  We examine the evolution of non-relativistic cold dark matter gravitationally
coupled to baryons with modes deep inside the Hubble radius (sub-horizon
regime) using akinetic theory approach within the realm of Newtonian theory. We
obtain the general solution for the total density perturbation and we also show
that a baryon perturbation catches up with the dark matter perturbation at late
times, which in turn makes possible the formation of bound structures. We
extend the linear perturbation analysis by considering the turn-around event,
the collapse of matter, and its virialization process.
