"WIMPs are particles that have been theorized but never observed, and they could be the ideal candidate for dark matter," said Pedro De la Torre Luque, a physicist at the Institute of Theoretical Physics in Madrid. He further explained that these particles would only interact with normal matter via gravity and the weak interaction force, one of the four fundamental forces that operates at close distances.
Several years ago, WIMPs appeared to be a promising solution for dark matter, but despite extensive research, no direct evidence has been found. Many WIMP models have since been ruled out. "Of the numerous best-motivated proposed models, most have been ruled out today and only a few of them survive," De la Torre Luque added.
However, a new development has sparked renewed interest. "These are some observations from the AMS-02 experiment," said De la Torre Luque. The Alpha Magnetic Spectrometer (AMS-02), stationed on the International Space Station, studies cosmic rays and recently detected traces of antinuclei, specifically antihelium, that no one had predicted.
Antimatter, which consists of particles with electrical charges opposite to their normal matter counterparts, is typically scarce in our universe. Yet, the discovery of antihelium nuclei is significant. "If you see the production of antiparticles in the interstellar medium, where you expect very little, it means something unusual is happening," De la Torre Luque explained. This discovery could indicate that WIMPs are responsible for the observed antimatter, as certain WIMP interactions are theorized to produce both matter and antimatter particles.
The study also highlights that the amount of antihelium detected far exceeds predictions based on known cosmic-ray interactions. "We expected to detect one antihelium event every few tens of years, but the around ten antihelium events observed by AMS-02 are many orders of magnitude higher than the predictions," said De la Torre Luque. This anomaly suggests that WIMPs, or even more exotic particles, could be the source.
Interestingly, the AMS-02 detected two types of antihelium isotopes-antihelium-3 and antihelium-4. The latter is heavier and far rarer, making its detection especially surprising. Even in optimistic WIMP models, the abundance of antihelium-4 is difficult to explain, which could imply the existence of an unknown, even more "exotic" class of particles.
De la Torre Luque and his colleagues suggest that further research and more precise observations are needed to explore these findings. Expanding the theoretical framework to include a new dark sector in the standard model may hold the key to understanding these unexpected discoveries.
Research Report:Cosmic-Ray Propagation Models Elucidate the Prospects for Antinuclei Detection
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