An Ultimate Target for Dark Matter Searches
  The combination of S-matrix unitarity and the dynamics of thermal freeze-out
for massive relic particles (denoted here simply by WIMPs) implies a lower
limit on the density of such particles, that provide a (potentially
sub-dominant) contribution to dark matter. This then translates to lower limits
to the signal rates for a variety of techniques for direct and indirect
detection of dark matter. For illustration, we focus on models where
annihilation is s-wave dominated. We derive lower limits to the flux of
gamma-rays from WIMP annihilation at the Galactic center; direct detection of
WIMPs; energetic neutrinos from WIMP annihilation in the Sun; and the effects
of WIMPs on the angular power spectrum and frequency spectrum of the cosmic
microwave background radiation. The results suggest that a variety of
dark-matter-search techniques may provide interesting avenues to seek new
physics, even if WIMPs do not constitute all the dark matter. While the limits
are quantitatively some distance from the reach of current measurements, they
may be interesting for long-range planning exercises.
