This study examines the head-on collision of ion-acoustic solitons in a one-dimensional, hot, collisionless electron-positron-ion (e-p-i) plasma, incorporating mobile ions, \(\kappa \) -distributed trapped electrons, and Maxwellian positrons. Using the modified Poincare-Lighthill-Kuo (PLK) method, we derive modified Korteweg-de Vries (mKdV) equations and analyze phase shifts in soliton trajectories post-interaction. Results reveal that only rarefactive electrostatic nonlinear waves can propagate within the range of parameters relevant to experiments, showing symmetrical soliton behavior during head-on collisions, with identical amplitude and width. Additionally, soliton amplitude is found to decrease as the electron spectral index ( \(\kappa _e\) ) and positron-to-electron temperature ratio ( \(\beta _e\) ) increase, with a sharp decline observed within the range \(0<\kappa _e<5\) . Phase shift analysis shows that smaller \(\kappa _e\) values result in a steady increase in phase shifts, which becomes asymptotic as \(\kappa _e\) grows, while phase shifts decrease with rising \(\sigma _i\) (temperature ratio of ions to electrons). These results have practical applications in astrophysical and laboratory plasma environments where soliton interactions play a crucial role. Understanding head-on soliton collisions helps predict plasma behavior in environments such as the interstellar medium, fusion devices, and space plasmas, where wave stability, energy transport, and plasma heating are influenced by nonlinear interactions in systems with trapped particles and nonthermal distributions.
