Three-Technology Ultra-High-Energy Neutrino Flavor Measurement

Abstract

Ultra-high-energy (UHE) neutrinos, with energies above $100\mathrm{PeV}$, are powerful probes of fundamental physics, offering unique opportunities to test and constrain models beyond the Standard Model. A central challenge is achieving sensitivity to their flavor composition, which encodes information about production mechanisms at the source as well as potential new physics during propagation. We propose, for the first time, a three-technology strategy to measure the flavor composition of UHE neutrinos by leveraging the complementary strengths of planned and existing experiments. This approach integrates in-ice radio (ARA, ARIANNA, RNO-G, the IceCube-Gen2 radio array), Earth-skimming (TAMBO, POEMMA, Trinity, AUGER, GRAND200k), and in-ice optical Cherenkov detectors (the IceCube-Gen2 optical array). We demonstrate the potential to achieve unprecedented sensitivity to UHE neutrino flavors. The method can be used to probe an energy-dependent neutrino flavor transition at the source across energies ranging from TeV to EeV. As such, this article highlights the discovery potential of a coordinated, multi-technology program for advancing both high-energy and ultra-high-energy neutrino astrophysics.