Direct and Indirect Searches for Top-Higgs FCNC Couplings

TL;DR

This paper investigates the potential to detect top-Higgs flavor-changing neutral currents (FCNC) through direct collider searches and indirect constraints, setting new bounds on the branching ratio and coupling strength.

Contribution

It introduces a detailed analysis of top-Higgs FCNC couplings via e+e- collisions and updates constraints using electroweak precision measurements.

Findings

Branching ratio for t→qH can be probed down to 1.12×10⁻³ at 95% CL.

Electroweak precision observables provide updated constraints on FCNC couplings.

The study demonstrates the sensitivity of future colliders to top-Higgs FCNC interactions.

Abstract

Large top quark flavor changing through neutral currents is expected by many extensions of the standard model. Direct and indirect searches for flavor changing neutral currents (FCNC) in the top quark decays to an up type quark (up,charm) and a Higgs boson are presented. We probe the observability of the top-Higgs FCNC couplings through the process e$^-$e$^+ \rightarrow t (\rightarrow \ell \nu_{\ell} b) \,\, \bar{t} (\rightarrow q H)$, where $\ell$ = e, $\mu$ and $q$ reflects up and charm quarks. It is shown that the branching ratio $Br(t\rightarrow qH)$ can be probed down to $1.12\times 10^{-3}$ at $95\%$ C.L. at the center-of-mass energy of 500 GeV with the integrated luminosity of 3000 fb$^{-1}$. We also update the constraint on the top-Higgs FCNC coupling using the electroweak precision observables related to $Z\rightarrow c\bar{c}$ decay.