Interpreting the high-energy neutrino sky through an angular power spectrum analysis

The origin of high-energy neutrinos, observed in the last 10 years by IceCube, is unknown. We gain more insight by studying the expected angular distribution of potential source populations, considering that IceCube observes a neutrino sky consistent with an isotropic distribution. We simulate neutrino skymaps by applying statistical distributions for the fluxes of extra-galactic sources and investigate the sensitivities of current (IceCube) and future (IceCube-Gen2 and KM3NeT) experiments. The angular power spectrum is a powerful probe to assess the angular characteristics of neutrino data and we can constrain rare and bright source classes with current IceCube data. Another potential source is the decay or annihilation of dark matter, suggested by the observed excess in the High-Energy-Starting-Event (HESE) data set of IceCube. These neutrinos are expected to correlate with the galactic centre, allowing us to distinguish between dark matter and astrophysical origin. We apply the angular power spectrum analysis to the HESE data, and set model-independent limits on dark matter properties. This method relies only on the angular distribution of neutrino events and is therefore stable against astrophysical uncertainties. Moreover we perform a sensitivity forecast for IceCube-Gen2 and KM3NeT exposure for different decaying and annihilating channels. KM3NeT is especially sensitive to low dark matter masses due to its visibility towards the galactic centre.