Freeze-in Production of Non-Abelian Millicharged Vector Dark Matter

Abstract: We present the first predictive realization of vector freeze-in dark matter from a hidden non-Abelian gauge sector, spontaneously broken to a residual $U(1)$ with a massless dark photon mediator. A massive dark vector particle-antiparticle pair acquires small millicharges via a dimension-five kinetic mixing operator that induces a dimension-four mixing term with effective coefficient $ε$, and interacts through the hidden gauge coupling $g_D$, linking it weakly to the Standard Model. Solving the relic abundance with a two-temperature Boltzmann evolution including plasmon decays, we find that $ε, g_D \sim 10^{-7}$ reproduce the observed density while satisfying astrophysical and cosmological bounds. This minimal framework links non-Abelian vector dynamics, long-range dark forces, and dark matter, and can be testable with upcoming sub-GeV dark matter direct-detection experiments.