  Topological defects are generically expected to form in models of brane
inflation. Brane-anti-brane annihilation provides a way to gracefully end
inflation, and the dynamics of the tachyon field results in defect formation.
The formation of defects has been studied mainly from the brane world-volume
point of view, but the defects are themselves lower-dimensional branes, and as
a result they couple to bulk fields. To investigate the impact of bulk fields
on brane defect formation, we construct a toy model that captures the essential
features of the tachyon condensation with bulk fields. In this toy model, we
study the structure of defects and simulate their formation and evolution on a
lattice. We find that while bulk fields do not have a significant effect on
defect formation, they drastically influence the subsequent evolution of the
defects, as they re-introduce long-range interactions between them.
