In the standard model (SM) of particle physics, the Higgs boson is deeply related to the mechanism that creates the masses of elementary particles and, as such, has very characteristic properties, which are different from any other known particle. While the experimental results so far are consistent with a SM nature of the Higgs boson, it might well be part of an extended Higgs sector, which is predicted in many beyond-the-SM (BSM) scenarios that address mysteries the SM cannot explain. The large data samples collected at the CERN Large Hadron Collider (LHC), together with new analysis techniques, allow measurements of the Higgs boson properties at unprecedented precision as well as direct searches for additional Higgs bosons with highest reach. The results play a crucial role in probing the SM and provide a unique window to potential BSM effects.
The coupling of the Higgs boson to the heaviest known quark, the top quark, is particularly exciting because it is large and, therefore, it plays a special role in the SM or possible BSM physics. In the presentation, I will discuss different techniques to explore the Higgs sector using top quarks, and I will highlight two recent results: a measurement of Higgs boson production in association with top quarks (ttH and tH production), which provide direct probes of the top-Higgs coupling, in the bb decay channel of the Higgs boson; and a brand-new search for heavy additional Higgs bosons decaying to a Z boson and a top quark-antiquark pair (ttZ final state). The search accesses a mostly unexplored part of the Two Higgs Double Model (2HDM) parameter space that is relevant in models of baryogenesis and could explain the matter-antimatter asymmetry in the Universe.