Flaring of tidally compressed dark-matter clumps
  We explore the physics and observational consequences of tidal compression
events (TCEs) of dark-matter clumps (DMCs) by supermassive black holes (SMBHs).
Our analytic calculations show that a DMC approaching a SMBH much closer than
the tidal radius undergoes significant compression along the axis perpendicular
to the orbital plane, shortly after pericenter passage. For DMCs composed of
self-annihilating dark-matter particles, we find that the boosted DMC density
and velocity dispersion lead to a flaring of the annihilation rate, most
pronounced for a velocity- dependent annihilation cross section. If the end
products of the annihilation are photons, this results in a gamma-ray flare,
detectable (and possibly already detected) by the Fermi telescope for a range
of model parameters. If the end products of dark-matter annihilation are
relativistic electrons and positrons and the local magnetic field is large
enough, TCEs of DMCs can lead to flares of synchrotron radiation. Finally, TCEs
of DMCs lead to a burst of gravitational waves, in addition to the ones
radiated by the orbital motion alone, and with a different frequency spectrum.
These transient phenomena provide interesting new avenues to explore the
properties of dark matter.
