  We study a gauge-singlet vector-like fermion hidden-sector dark matter model,
in which the communication between the dark matter and the visible standard
model sector is via the Higgs-portal scalar-Higgs mixing, and also via a
hidden-sector scalar with loop-level couplings to two gluons and also to two
hypercharge gauge bosons induced by a vector-like quark. We find that the
Higgs-portal possibility is stringently constrained to be small by the recent
LHC di-Higgs search limits, and the loop-induced couplings are important to
include. In the model parameter space, we present the dark matter
relic-density, the dark-matter-nucleon direct-detection scattering
cross-section, the LHC diphoton rate from gluon-gluon fusion, and the
theoretical upper-bounds on the fermion-scalar couplings from perturbative
unitarity.
