Dark Matter Velocity Spectroscopy
  Dark matter decays or annihilations that produce line-like spectra may be
smoking-gun signals. However, even such distinctive signatures can be mimicked
by astrophysical or instrumental causes. We show that velocity spectroscopy-the
measurement of energy shifts induced by relative motion of source and
observer-can separate these three causes with minimal theoretical
uncertainties. The principal obstacle has been energy resolution, but upcoming
experiments will reach the required 0.1% level. As an example, we show that the
imminent Astro-H mission can use Milky Way observations to separate possible
causes of the 3.5-keV line. We discuss other applications.
