Scalar-Mediated Flavor-Changing Neutral Currents

TL;DR

This paper explores how adding a scalar doublet to the standard model can cause flavor-changing neutral currents, analyzing their effects, constraints, and potential experimental signatures, especially in B meson decays and muon magnetic moments.

Contribution

It introduces a detailed analysis of scalar-mediated flavor-changing neutral currents in the two-Higgs model, including phenomenological bounds and experimental signatures.

Findings

Potentially observable effects in B_s --> μτ decays

Constraints from μ --> eγ decay

Significant impact on muon anomalous magnetic moment

Abstract

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 $B_s --> \mu\tau$, $\mu --> e\gamma$, etc. We then include the newest result which shows potentially significant effects on the anomalous magnetic moment of the muon.