  Many models of baryogenesis rely on anomalous particle physics processes to
give baryon number violation. By numerically evolving the electroweak equations
on a lattice, we show that baryogenesis in these models creates helical cosmic
magnetic fields. After a transitory period, electroweak dynamics is found to
conserve the Chern-Simons number and the total electromagnetic helicity. We
argue that baryogenesis could lead to magnetic fields of nano-Gauss strength
today on astrophysical length scales. In addition to being astrophysically
relevant, such helical magnetic fields can provide an independent probe of
baryogenesis and CP violation in particle physics.
