Speaker
Description
Among the few ways to probe the early Universe, high energy neutrinos offer a unique window on phenomena occurring before recombination. We discuss primordial high energy neutrinos (PHENUs): neutrinos produced from the decay or annihilation of long-lived relics in the early Universe, arriving at detectors today with energies in the GeV-PeV range. We summarise the results of a general study of this scenario, covering the sharp spectral features such fluxes would display, the theoretical (BBN and CMB) and experimental constraints on the source particle parameter space, and the regions that could realistically be probed by current and future neutrino telescopes. We then present a dedicated Monte Carlo code for computing the distortion of the PHENU spectrum by final state radiation and interactions with the cosmic neutrino background during propagation, and apply it to assess whether the ultrahigh energy neutrino event detected by KM3NeT could be of primordial origin.