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

TL;DR

This paper investigates the potential to detect and constrain additional top Yukawa couplings, specifically $ ho_{tt}$, through $tar th$ production measurements at the LHC, with implications for electroweak baryogenesis.

Contribution

It demonstrates how Higgs measurements at the HL-LHC can limit the parameter space of extra top Yukawa couplings relevant for baryogenesis, highlighting the need for improved Higgs width measurements.

Findings

$tar th$ measurements can constrain $ ho_{tt}$ parameters.

Higgs width measurements need significant improvement.

Constraints can inform electroweak baryogenesis models.

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.