On the Direct Detection of Dark Matter Annihilation
  We investigate the direct detection phenomenology of a class of dark matter
(DM) models in which DM does not directly interact with nuclei, {but rather}
the products of its annihilation do. When these annihilation products are very
light compared to the DM mass, the scattering in direct detection experiments
is controlled by relativistic kinematics. This results in a distinctive recoil
spectrum, a non-standard and or even absent annual modulation, and the ability
to probe DM masses as low as a $\sim$10 MeV. We use current LUX data to show
that experimental sensitivity to thermal relic annihilation cross sections has
already been reached in a class of models. Moreover, the compatibility of dark
matter direct detection experiments can be compared directly in $E_{{\rm min}}$
space without making assumptions about DM astrophysics, mass, or scattering
form factors. Lastly, when DM has direct couplings to nuclei, the limit from
annihilation to relativistic particles in the Sun can be stronger than that of
conventional non-relativistic direct detection by more than three orders of
magnitude for masses in a 2-7 GeV window.
