  A gauge invariant UV-completion for singlet fermion DM interacting with the
standard model (SM) particles involves a new singlet scalar. Therefore the
model contains two scalar mediators, mixtures of the SM Higgs boson and a
singlet scalar boson. Collider phenomenology of the interference effect between
these two scalar propagators is studied in this work. This interference effect
can be either constructive or destructive in the DM production cross section
depending on both singlet scalar and DM masses, and it will soften the final
state jets in the full mass region. Applying the CMS mono-jet search to our
model, we find the interference effect plays a very important role in the DM
search sensitivity, and the DM production cross section of our model is more
than one order of magnitude below the LHC sensitivity at current stage.
