Baryonic Axion in neutron-antineutron oscillation

The accidental baryonic symmetry is expected to be broken and required from the observed matter-antimatter asymmetry. The neutron-antineutron oscillating system is the hallmark of $\mathrm{\Delta }\mathcal{B}=2$ models which have the benefits of not inducing proton decay. We study this system in a framework allowing the most general couplings to understand how a dark matter candidate such as the axion may couple to the oscillation. In particular a Rabi resonance phenomenon occurs, and this effect is unconstrained for Axion Like Particles (ALPs) models. Regarding the QCD axion, its Goldstone nature leads to a robust exclusion of the majority of scenarios allowed.