2026/07/21 by Dibya S. Chattopadhyay, Carlos A. Argüelles, Vedran Brdar
#astro-ph.HE #hep-ex #hep-ph
The four near-horizon neutrino-like events reported by ANITA-IV and the ultra-high-energy track-like event KM3-230213A observed by KM3NeT imply neutrino event rates that are in tension with the absence of corresponding events at IceCube. In this work, we perform a joint analysis of these events, taking into account the absence of any corresponding ones at IceCube. We construct semi-analytic, energy- and direction-dependent effective areas for the three detectors and account for the time-dependent ANITA-IV and KM3NeT exposures. For a diffuse all-sky power-law flux varying both the normalization and the spectral index, the measured event rates across the three detectors are not reproduced. The best-fit configuration, corresponding to a tension of ∼7.5σ, predicts approximately five IceCube events while strongly underpredicting the ANITA-IV and KM3NeT counts. In contrast to the diffuse scenario, the tension can be substantially alleviated if the events arise from short-duration transients that occur exactly along the observed directions during the ANITA-IV and KM3NeT detection windows. Such a realization, however, is highly fine-tuned. If rare transients are instead distributed randomly across the full sky over the ∼15-year IceCube observation period, additional sources inevitably contribute to the IceCube exposure. For benchmark populations with a probability of approximately 10-4 to produce four favorable transients at ANITA-IV, the best-fit configuration of sources, out of 105 Monte Carlo realizations, remains in 5.9σ tension. We conclude that, within the Standard Model, directional and temporal variations alone can not reconcile the ANITA-IV and KM3NeT observations with the IceCube null result, under both a diffuse all-sky flux and a rare-transient source hypothesis.