Probing exotic triple Higgs couplings at the LHC

In extended Higgs sectors that exhibit alignment without decoupling, the additional scalars are allowed to have large couplings to the Standard Model Higgs. We show that current nonresonant di-Higgs searches can be straightforwardly adapted to look for additional Higgses in these scenarios, where pair production of non-SM Higgses can be enhanced. For concreteness, we study pair production of exotic Higgses in the context of an almost inert two Higgs doublet model, where alignment is explained through an approximate ℤ₂ symmetry under which the additional scalars are odd. In this context, the smallness of the ℤ₂ violating parameter suppresses single production of exotic Higgses, but it does not prevent a sizeable trilinear coupling hHH between the SM Higgs (h) and the additional states (H). We study the process pp → h^* → HH in the final states bb¯ bb¯ , bb¯ γγ, and multi-leptons. We find that at the HL-LHC these modes could be sensitive to masses of the additional neutral scalars in the range 130 GeV ≲ m_H ≲ 290 GeV.