Kinetic effects on the parametric decays of circularly polarized electromagnetic waves in an electron-positron plasma

Abstract

We study parametric decays of a circularly polarized wave in an electron-positron plasma, including weakly relativistic effects on the particle motion in the wave field. Although we are considering nonrelativistic temperatures, relativistic effects must be taken into account in the pressure gradient term of the fluid equation of motion. There are two types of decays: one in which the pump wave decays into two electromagnetic waves, and the other where the pump wave decays into electromagnetic waves and electroacoustic pseudomodes. Since the electroacoustic pseudomodes satisfy ω/kvth∼1, one would expect these modes to be strongly Landau damped. Therefore, it is important to include kinetic effects in these studies. To this end, using kinetic theory we calculate the nonlinear dispersion relation for the parametric decays of the circularly polarized waves.