Abstract
We initiate the study of dark matter models based on a gapped continuum. Dark matter consists of a mixture of states with a continuous mass distribution, which evolves as the universe expands. We present an effective field theory describing the gapped continuum, outline the structure of the Hilbert space and show how to deal with the thermodynamics of such a system. This formalism enables us to study the cosmological evolution and phenomenology of gapped continuum DM in detail. As a concrete example, we consider a weakly-interacting continuum (WIC) model, a gapped continuum counterpart of the familiar WIMP. The DM interacts with the SM via a Z-portal. The model successfully reproduces the observed relic density, while direct detection constraints are avoided due to the effect of continuum kinematics. The model has striking observational consequences, including continuous decays of DM states throughout cosmological history, as well as cascade decays of DM states produced at colliders. We also describe how the WIC theory can arise from a local, unitary scalar QFT propagating on a five-dimensional warped background with a soft wall.
Highlights
The microscopic nature of dark matter (DM) remains one of the most important outstanding questions in fundamental physics [1]
We presented a novel type of DM model, where the role of the dark sector is played by a weakly interacting continuum (WIC)
The continuum is assumed to be gapped at the weak scale, and interact with the Standard Model (SM) EW sector, producing a continuum version of standard weakly interacting massive particle (WIMP) models
Summary
The microscopic nature of dark matter (DM) remains one of the most important outstanding questions in fundamental physics [1]. A scalar field with a bulk mass in flat 5D space will produce a gapped continuum spectrum in the limit when the size of the fifth dimension is infinite (see Appendix A), but in this limit gravity will be five-dimensional at all scales, so the model is not phenomenologically viable. Another familiar example, slices of AdS space, in the limit when the KK spacing vanishes generically produce a gapless continuum, which cannot play the role of dark matter.
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