A connection between flavour anomaly, neutrino mass, and axion

Understand

We propose a minimal model in which the flavour anomaly in the $b \to s \mu^+ \mu^-$ transition is connected to the breaking of Peccei-Quinn (PQ) symmetry.

• The flavour anomaly is explained from new physics contribution by introducing one generation of heavy quark and heavy lepton which are vector-like under the standard model (SM) gauge group but charged under a local $U(1)_X$ group.
• They mix with the SM quarks and leptons, inducing flavour-changing $Z^\prime$ couplings, which generates the $b \to s \mu^+\mu^-$ anomaly at tree level.
• On the other hand the new fermions are chiral under the global Peccei-Quinn(PQ) symmetry.