Researchers led by Lei Zu report a combined, roughly 3σ preference for weak scattering between neutrinos and dark matter after analyzing two CMB measurements, three BAO catalogs, and the Dark Energy Survey. This interaction could modestly extend the Standard Cosmological Model and help resolve a tension between early-Universe probes and the observed large-scale structure. The result is intriguing but not conclusive; further observations and theoretical work are required.
Ghost Particles May Be Whispering To Dark Matter — New Study Finds ~3σ Signal
abstract image of tiny metal spheres
A new analysis led by physicist Lei Zu, conducted while at Poland's National Centre for Nuclear Research and now based at the National Astronomical Observatory of Japan, reports a mild but intriguing preference for weak scattering between neutrinos (the so-called "ghost particles") and dark matter. The study combines multiple cosmological probes and finds a combined signal at roughly three sigma: not definitive, but strong enough to merit close attention.
Why This Matters
Neutrinos and dark matter are both famously elusive: neutrinos interact extremely weakly with ordinary matter, and dark matter so far reveals itself primarily through gravity. The new result suggests that faint neutrino–dark matter scattering could slightly relax the usual assumption that dark matter is completely collisionless. That change could help resolve a persistent mismatch between predictions based on early-Universe measurements and observations of today's large-scale structure.
Data and Method
The team compiled one of the most comprehensive combined datasets to test this hypothesis: two independent Cosmic Microwave Background (CMB) measurements, three Baryon Acoustic Oscillation (BAO) catalogs, and imaging and clustering data from the Dark Energy Survey (DES). They ran cosmological simulations for each dataset separately and in combination, explicitly including a model for neutrino–dark matter scattering.
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Results
Individually, the datasets showed a mild preference for scattering. When combined, the preference strengthened to about a 3σ detection — significant enough to be interesting but short of the 5σ standard usually required for a discovery in physics. The preferred scattering produces simulated Universes that better match the observed level of clumpiness in the late-time Universe compared with models that assume no interaction.
"This tension does not mean the standard cosmological model is wrong, but it may suggest that it is incomplete," says cosmologist Eleonora Di Valentino of the University of Sheffield. "Interactions between dark matter and neutrinos could help explain this difference, offering new insight into how structure formed in the Universe."
Implications and Next Steps
If neutrino–dark matter scattering is confirmed, it would be a major advance: it could point particle physicists to specific interaction properties to search for in laboratory experiments and offer a concrete way to alleviate tensions between early- and late-time cosmological probes. However, the authors and other experts emphasize caution. Further observational tests, improved theoretical modeling, and more rigorous treatments of the particle physics involved are required before the effect can be considered established.
The results are published in Nature Astronomy. Follow-up work will aim to refine the theoretical models and exploit upcoming cosmological surveys to test the signal more stringently.
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