Dark matter phenomenology of high speed galaxy cluster collisions
  We perform a general computational analysis of possible post-collision mass
distributions in high-speed galaxy cluster collisions in the presence of weakly
self-interacting dark matter. Using this analysis, we show that weakly
self-scattering dark matter can impart subtle yet measurable features in the
mass distributions of colliding galaxy clusters even without significant
disruptions to the dark matter halos of the colliding galaxy clusters
themselves. Most profound such evidences are found to reside in the tails of
dark matter halos' distributions, in the space between the colliding galaxy
clusters. This feature appears in our simulations as shells of scattered dark
matter expanding in alignment with the outgoing original galaxy clusters,
contributing significant densities to projected mass distributions at large
distances from collision centers and large scattering angles up to $90^\circ$.
Our simulations indicate that as much as 20% of the total collision's mass may
be deposited into such structures without noticeable disruptions to the main
galaxy clusters. Such structures at large scattering angles are forbidden
however in purely gravitational high-speed galaxy cluster collisions.
Convincing identification of such structures in real colliding galaxy clusters
would be a clear indication of the self-interacting nature of dark matter. Our
findings may explain the dark matter ring feature recently found in the
long-range reconstructions of the mass distribution of the colliding galaxy
cluster CL0024+017.
