Left panel: Combinations of neutrino self-interaction strength λ _ϕ and mediator mass m _ϕ that produce sterile-neutrino DM at the correct relic abundance, for a DM mass of m ₄ = 40.3 keV and vacuum mixing angle of ﹩{\sin }^{2}2\theta =8.6\times {10}^{-13}﹩. Points in the three DM production regimes are labeled with A, B, and C, corresponding to the Cases described in the text. Middle panel: The corresponding DM phase-space distributions. For comparison, we also show the original DW model with no neutrino interactions as a dotted line, and the thermal-relic WDM model as a dotted–dashed line (evaluated at the 95% confidence 6.5 keV WDM mass bound from Nadler et al. (2021). Right panel: The corresponding suppression of DM clustering is illustrated as the ratio of the linear matter power spectrum in sterile-neutrino DM models to that of CDM. The vertical line indicates the half-mode scale k _hm of the ruled-out WDM model.