MODULATION INSTABILITY OF LANGMUIR-WAVES IN ELECTRON-POSITRON PLASMA

A steady Langmuir wave in a cold one-dimensional electron-positron pla sma is considered. Unlike the case of an electron plasma, such a wave is shown to have a nonlinear frequency shift even in the limit of zero temperature (T --> 0) and infinite velocity of light (c --> infinity) . The stability of this wave is investigated. Depending on the paramet ers of the pumping wave, either the modulation instability, or the con densate instability is developed. The obtained results are of interest for astrophysics.