  Dark sector mass relations, such as those which permit near-threshold or
near-resonance annihilation in the early universe, could arise due to
IR-attractive ratios in renormalization group equations. Achieving a particular
ratio requires specific dark matter gauge charges or interactions, leading to
predictions about the dark matter properties. Furthermore, additional states
with masses comparable to the dark matter mass may be necessary, potentially
giving rise to novel phenomenology. We explore this idea in the context of dark
matter charged under a new gauged $U(1)_X$ that kinetically mixes with the
Standard Model hypercharge.
