Nucleus-acoustic envelope solitons and their modulational instability in a degenerate quantum plasma system

The existence and the basic features of nucleus-acoustic (NA) envelope bright and dark solitons in a degenerate quantum plasma system (DQPSs) (containing non-relativistically degenerate nuclei and inertialess ultra-relativistically degenerate electrons and positrons), have been theoretically investigated by deriving the nonlinear Schrödinger (NLS) equation. The reductive perturbation method, which is valid for a small but finite amplitude limit, is employed. The plasma parametric regimes for both modulationally stable and unstable NA waves (NAWs) are observed. It is found that the growth rate of the modulationally unstable NAWs is significantly modified by the number density of nucleus species. It is also observed that the modulationally stable (unstable) NAWs give rise to stable dark (bright) envelope solitons. The implications of our results obtained from our present investigation in astrophysical and laboratory DQPSs are briefly discussed.