  We reexamine the simplified dark matter (DM) models with fermionic DM
particle and spin-0 mediator. The DM-nucleon scattering cross sections of these
models are low-momentum suppressed at tree-level, but receive sizable
loop-induced spin-independent contribution. We perform one-loop calculation for
scalar-type and twist-2 DM-quark operators and complete two-loop calculation
for scalar-type DM-gluon operator. By analyzing the loop-level contribution
from new operators, we find that future direct detection experiments can be
sensitive to a fraction of parameter space. The indirect detection and collider
search also provide complementary constraints on these models.
