Combined signatures of heavy Higgses and vectorlike fermions at the HL-LHC

Abstract: In extensions of two Higgs doublet models with vectorlike quarks and leptons the decays of new scalars or fermions can be altered by the presence of the other, depending on the hierarchy of new physics. If new fermions are heavier than Higgses, their decays may be dominated by cascade decays through charged and neutral heavy Higgs bosons. In the opposite hierarchy, the decay of a heavy Higgs can lead to single production of vectorlike quarks and leptons when Yukawa couplings to SM fermions are present. We explore the resulting novel collider signatures in either case and present projected sensitivities of future runs of the LHC to the masses and branching ratios of new fermions and heavy Higgses. Importantly, we discuss kinematic challenges of the signatures and suggest strategic observables which could be adopted in future analyses. Interpreting the prospective reach of the LHC in the context of a type-II 2HDM, we find that in the presence of vectorlike fermions heavy Higgs boson masses slightly above 2 TeV can be explored at the HL-LHC even at low $\tan\beta$. For heavy Higgs decays through vectorlike leptons, this reach extends to slightly above 3 TeV for $\tan\beta \gtrsim 10$. Further, these search strategies imply a reach for vectorlike quark and lepton masses close to 2.4 TeV and 1.5 TeV, respectively. This article is partly based on Refs. [1-6]