Multimessenger Constraints on Nuclear Acceleration in Neutrino-Emitting Seyfert Coronae

High-energy neutrinos from Seyfert galaxies probe particle acceleration near supermassive black holes, but the accelerated nuclear composition remains uncertain. We connect stochastic acceleration to nuclear and radiative cascades to assess nuclear contributions. Acceleration and losses limit the energy per nucleon available to nuclear cascades; without secondary reacceleration, fragmentation cannot raise this scale. For NGC 1068, joint neutrino and gamma-ray constraints depend on the nuclear mixture: helium-dominated injection permits larger nuclear power fractions than the heavier mixtures considered. For the harder candidate neutrino spectrum of NGC 7469, the adopted model yields more energetic nuclear cascades, while the source-specific flux selections allow larger nuclear fractions for the heavier mixtures than in NGC 1068. These results show that composition constraints depend on nuclear yields as well as acceleration conditions and available power.