I will first explore scenarios and experimental signatures beyond light sterile neutrinos that can be probed at future facilities. In particular, I will show how composite neutrinos can disintegrate at high-energy  into invisible or emerging semi-visible jets at experiments such as FASER and DUNE. I will compare these signals to existing LEP constraints and discuss the future discovery prospects at FCC-ee.

I will then switch gears and look behind ultra–high-energy neutrino events by presenting a framework that connects theoretical predictions for neutrino fluxes to the expected number of track events at detectors such as IceCube and KM3NeT. This framework enables a faithful marginalization over theoretical systematics, allowing for robust comparisons between models and data. I will then apply this framework to the recently found KM3-230213A event.