It was recently suggested that dark matter consists of ∼ GeV particles that carry baryon number and mix with the neutron. We demonstrate that this could allow for resonant dark matter–neutron oscillations in the early Universe, at finite temperature, leading to low-scale baryogenesis starting from a primordial dark matter asymmetry. In this scenario, the asymmetry transfer happens around 30 MeV, just before big bang nucleosynthesis. We illustrate the idea using a model with a dark U(1)′ gauge interaction, which has recently been suggested as a way of addressing the neutron lifetime anomaly. The asymmetric dark matter component of this model is both strongly self-interacting and leads to a suppression of matter density perturbations at small scales, allowing it to mitigate the small-scale problems of cold dark matter cosmology. Future cosmic microwave background experiments will be able to consistently probe, or firmly exclude, this scenario.
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