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

The recent measurement of the muon anomalous magnetic moment ashows a 2.6� 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 Higgs bosons 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�. At 95% C.L., the upper limit for mA is 29(55)(85) GeV for tan� = 30(45)(60), and tanis 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.