Multirefringence phenomena in nonlinear electrodynamics

Wave propagation in nonlinear theories of the electromagnetism described by Lagrangian densities dependent upon its two local invariants L(F, G) is revisited. On the light of the recent findings in metamaterials, it is here shown that trirefringence is also a possible phenomenon to occur in the realm of such nonlinear theories. A specific model exhibiting this effect is investigated both in terms of phase and group velocities. It is claimed that wave propagation in some well known nonlinear models for spin-one fields, like QED and QCD in certain regimes, may exhibit trirefringence.