  The emerging cosmological picture is of a spatially flat universe composed
predominantly of three components: ordinary baryons ($\Omega_B \approx 0.05$),
non-baryonic dark matter ($\Omega_{Dark} \approx 0.22$) and dark energy
($\Omega_{\Lambda} \approx 0.7$). We recently proposed that ordinary matter was
synthesised from mirror matter, motivated by the argument that the observed
similarity of $\Omega_B$ and $\Omega_{Dark}$ suggests an underlying similarity
between the fundamental properties of ordinary and dark matter particles. In
this paper we generalise the previous analysis by considering a wider class of
effective operators that non-gravitationally couple the ordinary and mirror
sectors. We find that while all considered operators imply $\Omega_{Dark} = $
few$\times \Omega_B$, only a subset quantitatively reproduce the observed ratio
$\Omega_B/\Omega_{Dark} \approx 0.20$. The $\sim 1$ eV mass scale induced
through these operators hints at a connection with neutrino oscillation
physics.
