The Flavor of QCD Axion Dark Matter

Understand

We argue that demanding a consistent cosmological history, including the absence of domain walls and strongly interacting relics at the Peccei-Quinn scale, singles out two concrete realizations of hadronic QCD axions as viable dark matter models.

• These realizations generally feature flavor-violating axion couplings to Standard Model quarks that are unsuppressed at low energies.
• As a consequence, experiments looking for flavor-violating hadronic processes involving the axion can be sensitive probes of QCD axion dark matter models.
• In particular, we show that the NA62 and KOTO experiments could detect the $K\rightarrow\pi + a$ decay for axions consistent with the observed dark matter abundance via the post-inflationary misalignment mechanism.