Science › Big Bang & cosmos
WIMPs: heavy, shy particles
1985· Theory
SpeculativeA serious idea with no experimental proof yet.
Weakly interacting massive particles: hypothetical dark-matter particles roughly 10 to 1,000 times a proton's mass that touch ordinary matter at most through the weak force.
See it on the Science map →How it works
WIMPs would be heavy, stable, electrically neutral and nearly invisible; if they exist, hundreds of millions pass through each square meter every second. Three hunts run in parallel. Underground tanks of liquid xenon wait for one to bump an atom's nucleus. Space telescopes look for gamma rays from WIMPs destroying each other in the galaxy's center. The Large Hadron Collider looks for collisions where energy goes missing, carried off unseen. Gary Steigman and Michael Turner coined the name in 1985.
Why it matters
For 30 years they were the favorite dark-matter candidate, because the right amount would emerge naturally from the hot early universe. Their absence is reshaping the search.
How we know
None found. LZ, nearly 1.5 kilometers under South Dakota, reported no WIMPs in 2022 and set record limits in 2024; XENONnT in Italy and PandaX-4T in China agree. The LHC has found no candidate either.
Still a mystery
Detectors are reaching the 'neutrino fog': in 2024 XENONnT and PandaX-4T saw solar neutrinos nudging xenon nuclei, mimicking WIMPs. A gamma-ray glow from the galaxy's center, seen since 2009, remains unexplained.
Connections (2)
▸Dark matter may be made of WIMPs: heavy, shy particlesSpeculative
The relationship
In the hot early universe, WIMPs and their antiparticles would be constantly created and destroyed in pairs. As space cooled and thinned, they stopped finding each other, and a fixed amount 'froze out'. For a particle with weak-force-strength interactions and a mass near 100 protons, the leftover matches today's dark matter. Physicists called this coincidence the 'WIMP miracle'.
How the link was found
Benjamin Lee and Steven Weinberg (1977), among others, calculated such leftovers for heavy neutrinos. Mark Goodman and Edward Witten proposed in 1985 detecting them by their rare bumps into atomic nuclei.
Is it proven?
Not proven. The freeze-out arithmetic is solid, but the 'miracle' may be coincidence. Every direct, indirect and collider search so far has come up empty, ruling out the simplest WIMP models.
Open questions and mysteries
Are WIMPs ruled out, or just shyer than hoped? Detectors face a floor of neutrino noise. Heavier or lighter dark particles, outside the classic range, remain possible.
▸The Standard Model would need new particles like WIMPs: heavy, shy particlesSpeculative
The relationship
The Standard Model has no particle that is heavy, stable and dark. But theories built to fix a different puzzle, why the Higgs boson is so light, often add one. In supersymmetry, every known particle has a heavier partner, and the lightest partner, in many versions the neutralino, cannot decay. It would be a natural WIMP, at about the mass scale the LHC was built to explore.
How the link was found
Heinz Pagels and Joel Primack (1982) suggested supersymmetric dark matter; Haim Goldberg (1983) and John Ellis and colleagues (1984) singled out the neutralino.
Is it proven?
Not proven. The LHC has found no supersymmetric partners, ruling out those of quarks and gluons up to roughly 1–2 TeV, about 1,000–2,000 proton masses, in simple versions.
Open questions and mysteries
Is supersymmetry absent, or just heavier than the LHC can reach? Without it, the light Higgs and the WIMP lose their shared explanation.