Luísa Pseudo-Dirac Neutrinos and Relic Neutrino Matter Effect on the High-energy Neutrino Flavor Composition P. S. Bhupal Dev, Pedro A. N. Machado, Ivan Martinez-Soler Hide abstract | Show figures | Show BibTeX | Show discussion | View PDF | 2406.18507v2 We show that if neutrinos are pseudo-Dirac, they can potentially affect the flavor ratio predictions for the high-energy astrophysical neutrino flux observed by IceCube. In this context, we point out a novel matter effect induced by the cosmic neutrino background (CνB) on the flavor ratio composition. Specifically, the active-sterile neutrino oscillations over the astrophysical baseline lead to an energy-dependent flavor ratio at Earth due to the CνB matter effect, which is distinguishable from the vacuum oscillation effect, provided there is a local CνB overdensity. Considering the projected precision of the 3-neutrino oscillation parameter measurements and improved flavor triangle measurements, we show that the next-generation neutrino telescopes, such as IceCube-Gen2 and KM3NeT, can probe the pseudo-Dirac neutrino hypothesis in a distinctive way. Authors' comments: 14 pages, 6 figures; added references in v2