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.