Influence of Electron Drift Velocity on Ion-Acoustic Solitary Waves in Collisionless Electron–Positron-Ion Plasmas

Abstract This study explores the complex behavior of ion-acoustic (IA) solitary waves (SWs) in unmagnetized collisionless plasmas composed of electrons, thermal positrons, and positive ions, with particular attention to the influence of electron drift velocity. By employing a fluid model and the reductive perturbation method (RPM), we retrieve the Korteweg-de Vries (KdV) equation, which describes the weakly nonlinear progression of such waves. The findings show the presence of two distinct IA modes, i.e., fast and slow. In the fast mode, KdV solitons occur within two different ranges of drift velocities ( $$0&lt;{{v}_{e}^{\prime}}\le 172$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>&lt;</mml:mo> <mml:msubsup> <mml:mi>v</mml:mi> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mo>′</mml:mo> </mml:msubsup> <mml:mo>≤</mml:mo> <mml:mn>172</mml:mn> </mml:mrow> </mml:math> and $${{v}_{e}^{\prime}}\ge 199$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>v</mml:mi> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mo>′</mml:mo> </mml:msubsup> <mml:mo>≥</mml:mo> <mml:mn>199</mml:mn> </mml:mrow> </mml:math> ), whereas for the slow mode, solitons appear when $${{v}_{e}^{\prime}}\ge 223$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>v</mml:mi> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mo>′</mml:mo> </mml:msubsup> <mml:mo>≥</mml:mo> <mml:mn>223</mml:mn> </mml:mrow> </mml:math> . Numerical simulations indicate that the fast mode supports both compressive and rarefactive solitons, while the slow mode only supports compressive solitons. The study underscores the importance of distinct factors such as positron density $$\left(\mu \right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mi>μ</mml:mi> </mml:mfenced> </mml:math> , electron drift velocity $$\left({v}_{e}^{\prime}\right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:msubsup> <mml:mi>v</mml:mi> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mo>′</mml:mo> </mml:msubsup> </mml:mfenced> </mml:math> , and temperature ratios of electron to positron $$\left(\delta \right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mi>δ</mml:mi> </mml:mfenced> </mml:math> in determining the properties of solitons. The results offer valuable insights into space plasmas where similar plasma compositions and drift velocities can affect the transmission of IA waves in planetary ionospheres and interstellar spaces.