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

TL;DR

This paper proposes two dark matter models involving an axion-like particle and a dark photon to explain the Belle II excess in $B^+ o K^+ +$ invisible events, linking particle physics anomalies with dark matter relic abundance.

Contribution

The paper introduces two novel dark matter models that simultaneously explain the Belle II excess and account for the observed dark matter relic density.

Findings

Models can explain the Belle II excess

Both models match dark matter relic abundance

Potential testable predictions for future experiments

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.