The study examines how such interactions could influence the formation of galaxies and other large-scale structures, addressing a known mismatch between predictions from early-universe measurements and observations of the present-day cosmos.

Researchers combined data that track the universe across its history, including measurements of the cosmic microwave background and maps of galaxy clustering, to look for subtle signatures of dark matter-neutrino interactions.

Information from the early universe comes from the ground-based Atacama Cosmology Telescope and the European Space Agency's Planck space observatory, both tuned to detect the faint microwave afterglow of the Big Bang.

Late-time structure was characterized using observations from the Dark Energy Camera on the Victor M. Blanco Telescope in Chile together with large galaxy catalogues from the Sloan Digital Sky Survey.

The combined data strengthen an existing tension in cosmology: early-universe measurements imply that matter clumping, quantified by parameters such as S8, should be stronger than what is inferred from surveys of the nearby universe.

Co-author Dr. Eleonora Di Valentino, Senior Research Fellow at the University of Sheffield, said: "The better we understand dark matter, the more insight we gain into how the Universe evolves and how its different components are connected."

"Our results address a long-standing puzzle in cosmology. Measurements of the early Universe predict that cosmic structures should have grown more strongly over time than what we observe today."

"However, observations of the modern Universe indicate that matter is slightly less clumped than expected, pointing to a mild mismatch between early- and late-time measurements."

"This tension does not mean the standard cosmological model is wrong, but it may suggest that it is incomplete."

"Our study shows that interactions between dark matter and neutrinos could help explain this difference, offering new insight into how structure formed in the Universe."

The authors find that allowing dark matter to scatter with neutrinos can reduce the predicted level of clustering, bringing early- and late-time measurements into closer agreement while remaining consistent with other cosmological constraints.

The work outlines how future cosmic microwave background experiments and weak gravitational lensing surveys, which track tiny distortions in the shapes of distant galaxies, could test this interaction scenario with higher precision.

Dr. William Giare, co-author of the study and former Postdoctoral Researcher at the University of Sheffield, now at the University of Hawai?i, said: "If this interaction between dark matter and neutrinos is confirmed, it would be a fundamental breakthrough."

"It would not only shed new light on a persistent mismatch between different cosmological probes, but also provide particle physicists with a concrete direction, indicating which properties to look for in laboratory experiments to help finally unmask the true nature of dark matter."

Research Report:A solution to the S8 tension through neutrino-dark matter interactions

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