Leptogenesis via collisions: Leaking lepton number to the hidden sector

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 --> l'phi', (l) over bar'<(<phi>)over bar>' mediated by the heavy Majorana neutrinos N of the seesaw mechanism, where l and phi are ordinary lepton and Higgs doublets and l, phi' 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) GeV.