Flavour-changing top decays in the aligned two-Higgs-doublet model

TL;DR

This paper provides a detailed one-loop analysis of flavour-changing top decays in the aligned two-Higgs-doublet model, showing that predicted rates are below future LHC sensitivity but are constrained by Higgs measurements.

Contribution

It offers the first comprehensive one-loop calculation of these decays within this specific model, incorporating experimental constraints and Higgs data.

Findings

Decay rates are below future LHC sensitivity.

Higgs di-photon measurements constrain decay rates.

Light charged scalars significantly impact decay predictions.

Abstract

We perform a complete one-loop computation of the two-body flavour-changing top decays $t \rightarrow c h$ and $t \rightarrow c V$ ($V= \gamma, Z$), within the aligned two-Higgs-doublet model. We evaluate the impact of the model parameters on the associated branching ratios, taking into account constraints from flavour data and measurements of the Higgs properties. Assuming that the $125$~GeV Higgs corresponds to the lightest CP-even scalar of the CP-conserving aligned two-Higgs-doublet model, we find that the rates for such flavour-changing top decays lie below the expected sensitivity of the future high-luminosity phase of the LHC. Measurements of the Higgs signal strength in the di-photon channel are found to play an important role in limiting the size of the $t \rightarrow c h$ decay rate when the charged scalar of the model is light.