The Stellar Stream Gap Deficit: Observational Constraints on Dark Matter Subhalo Populations

A systematic analysis of stellar stream gaps across 20 streams (1308° on sky) revealing a significant deficit compared to ΛCDM predictions. Key findings: Observed gap rate: 0.69 ± 0.23 per 100° CDM prediction: 5–15 per 100° Tension: 6σ (P ≈ 10⁻¹⁰) even after accounting for 50% detection incompleteness The gap deficit favors gravitational theories with smoother potentials, including warm dark matter, self-interacting dark matter, or baryonic-only models. The GD-1 spur is shown to be statistically expected from rare baryonic encounters (P ≈ 70%).