On the existence of invariant tori in non-conservative dynamical systems with degeneracy and finite differentiability

Abstract

In this paper, we establish a KAM-theorem about the existence of invariant tori in non-conservative dynamical systems with finitely differentiable vector fields and multiple degeneracies under the assumption that the integrable part is finitely differentiable with respect to parameters, instead of the usual assumption of analyticity. We prove these results by constructing approximation and inverse approximation lemmas in which all functions are finitely differentiable in parameters.