  Even if new physics beyond the Standard Model (SM) indeed exists, the energy
scale of new physics might be beyond the reach at the Large Hadron Collider
(LHC) and the LHC could find only the Higgs boson but nothing else. This is the
so-called "nightmare scenario". On the other hand, the existence of the dark
matter has been established from various observations. One of the promising
candidates for thermal relic dark matter is a stable and electric
charge-neutral Weakly Interacting Massive Particle (WIMP) with the mass below
the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter
singlet under the SM gauge group, which only couples to the Higgs doublet at
the lowest order, and investigate a possibility that such WIMP dark matter can
be a clue to overcome the nightmare scenario via various phenomenological tests
such as the dark matter relic abundance, the direct detection experiments for
the dark matter particle, and the production of the dark matter particle at the
LHC.
