  The coupling of an axion-like particle driving inflation to the Standard
Model particle content through a Chern-Simons term generically sources a dual
production of massless helical gauge fields and chiral fermions. We demonstrate
that the interplay of these two components results in a highly predictive
baryogenesis model, which requires no further ingredients beyond the Standard
Model. If the helicity stored in the hyper magnetic field and the effective
chemical potential induced by the chiral fermion production are large enough to
avoid magnetic diffusion from the thermal plasma but small enough to
sufficiently delay the chiral plasma instability, then the non-vanishing
helicity survives until the electroweak phase transition and sources a net
baryon asymmetry which is in excellent agreement with the observed value. If
any of these two conditions is violated, the final baryon asymmetry vanishes.
The observed baryon asymmetry can be reproduced if the energy scale of
inflation is around $H_\text{inf} \sim 10^{10}$ - $10^{12}$ GeV with a moderate
dependence on inflation model parameters.
