Minimal Dark Matter: Generalized Framework and Direct-Detection Sensitivity

Abstract

Minimal electroweak dark matter models are compelling due to their simplicity, though calculations of their freezeout abundance are complicated by nonperturbative effects due to Sommerfeld enhancement and bound-state formation. It has been shown that all individual multiplet scenarios beyond the doublet lead to direct-detection signals above the neutrino floor and thus within the reach of next-generation experiments. If no signals are found, would minimal dark matter be excluded? Yes for the simplest models, but it has been unknown for the important extension of two multiplets coupled by Higgs interactions (Higgs-coupled minimal dark matter). We present a generalized framework for calculating nonperturbative effects for such models that also covers the case of individual multiplets. In this framework, we calculate nonperturbative effects on freezeout as well as the prospects for direct detection, correcting shortcomings and omissions in the literature. Importantly, for the mixed Majorana (odd) and Dirac (even) multiplet combinations 3M2D, 5M4D, and 7M6D, we find that the predicted direct-detection signals can extend below the neutrino floor. Fully testing minimal dark matter will thus require more than direct-detection experiments.

Figures (16)

• Figure 1: Schematic diagram illustrating the salient differences between the MDM and HC-MDM models.
• Figure 2: Diagrams for the interactions generating long-range potentials among $M$ and $D$. The spin indices are omitted because particle spins are individually conserved in the non-relativistic limit. The $M \overline{D}$ diagrams are omitted but follow straightforwardly from the $MD$ cases.
• Figure 3: Diagrams for bound-state formation through vector-boson emission. Mediators of the potential are not shown.
• Figure 4: Diagrams for $MM$ bound-state formation through $H$ emission. We follow the convention of Fig. \ref{['fig:vector emmision diagrams']} and omit the mediators of the potential.
• Figure 5: Diagrams for $M \overline{D}$ bound-state formation through $H$ emission. We follow the convention of Fig. \ref{['fig:vector emmision diagrams']} and omit the mediators of the potential.