Abstract
The mechanism of thermal leptogenesis is investigated in the high-energy regime of braneworld cosmology. Within the simplest seesaw framework with hierarchical heavy Majorana neutrinos, we study the implications of the modified Friedmann equation on the realization of this mechanism. In contrast with the usual leptogenesis scenario of standard cosmology, where low-energy neutrino data favors a mildly strong washout regime, we find that leptogenesis in the braneworld regime is successfully realized in a weak washout regime. Furthermore, a quasidegenerate light neutrino mass spectrum is found to be compatible with this scenario. For an initially vanishing heavy Majorana neutrino abundance, thermal leptogenesis in the brane requires the decaying heavy Majorana neutrino mass to be ${M}_{1}\ensuremath{\gtrsim}{10}^{10}$ GeV and the fundamental five-dimensional gravity scale ${10}^{12}\ensuremath{\lesssim}{M}_{5}\ensuremath{\lesssim}{10}^{16}$ GeV, which corresponds to a transition from brane to standard cosmology at temperatures ${10}^{8}\ensuremath{\lesssim}{T}_{t}\ensuremath{\lesssim}{10}^{14}$ GeV.
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