Covariant and gauge-invariant linear scalar perturbations in multiple scalar field cosmologies

We derive a set of equations monitoring the evolution of covariant and gauge-invariant linear scalar perturbations of Friedman-Lemaitre-Robertson-Walker models with multiple interacting nonlinear scalar fields. We use a dynamical systems approach in order to perform a stability analysis for some classes of scalar field potentials. In particular, using a recent approximation for the inflationary dynamics of the background solution, we derive conditions under which homogenization occurs for chaotic (quadratic and quartic potentials) and new inflation. We also prove a cosmic no-hair result for power-law inflation and its generalization for two scalar fields with independent exponential potentials (assisted power-law inflation).