  We study the stability and the scattering properties of a spacetime with a
topological defect along a spherical bubble. This bubble connects two flat
spacetimes which are asymptotically Minkowski, so that the resulting universe
may be regarded as containing a wormhole. Its distinguished feature is the
absence of exotic matter, i.e., its matter content respects all the energy
conditions. Although this wormhole is nontraversable, waves and quantum
particles can tunnel between both universes. Interestingly enough, the wave
equation alone does not uniquely determine the evolution of scalar waves on
this background, and the theory of self-adjoint extensions of symmetric
operators is required to find the relevant boundary conditions in this context.
Here we show that, for a particular boundary condition, this spacetime is
stable and gives rise to a scattering pattern which is identical to the more
usual thin-shell wormhole composed of exotic matter. Other boundary conditions
of interest are also analyzed, including an unstable configuration with sharp
resonances at well defined frequencies.
