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The Belle II collaboration recently announced that they observed the B+→K+νν¯ decay process for the first time. However, their result encounters a 2.7σ deviation from the Standard Model (SM) calculation. Additionally, Fermilab released new data on muon g−2 away from the SM expectation with 5.1σ. In this paper, we study the simplest UV-complete U(1)Lμ−Lτ-charged complex scalar dark matter (DM) model. Thanks to the existence of light dark Higgs boson and light dark photon, we can explain the observed relic density of DM and resolve the results reported by both Belle II and Fermilab experiments simultaneously. As a by-product, the Hubble tension can be alleviated by taking ΔNeff≃0.3 induced by the light dark photon, which could be tested by CMB stage-4 and new NA64 experimental data in the near future. In addition, our light DM mass is highly testified by future data released by Belle II and CMB stage-4.
Ho et al. (Thu,) studied this question.