A nongravitational wormhole
  Using the effective metric formalism for photons in a nonlinear electromagnetic theory, we show that a certain field configuration in Born-Infeld electromagnetism in flat spacetime can be interpreted as an ultrastatic spherically symmetric wormhole. We also discuss some properties of the effective metric that are valid for any field configuration. 
F. Baldovin, M. Novello, S. E. Perez Bergliaffa, and J.M. Salim