Abstract
The nonlinear properties of small amplitude electron-acoustic solitary waves (EASWs) have been investigated in an unmagnetized collisionless four-component plasma system consisting of a cold relativistic electron fluid, non-thermal hot electrons obeying a non-thermal distribution, a relativistic electron beam and stationary ions. It is found that the basic set of fluid equations is reduced to a Korteweg-de Vries (KdV) equation, which governs the nonlinear characteristics of EASWs. The effects of relativistic electrons and energetic population parameter delta on the nature of EASWs are discussed.