Is Dark Matter the origin of the $B\to K\nu \bar{\nu }$ excess at Belle II?

Abstract

We present two models of dark matter (DM) that can provide a natural explanation of the excess of $B^{+}\to K^{+}+\text{invisible}$ events with respect to the Standard Model (SM) prediction for $B^{+}\to K^{+}\nu \bar{\nu }$, which has been reported by the Belle II collaboration. Interactions between the dark and the visible sector are mediated by an axion-like particle (ALP) in one case, by the kinetic mixing between a dark photon and the SM photon in the second case. Both models encompass a light fermion singlet as the DM candidate and can account for the observed DM relic abundance through, respectively, the freeze-in and the freeze-out production mechanism, while simultaneously explaining the Belle II excess.

v4 : version published in PRD