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

Understand

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.