Probing Inelastic Dark Matter via Cosmic-Ray Upscattering in NGC 1068

We study constraints on sub-GeV inelastic dark matter (iDM) from cosmic-ray (CR) cooling in the active galactic nucleus (AGN) NGC 1068. In dense dark matter (DM) spikes surrounding supermassive black holes, high-energy CR protons can efficiently lose energy through scatterings with dark matter particles. We consider a minimal vector-portal iDM framework and consistently include both elastic and deep inelastic scattering (DIS) contributions to the CR energy-loss rate. We find that DIS processes dominate at high momentum transfer and substantially enhance the DM-induced cooling effect. By requiring the resulting cooling timescale to remain compatible with the observed Standard Model cooling in NGC 1068, we derive constraints on the iDM parameter space. Our results demonstrate that AGN cosmic-ray cooling probes previously unexplored regions of sub-GeV iDM parameter space inaccessible to current direct-detection experiments.