Parametric decays of a linearly polarized electromagnetic wave in an electron-positron plasma

Abstract

We study the parametric decays of a large amplitude, linearly polarized electromagnetic wave in an electron-positron plasma. We include harmonic generation, the ponderomotive force, and weakly relativistic effects. It is shown that when [Formula Presented] ([Formula Presented] is the electroacoustic velocity, [Formula Presented] is the speed of light, and [Formula Presented] is the phase velocity of the electromagnetic wave), there are two instabilities. One is an ordinary decay instability, in which the pump wave decays into a sideband wave, propagating backward relative to the pump wave, and an electroacoustic mode propagating forward. The other is an essentially electromagnetic nonresonant modulational instability (which is due to higher order effects of the pump wave amplitude), in which the pump wave decays into two sideband waves. When [Formula Presented] there is a modulational nonresonant instability, and an ordinary modulational instability, in which the pump wave decays into