$t \to cWW$ and $WW \to \bar{t}c + t\bar{c}$ in Extended Models

TL;DR

This paper investigates the potential for flavor-changing top quark decays and related processes in extended models, calculating branching ratios and production rates, highlighting possible resonant enhancements and experimental challenges at the LHC.

Contribution

It provides a comprehensive calculation of $t o cW^+W^-$ branching ratios and $WW o ar{t}c + tar{c}$ production rates in models beyond the standard model, including resonant effects.

Findings

Scalar exchange can enhance $t o cW^+W^-$ branching ratio to a few tenths of a percent.

Single-top/charm production rates at the LHC are significant but likely overshadowed by background.

Resonant enhancements occur for scalar masses between $2m_W$ and 200 GeV.

Abstract

Jenkins has pointed out that the process $t\to cW^+W^-$ is GIM suppressed in the standard model. In this note, we calculate the branching ratio for a wide range of models, in which the decay occurs at tree level through exchange of a scalar, fermion or vector. In the case of scalar exchange, a scalar mass between $2m_W$ and 200 GeV leads to a resonant enhancement, giving a branching ratio as high as a few tenths of a percent. We then note that all of these models will also allow $W^+W^-\to \bar{t}c+t\bar{c}$, and we calculate the single-top/single-charm production rate at the LHC. The rates aren't negligibly small, but the background from single-top/single-bottom production will probably swamp the signal.