Forging Antihelium in a Dark Matter Crucible

The baryon sector of the present universe is almost entirely matter and no antimatter. High energy astrophysical events can only produce a tiny amount of antimatter, a minuscule fraction of which may form nuclear bound states.  Given the prediction of extremely low astrophysical antinuclei backgrounds, a robust detection of even a handful of antinuclei from space would be revolutionary. Recently, members of the AMS-02 collaboration gave talks at conferences about possible detections of antihelium nuclei at the rate of about 1 event/year, many orders of magnitude above the conventional expectation. If we take these events at face value and interpret them as originating from the dark sector, they provide valuable clues for particle physics model building. I will argue that salient features of these events are naturally explained by sudden and localized injections of energetic antibaryons in our Galaxy that subsequently thermalize into optically-thick fireballs. While the post-injection physics is agnostic to the source of injections, a plausible scenario is that these injections originate from mergers of ultraheavy composite dark matter states.