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

Abstract

The observation of $t\bar th(125)$ 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 $t\bar th$ and Higgs property measurements at the High Luminosity LHC can constrain the ${\rm Re}\,\rho_{tt}$--${\rm Im}\,\rho_{tt}$ parameter space that could drive electroweak baryogenesis, but the $\Gamma_h$ width measurement must be considerably improved beyond current projections.