  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 to
mitigate the small-scale problems of cold dark matter cosmology. Future CMB
experiments will be able to consistently probe, or firmly exclude, this
scenario.
