An architect checks the blueprint when building a house. For cosmologists, the blueprint is the Standard Model, and the measuring tape is the light from distant galaxies. Recently, a new 'tape measure,' the DESI instrument, measured distances to millions of galaxies with unprecedented precision. And the numbers didn't match the blueprint. It's as if the walls turned out to be a centimeter longer than specified — a small detail, but it throws the whole project into question.
The missing centimeters turned out to be the density of matter. To reconcile DESI data with observations of the cosmic microwave background (the echo of the big bang), scientists proposed that an invisible 'glue' operated in the early universe — a new type of neutrino. Ordinary neutrinos are almost intangible, but these sterile ones are even more ghostly: they don't participate even in weak interactions, communicating with the world only through a light mediator particle. This mediator causes radiation and neutrinos to exchange energy, like two communicating vessels.
As a result, this 'glue' alters the picture of the cosmic microwave background, lowers the inferred matter density, and brings DESI's readings closer to those of other experiments. Importantly, it also resolves a long-standing dispute over neutrino mass: laboratory experiments gave one value, cosmological observations another. The new model reconciles them. Moreover, it even eases the famous Hubble constant tension — the discrepancy in the universe's expansion rate as measured by different methods.
The analysis shows that the data prefer the sterile neutrino model at the 2.7 sigma level. This isn't a definitive discovery, but it's a serious claim. It's like a voice finally cutting through the noise — still indistinct, but no longer random.
as written by the authors arXiv:2605.18716
Recent DESI BAO measurements, combined with CMB data, reveal a tension within the $$\Lambda$$CDM model that leads to a discrepancy between cosmological and laboratory bounds on the summed neutrino mass. We show that a recoupled interacting radiation component can alleviate this cosmological tension, as well as the one with neutrino oscillation experiments. Sterile neutrinos interacting through a light pseudoscalar mediator provide a concrete realization of this scenario. The resulting interacting fluid modifies the CMB phenomenology, lowers the preferred matter density, and improves the consistency between CMB and DESI BAO measurements. Combining CMB with DESI DR2 BAO measurements, we find a $$2.7 \sigma$$ preference for a nonzero interacting sterile neutrino component, $$ sp=0.253 \pm 0.094$$, corresponding to an improvement $$\Delta \chi^2=-8.98$$ relative to $$\Lambda$$CDM. The model also reduces the tension with the SH0ES determination of the Hubble constant to the $$2.4\sigma$$ level.
Sterile neutrinos are so elusive that they could pass through a lead slab a light-year thick without hitting a single atom.
In Liu Cixin's novel 'The Three-Body Problem,' aliens use neutrinos for faster-than-light communication — science fiction, but sterile neutrinos could be the perfect messengers across the stars.