  We demonstrate how loop effects in gravitational backgrounds lead to a
difference in the propagation of matter and antimatter, and show this is
forbidden in flat space due to CPT and translation invariance. This mechanism,
which is naturally present in beyond the standard model (BSM) theories
exhibiting C and CP violation, generates a curvature-dependent chemical
potential for leptons in the low-energy effective Lagrangian, allowing a
matter-antimatter asymmetry to be generated in thermodynamic equilibrium, below
the BSM scale.
