Nonlinear Vacuum Phenomena in Noncommutative Qed

We show that the classic results of Schwinger on the exact propagation of particles in the background of constant field-strengths and plane waves can be readily extended to the case of nocommutative QED. It is shown that nonperturbative effects on constant backgrounds are the same as their commutative counterparts, provided the on-shell gauge-invariant dynamics are referred to a nonperturbatively related space–time frame. For the case of the plane wave background, we find evidence of the effective extended nature of noncommutative particles, producing retarded and advanced effects in scattering. Besides the known "dipolar" character of noncommutative neutral particles, we find that charged particles are also effectively extended, but they behave instead as "half-dipoles."