Preserving the lepton asymmetry in the brane world

In models where the Standard Model spectrum is localized on a brane embedded in a higher-dimensional spacetime, we discuss the lepton number violation induced by the emission of right-handed neutrinos from the brane. We show that the presence of the right-handed neutrinos in the bulk may lead to rapid lepton number violating processes which above the electroweak scale would wash away any prior lepton or baryon asymmetry. We derive constraints on the Yukawa couplings of these states in order to preserve the lepton asymmetry. We show that this has a natural interpretation in the brane world.