A generic framework of adiabatic approximation for nonlinear evolutions

In the study of evolution equations, the method of adiabatic approximation is an essential tool to reduce an infinite-dimensional dynamical system to a simpler, possibly finite-dimensional one. In this paper, we formulate a generic scheme of adiabatic approximation that is valid for an abstract nonlinear evolution under mild regularity assumptions. The key prerequisite for the scheme is the existence of what we call approximate solitons. These are some low energy but not necessarily stationary configurations. The approximate solitons are characterized by a number of parameters (possibly infinitely many) and have a manifold structure. The adiabatic scheme reduces the given abstract evolution equation to an effective equation on the manifold of approximate solitons. We give sufficient conditions for the approximate solitons so that the reduction scheme is valid up to a large time. The validity is determined by the energy property of the original evolution as well as the adiabaticity of the approximate solitons.