  We predict the existence of new nonlinear electromagnetic wave modes in pair
plasmas. The plasma may be either non-magnetized or immersed in an external
magnetic field. The existence of these modes depends on the interaction of an
intense circularly polarized electromagnetic wave with a plasma, where the
nonlinear quantum vacuum effects are taken into account. This gives rise to new
couplings between matter and radiation. We focus on pair plasmas, since the new
modes are expected to exist in highly energetic environments, such as pulsar
magnetospheres and the next generation of laser--plasma systems.
