We propose a leptobaryogenesis mechanism in which the nonzero $B-L$ 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 $l\phi \to l^{\prime }{\phi }^{\prime },{\overline{l}}^{\prime }{\overline{\phi }}^{\prime }$ mediated by the heavy Majorana neutrinos $N$ of the seesaw mechanism, where $l$ and $\phi$ are ordinary lepton and Higgs doublets and $l^{\prime }$, ${\phi }^{\prime }$ are their hidden counterparts. Such a leptogenesis mechanism is effective even if the reheat temperature is much smaller than the heavy neutrino masses. In particular, it can be as low as ${10}^9\mathrm{GeV}$.

• Received 6 August 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.231304