  We propose a generalized Kim-Shifman-Vainshtein-Zakharov-type axion framework
in which colored fermions and scalars act as two-loop Majorana neutrino-mass
mediators. The global Peccei-Quinn symmetry under which exotic fermions are
charged solves the strong CP problem. Within our general proposal, various
setups can be distinguished by probing the axion-to-photon coupling at
helioscopes and haloscopes. We also comment on axion dark-matter production in
the early Universe.
