  We propose a lepto-baryogenesis mechanism in which the non-zero B-L of the
universe is produced in out-of-equilibrium, lepton number and CP violating
scattering processes that convert ordinary particles into particles of some
hidden sector. In particular, we consider the processes $l \phi > l' \phi',
\bar l' \bar phi'$ mediated by the heavy Majorana neutrinos $N$ of the seesaw
mechanism, where $l$ and $\phi$ are ordinary lepton and Higgs doublets and
$l'$, $\phi'$ their hidden counterparts. Such a leptogenesis mechanism is
effective even if the reheating temperature is much smaller than the heavy
neutrino masses. In particular, it can be as low as $10^{9}$ GeV.
