  In the presence of background fields that spontaneously violate Lorentz
invariance, a matter-antimatter asymmetry can be generated even in thermal
equilibrium. In this paper we systematically investigate models of this type,
showing that either high-energy or electroweak versions of baryogenesis are
possible, depending on the dynamics of the Lorentz-violating fields. We
identify two scenarios of interest: baryogenesis from a weak-scale
pseudo-Nambu-Goldstone boson with intermediate-scale baryon-number violation,
and sphaleron-induced baryogenesis driven by a constant-magnitude vector with a
late-time phase transition.
