Modulational instability and generation of envelope solitons in four-component space plasmas

The four-component space plasma (containing immobile positive ions, inertial cold positrons, and inertia-less hot electrons and positrons following Cairns' non-thermal distribution function) is considered. The modulational instability and the generation of positron-acoustic (PA) envelope solitons in such a space plasma system are investigated by deriving the non-linear Schrodinger (NLS) equation. It is found from the numerical analysis of the NLS equation that the plasma system under consideration supports the existence of both dark and bright envelope solitons associated with the PA waves. It is also observed that the instability criterion and the growth rate of the unstable PA waves are significantly modified by the plasma parameters (i.e. temperature and number density of different plasma species). The implications of the results to space plasma research are briefly discussed.