Positron acoustic solitary waves in electron–positron–ion plasmas with regularized kappa distributed electrons

Nonlinear positron acoustic (PA) structures were investigated in unmagnetized electron–positron–ion plasma in which hot electrons obey a regularized kappa distribution (RKD). In contrast to the standard kappa distribution, the RKD incorporates an exponential cutoff to eliminate divergences in velocity moments at low spectral indices κ, thus permitting a valid fluid model for all κ > 0. By employing a fluid description with inertial cold positrons, stationary ions, and inertialess RKD electrons, the Korteweg–de Vries equation was derived using the reductive perturbation method. The nonlinear and dispersive coefficients depend explicitly on the RKD moments, establishing a direct connection between the spectral index κ, cutoff parameter α, and properties of PA solitary waves. The numerical analysis shows that decreasing either κ or α enhances the phase velocity, amplitude, and width of compressive PA solitons, whereas rarefactive solitons exhibit the opposite trend. Physically meaningful solitons persist even in strongly suprathermal regimes, where the standard kappa model fails, demonstrating that RKD provides a robust framework for modeling nonlinear PA waves in space and astrophysical plasmas.