Abstract
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.
Highlights
Axions and axionlike particles are new types of elementary particles, which arise in a large class of extensions of the standard model (SM) and are well motivated theoretically
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
Summary
Martin Bauer ,1 Matthias Neubert ,2,3,4 Sophie Renner ,5 Marvin Schnubel ,2 and Andrea Thamm 6. We derive model-independent results for the decays K− → π−a and π− → e−νea at leading order in the chiral expansion and for arbitrary axion couplings and mass. Axions and axionlike particles (collectively referred to as ALPs in this work) are new types of elementary particles, which arise in a large class of extensions of the standard model (SM) and are well motivated theoretically. They can provide an elegant solution to the strong CP problem based on the Peccei-Quinn mechanism [1,2,3,4,5,6,7,8]. The starting point of our study is the effective ALP Lagrangian at a scale of order μχ ≈ 1.6 GeV, which we write in the form [13]
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