  We point out qualitatively different possibilities on the role of
CP-conserving processes in generating cosmological particle-antiparticle
asymmetries, with illustrative examples from models in leptogenesis and
asymmetric dark matter production. In particular, we consider scenarios in
which the CP-violating and CP-conserving processes are either both decays or
both scatterings, thereby being naturally of comparable rates. This is in
contrast to the previously considered CP-conserving processes in models of
leptogenesis in different see-saw mechanisms, in which the CP-conserving
scatterings typically have lower rates compared to the CP-violating decays, due
to a Boltzmann suppression. We further point out that the CP-conserving
processes can play a dual role if the asymmetry is generated in the mother
sector itself, in contrast to the conventional scenarios in which it is
generated in the daughter sector. This is because, the CP-conserving processes
initially suppress the asymmetry generation by controlling the
out-of-equilibrium number densities of the bath particles, but subsequently
modify the ratio of particle anti-particle yields at the present epoch by
eliminating the symmetric component of the bath particles through
pair-annihilations, leading to a competing effect stemming from the same
process at different epochs. We find that the asymmetric yields for relevant
particle-antiparticle systems can vary by orders of magnitude depending upon
the relative size of the CP-conserving and violating reaction rates.
