QCD axion, colour-mediated neutrino masses, and $B^{+}\to K^{+}+E_{\text{miss}}$ anomaly

Abstract

Motivated by the recent Belle II result indicating a $2.7\sigma$ excess of $B^{+}\to K^{+}+E_{\text{miss}}$ events compared to the Standard Model (SM) prediction for $B^{+}\to K^{+}\nu \bar{\nu }$, we explore an explanation to this anomaly based on a KSVZ-type QCD axion model featuring a Peccei-Quinn (PQ) symmetry breaking at high-scale, that can provide a solution to the strong CP problem with dark matter relic abundance. The model contains a PQ-charged scalar} leptoquark which can interact with the SM quarks only via mass-mixing of the latter with vector-like quarks. The mixing between SM and vector-like quarks is determined by the PQ mass scales and can explain the excess $B^{+}\to K^{+}+E_{\text{miss}}$ events while respecting other flavour constraints. The same PQ-charged scalar leptoquarks and vector-like quarks also mediate the two-loop radiative neutrino masses.

25 pages, 6 figures, matches published version