  Recently, Randall and Sundrum proposed a solution to the hierarchy problem
where the background spacetime is five dimensional. There are two 3-branes, and
the mass scale for fields that propagate on one of the 3-branes is
exponentially suppressed relative to the fundamental scale of theory, which is
taken to be the Planck mass, M_Pl. In this letter we show that bulk fields with
a five dimensional mass term of order M_Pl have, after integrating over the
extra dimension, modes with four-dimensional masses that are exponentially
suppressed as well. This opens the possibility that in this scenario the
Standard Model matter fields may correspond to degrees of freedom that are not
confined to a 3-brane.
