Gravitational leptogenesis from metric perturbations

In this work we make the observation that the gravitational leptogenesis mechanism can be implemented without invoking new axial couplings in the inflaton sector. We show that in the perturbed Robertson-Walker background emerging after inflation, the spacetime metric itself breaks parity symmetry and generates a non-vansihing Pontryagin density which can produce a matter-antimatter asymmetry. We analyze the produced asymmetry in different inflationary and reheating scenarios. We show that the generated asymmetry can be locally comparable to observations in certain cases, although the size of the matter-antimatter regions is typically much smaller than the present Hubble radius.