Electromagnetic solitons in fully relativistic electron-positron plasmas with finite temperature

The existence of localized structure of electromagnetic waves in relativistic electron-positron plasmas is investigated based on the pseudo-potential theory, without making any assumptions on the magnitudes of the flow velocity and temperature of the medium. The conditions for the localization of electromagnetic wave in the form of dark (dip type) soliton are found. In the small amplitude approximation, it is found that the dip becomes deeper and narrower as the temperature is raised. In low temperature T << mc2, localized solution exists only if the equilibrium longitudinal fluid velocity (parallel to the direction of propagation) in the wave frame is larger than the classical thermal velocity √(T/m) of the plasma. For ultra-relativistically high temperature T >> mc2, it is shown that dark soliton can exist if the equilibrium longitudinal velocity is larger than c/√(3).