Making the Universe at 20 MeV
  We present a testable mechanism of low-scale baryogenesis and dark matter
production in which neither baryon nor lepton number are violated. Charged $D$
mesons are produced out-of-equilibrium at tens of MeV temperatures. The $D$
mesons quickly undergo CP-violating decays to charged pions, which then decay
into dark-sector leptons without violating lepton number. To transfer this
lepton asymmetry to the baryon asymmetry, the dark leptons scatter on
additional dark-sector states charged under lepton and baryon number.
Amusingly, this transfer proceeds without electroweak sphalerons, which are no
longer active at such low scales. We present two example models which can
achieve this transfer while remaining consistent with current limits. The
required amount of CP violation in charged $D$ meson decays, while currently
allowed, will be probed by colliders. Additionally, the relevant decays of
charged pions to dark-sector leptons have been constrained by the PIENU and PSI
experiments and will be further explored in upcoming experiments.
