Ion acoustic solitary waves in a plasma with superthermal electrons and positrons

The problem of arbitrary amplitude ion acoustic solitary waves in a plasma with Boltzmann distributed positrons and superthermal electrons is addressed. The domain of their allowable Mach numbers is shifted towards lower values as the positron-to-electron density ratio p is increased. Beyond a certain critical value of p only subsonic ion-acoustic solitons are admitted. This threshold for the onset of subsonic ion-acoustic solitons is lowered as the superthermal character of the plasma is increased. In the limit of small spectral index k, the ion-acoustic solitons are subsonic over the entire range of p. Cusped ion-acoustic solitons may arise as the electrons evolve far away from their thermodynamic equilibrium. Our results should help to understand the localized structures that may occur in space plasmas.