Explaining the MiniBooNE Anomalous Excess via Leptophilic ALP-Sterile Neutrino Coupling

Abstract

Recently, the MiniBooNE experiment at Fermilab has updated the results with increased data and reported an excess of $560.6\pm 119.6$ electronlike events ($4.7\sigma$) in the neutrino operation mode. In this paper, we propose a scenario to account for the excess where a Dirac-type sterile neutrino, produced by a charged kaon decay through the neutrino mixing, decays into a leptophilic axionlike particle ($\ell$ALP) and a muon neutrino. The electron-positron pairs produced from the $\ell$ALP decays can be interpreted as electronlike events provided that their opening angle is sufficiently small. In our framework, we consider the $\ell$ALP with a mass $m_a^{}=20\text{MeV}$ and an inverse decay constant $c_e^{}/f_a^{}=10^{-2}{\text{GeV}}^{-1}$, allowed by the astrophysical and experimental constraints. Then, after integrating the predicted angular or visible energy spectra of the $\ell$ALP to obtain the total excess event number, we find that our scenario with sterile neutrino masses within $150\text{MeV}\lesssim m_N^{}\lesssim 380\text{MeV}$ ($150\text{MeV}\lesssim m_N^{}\lesssim 180\text{MeV}$) and neutrino mixing parameters between $10^{-10}\lesssim |U_{\mu 4}{|}^2\lesssim 10^{-8}$ ($3\times 10^{-7}\lesssim |U_{\mu 4}{|}^2\lesssim 8\times 10^{-7}$) can explain the MiniBooNE data.

19+1 pages, 8+1 figures, and 1 table; v2: Typos fixed, figure added, note added, references added, matched to the published version

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