Scalar FCNC and rare top decays in a two Higgs doublet model "for the top"

TL;DR

This paper investigates rare top quark decays in a specialized two Higgs doublet model for the top, finding that scalar flavor-changing neutral currents can significantly enhance decay rates to detectable levels at the LHC.

Contribution

It provides the first detailed calculation of t->ch and h->tc decay rates in the T2HDM, highlighting the potential for observable signals due to scalar FCNC effects.

Findings

1-loop decay BRs can reach ~10^-4, within LHC detection.

Scalar FCNC effects are more significant in T2HDM than in other 2HDMs.

Enhanced decay rates could serve as signals for T2HDM at colliders.

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 (FCNC) only in the up-quark sector. In this paper we calculate the branching ratio (BR) for the rare decays t->ch and h->tc (h is a neutral Higgs) 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 FCNC 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 to the 2HDM of types I and II, in some instances reaching BR~10^-4 which is within the detectable level at the LHC.