Light thermal dark matter has emerged as an attractive theoretical
possibility and a promising target for discovery at experiments in the near
future. Such scenarios generically invoke mediators with very small couplings
to the Standard Model, but moderately strong couplings within the dark sector,
calling into question theoretical estimates based on the lowest order of
perturbation theory. As an example, we focus on a scenario in which
(pseudo)-Dirac fermion dark matter is connected to the standard model via a
dark photon charged under a new $U(1)^{\prime}$ extension of the standard
model, and we investigate the impact of the next-to-leading order corrections
to annihilation and scattering. We find that radiative corrections can
significantly impact model predictions for the relic density and scattering
cross-section, depending on the strength of the dark sector coupling and ratio
of the dark matter to mediator mass. We also show why factorization into the
yield parameter $Y$ typically presented in literature leads to imprecision. Our
results are necessary to accurately map experimental searches into the model
parameter space and assess their ability to reach thermal production targets.
