  In quantum electrodynamics, photon--photon scattering can be the result of
the exchange of virtual electron--positron pairs. Effectively, this gives rise
to self-interaction terms in Maxwell's equations, similar to the nonlinearities
due to polarization in nonlinear optics. These self-interaction terms vanish in
the limit of parallel propagating waves. However if the modes generated in
bounded regions are used, there will be a non-zero total effect. We show that
stationary two-dimensional light bullets can form in guiding structures, due to
the balancing effect of quantum electrodynamical vacuum nonlinearities on
dispersion and diffraction. These light bullets are unstable and exhibit the
possibility of self-focusing collapse. The consequences of our results are also
discussed.
