Constraints on leptophilic axion-like particles from leptonic decays of charged pseudoscalar mesons

Abstract We consider the constraints of the purely leptonic decays of charged pseudoscalar mesons P (being π ± , K ± , D ( s ) ± or B ± ) and the gauge boson W , P → ℓν ℓ , P → ℓ ν ℓ ν ν ¯ , P → ℓν ℓ e + e − and W → ℓν ℓ , on the leptophilic axion-like particles ( ℓ ALPs, denoted as a ) with masses in the range 10–100 MeV via the decays P → ℓν ℓ a and W → ℓν ℓ a , where a is assumed to escape the detector as missing energy or to decay into a pair of charged leptons. Comparing our numerical results with the latest experimental data, we find that some of these decay processes for P being π ± and K ± can give meaningful constraints on the flavor-diagonal coupling parameter g ℓ / f a with the ℓ ALP mass in the range considered in this paper. The strongest constraints come from the decay K + → μ + ν μ ν ν ¯ , which set upper limits of 7.60 × 10 −2 –1.03 × 10 −1 GeV −1 on g ℓ / f a at the 90% C.L.