Abstract The nature of dark matter remains unknown, motivating the study of fuzzy/wave dark matter (FDM/ ψ DM) and self-interacting dark matter (SIDM) as alternative frameworks to address small-scale discrepancies in halo profiles inferred from observations. This study presents a nonparametric reconstruction of the mass distribution of the previously found dark subhalo in the strong lensing system JVAS B1938+666. Compared with the standard Navarro–Frenk–White profile, both SIDM and ψ DM ( m ψ = 1.3 2 − 0.31 + 0.22 × 1 0 − 22 eV ) provide significantly better fits to the resulting density profile. Moreover, the SIDM model is favored over ψ DM with a Bayes factor of 14.44. The reconstructed density profile features a characteristic kiloparsec-scale core ( r c ≈ 0.5 kpc) with central density ρ c ≈ 2.5 × 1 0 7 M ⊙ kpc − 3 , exhibiting remarkable consistency with the core–halo mass scaling relations observed in Local Group dwarf spheroidals. These findings offer insights that may help address the core–cusp discrepancy in ΛCDM substructure predictions.
Lei et al. (Fri,) studied this question.