The Flavor of QCD Axion Dark Matter

TL;DR

This paper identifies two specific QCD axion models compatible with cosmology that could be detected through flavor-violating processes in kaon decays, offering new experimental avenues for dark matter detection.

Contribution

It presents concrete hadronic QCD axion models with flavor-violating couplings that are testable in current experiments, linking cosmological viability with experimental signatures.

Findings

NA62 and KOTO experiments can detect axion-induced kaon decays.

Flavor-violating axion couplings are unsuppressed at low energies.

Models are consistent with cosmological constraints and dark matter abundance.

Abstract

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.