$B\to K\nu \bar{\nu }$, MiniBooNE and muon $g-2$ anomalies from a dark sector

Belle II has reported the first evidence for $B^{+}\to K^{+}\nu \bar{\nu }$ with a branching ratio $2.7\sigma$ higher than the standard model expectation. We explain this, and the MiniBooNE and muon anomalous magnetic moment anomalies in a model with a dark scalar that couples to a slightly heavier sterile Dirac neutrino and that communicates with the visible sector via a Higgs portal. We make predictions for rare kaon and other $B$ meson decays.