Asymmetric Dark Matter via Spontaneous Co-Genesis

We investigate, in the context of asymmetric dark matter (DM), a new mechanism of spontaneous co-genesis of linked DM and baryon asymmetries, explaining the observed relation between the baryon and DM densities, Omega_DM/Omega_B ~ 5. The co-genesis mechanism requires a light scalar field, phi, with mass below 5 eV which couples derivatively to DM, much like a `dark axion’. The field phi can itself provide a final state into which the residual symmetric DM component can annihilate away.