Naturally resonant two-mediator model of self-interacting dark matter with decoupled relic abundance

Abstract

It proposes a minimal, fully thermal mechanism that resolves the long-standing tension between achieving the observed dark-matter relic abundance and explaining the astrophysical signatures of self-interactions. The framework introduces two mediators: a light scalar φ (MeV scale) that yields the required, velocity-dependent self-interactions, and a heavy scalar resonance (TeV scale) with mass that opens an s-channel resonant annihilation during freeze-out. This clearly decouples early-Universe annihilation from late-time halo dynamics. A detailed numerical analysis identifies a narrow predictive island of viability. A representative benchmark reproduces the relic density and yields at dwarf-galaxy velocities while satisfying cluster bounds. The model makes sharp, testable predictions: a narrow resonance near 1.2 TeV within HL-LHC reach, and a spin-independent direct-detection signal.