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Matter effects on flavor composition of astrophysical neutrinos

P. S. Bhupal Dev1,*, Sudip Jana2,3,†, and Yago Porto4,5,‡

  • *Contact author: bdev@wustl.edu
  • †Contact author: sudip.jana@mpi-hd.mpg.de
  • ‡Contact author: yago.porto@ufabc.edu.br
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Phys. Rev. D 112, 093003 – Published 12 November, 2025

DOI: https://doi.org/10.1103/mdhq-s9yp

Abstract

We show that high-energy astrophysical neutrinos produced in the cores of heavily obscured active galactic nuclei (AGNs) can undergo strong matter effects, thus significantly influencing their source flavor ratios. In particular, matter effects can completely modify the standard interpretation of the flavor ratio measurements in terms of the physical processes occurring in the sources (e.g., pp versus pγ, full pion-decay chain versus muon-damped pion decay). We contrast our results with the existing flavor ratio measurements at IceCube, as well as with projections for next-generation neutrino telescopes like IceCube-Gen2. Signatures of these matter effects in neutrino flavor composition would not only bring more evidence for neutrino production in central AGN regions, but would also be a powerful probe of heavily Compton-thick AGNs, which escape conventional observation in x-rays and other electromagnetic wavelengths.

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Phys. Rev. D 112, 093003– Published 12 November, 2025
  • Received 5 March 2024
  • Accepted 18 October 2025
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