Looking through the pseudoscalar portal into dark matter: Novel mono-Higgs and mono- Z signatures at the LHC

Mono-X signatures are a powerful collider probe of the nature of dark matter. We show that mono-Higgs and mono-Z may be key signatures of pseudoscalar portal interactions between dark matter and the standard model. We demonstrate this using a simple renormalizable version of the portal, with a two-Higgs-doublet model as an electroweak symmetry breaking sector. Mono-Z and mono-Higgs signatures in this scenario are of resonant type, which constitutes a novel type of dark matter signature at the LHC.