Scalar flavor changing neutral currents and rare top quark decays in a two Higgs doublet model “for the top quark”

Abstract

In the so-called two Higgs doublet model for the top quark (T2HDM), first suggested by Das and Kao, the top quark receives a special status, which endows it with a naturally large mass, and also potentially gives rise to large flavor changing neutral currents only in the up-quark sector. In this paper, we calculate the branching ratio for the rare decays $t\ensuremath{\rightarrow}ch$ and $h\ensuremath{\rightarrow}\overline{t}c$ ($h$ is a neutral Higgs scalar) in the T2HDM, at tree level and at 1-loop when it exceeds the tree level. We compare our results to predictions from other versions of 2HDM's and find that the scalar flavor changing neutral currents in the T2HDM can play a significant role in these decays. In particular, the 1-loop mediated decays can be significantly enhanced in the T2HDM compared with the 2HDM of types I and II, in some instances reaching $\mathrm{BR}\ensuremath{\sim}{10}^{\ensuremath{-}4}$, which is within the detectable level at the LHC.