Scalar-mediated inelastic dark matter as a solution to small-scale structure anomalies
Year: 2026
Type: article
Abstract: We propose a novel self-interacting dark matter (SIDM) model mediated by a light leptophilic scalar boson to solve long-standing small-scale structure problems within the Lambda cold dark matter ( Λ CDM ) framework. Small-scale anomalies such as the core-cusp problem challenge the traditional CDM framework. Therefore, we introduce a scalar-mediated SIDM model as an alternative to CDM that naturally addresses these problems. It also exhibits p -wave-suppressed annihilation and avoids constraints from the cosmic microwave background. In our model, we assume pseudo-Dirac dark matter with a small mass splitting of order 10 2 eV to ensure kinematic scattering suppression in satellites. We also introduce a dimension-five transition magnetic dipole operator to satisfy big bang nucleosynthesis requirements. It allows the decay χ 2 → χ 1 γ , so the excited-state abundance is primarily depleted by exothermic self-interactions ( χ 2 χ 2 → χ 1 χ 1 ) in the early Universe. This ensures that the excited-state population is negligible for structure formation at the dipole scale Λ eff ≳ 10 7 GeV . The model is made inelastic by a dark discrete Z 2 symmetry that prevents tree-level elastic scattering. Treating the scattering dynamics nonperturbatively in a Schrödinger framework yields a relatively small residual resonant benchmark window ( m χ ≈ 40 GeV , Δ m ≈ 100 eV , m ϕ ≈ 20 MeV ). In such a system, the kinematic threshold minimizes interactions in ultrafaint Milky Way satellites, while resonant effects produce large cross sections, σ / m ∼ O ( 10 ) cm 2 / g , in field dwarf galaxies. Current direct-detection prospects are weak, and the leptophilic scalar mediator keeps the model away from existing nuclear recoil constraints. However, the low-threshold dipole operator provides a potential discovery channel for future xenon-based experiments.
DOI: 10.1103/lcbj-grg8
Author: Zihan Wang
Institution: University of Oxford
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W7154580108
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