  In extensions of the standard model with a heavy fourth generation one
important question is what makes the fourth-generation lepton sector,
particularly the neutrinos, so different from the lighter three generations. We
study this question in the context of models of electroweak symmetry breaking
in warped extra dimensions, where the flavor hierarchy is generated by the
localization of the zero-mode fermions in the extra dimension. In this setup
the Higgs sector is localized near the infrared brane, whereas the Majorana
mass term is localized at the ultraviolet brane. As a result, light neutrinos
are almost entirely Majorana particles, whereas the fourth generation neutrino
is mostly a Dirac fermion. We show that it is possible to obtain heavy
fourth-generation leptons in regions of parameter space where the light
neutrino masses and mixings are compatible with observation. We study the
impact of these bounds, as well as the ones from lepton flavor violation, on
the phenomenology of these models.
