A phenomenological profile of Higgs portals at future colliders

Abstract: Should the Higgs boson be found to couple to a hidden dark sector, it will become necessary to determine the nature of the Higgs portal responsible. Could the minimal, marginal Higgs portal operator be distinguished from a Higgs portal interaction involving a higher-dimensional operator? This is unlikely for Higgs portals with on-shell invisible decays to light dark sectors, but for an off-shell Higgs portal above threshold, where the dark sector is too heavy to contribute to the invisible Higgs decay width, we find that the higher-dimensional Higgs portal operators could in principle be differentiated by combining measurements across the integrated programme of HL-LHC, FCC-ee, and FCC-hh. This illustrates the complementarity of precision and high-energy exploration to phenomenologically profile Higgs portal interactions and probe possible connections between the electroweak scale and a hidden universe.