Year: 2026
Type: article
Abstract: A bstract In this paper we study axion-like particles (ALPs) with lepton-flavour-violating (LFV) couplings in the mass regime above the muon threshold, m a > m μ , where the strong bound from the exotic muon decay μ → ea no longer apply and the decay channel a → eμ becomes kinematically accessible. In this region, the ALP typically decays promptly, motivating new search strategies based on its production in decays involving virtual muons. We analyse charged-meson and W decays, neutral-current processes such as Z and quarkonium decays, and, when couplings to the third generation are present, LFV τ decays. The subsequent decay a → eμ leads to striking LFV signatures with negligible Standard Model backgrounds. Combining these production modes with current low-energy constraints, we assess the sensitivity of future high-energy e + e − colliders, flavour factories such as Belle II and STCF, fixed-target experiments such as NA62, and proton beam-dump facilities such as SHiP. Overall, our results identify LFV ALP production in meson, gauge-boson, quarkonium and τ decays (with displaced vertices) as a promising and largely unexplored avenue to test ALP interactions with charged leptons above the muon mass threshold.
Source: Journal of High Energy Physics
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
Awards: G103507813, G1105844351, G1175115578, G1272900390, G1422035950, G1938719665, G2121348967, G2262748287, G2917513873, G2931447263, G300979063, G3220251042, G3480869486, G3565621276, G3681454997, G3857581125, G4042783231, G425668148, G464105488, G4861624602, G491712853, G5080475149, G5209569390, G5635532810, G603324873, G633297219, G7084143925, G714608666, G7563990732, G7805626310, G7863371703, G8269025138, G8497050386, G972786147
OpenAlex ID: W7154495365