Ghost Condensates and Pure Kinetic k-Essence Condensates in the Presence of Field-Fluid Non-Minimal Coupling in the Dark Sector

In this article, we try to determine the conditions when a ghost field, in conjunction with a barotropic fluid, produces a stable accelerating expansion phase of the universe. It is seen that, in many cases, the ghost field produces a condensate and drives the fluid energy density to zero in the final accelerating phase, but there can be other possibilities. We have shown that a pure kinetic k-essence field (which is not a ghost field) interacting with a fluid can also form an interaction-induced condensate and produce a stable accelerating phase of the universe. In the latter case, the fluid energy density does not vanish in the stable phase.