Z-portal Continuum Dark Matter
  We examine the possibility that dark matter (DM) consists of a gapped
continuum, rather than ordinary particles. A Weakly-Interacting Continuum (WIC)
model, coupled to the Standard Model via a Z-portal, provides an explicit
realization of this idea. The thermal DM relic density in this model is
naturally consistent with observations, providing a continuum counterpart of
the "WIMP miracle". Direct detection cross sections are strongly suppressed
compared to ordinary Z-portal WIMP, thanks to a unique effect of the continuum
kinematics. Continuum DM states decay throughout the history of the universe,
and observations of cosmic microwave background place constraints on potential
late decays. Production of WICs at colliders can provide a striking
cascade-decay signature. We show that a simple Z-portal WIC model provides a
fully viable DM candidate consistent with all current experimental constraints.
