  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 DP, 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 PM 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 PM and SM fields with the same electric
charge thus altering the DP interactions with (at least some of) the SM fields
and also providing a path for the PM fields to decay. In this paper we briefly
explore the phenomenology of some specific simple models of this PM including,
for the case where the PM 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 PM, their direct pair- and
single-production at the LHC is shown to be observable in final states that
include missing $E_T$ and/or very highly boosted lepton-jets together with
pairs of high $p_T$ 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 PM.
