Kinetic mixing and portal matter phenomenology

Dark photons are interesting as potential mediators between the dark matter 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, 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 vectorlike with respect to the SM and dark gauge groups and, in particular, is shown to be allowed only to transform as vectorlike 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 quarklike portal matter, 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 vectorlike quarks at the LHC and, furthermore, we demonstrate that the conventional signal channels for vectorlike 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.