ATLAS sensitivity to Two-Higgs-Doublet models with an additional pseudoscalar exploiting four top quark signatures with 3ab$^{-1}$ of $\sqrt{s}=14$ TeV proton-proton collisions

This document summarises the expected ATLAS sensitivity to four top-quark signatures in models involving two Higgs doublets and an additional pseudo-scalar mediator that couples to dark matter particles. The sensitivity is estimated using 3000 fb$^{-1}$ of proton-proton collisions in the context of the High Luminosity LHC update. The experimental signatures investigated include at least two charged leptons with the same electric charge or at least three leptons.