Alfvenic solitons in ultrarelativistic electron-positron plasmas

Abstract

In electron-positron plasmas some of the plasma modes are decoupled due to the equal charge-to-mass ratio of both species. We derive the dispersion law for a low-frequency, generalized X-mode, which exists at all angles of propagation with respect to the static magnetic field. Its nonlinear evolution is governed by a Korteweg-de Vries equation, valid at all angles of propagation except strictly parallel propagation, for which a different approach leads to a vector form of the modified Korteweg-de Vries equation. The nonlinearity is strongest at perpendicular propagation. Ultrarelativistic effects are discussed.