Dark matter, which makes up over 85% of the universe's matter, remains one of cosmology’s biggest mysteries. A new study published in Journal of Cosmology and Astroparticle Physics has revived interest in a potential dark matter candidate: WIMPs (Weakly Interacting Massive Particles). Although never directly observed, WIMPs were once considered the leading explanation for dark matter. However, over the years, many WIMP models have been ruled out, narrowing the search. But recent findings from the AMS-02 experiment aboard the International Space Station have sparked renewed interest.

AMS-02 tentatively detected unexpected traces of antimatter—specifically antihelium—in cosmic rays, which some scientists believe could be a sign of WIMP particles. When two WIMPs annihilate each other, they may produce antimatter. The amount of antihelium observed by AMS-02 is far higher than expected, which suggests that standard cosmic ray interactions cannot fully explain these results.

Pedro de la Torre Luque, a recent member of the Oskar Klein Center, explains:

If you see the production of antiparticles in the interstellar medium, where you expect very little, it means something unusual is happening. That's why the observation of antihelium was so exciting.

The study shows that while some WIMP models are consistent with the observed amount of antideuterons and antihelium-3, no common WIMP model is compatible with antihelium-4. In particular, the detection of antihelium-4, a heavier and rarer isotope, hints at the possibility of even more "exotic" dark matter particles. While WIMPs remain a promising dark matter candidate, these new observations suggest that our understanding of dark matter might need to be expanded with more precise experiments and new theoretical models.

Tim Linden says:

Searches for heavy antinuclei are one of the most exciting prospects for detecting dark matter. This is due to the fact that astrophysical mechanisms (which are made almost entirely of matter and not antimatter) are extremely bad at producing any antinuclei flux, while dark matter is also expected to only produce a small antinuclei flux, it appears be relatively good at producing stable antinuclei, compared to astrophysical mechanisms. This paper makes important progress in calculating just how small the antinuclei flux from normal astrophysical sources should be – allowing us to make more robust predictions about any upcoming (or already existing) antinuclei signal.

Together with colleagues Thong T. Q. Nguyen (also from the OKC) and Tim M. P. Tait, Tim Linden’s science was also featured as an ESA picture of the month for the INTEGRAL gamma-ray observatory. Their work put constraints on the possible existence ”dark photons”, a hypothetical particle interacting with dark matter.