Dark matter and Higgs boson collider implications of fermions in an Abelian-gauged hidden sector

We add fermions to an Abelian-gauged hidden sector. We show that the lightest can be the dark matter with the right thermal relic abundance, and discovery is within reach of upcoming dark matter detectors. We also show that these fermions change Higgs boson phenomenology at the Large Hadron Collider (LHC), and in particular could induce a large invisible width to the lightest Higgs boson state. Such an invisibly decaying Higgs boson can be discovered with good significance in the vector boson fusion channel at the LHC.