Nonuniform Almost Reducibility of Nonautonomous Linear Differential Equations

Abstract

We prove that a linear nonautonomous differential system with nonuniform hyperbolicity on the half line can be expressed as diagonal system with a perturbation which is small enough. Moreover we show that the diagonal terms are contained in the nonuniform exponential dichotomy spectrum. For this purpose we introduce the concepts of \textit{nonuniform almost reducibility} and \textit{nonuniform contractibility} which are generalization of this notions originally defined in a uniform context.