Higher-dimensional origin of heavy sneutrino domination and low-scale leptogenesis

摘要

If the expectation value of the right-handed (rhd) sneutrino comes to dominate the universe, its decay naturally leads to successful leptogenesis, as well as significant dilution of dangerous inflationary relics, such as the gravitino. The resulting baryon asymmetry is independent of other cosmological initial conditions. This attractive variant of leptogenesis requires at least one of the rhd neutrinos to have small Yukawa coupling and to have mass similar to 10(6) GeV, much smaller than the grand unified (GUT) scale. We show that these features naturally arise in the context of independently motivated and successful 5d orbifold GUTs with inverse-GUT-scale-sized extra dimensions. Rbd neutrinos are realized as bulk fields N-i with 5d bulk masses, while Yukawa couplings and lepton-number-violating masses for the N-i are localized at the SM boundary. The exponential suppression of the would-be N-i zero-modes leads to the desired small 4d Yukawa couplings and small masses for the rhd neutrino states. The see-saw prediction for the rhd neutrino mass scale is automatically maintained. We show that this realization of rhd neutrinos is nicely accommodated within an attractive orbifold-GUT flavour model, where all flavour hierarchies have a geometrical origin. (C) 2002 Published by Elsevier Science B.V. References: 37