Off-Diagonal Dark-Matter Phenomenology: Exploring Enhanced
  Complementarity Relations in Non-Minimal Dark Sectors
  In most multi-component dark-matter scenarios, two classes of processes
generically contribute to event rates at experiments capable of probing the
nature of the dark sector. The first class consists of "diagonal" processes
involving only a single species of dark-matter particle -- processes analogous
to those which arise in single-component dark-matter scenarios. By contrast,
the second class consists of "off-diagonal" processes involving dark-matter
particles of different species. Such processes include inelastic scattering at
direct-detection experiments, asymmetric production at colliders, dark-matter
co-annihilation, and certain kinds of dark-matter decay. In typical
multi-component scenarios, the contributions from diagonal processes dominate
over those from off-diagonal processes. Unfortunately, this tends to mask those
features which are most sensitive to the multi-component nature of the dark
sector. In this paper, by contrast, we point out that there exist natural,
multi-component dark-sector scenarios in which the off-diagonal contributions
actually dominate over the diagonal. This then gives rise to a new, enhanced
picture of dark-matter complementarity. In this paper, we introduce a scenario
in which this situation arises and examine the enhanced picture of dark-matter
complementarity which emerges.
