Strong lensing observations of galaxy clusters reveal an excess of small-scale substructures by ~10× over ΛCDM predictions, with subhalos more compact and efficient at lensing than simulations expect (Meneghetti 2020; Natarajan 2017). The substructure crisis: real dark-matter structures are more resilient or numerous than collisionless CDM allows.
The standard model has subhalos forming through hierarchical accretion in cuspy CDM halos with abundance + radial distribution + tidal-survival rates set by N-body simulations. The observed factor-of-10 GGSL excess demands either steeper inner DM profiles, modified DM physics (self-interacting DM, fuzzy DM), or finely tuned baryonic feedback. None is parsimonious.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field. From this single change, the cluster substructure excess is a gravitational-superposition signature. Substructure compactness comes from constructive coherent superposition of comoving baryonic matter throughout the parent hierarchy: Φ_eff = Φ_local + Φ_mesh (P50, P51), with the Φ_mesh contribution providing the additional gravitational binding that ΛCDM attributes to extra-CDM substructure.
The substructure-amplification factor A_sub² ≈ 10 to 16 (P52, Paper 13 Pred 34: A ∝ σ_v / v_cross from substructure velocity dispersion + crossing velocity) matches the Meneghetti GGSL factor-of-10 excess parameter-free. The compactness comes from the smoother mesh-superposition profile compared to NFW: substructure-scale Φ_mesh contribution is concentrated where the constituent baryons are coherent, producing compact lensing signatures without requiring exotic DM concentration.
Pre-existing matter (P25) gives substructure-population diversity. Angular-momentum inheritance (P31, P32) gives substructure orientation alignments through cascade-J inheritance. The same M6 framework that resolves the A_lens excess (recid 16, 30), the time-delay lensing H₀ offset (recid 54), the rotation-curve diversity (recid 112), the SHMR (recid 115), and the broader no-DM-particle phenomenology accounts for the cluster substructure excess. There is no need for modified DM physics or fine-tuned feedback.
If precision JWST + Euclid + Roman cluster GGSL surveys find substructure excess fully resolvable by improved CDM-feedback prescriptions at the 5% level (no Φ_mesh-coherent-superposition signature), the M6 explanation is refuted. The signature SCT prediction is the A_sub² ~ 10 to 16 amplification matching the constructive-superposition formula across cluster + substructure populations.