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

TL;DR

This paper presents evidence that interactions between dark matter and neutrinos can resolve the $S_8$ tension in cosmology, supported by current observational data and suggesting new physics beyond the standard model.

Contribution

It demonstrates that DM-neutrino interactions with a specific strength can explain discrepancies in cosmological measurements and aligns multiple observational datasets, challenging the standard $ extLambda$CDM model.

Findings

DM-neutrino interactions with $u \,\sim 10^{-4}$ reconcile ACT and cosmic shear data.

Combining early and late universe data yields a nearly 3σ preference for non-zero interactions.

Results challenge the standard cosmological model and suggest new physics in the dark sector.

Abstract

Neutrinos and dark matter (DM) are two of the least understood components of the Universe, yet both play crucial roles in cosmic evolution. Clues about their fundamental properties may emerge from discrepancies in cosmological measurements across different epochs of cosmic history. Possible interactions between them could leave distinctive imprints on cosmological observables, offering a rare window into dark sector physics beyond the standard $\Lambda$CDM framework. We present compelling evidence that DM-neutrino interactions can resolve the persistent structure growth parameter discrepancy, $S_8 = \sigma_8\,\sqrt{\Omega_m/0.3}$, between early and late universe observations. By incorporating cosmic shear measurements from current Weak Lensing surveys, we demonstrate that an interaction strength of $u \sim 10^{-4}$ not only provides a coherent explanation for the high-multipole observations from the Atacama Cosmology Telescope (\texttt{ACT}), but also alleviates the $S_8$ discrepancy. Combining early universe constraints with \texttt{DES Y3 cosmic shear} data yields a nearly $3\sigma$ preference for non-zero DM neutrino interactions. This strengthens previous observational claims and provides a clear path toward a significant breakthrough in cosmological research. Our findings challenge the standard $\Lambda$CDM paradigm and highlight the potential of future large-scale structure surveys, which can rigorously test this interaction and unveil the fundamental properties of DM.