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Neutron portal to ultrahigh-energy neutrinos

Gustavo F. S. Alves1,*, Matheus Hostert2,†, and Maxim Pospelov3,4,‡

  • 1Instituto de Física, Universidade de São Paulo, C.P. 66.318, 05315-970 São Paulo, Brazil
  • 2Department of Physics and Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge, Massachusetts 02138, USA
  • 3School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
  • 4William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA

  • *Contact author: gustavo.figueiredo.alves@usp.br
  • †Contact author: mhostert@g.harvard.edu
  • ‡Contact author: pospelov@umn.edu
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Phys. Rev. D 113, 075035 – Published 24 April, 2026

DOI: https://doi.org/10.1103/9hwd-z79r

Abstract

Current data on ultrahigh-energy (UHE) cosmic rays suggest they are predominantly made of heavy nuclei. This indicates that, in the absence of a subdominant proton component, the flux of neutrinos produced from cosmic ray collisions on the cosmic microwave background is small and hard to observe. Motivated by the recent extremely high-energy muon event reported by KM3NeT, we explore the possibility of enhancing the energy-flux of cosmogenic neutrinos through nuclear photodisintegration in the presence of new physics. Specifically, we speculate that UHE neutrons may oscillate into a new state, dark (or mirror) neutron n′ that in turn decays injecting large amount of energy to neutrinos, n→n′→νUHE. While this mechanism does not explain the tension between the KM3NeT event and null results from IceCube, it reconciles the experimental preference for a heavier cosmic ray composition with a large diffuse cosmogenic flux of UHE neutrinos.

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Phys. Rev. D 113, 075035– Published 24 April, 2026
  • Received 13 May 2025
  • Accepted 15 January 2026
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