Exploring the anomalous Higgs-top couplings

The top quark with its large Yukawa coupling is crucially important to explore TeV scale physics. Therefore, the study of the Higgs-top sector is highly motivated to look for any deviations from the standard model predictions. The most general lowest-order Lagrangian for the Higgs-top Yukawa coupling has scalar ($\kappa$) and pseudoscalar ($\tilde{\kappa }$) components. Currently, these couplings are constrained indirectly using the present experimental limits on the Higgs-$\gamma$-$\gamma$ and Higgs-gluon-gluon couplings. Furthermore, stronger bounds on $\kappa$ and $\tilde{\kappa }$ are obtained using the limits on the electric dipole moments (EDM). In this paper, we propose an asymmetrylike observable $O_{\varphi }$ in $t\overline{t}H$ production at the LHC to probe the Higgs-top coupling and to distinguish between the scalar and pseudoscalar components. We also show that the presence of the pseudoscalar component in the Higgs-top Yukawa coupling leads to a sizeable value for the top quark EDM. It is shown that a limit of $10^{-19}e\mathrm{.}\mathrm{cm}$, which is achievable by the future $e^{-}{e}^{+}$ collider, allows us to exclude a significant region in the $(\kappa ,\tilde{\kappa })$ plane.

Figure 1

The distributions of the angular separations of $t\overline{t}$ and $tH$ for $t\overline{t}H$ final state in proton-proton collisions at $\sqrt{s}=14\mathrm{TeV}$ for different values of cut on the transverse Higgs momentum.

Figure 2

Left: the shape of $O_{\varphi }$ for the SM and several values of $\tilde{\kappa }$ versus cuts on the transverse Higgs momentum. Right: the shape of $O_{\varphi }$ of $t\overline{t}H$ for the SM case and for the $t\overline{t}H$ plus the main background $t\overline{t}+\text{jets}$.

Figure 3

The shape of $O_{\varphi }$ before applying any kinematic cuts on the final state particles, after cuts on the transverse momenta of lepton and jets and after applying all kinematic cuts. The trend does not change while the amount of $O_{\varphi }$ increases at any value of Higgs transverse momentum cut.

Figure 4

Left: The significance as a function of $\tilde{\kappa }$ for integrated luminosities of 10, 50, $100{\mathrm{fb}}^{-1}$. Right: The 1, 3, and 5 sigma regions of $\tilde{\kappa }$ as a function of the integrated luminosity in $pp$ collisions at the center-of-mass energy of 14 TeV.

Figure 5

68% C.L. allowed region from the global analysis taken from [8] (violet dashed curve), the $1\sigma$ and $3\sigma$ allowed region obtained using the $O_{\varphi }$ observable with $30{\mathrm{fb}}^{-1}$ of the LHC data at 14 TeV. The red solid curve shows the allowed region that could be obtained by the future upper limit on the top quark EDM ($d_t<10^{-19}e\mathrm{.}\mathrm{cm}$).