  We consider a simple extension of the Standard Model (SM) that incorporates a
Majorana fermion dark matter and a charged scalar particle with a coupling to
the SM leptons through renormalizable terms. Another renormalizable term
involving the charged scalar and the Higgs boson gives rise to interactions
between the dark matter and SM quarks at the one-loop level, which induce the
elastic scatterings between dark matter and nucleus. The same term also affects
the effective coupling of the Higgs boson to diphoton through a one-loop
diagram with the charged scalar. Therefore, our model predicts a correlation
between the spin-independent cross section for dark matter-nucleus elastic
scatterings and a new contribution to the effective Higgs boson coupling to
diphoton. When the spin-dependent cross section is large enough to be tested in
future direct dark matter detection experiments, the Higgs-diphoton decay rate
shows a sizable deviation from the SM prediction. We also consider the case
where the fermion dark matter is a Dirac particle. Most of discussions is
similar to the Majorana case, but we find that the magnetic dipole moment of
the Dirac fermion dark matter is loop-induced and this interaction dominates
the spin-independent cross section for dark matter-nucleus elastic scatterings.
We find that the resultant cross section is about an order of magnitude below
the current experimental bound and hence can be tested in the near future.
