Phase Space Analysis of the Accelerating Multi-fluid Universe
  We study in detail the phase space of a Friedmann-Robertson-Walker Universe
filled with various cosmological fluids which may or may not interact. We use
various expressions for the equation of state, and we analyze the physical
significance of the resulting fixed points. In addition we discuss the effects
of the stability or an instability of some fixed points. Moreover we study an
interesting phenomenological scenario for which there is an oscillating
interaction between the dark energy and dark matter fluid. As we demonstrate,
in the context of the model we use, at early times the interaction is
negligible and it starts to grow as the cosmic time approaches the late-time
era. Also the cosmological dynamical system is split into two distinct
dynamical systems which have two distinct de Sitter fixed points, with the
early-time de Sitter point being unstable. This framework gives an explicit
example of the unification of the early-time with late-time acceleration.
Finally, we discuss in some detail the physical interpretation of the various
models we present in this work.
