Yosida Distance and Existence of Invariant Manifolds in the Infinite-Dimensional Dynamical Systems

TL;DR

This paper introduces the Yosida distance to analyze the stability and persistence of invariant manifolds in infinite-dimensional dynamical systems, providing new insights into perturbation effects without domain restrictions.

Contribution

It defines a novel Yosida distance between operators and applies it to establish the existence of invariant manifolds under small perturbations in infinite-dimensional systems.

Findings

Yosida distance effectively measures operator perturbations.

Invariant manifolds persist under small Yosida perturbations.

Results do not require domain restrictions on perturbations.

Abstract

We introduce a new concept of Yosida distance between two (unbounded) linear operators $A$ and $B$ in a Banach space $\mathbb{X}$ defined as $d_Y(A,B):=\limsup_{\mu\to +\infty} \| A_\mu-B_\mu\|$, where $A_\mu$ and $B_\mu$ are the Yosida approximations of $A$ and $B$, respectively, and then study the persistence of evolution equations under small Yosida perturbation. This new concept of distance is also used to define the continuity of the proto-derivative of the operator $F$ in the equation $u'(t)=Fu(t)$, where $F \colon D(F)\subset \mathbb{X} \rightarrow \mathbb{X}$ is a nonlinear operator. We show that the above-mentioned equation has local stable and unstable invariant manifolds near an exponentially dichotomous equilibrium if the proto-derivative of $F$ is continuous. The Yosida distance approach to perturbation theory allows us to free the requirement on the domains of the perturbation operators. Finally, the obtained results seem to be new.