  We examine the origin of neutrino masses and oscillations in the context of
the six-dimensional standard model. The space-time symmetries of this model
explain proton stability and forbid Majorana neutrino masses. The consistency
of the six-dimensional theory requires three right-handed neutrinos, and
therefore Dirac neutrino masses are allowed. We employ the idea that the
smallness of these masses is due to the propagation of the right-handed
neutrinos in a seventh, warped dimension. We argue that this class of theories
is free of gravitational anomalies. Although an exponential hierarchy arises
between the neutrino masses and the electroweak scale, we find that the mass
hierarchy among the three neutrino masses is limited by higher-dimension
operators. All current neutrino oscillation data, except for the LSND result,
are naturally accommodated by our model. In the case of the solar neutrinos,
the model leads to the large mixing angle, MSW solution. The mechanism
employed, involving three right-handed neutrinos coupled to a scalar in an
extra dimension, may explain the features of the neutrino spectrum in a more
general class of theories that forbid Majorana masses.

High Energy Physics - Phenomenology;High Energy Physics - Theory