REMARKS ON MODELS WITH SINGLET NEUTRINO IN LARGE EXTRA DIMENSIONS

In this talk, we discuss two non-minimal models with singlet neutrino in large extra dimensions: (1) singlet neutrino in a sub-space of the bulk and (2) Dirac mass for singlet with lepton number violating Yukawa couplings. The motivation is to obtain the mass scale relevant for atmospheric neutrino oscillations with a quantum gravity scale M_* ~ a few TeV and with at most O(1) higher-dimensional couplings. In both non-minimal models, such a low M_* can be consistent with the limit on BR(μ → eγ) (unlike in the minimal model). We also show that in this scenario, with 2 Higgs doublets, the decay of charged Higgs into left-handed τ can be significantly enhanced, with O(1) branching ratio, due to the large number of Kaluza-Klein states of the right-handed neutrino.