Shining light on cosmogenic axions with neutrino experiments

While most searches for cosmic axions so far focused on their cold relics as (a component of) dark matter, various well-motivated cosmological sources can produce “boosted” axions that re-main relativistic today. We demonstrate that existing/upcoming neutrino experiments such as Super-Kamiokande, Hyper-Kamiokande, DUNE, JUNO, and IceCube can probe such energetic axion relics. The characteristic signature is the mono-energetic single photon signal from axion absorption induced by the axion-photon coupling. This proposal offers to cover parameter ranges complementary to existing axion searches and provides new opportunities for discovery with neutrino facilities. progenitor lifetime of the τ X = 35 t 0 compatible with current constraints on DM decay. Since the mono- γ signal is largely background-free in DUNO and JUNO, we show the conservative (3 events per year, dashed curves) and aggressive (1 event per year, solid curves) projections for demonstration. We truncate at m X = 10 4 GeV as the sensitivity reach of experiments only becomes weaker due to a smaller flux. We find that both DUNE and JUNO can improve the sensitivity for m X ∼ O (10–100 GeV) beyond astrophysical constraints.