Hints of self-interacting dark matter from strong gravitational lensing
An analysis of 29 quadruply imaged quasars hints at dark matter halo densities consistent with gravothermal core collapse, a key prediction of self-interacting dark matter. We interpret this evidence through elastic Yukawa scattering, combining lensing with upper limits on the cross-section strength from galaxy clusters and Milky Way satellite evaporation. Favored models have dark matter masses of $20$-$80\,{\rm GeV}$, MeV-scale mediators, and Yukawa-potential strengths near $10^{-3}$, yielding cross-sections of $10^2$--$10^4 \, {\rm cm^2\,g^{-1}}$ at $10\,{\rm km\,s^{-1}}$. Cosmological, direct and indirect detection bounds on MeV-scale mediators motivate a neutrinophilic scalar dilepton that decays invisibly without Higgs mixing. These results demonstrate how inferences on core collapse constrain dark sector physics.