at direct detection experiments. However we find that CMB constraints are at the border of excluding this as an interpretation of the DAMA signal. The annihilating DM interpretation of the X-ray line is found to be in tension with CMB constraints. Lastly, a generalized version of decaying DM can account for the data while remaining consistent with null X-ray line searches from Andromeda for DM masses ~< 100 keV.