Scalar-Mediated Flavor-Changing Neutral Currents

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The simplest extension of the standard model involves adding a scalar doublet--the so-called two-Higgs model. In general, the additional scalar will mediate tree-level flavor-changing neutral currents. Although one can arbitrarily impose a discrete symmetry to avoid these, it isn't necessary to do so; reasonable assumptions about the size of the flavor-changing couplings can make them sufficiently small as to avoid problems in the kaon sector. However, these same assumptions give much larger effects in the third-family case. We discuss the model, the "reasonable assumptions" on the size of the couplings, and examine phenomenological bounds on the couplings, showing that the most promising signatures are from Bₛ --> μτ, μ--> eγ, etc. We then include the newest result which shows potentially significant effects on the anomalous magnetic moment of the muon.