Brane Death via Born-Infeld String

I revisit the solution of Born-Infeld theory which corresponds to a 3-brane and anti-brane joined by a (fundamental) string. The global instability of this configuration makes possible the semiclassical tunneling into a wide, short tube which keeps expanding out, thus annihilating the brane . This tunneling is suppressed exponentially as $\exp(- S_{cl}/g)$. The attraction between the branes causes them to approach and at some point to tunnel, because the action of the bounce solution goes to zero. The energy of the solution at the top of the barrier, the sphaleron, goes like $\sim D^3$ for large separarions D, while the energy of the string is proportional to its length D.