Linear and nonlinear coupled kinetic Alfven acoustic (CKAA) waves in low-β electron–positron–ion (e-p-i) plasmas are investigated in this paper, and the main focus is on highlighting the role of non-thermal electrons and positrons that follow the generalized (r, q) distribution. In this regard, a linear dispersion relation is derived, and the effect of positron concentration and (r, q) distributed electrons and positrons is explored. Nonlinear analysis is performed by using the Sagdeev potential approach and two-potential theory. The results are compared with those of the previous studies of CKAA waves in e-p-i plasmas where electrons and positrons follow Maxwellian and kappa distributions. An important feature of our study is the observation of the existence of density dip solitons for spiky distribution. It is shown that the inclusion of positrons alters the existence regimes of the solitary structures, and, interestingly, the behavior of soliton propagation is different in the two existence regimes for increasing or decreasing concentration of positrons. Most importantly, it is shown that the spatial scales over which solitons form in e-p-i plasmas are shorter than the ones that form in e-i plasmas for compressive solitary structures. Interestingly, the situation is reversed for rarefactive solitary structures. The present study is beneficial in comprehending the linear and nonlinear propagation of CKAA waves in plasmas where positrons are present, and there is a simultaneous presence of nonthermal features in the observed distribution functions.

Linear and nonlinear coupled kinetic Alfvén-acoustic (CKAA) waves have been studied using the two-potential theory in non-Maxwellian plasmas where electrons follow the $(r,\hspace{0.17em}q)$ distribution function. For the first time, a comprehensive study has been carried out to ascertain how the formation of compressive and rarefactive solitary structures of CKAA waves depends on the low and high energy parts of the electron distribution function. We have found that the flat-tops at low energies of the electron distribution are responsible for the formation of compressive solitary structures, whereas the spikes at low energies allow the formation of both compressive and rarefactive solitary structures. A detailed comparison of generalized (r, q), kappa, Cairns, and Maxwellian distributions has been given, and important differences have also been highlighted. The relevance of the present study with special reference to space plasmas has also been pointed out.

The influence of the low energy part of the velocity distribution on the propagation characteristics of the nonlinear ion-acoustic waves is investigated in this study by employing the double spectral index (r, q) distribution function. We present an ample study to ascertain how the formation of compressive and rarefactive ion-acoustic solitary structures is influenced by the low energy particles in the distribution profile. We found that only compressive structures are formed for flat top distribution; however, both compressive and rarefactive structures are admissible for spiky distribution. The effect of spectral indices r and q on the formation of solitary structures is explored in detail, and a brief comparison with the Maxwellian and kappa distribution is also given. The present study is imperative in understanding the role of flat top or spiky distributions in plasmas, where positrons are present, and simultaneous observations of such distributions.