Abstract
We revisit the flavor-changing processes involving an axion-like particle (ALP) in the context of generic ALP effective lagrangian with a discussion of possible UV completions providing the origin of the relevant bare ALP couplings. We focus on the minimal scenario that ALP has flavor-conserving couplings at tree level, and the leading flavor-changing couplings arise from the loops involving the Yukawa couplings of the Standard Model fermions. We note that such radiatively generated flavor-changing ALP couplings can be easily suppressed in field theoretic ALP models with sensible UV completion. We discuss also the implication of our result for string theoretic ALP originating from higher-dimensional p-form gauge fields, for instance for ALP in large volume string compactification scenario.
Highlights
JHEP11(2017)070 with a discussion of the possible UV completion providing the origin of the relevant bare axion-like particle (ALP) couplings
It is noted that the most dangerous flavor-changing ALP couplings to down-type quarks can be naturally suppressed in field theoretic ALP models with sensible UV completion, in which the ALP originates from the phase degrees of complex scalar fields X charged under the Peccei-Quinn (PQ) symmetry in a UV theory with cutoff scale significantly higher than the PQ scale fa ∼ X
We focus on the minimal scenario that ALP has only flavor-conserving couplings at tree level, and the dominant flavor-violating couplings are induced at one loop order due to the SM Yukawa couplings
Summary
We discuss radiatively induced flavor-changing couplings of an axion-like particle in the context of generic effective lagrangian defined at scales above the weak scale, but below the ALP decay constant fa. In the GKR basis, PQ-invariant ALP interactions at scales below fa, which are relevant for our subsequent discussion, can be generally written as. Making an appropriate ALP-dependent phase rotation of ψ and Hα, together with a proper redefinition of the PQ symmetry, one may choose a specific form of GKR basis for which some of the ALP couplings (cψ, cHα) are vanishing. As we are interested in the UV origin of the above ALP couplings, which will be discussed, here we take more general field basis which allows a straightforward matching to the UV completion. It is straightforward to extend the discussion to models with more Higgs doublets or to the SM without H1, in which Hd = He = iσ2H2∗. As U(1)PQ is an approximate symmetry, there can be PQ-breaking ALP interactions the non-derivative couplings to gauge fields and the scalar potential providing a nonzero ALP mass:
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