PBR sensitivity to boosted dark matter explanation for the KM3-230213A event

POEMMA-Balloon with Radio (PBR) is a hybrid fluorescence and optical Cherenkov telescope that is a pathfinder instrument for a future Probe Of Extreme Multi-Messenger Astrophysics (POEMMA), together with a radio instrument, to be flown on a super pressure balloon in Spring 2028. One of its science objectives is follow up of astrophysical event alerts via signals of tau decays in the atmosphere, sourced by Earth-skimming tau neutrinos. The recent report of the KM3NeT Collaboration's muon event with $E_μ=120^{+110}_{-60}$ PeV sparked searches for beyond the standard model (BSM) physics explanations. Using a specific, boosted dark matter scenario which together with the KM3NeT observation, sets a scale for the fluence of boosted dark matter in this energy range, we assess the capabilities of PBR to constrain or discover such a source for a boosted dark matter energy spectrum above $\sim 10^8$ GeV. PBR has discovery potential for dark matter energies above $10^9$ GeV, and depending on BSM input parameters, to dark matter energies as low as $1.5\times 10^8$ GeV. While the analysis is focused on one BSM example, the methodology is applicable to any BSM physics that affects tau production in the Earth.