Inverted dipole feature in directional detection of exothermic dark
  matter
  Directional dark matter detection attempts to measure the direction of motion
of nuclei recoiling after having interacted with dark matter particles in the
halo of our Galaxy. Due to Earth's motion with respect to the Galaxy, the dark
matter flux is concentrated around a preferential direction. An anisotropy in
the recoil direction rate is expected as an unmistakable signature of dark
matter. The average nuclear recoil direction is expected to coincide with the
average direction of dark matter particles arriving to Earth. Here we point out
that for a particular type of dark matter, inelastic exothermic dark matter,
the mean recoil direction as well as a secondary feature, a ring of maximum
recoil rate around the mean recoil direction, could instead be opposite to the
average dark matter arrival direction. Thus, the detection of an average
nuclear recoil direction opposite to the usually expected direction would
constitute a spectacular experimental confirmation of this type of dark matter.
