Consistent Treatment of Axions in the Weak Chiral Lagrangian.

We present a consistent implementation of weak decays involving an axion or axionlike particle in the context of an effective chiral Lagrangian. We argue that previous treatments of such processes have used an incorrect representation of the flavor-changing quark currents in the chiral theory. As an application, we derive model-independent results for the decays K^{-}→π^{-}a and π^{-}→e^{-}ν[over ¯]_{e}a at leading order in the chiral expansion and for arbitrary axion couplings and mass. In particular, we find that the K^{-}→π^{-}a branching ratio is almost 40 times larger than previously estimated.

Axionlike Particles, Lepton-Flavor Violation, and a New Explanation of a_{µ} and a_{e}.

Axionlike particles (ALPs) with lepton-flavor-violating couplings can be probed in exotic muon and tau decays. The sensitivity of different experiments depends strongly on the ALP mass and its couplings to leptons and photons. For ALPs that can be resonantly produced, the sensitivity of three-body decays such as µâ†’3e and τ→3µ exceeds by many orders of magnitude that of radiative decays like µâ†’eγ and τ→µÎ³. Searches for these two types of processes are therefore highly complementary. We discuss experimental constraints on ALPs with a single dominant lepton-flavor-violating coupling. Allowing for one or more such couplings offers qualitatively new ways to explain the anomalies related to the magnetic moments of the muon or the electron. The explanation of both anomalies requires lepton-flavor-nonuniversal or lepton-flavor-violating ALP couplings.