Roadmap to Thermal Dark Matter Beyond the WIMP Unitarity Bound

Abstract

We study the general properties of the freezeout of a thermal relic. We give analytic estimates of the relic abundance for an arbitrary freezeout process, showing when instantaneous freezeout is appropriate and how it can be corrected when freezeout is slow. This is used to generalize the relationship between the dark mater mass and coupling that matches the observed abundance. The result encompasses well-studied particular examples, such as WIMPs, SIMPs, coannihilation, coscattering, inverse decays, and forbidden channels, and generalizes beyond them. In turn, this gives an approximate perturbative unitarity bound on the dark matter mass for an arbitrary thermal freezeout process. We show that going beyond the maximal masses allowed for freezeout via dark matter self-annihilations (WIMP-like, $m_{\mathrm{DM}}\gg \mathcal{O}(100\mathrm{TeV})$) predicts that there are nearly degenerate states with the dark matter and that the dark matter is generically metastable. We show how freezeout of a thermal relic may allow for dark matter masses up to the Planck scale.

8 pages, 4 figrues

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• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Co-Decaying Dark Matter
• Light Dark Matter through Assisted Annihilation
• A search for photons with energies above $2\times 10^{17}$ eV using hybrid data from the low-energy extensions of the Pierre Auger Observatory
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• WIMP Dark Matter from a Natural Discrete Gauge Symmetry in the Standard Model
• Probing Heavy Dark Matter in Red Giants