Evidence for Discrete Structure in Black-Hole Ringdown Deviations from General Relativity

This work analyzes publicly available gravitational-wave ringdown events (GW150914, GW170104, GW190521) and reports evidence for a non-continuous organization in a dimensionless observable combining frequency deviations and horizon-scale quantities. The observed clustering is robust under posterior resampling, area-scaling variations, and spin-projection tests, and does not assume a specific microscopic model. The results motivate an interpretation of ringdown deviations as horizon-linked spectroscopy and provide a falsifiable framework to be tested with future gravitational-wave detections.