An international team of scientists has published research findings in the prestigious journal Nature Astronomy indicating possible links between dark matter and neutrinos. The key analysis that led to these conclusions was led by researchers from the National Centre for Nuclear Research (NCBJ). 

According to the standard cosmological model, the evolution of the early universe was the result of a "dance" between hot radiation and matter, dominated by the still mysterious dark matter. These two components determined the initial distribution of structures from which galaxies emerged – including our Milky Way. Neutrinos, the most elusive particles known to us, also played an important, though still lesser-known, role in this process.

Theory predicts that ancient neutrinos, formed shortly after the Big Bang, should fill the cosmos similarly to the ubiquitous cosmic microwave background (CMB) radiation. Unfortunately, current detectors are not sensitive enough to detect this "cosmic neutrino background" directly. Therefore, researchers are focusing their attention on the infant period of the Universe, when neutrinos were much more numerous and had a greater impact on their surroundings.

The debate over whether neutrinos could have interacted with dark matter at that time has been going on for more than two decades. However, recent years have brought new and interesting results. The first signs of a possible interaction between these components appeared in data on the so-called Lyman-alpha forest. This is a thicket of absorption lines in the spectrum of distant quasars, which allows astronomers to map the distribution of matter. Similar subtle signals were then detected in data from the Planck satellite.

The latest work adds a new piece to this puzzle: an analysis of weak gravitational lensing. This phenomenon involves minimal distortions of images of distant galaxies caused by the bending of their light by massive objects lying in the path to Earth. This analysis suggests that matter in the Universe is distributed slightly more evenly than simple models assumed. Neutrino interactions with dark matter may perfectly explain this anomaly.

The first author of the article is dr Lei Zu, who conducted the research as a NAWA Ulam programme fellow at NCBJ, in a team led by dr hab. Sebastian Trojanowski (NCBJ's Theoretical Physics Division and Astrocent/CAMK PAN). - Identifying this effect required an innovative approach to studying nonlinear perturbations in the structure of the cosmos. We based our analysis on advanced multi-body simulations and approximations obtained using machine learning methods- comments Dr Zu, who is currently continuing his career at the National Astronomical Observatory of Japan.

The new method allowed researchers to show that the statistical significance of the anomaly increased after additional data was taken into account. This consistency of results is intriguing, but scientists remain cautious. - Explaining and rigorously testing such a clear effect requires going beyond the typical approximations used in particle cosmology, which will be the subject of further research - adds dr Trojanowski. The final verdict will come from upcoming large sky surveys, such as those from the Vera C. Rubin Observatory, and more precise theoretical work. These will allow us to determine whether we are witnessing a new discovery in the dark sector or whether our cosmological models require further adjustment. However, each of these scenarios brings us closer to solving the mystery of dark matter.

The research presented in the paper was funded by the NCN SONATA BIS grant No. 2021/42/E/ST2/00031 and the NAWA Ulam programme No. BPN/ULM/2023/1/00107/U/00001.