Dark photons (DP) are interesting as potential mediators between the dark
matter (DM) sector and the fields of the Standard Model (SM). The
interaction of the dark photon, described by a broken U(1)_D gauge symmetry,
with the SM is usually generated at the one-loop level via kinetic mixing
through the existence of portal matter (PM), here assumed to be fermionic,
which carries both a dark charge as well as a SM U(1)_Y hypercharge. For
theoretical consistency, as well as for many phenomenological reasons, this
portal matter must be vector-like with respect to the SM and dark gauge
groups and, in particular, is shown to be allowed only to transform as
vector-like copies of the usual SM fields. The dark Higgs that is
responsible for the breaking of U(1)_D can then generate a mixing between
the portal matter and SM fields with the same electric charge thus altering
the dark photon/portal matter interactions with (at least some of) the SM
fields and also providing a path for the portal matter fields to decay. In
this paper we briefly explore the phenomenology of some specific simple
models of this portal matter including, for the case where the portal matter
is leptonic in nature, their potential impact on experiments probing low
energy parity-violation and the g-2 of the muon. In the case of
color-triplet, bottom quark-like portal matter, their direct pair- and
single-production at the LHC is shown to be observable in final states that
includemissing E_T and/or very highly boosted lepton-jets together with
pairs of high-pT b-jets that can be used to trigger on such events. These
signatures are quite distinct from those usually employed in the search for
vector- like quarks at the LHC and, furthermore, we demonstrate that the
conventional signal channels for vector-like quarks involving the SM Higgs
and gauge fields are essentially closed in the case of portal matter. Many
other more complex, and more realistic, portal matter scenarios of the type
discussed here are possible which can lead to wide-ranging signatures in
various classes of experiments.
