Coannihilation without chemical equilibrium
  Chemical equilibrium is a commonly made assumption in the freeze-out
calculation of coannihilating dark matter. We explore the possible failure of
this assumption and find a new conversion-driven freeze-out mechanism.
Considering a representative simplified model inspired by supersymmetry with a
neutralino- and sbottom-like particle we find regions in parameter space with
very small couplings accommodating the measured relic density. In this region
freeze-out takes place out of chemical equilibrium and dark matter
self-annihilation is thoroughly inefficient. The relic density is governed
primarily by the size of the conversion terms in the Boltzmann equations. Due
to the small dark matter coupling the parameter region is immune to direct
detection but predicts an interesting signature of disappearing tracks or
displaced vertices at the LHC. Unlike freeze-in or superWIMP scenarios,
conversion-driven freeze-out is not sensitive to the initial conditions at the
end of reheating.
