Muon Anomalous Magnetic Moment, Two-Higgs-Doublet Model, and Supersymmetry

The recent measurement on the muon anomalous magnetic moment $a_\mu$ shows a $2.6\sigma$ deviation from the standard model value. We show that it puts strong constraints on the parameter space of the two-higgs doublet model (2HDM) II. The dominant contribution of the Higgses comes at the two-loop level, and in order to explain the data it favors a pseudoscalar $A$ with a light mass range and a large $\tan\beta$. At 95% C.L., upper limit for $m_{\scriptscriptstyle A}$ is $29 (55) (85)$ GeV for $\tan\beta=30 (45) (60)$, and $\tan \beta$ is bounded below at 17. This is in sharp contrast to the conclusion one draws from considering one-loop Higgs contributions alone. Finally, we also discuss the role of the Higgs contributions in the minimal supersymmetric standard model.