Unveiling the CP -odd Higgs boson in a generalized 2HDM at a muon collider

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We revisit the generalized two-Higgs-doublet model (2HDM) with a lepton specific (Type-X) Yukawa sector in context of the muon collider. The model offers a large region of parameter space where it can provide a solution to the observed muon (g−2) excess. Specifically the low mass CP odd scalar of this model plays an important role to fit this anomaly. Interestingly, the coupling of the pseudoscalar with the muons is proportional to tanβ (which equals to the ratio of vacuum expectation values of the Higgs doublets) which dominantly controls the one loop and two loop contributions of the muon magnetic moment, therefore it can be probed directly at a muon collider with greater sensitivity in comparison to the Large Hadron Collider. Primarily focusing on a parameter space where muon g−2 anomaly is satisfied, we explore the available theoretical and experimental constraints arising from vacuum stability, unitarity, lepton flavor violation, electroweak precision constraint, B-meson decay, and collider experiments on the model. In the parameter space where all these constraints are satisfied, we propose to study the production of the light pseudoscalar A in association with a photon at a 3 TeV muon collider. Subsequent decay of A into a τ pair will produce a striking l+l−γ plus missing energy signature. Published by the American Physical Society 2025