Heavy Thermal Dark Matter from a New Collision Mechanism

Roadmap to Thermal Dark Matter beyond the Weakly Interacting Dark Matter Unitarity Bound

We study the general properties of the freeze-out of a thermal relic. We give analytic estimates of the relic abundance for an arbitrary freeze-out process, showing when instantaneous freeze-out is appropriate and how it can be corrected when freeze-out is slow. This is used to generalize the relationship between the dark matter mass and coupling that matches the observed abundance. The result encompasses well-studied particular examples, such as weakly interacting massive particles (WIMPs), strongly interacting massive particles, 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 freeze-out process. We show that going beyond the maximal masses allowed for freeze-out via dark matter self-annihilations [WIMP-like, m_{DM}≫O(100  TeV)] predicts that there are nearly degenerate states with the dark matter and that the dark matter is generically metastable.

Constraints on Heavy Decaying Dark Matter from 570 Days of LHAASO Observations

The kilometer square array (KM2A) of the large high altitude air shower observatory (LHAASO) aims at surveying the northern γ-ray sky at energies above 10 TeV with unprecedented sensitivity. γ-ray observations have long been one of the most powerful tools for dark matter searches, as, e.g., high-energy γ rays could be produced by the decays of heavy dark matter particles. In this Letter, we present the first dark matter analysis with LHAASO-KM2A, using the first 340 days of data from 1/2-KM2A and 230 days of data from 3/4-KM2A. Several regions of interest are used to search for a signal and account for the residual cosmic-ray background after γ/hadron separation. We find no excess of dark matter signals, and thus place some of the strongest γ-ray constraints on the lifetime of heavy dark matter particles with mass between 10^{5} and 10^{9}  GeV. Our results with LHAASO are robust, and have important implications for dark matter interpretations of the diffuse astrophysical high-energy neutrino emission.

Dark Matter from Exponential Growth

We propose a novel mechanism for the production of dark matter (DM) from a thermal bath based on the idea that DM particles χ can transform heat bath particles ψ: χψ→χχ. For a small initial abundance of χ, this leads to an exponential growth of the DM number density in close analogy to other familiar exponential growth processes in nature. We demonstrate that this mechanism complements freeze-in and freeze-out production in a generic way, opening new parameter space to explain the observed DM abundance, and we discuss observational prospects for such scenarios.

Dark Matter Freeze-Out via Catalyzed Annihilation

We present a new paradigm of dark matter freeze-out, where the annihilation of dark matter particles is catalyzed. We discuss in detail the regime in which the depletion of dark matter proceeds via 2χ→2A^{'} and 3A^{'}→2χ processes, where χ and A^{'} denote dark matter and the catalyst, respectively. In this regime, the dark matter number density is depleted polynomially rather than exponentially (Boltzmann suppression) as in classical weakly interacting massive particles and strongly interacting massive particles. The paradigm applies for a secluded weakly interacting dark sector with dark matter in the MeV-TeV mass range. The catalyzed annihilation paradigm is compatible with cosmic microwave background and big bang nucleosynthesis constraints, with enhanced indirect detection signals.