New tests for neutrino self-interactions using astrophysical neutrinos*

Neutrino self-interactions (nuSI) have been proposed to explain the muon g-2 anomaly, the short baseline anomalies, and the Hubble tension. Furthermore, nuSI can affect the evolution of neutrino-dense environments in our Universe. However, laboratory probes remain weak. We open new windows to test nuSI using astrophysical neutrino signals. Through simple and conservative arguments, we find that current data allow us to place world-leading constraints and that great improvements can be expected using forthcoming experiments.