Portal Matter Models of Kinetic Mixing with Two Light Dark Gauge Bosons

Abstract: The kinetic mixing (KM) portal mandates the existence of at least one new gauge boson, the dark photon (DP) based on the group $U(1)D$, which mixes with the Standard Model (SM) photon via loops of other new heavy particles carrying both SM and dark charges called portal matter (PM). Arguments exist based on the RGE running of the $U(1)_D$ gauge coupling suggesting that at higher scales $U(1)_D$ becomes part of a more complex non-Abelian group, a simple example being just the SM-like $G_D=SU(2)_I \times U(1){Y_I}$. In our past analyses it was always assumed that $G_D$ broke in a SM-like manner directly to the DP's $U(1)D$ which then subsequently broke at low energies $\lsim 1$ GeV. However, this need not be the case and $G_D$ can instead break to $U(1){T_{3I}}\times U(1){Y_I}$, with $T{3I}$ being the diagonal generator of $SU(2)_I$, now producing two light gauge bosons which obtain masses at the $\lsim 1$ GeV scale. In this paper we will explore the phenomenology of a very simple realization of this kind of alternative setup employing non-abelian KM and having a minimal, lepton-like PM sector, demonstrating its distinctive nature in comparison to the previously examined symmetry breaking path. The effects of interference between these gauge bosons on thermal dark matter annihilation, the production of new heavy gauge, Higgs and PM states at colliders, as well as the corresponding signatures for the light dark gauge bosons are examined.