Probing for Extra Top Yukawa Couplings in Light of $t\bar{t}h(125)$ Observation

The observation of $t\bar{t}h(125)$ production at the Large Hadron Collider (LHC) is the first direct measurement of the top Yukawa coupling. It opens the window on an extra top Yukawa coupling, ${\rho }_{tt}$, from a second Higgs doublet, without a $Z_2$ symmetry to forbid flavor changing neutral Higgs couplings. We show that $t\bar{t}h$ and Higgs property measurements at the High Luminosity LHC can constrain the $\mathrm{R}\mathrm{e}{\rho }_{tt}$–$\mathrm{I}\mathrm{m}{\rho }_{tt}$ parameter space that could drive electroweak baryogenesis, but the ${\mathrm{\Gamma }}_h$ width measurement must be considerably improved beyond current projections.