Abstract
Overtaking collisions of ion-acoustic (IA) solitons are examined in an unmagnetized pair-ion plasma containing degenerate electrons. A Korteweg-de Vries (KdV) equation governing nonlinear IA solitons in such a degenerate plasma model is obtained. At critical compositions, the nonlinear coefficient of the KdV equation vanishes. Therefore, a modified KdV (mKdV) equation describing nonlinear IA solitons in the degenerate plasma model has been derived by extending the analytic analysis to this critical case. Hirota's bilinear method has been applied to obtain the multisolitons solution and their corresponding phase shifts in these two situations. For an in-depth analysis, we investigated the dynamics of two solitons of the same polarity and opposite polarities resulting from the overtaking collision for discrete times. In particular, the phase shifts are obtained for the first time at critical components in degenerate plasmas. In these two cases, it is found that the magnitude of the phase shifts due to the overtaking interaction of two solitons increases with increasing the negative ion-to-positive ion number density ratio. The present study may help explain the properties of nonlinear waves in white dwarfs that support the propagation of solitons.