In this work, a cosmological model inspired by string theory with Gauss–Bonnet term coupled to the fermionic field is taken into consideration. The self-interaction potential is considered as a combination of the scalar and pseudoscalar invariants. Here the cosmological contribution of the coupling of Gauss–Bonnet term with a non-Dirac fermionic field — characterized by an interaction term[Formula: see text] — is investigated. It is observed that the new type of coupling plays a significant role in the accelerating behavior of the universe. Specifically, in addition to the late time acceleration for the universe, [Formula: see text] produces an early decelerating behavior. The behavior of the equation-of-state parameter (w) is such that it guarantees the stability of the theory.

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We have, in this paper, studied the stability of the ion-acoustic wave in a plasma composed of hydrogen, positively and negatively charged oxygen ions, and electrons, which approximates very well the plasma environment around a comet. Modelling each cometary component (H+, O+, and O−) by a ring distribution, we find that ion-acoustic waves can be generated at frequencies comparable to the hydrogen ion plasma frequency. The dispersion relation has been solved both analytically and numerically. We find that the ratio of the ring speed (u⊥s) to the thermal spread (vts) modifies the dispersion characteristics of the ion-acoustic wave. The contrasting behaviour of the phase velocity of the ion-acoustic wave in the presence of O− ions for u⊥s>vts (and vice versa) can be used to detect the presence of negatively charged oxygen ions and also their thermalization.

We investigate the existence of compressive and rarefactive solitary waves in a five-component plasma. Positively and negatively multiply charged heavier ions (dust), kappa function described photo-electrons, hot electrons and ions form the five components. The pseudo-potential approach is used to determine the existence of a soliton. We find that the Sagdeev potential as well as the amplitude of the solitary wave for both compressive and rarefactive solitons increases with increasing spectral indices of the kappa distributions describing the cometary species. The magnitude of the amplitude of the solitary wave increases with increasing positively charged ion densities and charge numbers, but decreases with increasing charge numbers of the negative ions for both type of solitons.