Abstract
Properties of fully nonlinear electron-acoustic solitary waves in an unmagnetized and collisionless electron-positron-ion plasma containing cold dynamical electrons, superthermal electrons and positrons obeying Cairns' distribution have been analyzed in the stationary background of massive positive ions. A linear dispersion relation has been derived, from which it is found that even in the absence of superthermal electrons, the superthermal positron component can provide the restoring force to the cold inertial electrons to excite electron-acoustic waves. Moreover, superthermal electron and positron populations seem to enhance the electron acoustic wave phase speed. For nonlinear analysis, Korteweg-de Vries equation is obtained using the reductive perturbation technique. It is found that in the presence of positron both hump and dip type solitons appear to excite. The present work may be employed to explore and to understand the formation of electron acoustic soliton structures in the space and laboratory plasmas with nonthermal electrons and positrons.