  The nature of dark matter (DM) and how it might interact with the particles
of the Standard Model (SM) is an ever-growing mystery. It is possible that the
existence of new `dark sector' forces, yet undiscovered, are the key to solving
this fundamental problem. In this paper, we construct a model in which a dark
photon mediates interactions with the SM via kinetic mixing. Unlike traditional
models, in which the dark photon, which couples to a dark charge, $Q_D$, mixes
with the hypercharge boson, our model effectively mixes the dark photon
directly with the photon after electroweak symmetry is broken, but remains
unmixed until the symmetry breaks. The kinetic mixing is generated at one loop
by fields which satisfy $\sum Q_D Q_{em} = 0$, a condition which guarantees a
finite result at one loop. In the literature, this has been traditionally
obtained via heavy fermions, which may lie out of the reach of current
accelerators. In this model, by contrast, this process is mediated by scalar
`portal matter' fields, which are charged under the $SU(2)_L \times U(1)_Y$ of
the standard model as well as the dark gauge group $U(1)_D$ and acquire
GeV-scale vevs which give mass to the dark Higgs and dark photon. The
additional scalar fields are relatively light, at or below the weak scale, yet
may remain undetected by current experiments since their couplings to SM
fermions come only through percent level mixing with the SM Higgs. At
colliders, these models are typified by relatively low MET due the BSM states
decaying into MET and SM bosons, with MET which is balanced by the decay of the
associated production object. Nevertheless, the higher statistics of HL-LHC may
be able to probe the entirety of the model space.
